Design and Characterization of Gelatin-Coated Upconversion Nanoparticles: Insights into Structural, Relaxometric, Luminescent, and Cytotoxic Properties

Design and Characterization of Gelatin-Coated Upconversion Nanoparticles: Insights into Structural, Relaxometric, Luminescent, and Cytotoxic Properties | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Design and Characterization of Gelatin-Coated Upconversion Nanoparticles: Insights into Structural, Relaxometric, Luminescent, and Cytotoxic Properties Joyce Francine da Silva de Lima, Giovanna Nogueira da Silva Avelino Oliveira, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3961971/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract T he present study aimed to develop a theranostic nanoprobe for application. This nanoprobe is composed of upconversion nanoparticles (NPs) coated with gelatin. Initially, erbium-ytterbium co-doped gadolinium oxide (Gd 2 O 3 :Yb/Er) was synthesized using the homogeneous precipitation technique. The Gd 2 O 3 :Yb/Er particles were coated with gelatin (Gd 2 O 3 :Yb/Er@Gelatin) using the desolvation method. Four syntheses were conducted with different gelatin concentrations and the use of glutaraldehyde (GA) as a cross-linking agent. The characterization of the nanoprobe included structural, relaxometric, luminescent, and cytotoxicity analyses. The results indicate that cross-linking with GA reduces the size of the NPs, suggesting a greater compaction of the gelatin chains. It was observed that the gelatin coating increases the concentration of water molecules near the NPs through hydrogen bonding interactions and modulates their diffusion time near the paramagnetic center, influencing the decrease in proton relaxation time. On the other hand, cross-linking with GA restricts the mobility of water molecules, by all relaxivity values were found to be higher than those of commercial contrast agents. The luminescent data showed that although the spectral emission profile of upconversion between Yb 3+ and Er 3+ ions did not change compared to the oxide, the emission intensity ratio (I R /I G ) decreased with coating, and the emission in the green region is generated by the absorption of three photons, while the emission in the red region is generated by the absorption of two photons. It was also observed that Gd 2 O 3 :Yb/Er and Gd 2 O 3 :Yb/Er@Gelatin NPs had no cytotoxic effect on healthy cells, with cell viability above 90%. The developed nanoprobe showed interesting luminescent and relaxometric properties, making it a promising tool for optical and magnetic bioimaging. upconversion glutaraldehyde relaxometry coating bioimaging. Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Introduction The upconversion nanoparticles (UCNPs) have garnered significant attention due to their remarkable optical characteristics such as fixed energy levels, high resistance to photodegradation, and lifetimes on the order of milliseconds [1; 2]. Additionally, UCNPs have been of considerable interest because of their intrinsic advantages, including a large anti-Stokes shift, deep tissue penetration capability, reduced photodamage effects, and superior photostability [3; 4; 5; 6]. Furthermore, UCNPs emerge as a promising solution to overcome the limitations of conventional photoluminescent (PL) imaging agents, such as small organic dyes, metallic complexes, fluorescent proteins, and quantum dots (QDs) in the context of live cell and tissue imaging [7; 8]. Gd 2 O 3 stands out as an excellent luminescent host material due to its low phonon energy (cut off at ar 600 cm − 1 ) and good thermal stability [ 9 ]. One class of UCNPs utilizes Yb 3+ e Er 3+ ions as sensitization and activation centers, respectively [4; 7; 8]. Typically, these nanomaterials emit light in the green region ( 4 I 11/2 → 4 F 7/2 and 4 I 13/2 → 4 F 9/2 ) and in the red region ( 4 F 9/2 → 4 I 15/2 ) and are widely used in various fields, including biomedicine [ 8 ]. The paramagnetic gadolinium ion (Gd 3+ ) is widely employed as contrast agent for magnetic resonance imaging (MRI) due to its seven unpaired electrons in the valence layer ( 4 f 7 ), giving it a high magnetic moment (S = 7/2). This magnetic property makes gadolinium highly responsive to external magnetic fields, such as those used in magnetic resonance imaging, establishing it as one of the most powerful paramagnetic elements. Consequently, Gd 2 O 3 :Yb/Er UCNPs enable the formation of a bimodal probe through the combination of magnetic resonance imaging and optical imaging techniques [ 10 ]. Multimodal probes have been extensively used as highly effective diagnostic tools for clinical diagnostics and cancer studies in the last decade. The surface modification of UCNPs with functional groups and biomolecules aims to address their potential applications in detection, bioimaging, and drug distribution, simultaneously improving their aqueous dispersibility, colloidal stability, biocompatibility, and non-toxicity [11; 12]. The use of natural biopolymers for core-shell coating of nanoparticles has attracted significant attention for biomedical applications due to their ability to bind to drugs, receptors, ligands, etc. [13; 14; 15]. Due to their intrinsic structure, these biopolymers possess various functional groups accessible on the surface, such as carboxylate (-COOH), hydroxyl (-OH), and amino (-NH 2 ), providing multiple possibilities for modification through covalent or non-covalent conjugation of chemical species [15; 16]. In this context, the functionalization of NPs with natural biopolymers has proven to be an important strategy to confer desired properties. Biopolymer-coated nanoparticles can play the role of efficient vehicles for controlled and targeted drug release, aiming to enhance therapeutic effects and reduce side effects associated with formulated drugs [16; 18]. It is worth noting that gelatin, as a highly versatile natural biopolymer, has been widely used in the pharmaceutical industry due to its biocompatibility, biodegradability, low cost, and numerous active groups available for binding with target molecules [19; 20]. In this study, our goal is to prepare, characterize, and evaluate the effect of coating Gd 2 O 3 :Yb/Er nanoparticles with gelatin (Gd 2 O 3 :Yb/Er@Gelatin) and its influence on physicochemical properties. We aim to investigate this approach as a promising strategy for drug transport, increased drug solubility, and toxicity acceptance. Materials and Methods Materials Gadolinium (III) oxide, ytterbium (III) oxide and erbium (III) oxide (Aldrich, 99,9%), urea (Vetec, P.A.), gelatin (Sigma-Aldrich), acetone (Dinâmica, P.A.), glutaraldehyde (GA) (Dinâmica, 25% P.S.), nitric acid (Alphatec, P.A.). Ln(NO 3 ) 3 .6H 2 O (with Ln 3+ = Er 3+ , Yb 3+ e Gd 3+ ) were obtained by reacting nitric acid with the corresponding trivalent lanthanide oxide. Synthesis procedures Synthesis of Gd 2 O 3 :Yb/Er The synthesis of Gd 2 O 3 :Yb/Er nanoparticles was conducted based on the work of Kamińska et al (2018) [ 21 ], using the homogeneous precipitation method. In a beaker was added 5.440 mmol (2.45 g) of Gd(NO 3 ) 3 .6H 2 O, 0.029 mmol (0.013 g) of Er(NO 3 ) 3 .6H 2 O, 0.530 mmol (0.25 g) of Yb(NO 3 ) 3 .6H 2 O and 0.040 mol (2.4 g) of urea and 100 mL of distilled water and was conditioned under stirring and heating in a glycerin bath at 75°C for 3 hours. Then, the formed precursor material (Gd(OH)CO 3 :Yb/Er) was separated by centrifugation at 5000 rpm for 15 minutes and dried at 80°C in an oven for 24 hours. Finally, the Gd(OH)CO 3 :Yb/Er nanoparticles were subjected to the calcination process at a temperature of 900°C, with a heating rate of 2°C/min for 3 hours. Synthesis of Gd 2 O 3 :Yb/Er@Gelatin The synthesis of Gd 2 O 3 :Yb/Er@Gelatin involves an adaptation of the two-step gelatin desolvation method proposed by Mozafari and Moztarzafari (2010) [ 22 ]. In order four syntheses were carried out under different conditions, as indicated in Table 1 . In the first step of the synthesis, the gelatin was dissolved in 100 mL of ultrapure water, and the solution was stirred at a temperature of 45°C until the gelatin completely dissolved. Then, 100 mL de acetone was slowly added to the solution to precipitate low weight gelatin chains. The supernatant was then discarded, and the gelatin settled at the bottom of the flask was dissolved in 100 mL of ultrapure water. Next 100 mL of a Gd 2 O 3 :Yb/Er suspension (1 mg/mL) was added under constant agitation for 30 minutes and at a constant temperature of 45°C. For the second step of the desolvation process, 150 mL of acetone, and finally 1 mL of glutaraldehyde 25% (GA) solution were added. The system was stirred for 20 hours at a temperature of 45°C. The gelatin-coated nanoparticles were washed with distilled water, followed by the collection of the solid via centrifugation at 5000 rpm for 20 minutes. Table 1 Conditions for the synthesis of Gd 2 O 3 :Yb/Er@Gelatin nanoparticles. Sample Glutaraldehyde (mL) Gelatin concentration (mg/mL) Gd 2 O 3 :Yb/Er@Gelatin1 - 10 Gd 2 O 3 :Yb/Er@Gelatin1_GA 1 10 Gd 2 O 3 :Yb/Er@Gelatin2 - 5 Gd 2 O 3 :Yb/Er@Gelatin2_GA 1 5 Nanoparticles characterization Powder X-ray Diffraction (XRD) data were recorded at room temperature on a Rigaku X-ray diffractometer with Cu Kα (λ = 1.5406 Å) radiation and a rotating anode X-ray source of 9 kW. The source was coupled to a high-resolution multidimensional 2D semiconductor detector, HyPix-300. The analysis was conducted in a 2θ range from 10 to 70, with a scanning speed of 1°/min and an increment of 0,02 °. Scanning Electron Microscopy (SEM), the samples were placed on aluminum stubs coated with carbon tape. Subsequently, the samples were metalized with a gold layer. Images were acquired using a Tescan scanning electron microscope, model MIRA3, equipped with a field emission electron beam source. Energy-dispersive X-ray spectroscopy (EDX) was coupled with SEM. Fourier Transform Infrared Spectroscopy (FT-IR) analysis was conducted, where absorption spectra in the infrared region were obtained at room temperature. This analysis was performed using a Fourier-transform spectroscopy from PerkinElmer. The frequency range analyzed covered from 4000 to 400 cm − 1 . A KBr pellet was used for this analysis. Thermogravimetric analyzer (TGA) was carried out using a Shimadzu, model TGA-50/50H. A platinum sample holder and a nitrogen atmosphere flow of 50 mL/min were employed. The heating rate was 10°C/min, ranging from 25 to 900°C. Photophysical properties Upconversion emission spectra were obtained using a 980 nm laser from Laser Tool as the excitation source, with power ranging from 500 to 1900 mW. These spectra were detected using the Fluorolog-3 ISA spectrofluorimeter from Horiba Jobin Yvon, which has a detection range covering from 400 to 750 nm. Intensity values obtained from the emission spectra were used to conduct studies to determine the number of photons involved in the upconversion emission. Relaxometric characterization Relaxometric characterization involved the measurement of longitudinal and transverse relaxation times ( T 1 and T 2 ) of 1H nuclei in water molecules. T 1 and T 2 values were measured at 37°C using Bruker relaxometers. The Minispec mq20 model with a magnetic field of 0.47 T and the Minispec mq60 model with a magnetic field of 1.41 T were used. For relaxometric analysis, five suspensions with different Gd 3+ concentrations (0.1, 0.08, 0.06, 0.04, and 0.02 mM) were prepared for each sample. These concentrations were prepared considering the nominal value of Gd 3+ in 1 mol of Gd 2 O 3 :Yb/Er, and the suspensions with different Gd 3+ concentrations of NPs Gd 2 O 3 :Yb/Er@Gelatin were prepared with the aid of TGA. These solutions were prepared using ultrapure water containing 0.0140 g of xanthan gum, which was used as a dispersing agent. The samples were subjected to ultrasonic bath treatment for 5 minutes. All experimental relaxation rate values were corrected to account for diamagnetic contributions using a xanthan gum solution in water. MTT cytotoxicity assay To evaluate the cytotoxicity of NPs, Vero cells were cultured in a 96-well plate for 24 hours with 1x10 4 cells per well. Subsequently, the culture medium was removed, and NPs at various concentrations (3, 6, 12, 25, 50, 100 µg/mL) were added. Furthermore, cells cultured only with the NP solubilization solution were used as a control. After 24 hours of incubation, 10 uL of MTT solution (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) was added at a concentration of 5 mg/mL to each well. After an additional 4-hour incubation, the solution's absorbance was measured at 570 nm using a Thermo Multiskan SkyHigh microplate spectrophotometer. Results and Discussion The structural characteristics of the compounds were evaluated using the X-ray diffraction powder (XRD). The Gd 2 O 3 :Yb/Er showed good correlation with the simulated diffraction pattern reported for Zachariasen et al. (1927) [ 23 ], indicating a structure similar to that of Gd 2 O 3 (cubic crystalline system and space group I-2 1 3), see Fig. 1 . The diffractograms for Gd 2 O 3 :Yb/Er@Gelatin1 (orange line), Gd 2 O 3 :Yb/Er@Gelatin1_GA (brown line), Gd 2 O 3 :Yb/Er@Gelatin2 (green line), Gd 2 O 3 :Yb/Er@Gelatin2_GA (red line), also maintained the diffraction peaks, which indicates that the gelatin coating process does not induce alterations in the crystalline structure of the Gd 2 O 3 :Yb/Er. These results are in line with the results of the study by Lin et al. (2017) [ 24 ], who investigated the nanoparticle coating process in an analogous process. SEM analysis of the Gd(OH)CO 3 :Yb/Er (Fig. 2 a) revealed the presence of nanoscale particles with spherical and uniform morphology, exhibiting an average particle size of 70.7 ± 9.2 nm ( Figure S1 a ). Gd 2 O 3 :Yb/Er (Fig. 2 b) spherical morphology was maintained, with a reduction in the average size of the nanoparticles to 57.7 ± 6.5 nm ( Figure S1 b ). This result can be attributed to the elimination of carbonate and hydroxide present in Gd(OH)CO 3 :Yb/Er during the calcination step. The Gd 2 O 3 :Yb/Er@Gelatin1 (Fig. 2 c) has an average size 88.5 ± 9.1 nm ( Figure S1 c ), while the Gd 2 O 3 :Yb/Er@Gelatin1_GA (Fig. 2 d) presents an average size 83.6 ± 9.8 nm ( Figure S1 d ). The Gd 2 O 3 :Yb/Er@Gelatin2 has a size of 78.1 ± 5.7 nm ( Figure S1 e ), and the Gd 2 O 3 :Yb/Er@Gelatin2_GA has a size of 73.9 ± 2.9 nm ( Figure S1 f ). It was observed that the spherical morphology was maintained, and in general, the average particle size was larger compared to the Gd 2 O 3 :Yb/Er compound. This suggests that the coating process allowed the formation of a gelatin layer around Gd 2 O 3 :Yb/Er. For the Gd 2 O 3 :Yb/Er@Gelatin1 and Gd 2 O 3 :Yb/Er@Gelatin1_GA compounds, which were synthesized with a higher concentration of gelatin (10 mg/mL), a larger increase in the average particle size was observed, approximately 30.8 ± 16.3 nm and 25.9 ± 15.6 nm, respectively, compared to Gd 2 O 3 :Yb/Er. Notably, the Gd 2 O 3 :Yb/Er@Gelatin1_GA NPs, which were cross-linked with GA, had the smallest size. On the other hand, in the Gd 2 O 3 :Yb/Er@Gelatin2 and Gd 2 O 3 :Yb/Er@Gelatin2_GA compounds, synthesized with a lower concentration of gelatin (5 mg/mL), a smaller increase in the average particle size was observed, approximately 20.4 ± 11.3 nm and 16.2 ± 12.2 nm, respectively, compared to Gd 2 O 3 :Yb/Er. The Gd 2 O 3 :Yb/Er@Gelatin2_GA NPs cross-linked with GA had the smallest size increase. In summary, the results indicate that cross-linking with GA reduces the size of the NPs, suggesting a more compact arrangement of the gelatin chains. Chemical, thermal and compositional analysis The semi-quantitative percentages values for the metals Gd 3+ , Yb 3+ e Er 3+ were obtained through the Energy-Dispersive X-ray Spectroscopy (EDX) for Gd(OH)CO 3 :Yb/Er and Gd 2 O 3 :Yb/Er, as shown in Table 2 .The result of mass percentages of Gd 3+ , Yb 3+ and Er 3+ show close values for both compounds, with Gd 2 O 3 :Yb/Er showing insertion of 24,6% of the sensitizer Yb 3+ and doping of 0,4% of the activator Er 3+ . Table 2 Semi-quantitative analysis of mass percentages for the metals Gd 3+ , Yb 3+ e Er 3+ obtained by EDS for the compound Gd(OH)CO 3 :Yb/Er and Gd 2 O 3 :Yb/Er. Sample Gd 3+ Yb 3+ Er 3+ Gd(OH)CO 3 :Yb/Er 75,5 ± 0,3 24,4 ± 0,1 0,1 ± 0,3 Gd 2 O 3 :Yb/Er 75,0 ± 0,4 24,6 ± 0,4 0,4 ± 0,3 Figure 3 a shows the FT-IR spectra for Gd(OH)CO 3 :Yb/Er and Gd 2 O 3 :Yb/Er. The Gd(OH)CO 3 :Yb/Er spectra show broad bands centered at 3434 cm − 1 , related to the O-H stretching bond and 1523 cm − 1 and 1403 cm − 1 , associated with asymmetric stretching of the C-O bond. Additionally, the bands at 1091 cm − 1 and 848 cm − 1 correspond to the symmetric stretching and deformation of the C-O, respectively, related to the carbonate ion [ 25 ]. Gd2O3:Yb/Er shows a significant change of spectra profile than Gd(OH)CO 3 :Yb/Er, which indicates the transformation of the precursor into Gd 2 O 3 :Yb/Er. Furthermore, a band centered at 561 cm − 1 , attributed to the Gd-O stretching bond, has emerged. The spectral profiles of Gd(OH)CO 3 :Yb/Er and Gd 2 O 3 :Yb/Er are very similar to those found in the literature [ 26 ]. In addition, the functionalization process of Gd 2 O 3 :Yb/Er with gelatin was also analyzed by FT-IR (Fig. 3 b). The spectra of Gd 2 O 3 :Yb/Er@Gelatin1 and Gd 2 O 3 :Yb/Er@Gelatin1_GA reveal a band centered at 3733 cm − 1 and 3292 cm − 1 , corresponding to the symmetric stretching of O-H e N-H, respectively. The band at 1665 cm − 1 is related to the C = O stretching amides. The band at 1538 cm − 1 is attributed to the deformation of the N-H bond of the amino group, and the band at 858 cm − 1 corresponds to the deformation of the N-H bond of amines. The band at 1380 cm − 1 corresponds to the stretching of the C-N bond of amines, and the band at 1236 cm − 1 is related to the stretching of the C-O bond. Finally, the band at 548 cm − 1 is attributed to the Gd-O bond present in the Gd 2 O 3 :Yb/Er compound [ 24 ]. On the other hand, the FT-IR spectrum obtained for Gd 2 O 3 :Yb/Er@Gelatin2 and Gd 2 O 3 :Yb/Er@Gelatin2_GA presents a broad band centered at 3413 cm − 1 , corresponding to the symmetric stretching of O-H and N-H bonds. The band at 1658 cm − 1 is attributed to the C = O stretching of amides. The band at 1519 cm − 1 is attributed to the deformation of the N-H bond of the amino group, and the band at 860 cm − 1 refers to the out-of-plane deformation of the N-H bond of amines. The band at 1382 cm − 1 corresponds to the stretching of the C-N bond of amines, while the band at 1238 cm − 1 is related to the stretching of the C-O bond. Finally, the band at 543 cm − 1 is attributed to the Gd-O bond present in the Gd 2 O 3 :Yb/Er compound. The identification of the amino group (-NH 2 ) in the gelatin coating suggests the possibility of functionalization at this site with drugs through covalent coupling reactions. TGA analysis were perform for Gd 2 O 3 :Yb/Er, Gd 2 O 3 :Yb/Er@Gelatin1, Gd 2 O 3 :Yb/Er@Gelatin2, Gd 2 O 3 :Yb/Er@Gelatin2_GA, as show Fig. 4 . The TGA analysis reveals two mass losses in gelatin-coated compounds, the first occurs approximately between 25 and 200°C, and the second occurs between 200 and 500°C. In the Gd 2 O 3 :Yb/Er@Gelatin2 system, the gelatin loss is about 3.40%. In the Gd 2 O 3 :Yb/Er@Gelatin2_GA system, the mass loss is approximately 4.58% of gelatin, suggesting that the Gd 2 O 3 :Yb/Er@Gelatin2_GA compound has a higher amount of gelatin than Gd 2 O 3 :Yb/Er@Gelatin2, even though both were synthesized with the same gelatin concentration. This indicates that cross-linking with GA increases the amount of gelatin around Gd 2 O 3 :Yb/Er, but in a compacted form, as the SEM analysis of Gd 2 O 3 :Yb/Er@Gelatin2_GA showed a smaller particle size. In the case of the Gd 2 O 3 :Yb/Er@Gelatin1 system, the loss is about 2.93% of gelatin, and in the Gd 2 O 3 :Yb/Er@Gelatin1_GA system, the loss was about 7.42%. It is observed again that the presence of GA increases the concentration of gelatin. In general, samples without GA showed the lowest percentage mass loss, while samples cross-linked with GA showed the highest percentage mass loss. Spectroscopic properties The photoluminescence properties of Gd 2 O 3 :Yb/Er were investigated using excitation at 980 nm with a power of 1900 mW spectra in solid state at room temperature (Fig. 5 a). Gd 2 O 3 Yb/Er exhibited maximum emission intensity at 659 nm, predominantly in the red region, referring to an upconversion process between Yb → Er, as previously reported in the literature [ 27 ]. Additionally, five sharp peaks centered at 653, 662, 667, 673, and 680 nm can also be observed. All these peaks can be attributed to the transition for Er 3+ : 4 F 9/2 → 4 I 15/2 . In addition, the emission spectra also reveals signal, predominantly in the green region, centered at 521 nm, with three additional peaks at wavelengths of 525, 532, and 537 nm, which can be attributed to the characteristic transitions of Er 3+ : 2 H 11/2 → 4 I 15/2 , and three additional peaks at 547, 552, and 561 nm, attributed to Er 3+ : 4 S 3/2 → 4 I 15/2 transition [ 27 ]. The upconversion (UC) mechanism was interpreted by recording the UC emission intensities as a function of pump-power intensities for the Gd 2 O 3 :Yb/Er sample. The relationship between emission intensity ( I up ) and pump power (P). The log ( I up ) versus log ( P N ) line is fitted according to Eq. 1 [ 28 ], se can be expressed as: $${I}_{up }\alpha {P}^{N}\to log\left({I}_{up}\right) = log\left(k{P}^{n}\right) = NlogP + C$$ 1 where N is the number of photons in the UC process and can be acquired from the slope of the straight line by linear fitting the plot of log ( I up ) and log(P), as shown in Fig. 5 d. The slopes for these red and green emission bands located were 2.53 (659 nm) and 1.54 (521 nm), respectively. The equation obtained for emission in the green region was y = 1.54x + 2.34, with an r-square value of 0.999, while the equation obtained for emission in the red region was y = 2.53x − 2.99, with an r-square value of 0.999. These results suggest that the three-photon process is responsible for upconversion of the 2 H 11/2 → 4 I 15/2 (green) transition, and the two-photon process is responsible for upconversion of the 4 F 9/2 → 4 I 15/2 (red) transition. Figure 6 shows the UC emission spectra for Gd 2 O 3 :Yb/Er, Gd 2 O 3 :Yb/Er@Gelatin1, Gd 2 O 3 :Yb/Er@Gelatin1_GA, Gd 2 O 3 :Yb/Er@Gelatin2, and Gd 2 O 3 :Yb/Er@Gelatin2_GA materials. The results revealed that the coating process does not alter the spectral profile of the materials, as previously reported from [ 26 ]. This result agrees with structural characterization, where the synthetic method does not affect the crystallinity of the Gd 2 O 3 :Yb/Er. Table 3 showed the intensity ratio between the red UC emission ( I R ) to and green UC emission ( I G ) for Gd 2 O 3 :Yb/Er@Gelatin1, Gd 2 O 3 :Yb/Er@Gelatin1_GA, Gd 2 O 3 :Yb/Er@Gelatin2, Gd 2 O 3 :Yb/Er@Gelatin2_GA. The results revealed a decrease of gelatin-coated intensity ratio values than Gd 2 O 3 :Yb/Er, indicating that the coating process reduces the relative green emission intensities ( I G ) due to the presence of a gelatin layer around Gd 2 O 3 :Yb/Er. Thus, the presence of the gelatin layer leads to an increase of the concentration of adsorbed water on the material's surface, enhancing the quenching effect of the UC emission intensities. On the other hand, the ratios between emission intensities for the compounds Gd 2 O 3 :Yb/Er@Gelatin1 and Gd 2 O 3 :Yb/Er@Gelatin2_GA showed the least decrease than Gd 2 O 3 :Yb/Er [ 29 ]. Table 3 Quantitative analysis of red intensity ( I R ), green intensity ( I G ) and the red-to-green intensity ratio ( I R / I G ) for the compounds Gd 2 O 3 :Yb/Er, Gd 2 O 3 :Yb/Er@Gelatin1, Gd 2 O 3 :Yb/Er@Gelatin1_GA, Gd 2 O 3 :Yb/Er@Gelatin2 and Gd 2 O 3 :Yb/Er@Gelatin2_GA. Sample I R (CPS) I G (CPS) I R / I G Gd 2 O 3 :Yb/Er 5,8.10 6 2,6.10 5 22,3 Gd 2 O 3 :Yb/Er@Gelatin1 4,6.10 5 4,2.10 4 11,0 Gd 2 O 3 :Yb/Er@Gelatin1_GA 8,2.10 5 1,9.10 5 4,3 Gd 2 O 3 :Yb/Er@Gelatin2 3,3.10 5 4,9.10 4 6,7 Gd 2 O 3 :Yb/Er@Gelatin2_GA 1,3.10 6 1,2. 10 5 11,0 Relaxivities The relaxometry data obtained at 60 MHz and 37°C for the Gd 2 O 3 :Yb/Er, Gd 2 O 3 :Yb/Er@Gelatin1, Gd 2 O 3 :Yb/Er@Gelatin1_GA, Gd 2 O 3 :Yb/Er@Gelatin2 e Gd 2 O 3 :Yb/Er@Gelatin2_GA (Table 4 ). Gd 2 O 3 :Yb/Er showed relaxivity values of r 1 = 2,70 ± 0,12 s − 1 mM –1 and r 2 = 10,32 ± 0,71 s − 1 mM –1 . These results indicate that the relaxation time decrease was less effective for T 1 than T 2 , suggesting that the water diffusion process between particles has a greater influence on the relaxometry process. Similar behavior was reported for Norek et al. (2007) [ 30 ], where Gd 2 O 3 NPs, in a 7 T field at 25 ºC, present a smaller effect on T 1 relaxation time than on T 2 . Gd 2 O 3 :Yb/Er@Gelatin1, Gd 2 O 3 :Yb/Er@Gelatin1_GA, Gd 2 O 3 :Yb/Er@Gelatin2, Gd 2 O 3 :Yb/Er@Gelatin2_GA materials have a significant effect on the relaxation time of the water protons compared to Gd 2 O 3 :Yb/Er, suggesting that the gelatin coating process promoted an increased of the relaxivity in the Gd 2 O 3 :Yb/Er@Gelatin NPs. Gelatin is composed of hydrophilic groups, allowing interactions of water molecules with its functional groups through hydrogen bonding. In this way, gelatin layers can attract water molecules, increasing the local water density and improving the water exchange rate of Gd 2 O 3 :Yb/Er@Gelatin [31; 32]. In addition, it can be seen that r 2 is greater than the r 1 values, which results in T 2 that are lower than T 1 values, indicating that the water diffusion process in the NPs is predominant, as seen previously in the relaxivity measurement for Gd 2 O 3 :Yb/Er. In the results obtained for Gd 2 O 3 :Yb/Er@Gelatin1 ( r 1 = 15,08 ± 0,46 and r 2 = 33,71 ± 2,47) and Gd 2 O 3 :Yb/Er@Gelatin2 ( r 1 = 9,24 ± 0,40 and r 2 = 20,32 ± 0,89) showed higher relaxivity values than Gd 2 O 3 :Yb/Er, suggesting that the presence of gelatin increases the concentration of water around the paramagnetic ion due to gelatin being a hydrophilic compound that retains water molecules in its structure through hydrogen bonds. NPs crosslinked with GA, the Gd 2 O 3 :Yb/Er@Gelatin1_GA and Gd 2 O 3 :Yb/Er@Gelatin2_GA, showed lower relaxivity values, suggesting that crosslinking with GA compacts the gelatin chains, reducing the mobility of water molecules. Additionally, this process reduces the concentration of water retained in the gelatin, hindering both the diffusion of external sphere water molecules and the water exchange rate with the bulk. In the results obtained, it is observed that among the NPs synthesized with the same amount of gelatin (10 mg/mL), Gd 2 O 3 :Yb/Er@Gelatin1 and Gd 2 O 3 :Yb/Er@Gelatin1_GA, as reported in Table 1 , Gd 2 O 3 :Yb/Er@Gelatin1 showed higher relaxivity values, probably due to the higher amount of gelatin-coated, as seen in the SEM analysis. This results in a change in the mobility of water molecule diffusion and the water exchange rate with the bulk. Comparing the relaxivity results between Gd 2 O 3 :Yb/Er@Gelatin2 and Gd 2 O 3 :Yb/Er@Gelatin2_GA, which were synthesized with the same amount of gelatin (5 mg/mL), as reported in Table 1 , it is suggested that the crosslink process did not significantly interfere with the mobility of water molecules, as the r 2 values were very close. Gd 2 O 3 :Yb/Er@Gelatin2 and Gd 2 O 3 :Yb/Er@Gelatin2_GA had lower relaxivity compared to Gd 2 O 3 :Yb/Er@Gelatin1, probably due to the lower amount of gelatin in the coating. Table 4 Relaxivities obtained for the systems at 37°C and 60 MHz (1.41 T). Sample r 1 ( s − 1 mM –1 ) r 2 ( s − 1 mM –1 ) Gd 2 O 3 :Yb/Er 2,70 ± 0,12 10,32 ± 0,71 Gd 2 O 3 :Yb/Er@Gelatin1 15,08 ± 0,46 33,71 ± 2,47 Gd 2 O 3 :Yb/Er@Gelatin1_GA 4,12 ± 0,083 13,62 ± 1,94 Gd 2 O 3 :Yb/Er@Gelatin2 9,24 ± 0,40 20,32 ± 0,89 Gd 2 O 3 :Yb/Er@Gelatin2_GA 12,17 ± 0,24 20,01 ± 2,17 Cell viability The cytotoxicity of Gd 2 O 3 :Yb/Er and Gd 2 O 3 :Yb/Er@Gelatin NPs was evaluated using the MTT assay with Vero cells, which are healthy cells. The concentration-dependent effect of the NPs was assessed in comparison to cells in the control experiment (without NPs), as shown in Fig. 7 . The NPs were found to be viable in the cells, with values exceeding 90% for all concentrations studied. A similar outcome was observed in the study by Chen et al. (2011) [33], in which NaYF 4 :Yb/Er NPs coated with chitosan and conjugated with folic acid also exhibited cell viability with values exceeding 90%. Moreover, Kaminska et al. (2015) [34] showed in their results that gadolinium oxide NPs, with erbium, ytterbium and zinc polyvinylpyrrolidone (PVP) coated are biocompatible at the NPs concentration of up to 50 µg/mL in 24h incubation. Additionally, it is important to note that the NPs promoted a proliferative effect for some of the concentrations studied, as evidenced by the observation of average cell viability exceeding 100%. In this sense, we can identify high biocompatibility and viability of Gd 2 O 3 :Yb/Er and Gd 2 O 3 :Yb/Er@Gelatin NPs for potential diagnosis of diseases and application in chemotherapy as a carrier. Based on the luminescence and relaxivity data, the Gd 2 O 3 :Yb/Er@Gelatin2_GA system exhibited more favorable results compared to the other systems under evaluation. This is evident when initaly observing that the emission intensities for the Gd 2 O 3 :Yb/Er@Gelatin2_GA compound shower the least reduction compared to Gd 2 O 3 :Yb/Er. On the other hand, despite the relaxivity of the Gd 2 O 3 :Yb/Er@Gelatin1 ( r 2 = 33,71 ± 2,47) being higher compared to the Gd 2 O 3 :Yb/Er@Gelatin2_GA system ( r 2 = 20,01 ± 2,17), Gd 2 O 3 :Yb/Er@Gelatin2_GA offers advantages in its chemical composition due to the use of GA in its synthesis as a cross-linking agent. Gelatin is a water-soluble compound due to its hydrophilic nature, but cross-linking with GA provides greater stability to the system, making the gelatin more resistant to dissolution in water. Furthermore, the cross-linking of gelatin with GA involves the reaction of free amino groups from lysine or hydroxylysine amino acid residues in the chains with the aldehyde groups of GA. This ensures that the coating of Gd 2 O 3 :Yb/Er with gelatin will remain intact during the desired biological application [36]. Additionally, the Gd 2 O 3 :Yb/Er@Gelatin2_GA system exhibited the smallest size, as revealed by SEM, and the smaller the NPs, the more efficient the penetration into tumor blood vessels will be. Conclusions In this study, a nanosensor was developed from UCNPs of Gd 2 O 3 :Yb/Er coated with gelatin, which proved to be viable for potencial theranostic application. X-ray diffraction (XRD) analysis confirmed the cubic crystalline structure for Gd 2 O 3 :Yb/Er and indicated that the gelatin coating did not affect its crystallinity. Scanning electron microscopy (SEM) analysis revealed a reduction in the nanoparticle diameter after the calcination of the precursor, indicating the formation of the oxide. The formation of a gelatin layer around Gd 2 O 3 :Yb/Er was evidenced by SEM, suggesting that cross-linking with GA reduced the size of the nanoparticles. Luminescence spectroscopy for Gd 2 O 3 :Yb/Er exhibited characteristic Yb 3+ /Er 3+ UC emission peaks, and it was observed that the coating process did not alter the photophysical properties of the material, although it affected the emission intensities. Relaxometric characterization of the gelatin-coated systems (Gd 2 O 3 :Yb/Er@Gelatin) indicated an increase in relaxivity, especially for T 2 , suggesting a greater interaction of gelatin with water molecules and the potential to enhance contrast in MRI applications. In addition, Gd 2 O 3 :Yb/Er and Gd 2 O 3 :Yb/Er@Gelatin NPs were viable in biological applications, as observed in the cytotoxicity analysis, where it was observed that Gd 2 O 3 :Yb/Er and Gd 2 O 3 :Yb/Er@Gelatin NPs had no cytotoxic effect on healthy cells, presenting cellular viability above 90%. In summary, the compound Gd 2 O 3 :Yb/Er@Gelatin2_GA was chosen as the most promising nanoparticle to continue the planned applications. These results pave the way for future research and clinical applications, where this functionalized nanosensor can be used in biomedical therapy and diagnosis. Declarations Credit authorship contribution statement J. F. S., Lima: Conceptualization, Methodology, Investigation, Writing - original draft. G. N. S. A., Oliveira: Methodology - relaxometry. D. K. D. N., Santos: Methodology - Cell viability. G. A. L., Pereira: Conceptualization, Investigation - relaxometry - review & editing. R. S. Viana: Conceptualization, Methodology, Writing - review & editing, Supervision. S. A., Júnior: Writing - review & editing, Supervision. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Funding This research has received support from the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES), the Conselho Nacional de Desenvolvimento Científico e Tecnológico - Brasil (CNPq), and the Fundação de Amparo à Pesquisa do Estado de Alagoas (FAPEAL; grant no. DCR2022051000008). Acknowledgments The authors thank the Optics and Nanoscopy Group (GON-IF-UFAL) and Earth Rare Laboratory (BSTR -UFPE) for the optical measurements. R.S.V gratefully acknowledged the FAPEAL/PDCTR/CNPq program for a scholarship (grant no. DCR2022051000008). References Li H, Wang X, Huang D, Chen G (2020) Recent advances of lanthanide-doped upconversion nanoparticles for biological applications. Nanotechnology, 31(7):072001. Zhang D, Peng R, Liu W, Donovan M J, Wang L, Ismail I, Li J, Li J, Qu F, Tan W (2021) Engineering DNA on the Surface of Upconversion Nanoparticles for Bioanalysis and Therapeutics. American Chemical Society Nano. 15(11):17257–17274. 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Li H, Song S, Wang W, Chem K (2015) In vitro photodynamic therapy based on magnetic-luminescent Gd 2 O 3 :Yb,Er nanoparticles with bright three-photon up-conversion fluorescence under near-infrared light. Dalton Transactions 44(36):16081–16090. Additional Declarations No competing interests reported. Supplementary Files Francineetal.manuscriptSupportinginformation.docx Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-3961971","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":274827706,"identity":"1e27b4c1-fa0d-4c65-9f4d-c0277f5e1a5f","order_by":0,"name":"Joyce Francine da Silva de Lima","email":"","orcid":"","institution":"Federal University of Pernambuco","correspondingAuthor":false,"prefix":"","firstName":"Joyce","middleName":"Francine da Silva","lastName":"de Lima","suffix":""},{"id":274827707,"identity":"8594b08a-b792-4f14-b4a3-361b7e44a910","order_by":1,"name":"Giovanna Nogueira da Silva Avelino Oliveira","email":"","orcid":"","institution":"Federal University of Pernambuco","correspondingAuthor":false,"prefix":"","firstName":"Giovanna","middleName":"Nogueira da Silva Avelino","lastName":"Oliveira","suffix":""},{"id":274827708,"identity":"3d8516d9-9bc5-4457-9bc2-9a3620394141","order_by":2,"name":"Dayane Kelly Dias do Nascimento Santos","email":"","orcid":"","institution":"Federal University of Pernambuco","correspondingAuthor":false,"prefix":"","firstName":"Dayane","middleName":"Kelly Dias do Nascimento","lastName":"Santos","suffix":""},{"id":274827709,"identity":"e8457d44-aa5d-4200-bf2d-e1c209d5716c","order_by":3,"name":"Giovannia Araújo de Lima Pereira","email":"","orcid":"","institution":"Federal University of Pernambuco","correspondingAuthor":false,"prefix":"","firstName":"Giovannia","middleName":"Araújo de Lima","lastName":"Pereira","suffix":""},{"id":274827710,"identity":"a8671d37-0d50-47ec-bcce-bee2306ba6d2","order_by":4,"name":"Rodrigo da Silva Viana","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABBUlEQVRIiWNgGAWjYLCCBAhlAGLIgVgHHpCixRisJYFIywxARGIDkiFYgXn/ATaJBzV35M3bm7d9ePDLJn1+2OGHQFvs5HQbsGuRuZHAJpFw7JnhnDPHimck9qXlbrydZgDUkmxsdgC7FgkJBmaDBLbDjDMkcowZEnsO526cnQDSciBxGy4t/AeAWv4dtodpSTecnf4BvxaGBMYHiW2HE8FaEn4cTpCXziFgi0Ri44PEvsPJM3iOFQODK81wg3ROwYEEAzx+4T984OCPb4dtZ7A3b2b88cdGXn52+uYPHyrs5HBpYWBgbEBitwFjB6zSAJdyDPCHgUG+gaCqUTAKRsEoGGEAAOkiY5vioxKpAAAAAElFTkSuQmCC","orcid":"","institution":"Federal University of Alagoas","correspondingAuthor":true,"prefix":"","firstName":"Rodrigo","middleName":"da Silva","lastName":"Viana","suffix":""},{"id":274827711,"identity":"2ee87456-4ddd-44c2-bd17-897e58017620","order_by":5,"name":"Severino Alves Junior","email":"","orcid":"","institution":"Federal University of Pernambuco","correspondingAuthor":false,"prefix":"","firstName":"Severino","middleName":"Alves","lastName":"Junior","suffix":""}],"badges":[],"createdAt":"2024-02-16 17:47:52","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3961971/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3961971/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":51668810,"identity":"bc34b384-d69b-4baa-9c47-2864260b1ebe","added_by":"auto","created_at":"2024-02-27 00:35:28","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":2095778,"visible":true,"origin":"","legend":"\u003cp\u003eX-ray diffraction (XRD) for Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er (black line) and simulated Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (gray line) obtained from the work by Zachariasen et al. (1927) [23], for the Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1 (orange line), Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1_GA (wine line), Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2 (green line), and Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2_GA (red line) compounds.\u003c/p\u003e","description":"","filename":"Figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-3961971/v1/99a18693fa06bd1babcec2af.png"},{"id":51668814,"identity":"78b6c4f1-47c7-4e9c-b6a8-7aa1bf1ac787","added_by":"auto","created_at":"2024-02-27 00:35:28","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":24610693,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images for the compounds a) Gd(OH)CO\u003csub\u003e3\u003c/sub\u003e:Yb/Er, b) Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er; c) Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1, d) Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1_GA, e) Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2 e f)\u0026nbsp; Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2_GA.\u003c/p\u003e","description":"","filename":"Figure2.png","url":"https://assets-eu.researchsquare.com/files/rs-3961971/v1/4a92f2de9ac5772c7ea0a536.png"},{"id":51668813,"identity":"2bb5fc8a-50b6-4f32-81c1-a2f742199e44","added_by":"auto","created_at":"2024-02-27 00:35:28","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":740366,"visible":true,"origin":"","legend":"\u003cp\u003ea) FT-IR spectra for the compounds Gd(OH)CO\u003csub\u003e3\u003c/sub\u003e:Yb/Er (gray line) and Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er (black line); b) FT-IR spectra for the compounds Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er (black line), Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1 (orange line), Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1_GA (wine line), Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2 (green line), and Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2_GA (red line).\u003c/p\u003e","description":"","filename":"Figure3.png","url":"https://assets-eu.researchsquare.com/files/rs-3961971/v1/a0edb45ce15b8c476fd66e8a.png"},{"id":51668812,"identity":"39be8802-95a1-487d-aef1-186f59fcb361","added_by":"auto","created_at":"2024-02-27 00:35:28","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":598139,"visible":true,"origin":"","legend":"\u003cp\u003eTGA for the compounds Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er (black line), Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1_GA (wine line), Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1 (orange line), Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2 (green line), Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2_GA (red line).\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e","description":"","filename":"Figure4.png","url":"https://assets-eu.researchsquare.com/files/rs-3961971/v1/4c2d7679e2a2db1dca38bd55.png"},{"id":51668816,"identity":"d2225d5c-58eb-4ace-adf0-a269783d6dac","added_by":"auto","created_at":"2024-02-27 00:35:29","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":1281009,"visible":true,"origin":"","legend":"\u003cp\u003ea) Upconversion emission spectrum of Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er, at a power of 1900 mW; (b) Upconversion emission spectra of Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er, with varied power (500 to 1900 mW) at 510 and 580 nm; (c) Upconversion emission spectra of the Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er compound, with varied power (500 to 1900 mW) from 630 to 710 nm; (d) Log-log plot of emission intensity as a function of pump power for Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er.\u003c/p\u003e","description":"","filename":"Figure5.png","url":"https://assets-eu.researchsquare.com/files/rs-3961971/v1/fcf2c8b4bc24926872fdcf2e.png"},{"id":51668815,"identity":"204bf2d2-66cb-477b-9ac3-c40c99b2ee3b","added_by":"auto","created_at":"2024-02-27 00:35:28","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":524345,"visible":true,"origin":"","legend":"\u003cp\u003eUpconversion emission spectra for the compounds Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er (black line), Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1 (orange line), Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1_GA (wine line), Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2 (green line), Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2_GA (red line) (λ\u003csub\u003eEx\u003c/sub\u003e = 980 nm), with a power of 1900 mW.\u003c/p\u003e","description":"","filename":"Figure6.png","url":"https://assets-eu.researchsquare.com/files/rs-3961971/v1/babebb71c56ecbcb509cf972.png"},{"id":51668817,"identity":"defdaba9-f5db-4c0d-b9c4-5f2cec96e1bb","added_by":"auto","created_at":"2024-02-27 00:35:29","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":420011,"visible":true,"origin":"","legend":"\u003cp\u003eCytotoxicity of the compounds a) Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er, b) Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1, c) Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1_GA, d) Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2 e e) Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2_GA.\u003c/p\u003e","description":"","filename":"Figure7.png","url":"https://assets-eu.researchsquare.com/files/rs-3961971/v1/0420a838621e24547b4ce2b0.png"},{"id":51668839,"identity":"b38721b3-c638-4eef-9319-4d27d1d714ac","added_by":"auto","created_at":"2024-02-27 00:43:30","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2709938,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3961971/v1/88223055-d4fd-4b27-98d2-4be8c933f10a.pdf"},{"id":51668811,"identity":"aa7d49bf-1fcd-43f0-a498-df22853dea04","added_by":"auto","created_at":"2024-02-27 00:35:28","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":147790,"visible":true,"origin":"","legend":"","description":"","filename":"Francineetal.manuscriptSupportinginformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-3961971/v1/e5e3ef7e9d1a1dc9767ba7c2.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Design and Characterization of Gelatin-Coated Upconversion Nanoparticles: Insights into Structural, Relaxometric, Luminescent, and Cytotoxic Properties","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe upconversion nanoparticles (UCNPs) have garnered significant attention due to their remarkable optical characteristics such as fixed energy levels, high resistance to photodegradation, and lifetimes on the order of milliseconds [1; 2]. Additionally, UCNPs have been of considerable interest because of their intrinsic advantages, including a large anti-Stokes shift, deep tissue penetration capability, reduced photodamage effects, and superior photostability [3; 4; 5; 6]. Furthermore, UCNPs emerge as a promising solution to overcome the limitations of conventional photoluminescent (PL) imaging agents, such as small organic dyes, metallic complexes, fluorescent proteins, and quantum dots (QDs) in the context of live cell and tissue imaging [7; 8]. Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e stands out as an excellent luminescent host material due to its low phonon energy (cut off at ar 600 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and good thermal stability [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. One class of UCNPs utilizes Yb\u003csup\u003e3+\u003c/sup\u003e e Er\u003csup\u003e3+\u003c/sup\u003e ions as sensitization and activation centers, respectively [4; 7; 8]. Typically, these nanomaterials emit light in the green region (\u003csup\u003e4\u003c/sup\u003eI\u003csub\u003e11/2\u003c/sub\u003e \u0026rarr; \u003csup\u003e4\u003c/sup\u003eF\u003csub\u003e7/2\u003c/sub\u003e and \u003csup\u003e4\u003c/sup\u003eI\u003csub\u003e13/2\u003c/sub\u003e \u0026rarr; \u003csup\u003e4\u003c/sup\u003eF\u003csub\u003e9/2\u003c/sub\u003e) and in the red region (\u003csup\u003e4\u003c/sup\u003eF\u003csub\u003e9/2\u003c/sub\u003e \u0026rarr; \u003csup\u003e4\u003c/sup\u003eI\u003csub\u003e15/2\u003c/sub\u003e) and are widely used in various fields, including biomedicine [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. The paramagnetic gadolinium ion (Gd\u003csup\u003e3+\u003c/sup\u003e) is widely employed as contrast agent for magnetic resonance imaging (MRI) due to its seven unpaired electrons in the valence layer (\u003csup\u003e4\u003c/sup\u003ef\u003csub\u003e7\u003c/sub\u003e), giving it a high magnetic moment (S\u0026thinsp;=\u0026thinsp;7/2). This magnetic property makes gadolinium highly responsive to external magnetic fields, such as those used in magnetic resonance imaging, establishing it as one of the most powerful paramagnetic elements. Consequently, Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er UCNPs enable the formation of a bimodal probe through the combination of magnetic resonance imaging and optical imaging techniques [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Multimodal probes have been extensively used as highly effective diagnostic tools for clinical diagnostics and cancer studies in the last decade. The surface modification of UCNPs with functional groups and biomolecules aims to address their potential applications in detection, bioimaging, and drug distribution, simultaneously improving their aqueous dispersibility, colloidal stability, biocompatibility, and non-toxicity [11; 12]. The use of natural biopolymers for core-shell coating of nanoparticles has attracted significant attention for biomedical applications due to their ability to bind to drugs, receptors, ligands, etc. [13; 14; 15]. Due to their intrinsic structure, these biopolymers possess various functional groups accessible on the surface, such as carboxylate (-COOH), hydroxyl (-OH), and amino (-NH\u003csub\u003e2\u003c/sub\u003e), providing multiple possibilities for modification through covalent or non-covalent conjugation of chemical species [15; 16]. In this context, the functionalization of NPs with natural biopolymers has proven to be an important strategy to confer desired properties. Biopolymer-coated nanoparticles can play the role of efficient vehicles for controlled and targeted drug release, aiming to enhance therapeutic effects and reduce side effects associated with formulated drugs [16; 18]. It is worth noting that gelatin, as a highly versatile natural biopolymer, has been widely used in the pharmaceutical industry due to its biocompatibility, biodegradability, low cost, and numerous active groups available for binding with target molecules [19; 20].\u003c/p\u003e \u003cp\u003eIn this study, our goal is to prepare, characterize, and evaluate the effect of coating Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er nanoparticles with gelatin (Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin) and its influence on physicochemical properties. We aim to investigate this approach as a promising strategy for drug transport, increased drug solubility, and toxicity acceptance.\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eMaterials\u003c/h2\u003e \u003cp\u003eGadolinium (III) oxide, ytterbium (III) oxide and erbium (III) oxide (Aldrich, 99,9%), urea (Vetec, P.A.), gelatin (Sigma-Aldrich), acetone (Din\u0026acirc;mica, P.A.), glutaraldehyde (GA) (Din\u0026acirc;mica, 25% P.S.), nitric acid (Alphatec, P.A.). Ln(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e.6H\u003csub\u003e2\u003c/sub\u003eO (with Ln\u003csup\u003e3+\u003c/sup\u003e = Er\u003csup\u003e3+\u003c/sup\u003e, Yb\u003csup\u003e3+\u003c/sup\u003e e Gd\u003csup\u003e3+\u003c/sup\u003e) were obtained by reacting nitric acid with the corresponding trivalent lanthanide oxide.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eSynthesis procedures\u003c/h2\u003e \u003cdiv id=\"Sec5\" class=\"Section3\"\u003e \u003ch2\u003eSynthesis of Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er\u003c/h2\u003e \u003cp\u003eThe synthesis of Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er nanoparticles was conducted based on the work of Kamińska et al (2018) [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e], using the homogeneous precipitation method. In a beaker was added 5.440 mmol (2.45 g) of Gd(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e.6H\u003csub\u003e2\u003c/sub\u003eO, 0.029 mmol (0.013 g) of Er(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e.6H\u003csub\u003e2\u003c/sub\u003eO, 0.530 mmol (0.25 g) of Yb(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e.6H\u003csub\u003e2\u003c/sub\u003eO and 0.040 mol (2.4 g) of urea and 100 mL of distilled water and was conditioned under stirring and heating in a glycerin bath at 75\u0026deg;C for 3 hours. Then, the formed precursor material (Gd(OH)CO\u003csub\u003e3\u003c/sub\u003e:Yb/Er) was separated by centrifugation at 5000 rpm for 15 minutes and dried at 80\u0026deg;C in an oven for 24 hours. Finally, the Gd(OH)CO\u003csub\u003e3\u003c/sub\u003e:Yb/Er nanoparticles were subjected to the calcination process at a temperature of 900\u0026deg;C, with a heating rate of 2\u0026deg;C/min for 3 hours.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eSynthesis of Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin\u003c/h2\u003e \u003cp\u003eThe synthesis of Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin involves an adaptation of the two-step gelatin desolvation method proposed by Mozafari and Moztarzafari (2010) [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. In order four syntheses were carried out under different conditions, as indicated in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. In the first step of the synthesis, the gelatin was dissolved in 100 mL of ultrapure water, and the solution was stirred at a temperature of 45\u0026deg;C until the gelatin completely dissolved. Then, 100 mL de acetone was slowly added to the solution to precipitate low weight gelatin chains. The supernatant was then discarded, and the gelatin settled at the bottom of the flask was dissolved in 100 mL of ultrapure water. Next 100 mL of a Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er suspension (1 mg/mL) was added under constant agitation for 30 minutes and at a constant temperature of 45\u0026deg;C. For the second step of the desolvation process, 150 mL of acetone, and finally 1 mL of glutaraldehyde 25% (GA) solution were added. The system was stirred for 20 hours at a temperature of 45\u0026deg;C. The gelatin-coated nanoparticles were washed with distilled water, followed by the collection of the solid via centrifugation at 5000 rpm for 20 minutes.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eConditions for the synthesis of Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin nanoparticles.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eGlutaraldehyde (mL)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eGelatin concentration (mg/mL)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1_GA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2_GA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eNanoparticles characterization\u003c/h2\u003e \u003cp\u003ePowder X-ray Diffraction (XRD) data were recorded at room temperature on a Rigaku X-ray diffractometer with Cu Kα (λ\u0026thinsp;=\u0026thinsp;1.5406 \u0026Aring;) radiation and a rotating anode X-ray source of 9 kW. The source was coupled to a high-resolution multidimensional 2D semiconductor detector, HyPix-300. The analysis was conducted in a 2θ range from 10 to 70, with a scanning speed of 1\u0026deg;/min and an increment of 0,02 \u0026deg;. Scanning Electron Microscopy (SEM), the samples were placed on aluminum stubs coated with carbon tape. Subsequently, the samples were metalized with a gold layer. Images were acquired using a Tescan scanning electron microscope, model MIRA3, equipped with a field emission electron beam source. Energy-dispersive X-ray spectroscopy (EDX) was coupled with SEM. Fourier Transform Infrared Spectroscopy (FT-IR) analysis was conducted, where absorption spectra in the infrared region were obtained at room temperature. This analysis was performed using a Fourier-transform spectroscopy from PerkinElmer. The frequency range analyzed covered from 4000 to 400 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. A KBr pellet was used for this analysis. Thermogravimetric analyzer (TGA) was carried out using a Shimadzu, model TGA-50/50H. A platinum sample holder and a nitrogen atmosphere flow of 50 mL/min were employed. The heating rate was 10\u0026deg;C/min, ranging from 25 to 900\u0026deg;C.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003ePhotophysical properties\u003c/h2\u003e \u003cp\u003eUpconversion emission spectra were obtained using a 980 nm laser from Laser Tool as the excitation source, with power ranging from 500 to 1900 mW. These spectra were detected using the Fluorolog-3 ISA spectrofluorimeter from Horiba Jobin Yvon, which has a detection range covering from 400 to 750 nm. Intensity values obtained from the emission spectra were used to conduct studies to determine the number of photons involved in the upconversion emission.\u003c/p\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003eRelaxometric characterization\u003c/h2\u003e \u003cp\u003eRelaxometric characterization involved the measurement of longitudinal and transverse relaxation times (\u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e) of 1H nuclei in water molecules. \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e values were measured at 37\u0026deg;C using Bruker relaxometers. The Minispec mq20 model with a magnetic field of 0.47 T and the Minispec mq60 model with a magnetic field of 1.41 T were used. For relaxometric analysis, five suspensions with different Gd\u003csup\u003e3+\u003c/sup\u003e concentrations (0.1, 0.08, 0.06, 0.04, and 0.02 mM) were prepared for each sample. These concentrations were prepared considering the nominal value of Gd\u003csup\u003e3+\u003c/sup\u003e in 1 mol of Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er, and the suspensions with different Gd\u003csup\u003e3+\u003c/sup\u003e concentrations of NPs Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin were prepared with the aid of TGA. These solutions were prepared using ultrapure water containing 0.0140 g of xanthan gum, which was used as a dispersing agent. The samples were subjected to ultrasonic bath treatment for 5 minutes. All experimental relaxation rate values were corrected to account for diamagnetic contributions using a xanthan gum solution in water.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e \u003ch2\u003eMTT cytotoxicity assay\u003c/h2\u003e \u003cp\u003eTo evaluate the cytotoxicity of NPs, Vero cells were cultured in a 96-well plate for 24 hours with 1x10\u003csup\u003e4\u003c/sup\u003e cells per well. Subsequently, the culture medium was removed, and NPs at various concentrations (3, 6, 12, 25, 50, 100 \u0026micro;g/mL) were added. Furthermore, cells cultured only with the NP solubilization solution were used as a control. After 24 hours of incubation, 10 uL of MTT solution (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) was added at a concentration of 5 mg/mL to each well. After an additional 4-hour incubation, the solution's absorbance was measured at 570 nm using a Thermo Multiskan SkyHigh microplate spectrophotometer.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"Results and Discussion","content":"\u003cp\u003eThe structural characteristics of the compounds were evaluated using the X-ray diffraction powder (XRD). The Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er showed good correlation with the simulated diffraction pattern reported for Zachariasen et al. (1927) [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e], indicating a structure similar to that of Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (cubic crystalline system and space group I-2\u003csub\u003e1\u003c/sub\u003e3), see Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The diffractograms for Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1 (orange line), Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1_GA (brown line), Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2 (green line), Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2_GA (red line), also maintained the diffraction peaks, which indicates that the gelatin coating process does not induce alterations in the crystalline structure of the Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er. These results are in line with the results of the study by Lin et al. (2017) [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e], who investigated the nanoparticle coating process in an analogous process.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eSEM analysis of the Gd(OH)CO\u003csub\u003e3\u003c/sub\u003e:Yb/Er (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea) revealed the presence of nanoscale particles with spherical and uniform morphology, exhibiting an average particle size of 70.7\u0026thinsp;\u0026plusmn;\u0026thinsp;9.2 nm (\u003cb\u003eFigure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003ea\u003c/b\u003e). Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb) spherical morphology was maintained, with a reduction in the average size of the nanoparticles to 57.7\u0026thinsp;\u0026plusmn;\u0026thinsp;6.5 nm (\u003cb\u003eFigure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003eb\u003c/b\u003e). This result can be attributed to the elimination of carbonate and hydroxide present in Gd(OH)CO\u003csub\u003e3\u003c/sub\u003e:Yb/Er during the calcination step. The Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1 (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec) has an average size 88.5\u0026thinsp;\u0026plusmn;\u0026thinsp;9.1 nm (\u003cb\u003eFigure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003ec\u003c/b\u003e), while the Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1_GA (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed) presents an average size 83.6\u0026thinsp;\u0026plusmn;\u0026thinsp;9.8 nm (\u003cb\u003eFigure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003ed\u003c/b\u003e). The Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2 has a size of 78.1\u0026thinsp;\u0026plusmn;\u0026thinsp;5.7 nm (\u003cb\u003eFigure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003ee\u003c/b\u003e), and the Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2_GA has a size of 73.9\u0026thinsp;\u0026plusmn;\u0026thinsp;2.9 nm (\u003cb\u003eFigure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003ef\u003c/b\u003e). It was observed that the spherical morphology was maintained, and in general, the average particle size was larger compared to the Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er compound. This suggests that the coating process allowed the formation of a gelatin layer around Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er. For the Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1 and Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1_GA compounds, which were synthesized with a higher concentration of gelatin (10 mg/mL), a larger increase in the average particle size was observed, approximately 30.8\u0026thinsp;\u0026plusmn;\u0026thinsp;16.3 nm and 25.9\u0026thinsp;\u0026plusmn;\u0026thinsp;15.6 nm, respectively, compared to Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er. Notably, the Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1_GA NPs, which were cross-linked with GA, had the smallest size. On the other hand, in the Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2 and Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2_GA compounds, synthesized with a lower concentration of gelatin (5 mg/mL), a smaller increase in the average particle size was observed, approximately 20.4\u0026thinsp;\u0026plusmn;\u0026thinsp;11.3 nm and 16.2\u0026thinsp;\u0026plusmn;\u0026thinsp;12.2 nm, respectively, compared to Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er. The Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2_GA NPs cross-linked with GA had the smallest size increase. In summary, the results indicate that cross-linking with GA reduces the size of the NPs, suggesting a more compact arrangement of the gelatin chains.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eChemical, thermal and compositional analysis\u003c/h2\u003e \u003cp\u003eThe semi-quantitative percentages values for the metals Gd\u003csup\u003e3+\u003c/sup\u003e, Yb\u003csup\u003e3+\u003c/sup\u003e e Er\u003csup\u003e3+\u003c/sup\u003e were obtained through the Energy-Dispersive X-ray Spectroscopy (EDX) for Gd(OH)CO\u003csub\u003e3\u003c/sub\u003e:Yb/Er and Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er, as shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.The result of mass percentages of Gd\u003csup\u003e3+\u003c/sup\u003e, Yb\u003csup\u003e3+\u003c/sup\u003e and Er\u003csup\u003e3+\u003c/sup\u003e show close values for both compounds, with Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er showing insertion of 24,6% of the sensitizer Yb\u003csup\u003e3+\u003c/sup\u003e and doping of 0,4% of the activator Er\u003csup\u003e3+\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSemi-quantitative analysis of mass percentages for the metals Gd\u003csup\u003e3+\u003c/sup\u003e, Yb\u003csup\u003e3+\u003c/sup\u003e e Er\u003csup\u003e3+\u003c/sup\u003e obtained by EDS for the compound Gd(OH)CO\u003csub\u003e3\u003c/sub\u003e:Yb/Er and Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eGd\u003csup\u003e3+\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eYb\u003csup\u003e3+\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eEr\u003csup\u003e3+\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGd(OH)CO\u003csub\u003e3\u003c/sub\u003e:Yb/Er\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e75,5\u0026thinsp;\u0026plusmn;\u0026thinsp;0,3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e24,4\u0026thinsp;\u0026plusmn;\u0026thinsp;0,1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e0,1\u0026thinsp;\u0026plusmn;\u0026thinsp;0,3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e75,0\u0026thinsp;\u0026plusmn;\u0026thinsp;0,4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e24,6\u0026thinsp;\u0026plusmn;\u0026thinsp;0,4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e0,4\u0026thinsp;\u0026plusmn;\u0026thinsp;0,3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea shows the FT-IR spectra for Gd(OH)CO\u003csub\u003e3\u003c/sub\u003e:Yb/Er and Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er. The Gd(OH)CO\u003csub\u003e3\u003c/sub\u003e:Yb/Er spectra show broad bands centered at 3434 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, related to the O-H stretching bond and 1523 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1403 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, associated with asymmetric stretching of the C-O bond. Additionally, the bands at 1091 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 848 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e correspond to the symmetric stretching and deformation of the C-O, respectively, related to the carbonate ion [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Gd2O3:Yb/Er shows a significant change of spectra profile than Gd(OH)CO\u003csub\u003e3\u003c/sub\u003e:Yb/Er, which indicates the transformation of the precursor into Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er. Furthermore, a band centered at 561 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, attributed to the Gd-O stretching bond, has emerged. The spectral profiles of Gd(OH)CO\u003csub\u003e3\u003c/sub\u003e:Yb/Er and Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er are very similar to those found in the literature [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. In addition, the functionalization process of Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er with gelatin was also analyzed by FT-IR (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). The spectra of Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1 and Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1_GA reveal a band centered at 3733 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 3292 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, corresponding to the symmetric stretching of O-H e N-H, respectively. The band at 1665 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is related to the C\u0026thinsp;=\u0026thinsp;O stretching amides. The band at 1538 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is attributed to the deformation of the N-H bond of the amino group, and the band at 858 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e corresponds to the deformation of the N-H bond of amines. The band at 1380 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e corresponds to the stretching of the C-N bond of amines, and the band at 1236 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is related to the stretching of the C-O bond. Finally, the band at 548 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is attributed to the Gd-O bond present in the Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er compound [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. On the other hand, the FT-IR spectrum obtained for Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2 and Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2_GA presents a broad band centered at 3413 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, corresponding to the symmetric stretching of O-H and N-H bonds. The band at 1658 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is attributed to the C\u0026thinsp;=\u0026thinsp;O stretching of amides. The band at 1519 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is attributed to the deformation of the N-H bond of the amino group, and the band at 860 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e refers to the out-of-plane deformation of the N-H bond of amines. The band at 1382 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e corresponds to the stretching of the C-N bond of amines, while the band at 1238 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is related to the stretching of the C-O bond. Finally, the band at 543 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is attributed to the Gd-O bond present in the Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er compound. The identification of the amino group (-NH\u003csub\u003e2\u003c/sub\u003e) in the gelatin coating suggests the possibility of functionalization at this site with drugs through covalent coupling reactions.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTGA analysis were perform for Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er, Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1, Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2, Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2_GA, as show Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. The TGA analysis reveals two mass losses in gelatin-coated compounds, the first occurs approximately between 25 and 200\u0026deg;C, and the second occurs between 200 and 500\u0026deg;C. In the Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2 system, the gelatin loss is about 3.40%. In the Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2_GA system, the mass loss is approximately 4.58% of gelatin, suggesting that the Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2_GA compound has a higher amount of gelatin than Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2, even though both were synthesized with the same gelatin concentration. This indicates that cross-linking with GA increases the amount of gelatin around Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er, but in a compacted form, as the SEM analysis of Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2_GA showed a smaller particle size. In the case of the Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1 system, the loss is about 2.93% of gelatin, and in the Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1_GA system, the loss was about 7.42%. It is observed again that the presence of GA increases the concentration of gelatin. In general, samples without GA showed the lowest percentage mass loss, while samples cross-linked with GA showed the highest percentage mass loss.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eSpectroscopic properties\u003c/h2\u003e \u003cp\u003eThe photoluminescence properties of Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er were investigated using excitation at 980 nm with a power of 1900 mW spectra in solid state at room temperature (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea). Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e Yb/Er exhibited maximum emission intensity at 659 nm, predominantly in the red region, referring to an upconversion process between Yb \u0026rarr; Er, as previously reported in the literature [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Additionally, five sharp peaks centered at 653, 662, 667, 673, and 680 nm can also be observed. All these peaks can be attributed to the transition for Er\u003csup\u003e3+\u003c/sup\u003e: \u003csup\u003e4\u003c/sup\u003eF\u003csub\u003e9/2\u003c/sub\u003e \u0026rarr; \u003csup\u003e4\u003c/sup\u003eI\u003csub\u003e15/2\u003c/sub\u003e. In addition, the emission spectra also reveals signal, predominantly in the green region, centered at 521 nm, with three additional peaks at wavelengths of 525, 532, and 537 nm, which can be attributed to the characteristic transitions of Er\u003csup\u003e3+\u003c/sup\u003e: \u003csup\u003e2\u003c/sup\u003eH\u003csub\u003e11/2\u003c/sub\u003e \u0026rarr; \u003csup\u003e4\u003c/sup\u003eI\u003csub\u003e15/2\u003c/sub\u003e, and three additional peaks at 547, 552, and 561 nm, attributed to Er\u003csup\u003e3+\u003c/sup\u003e: \u003csup\u003e4\u003c/sup\u003eS\u003csub\u003e3/2\u003c/sub\u003e \u0026rarr; \u003csup\u003e4\u003c/sup\u003eI\u003csub\u003e15/2\u003c/sub\u003e transition [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe upconversion (UC) mechanism was interpreted by recording the UC emission intensities as a function of pump-power intensities for the Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er sample. The relationship between emission intensity (\u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003eup\u003c/em\u003e\u003c/sub\u003e) and pump power (P). The log (\u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003eup\u003c/em\u003e\u003c/sub\u003e) versus log (\u003cem\u003eP\u003c/em\u003e\u003csup\u003e\u003cem\u003eN\u003c/em\u003e\u003c/sup\u003e) line is fitted according to Eq.\u0026nbsp;\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e], se can be expressed as:\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$${I}_{up }\\alpha {P}^{N}\\to log\\left({I}_{up}\\right) = log\\left(k{P}^{n}\\right) = NlogP + C$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere N is the number of photons in the UC process and can be acquired from the slope of the straight line by linear fitting the plot of log (\u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003eup\u003c/em\u003e\u003c/sub\u003e) and log(P), as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed.\u003c/p\u003e \u003cp\u003eThe slopes for these red and green emission bands located were 2.53 (659 nm) and 1.54 (521 nm), respectively. The equation obtained for emission in the green region was y\u0026thinsp;=\u0026thinsp;1.54x\u0026thinsp;+\u0026thinsp;2.34, with an r-square value of 0.999, while the equation obtained for emission in the red region was y\u0026thinsp;=\u0026thinsp;2.53x \u0026minus;\u0026thinsp;2.99, with an r-square value of 0.999. These results suggest that the three-photon process is responsible for upconversion of the \u003csup\u003e2\u003c/sup\u003eH\u003csub\u003e11/2\u003c/sub\u003e \u0026rarr; \u003csup\u003e4\u003c/sup\u003eI\u003csub\u003e15/2\u003c/sub\u003e (green) transition, and the two-photon process is responsible for upconversion of the \u003csup\u003e4\u003c/sup\u003eF\u003csub\u003e9/2\u003c/sub\u003e \u0026rarr; \u003csup\u003e4\u003c/sup\u003eI\u003csub\u003e15/2\u003c/sub\u003e (red) transition. Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e shows the UC emission spectra for Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er, Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1, Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1_GA, Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2, and Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2_GA materials. The results revealed that the coating process does not alter the spectral profile of the materials, as previously reported from [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. This result agrees with structural characterization, where the synthetic method does not affect the crystallinity of the Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e showed the intensity ratio between the red UC emission (\u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003eR\u003c/em\u003e\u003c/sub\u003e) to and green UC emission (\u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003eG\u003c/em\u003e\u003c/sub\u003e) for Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1, Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1_GA, Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2, Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2_GA. The results revealed a decrease of gelatin-coated intensity ratio values than Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er, indicating that the coating process reduces the relative green emission intensities (\u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003eG\u003c/em\u003e\u003c/sub\u003e) due to the presence of a gelatin layer around Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er. Thus, the presence of the gelatin layer leads to an increase of the concentration of adsorbed water on the material's surface, enhancing the quenching effect of the UC emission intensities. On the other hand, the ratios between emission intensities for the compounds Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1 and Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2_GA showed the least decrease than Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eQuantitative analysis of red intensity (\u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003eR\u003c/em\u003e\u003c/sub\u003e), green intensity (\u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003eG\u003c/em\u003e\u003c/sub\u003e) and the red-to-green intensity ratio (\u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003eR\u003c/em\u003e\u003c/sub\u003e/\u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003eG\u003c/em\u003e\u003c/sub\u003e) for the compounds Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er, Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1, Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1_GA, Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2 and Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2_GA.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003eR\u003c/em\u003e\u003c/sub\u003e (CPS)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003eG\u003c/em\u003e\u003c/sub\u003e (CPS)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003eR\u003c/em\u003e\u003c/sub\u003e/\u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003eG\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e5,8.10\u003csup\u003e6\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2,6.10\u003csup\u003e5\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e22,3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4,6.10\u003csup\u003e5\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e4,2.10\u003csup\u003e4\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e11,0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1_GA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e8,2.10\u003csup\u003e5\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1,9.10\u003csup\u003e5\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e4,3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3,3.10\u003csup\u003e5\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e4,9.10\u003csup\u003e4\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e6,7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2_GA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1,3.10\u003csup\u003e6\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1,2. 10\u003csup\u003e5\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e11,0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eRelaxivities\u003c/h2\u003e \u003cp\u003eThe relaxometry data obtained at 60 MHz and 37\u0026deg;C for the Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er, Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1, Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1_GA, Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2 e Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2_GA (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er showed relaxivity values of \u003cem\u003er\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;2,70\u0026thinsp;\u0026plusmn;\u0026thinsp;0,12 s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003emM\u003csup\u003e\u0026ndash;1\u003c/sup\u003e and \u003cem\u003er\u003c/em\u003e\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;10,32\u0026thinsp;\u0026plusmn;\u0026thinsp;0,71 s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003emM\u003csup\u003e\u0026ndash;1\u003c/sup\u003e. These results indicate that the relaxation time decrease was less effective for \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e than \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e, suggesting that the water diffusion process between particles has a greater influence on the relaxometry process. Similar behavior was reported for Norek et al. (2007) [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e], where Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e NPs, in a 7 T field at 25 \u0026ordm;C, present a smaller effect on \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e relaxation time than on \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003eGd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1, Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1_GA, Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2, Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2_GA materials have a significant effect on the relaxation time of the water protons compared to Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er, suggesting that the gelatin coating process promoted an increased of the relaxivity in the Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin NPs. Gelatin is composed of hydrophilic groups, allowing interactions of water molecules with its functional groups through hydrogen bonding. In this way, gelatin layers can attract water molecules, increasing the local water density and improving the water exchange rate of Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin [31; 32]. In addition, it can be seen that r\u003csub\u003e2\u003c/sub\u003e is greater than the r\u003csub\u003e1\u003c/sub\u003e values, which results in T\u003csub\u003e2\u003c/sub\u003e that are lower than T\u003csub\u003e1\u003c/sub\u003e values, indicating that the water diffusion process in the NPs is predominant, as seen previously in the relaxivity measurement for Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er. In the results obtained for Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1 (\u003cem\u003er\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;15,08\u0026thinsp;\u0026plusmn;\u0026thinsp;0,46 and \u003cem\u003er\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;33,71\u0026thinsp;\u0026plusmn;\u0026thinsp;2,47) and Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2 (\u003cem\u003er\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;9,24\u0026thinsp;\u0026plusmn;\u0026thinsp;0,40 and \u003cem\u003er\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;20,32\u0026thinsp;\u0026plusmn;\u0026thinsp;0,89) showed higher relaxivity values than Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er, suggesting that the presence of gelatin increases the concentration of water around the paramagnetic ion due to gelatin being a hydrophilic compound that retains water molecules in its structure through hydrogen bonds. NPs crosslinked with GA, the Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1_GA and Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2_GA, showed lower relaxivity values, suggesting that crosslinking with GA compacts the gelatin chains, reducing the mobility of water molecules. Additionally, this process reduces the concentration of water retained in the gelatin, hindering both the diffusion of external sphere water molecules and the water exchange rate with the bulk.\u003c/p\u003e \u003cp\u003eIn the results obtained, it is observed that among the NPs synthesized with the same amount of gelatin (10 mg/mL), Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1 and Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1_GA, as reported in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1 showed higher relaxivity values, probably due to the higher amount of gelatin-coated, as seen in the SEM analysis. This results in a change in the mobility of water molecule diffusion and the water exchange rate with the bulk. Comparing the relaxivity results between Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2 and Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2_GA, which were synthesized with the same amount of gelatin (5 mg/mL), as reported in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, it is suggested that the crosslink process did not significantly interfere with the mobility of water molecules, as the \u003cem\u003er\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e values were very close. Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2 and Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2_GA had lower relaxivity compared to Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1, probably due to the lower amount of gelatin in the coating.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eRelaxivities obtained for the systems at 37\u0026deg;C and 60 MHz (1.41 T).\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003er\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e ( s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003emM\u003csup\u003e\u0026ndash;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cem\u003er\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e ( s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003emM\u003csup\u003e\u0026ndash;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e2,70\u0026thinsp;\u0026plusmn;\u0026thinsp;0,12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e10,32\u0026thinsp;\u0026plusmn;\u0026thinsp;0,71\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e15,08\u0026thinsp;\u0026plusmn;\u0026thinsp;0,46\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e33,71\u0026thinsp;\u0026plusmn;\u0026thinsp;2,47\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1_GA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e4,12\u0026thinsp;\u0026plusmn;\u0026thinsp;0,083\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e13,62\u0026thinsp;\u0026plusmn;\u0026thinsp;1,94\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e9,24\u0026thinsp;\u0026plusmn;\u0026thinsp;0,40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e20,32\u0026thinsp;\u0026plusmn;\u0026thinsp;0,89\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2_GA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e12,17\u0026thinsp;\u0026plusmn;\u0026thinsp;0,24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e20,01\u0026thinsp;\u0026plusmn;\u0026thinsp;2,17\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eCell viability\u003c/h2\u003e \u003cp\u003eThe cytotoxicity of Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er and Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin NPs was evaluated using the MTT assay with Vero cells, which are healthy cells. The concentration-dependent effect of the NPs was assessed in comparison to cells in the control experiment (without NPs), as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e. The NPs were found to be viable in the cells, with values exceeding 90% for all concentrations studied. A similar outcome was observed in the study by Chen et al. (2011) [33], in which NaYF\u003csub\u003e4\u003c/sub\u003e:Yb/Er NPs coated with chitosan and conjugated with folic acid also exhibited cell viability with values exceeding 90%. Moreover, Kaminska et al. (2015) [34] showed in their results that gadolinium oxide NPs, with erbium, ytterbium and zinc polyvinylpyrrolidone (PVP) coated are biocompatible at the NPs concentration of up to 50 \u0026micro;g/mL in 24h incubation. Additionally, it is important to note that the NPs promoted a proliferative effect for some of the concentrations studied, as evidenced by the observation of average cell viability exceeding 100%. In this sense, we can identify high biocompatibility and viability of Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er and Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin NPs for potential diagnosis of diseases and application in chemotherapy as a carrier.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eBased on the luminescence and relaxivity data, the Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2_GA system exhibited more favorable results compared to the other systems under evaluation. This is evident when initaly observing that the emission intensities for the Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2_GA compound shower the least reduction compared to Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er. On the other hand, despite the relaxivity of the Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin1 (\u003cem\u003er\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;33,71\u0026thinsp;\u0026plusmn;\u0026thinsp;2,47) being higher compared to the Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2_GA system (\u003cem\u003er\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;20,01\u0026thinsp;\u0026plusmn;\u0026thinsp;2,17), Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2_GA offers advantages in its chemical composition due to the use of GA in its synthesis as a cross-linking agent. Gelatin is a water-soluble compound due to its hydrophilic nature, but cross-linking with GA provides greater stability to the system, making the gelatin more resistant to dissolution in water. Furthermore, the cross-linking of gelatin with GA involves the reaction of free amino groups from lysine or hydroxylysine amino acid residues in the chains with the aldehyde groups of GA. This ensures that the coating of Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er with gelatin will remain intact during the desired biological application [36]. Additionally, the Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2_GA system exhibited the smallest size, as revealed by SEM, and the smaller the NPs, the more efficient the penetration into tumor blood vessels will be.\u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusions","content":"\u003cp\u003eIn this study, a nanosensor was developed from UCNPs of Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er coated with gelatin, which proved to be viable for potencial theranostic application. X-ray diffraction (XRD) analysis confirmed the cubic crystalline structure for Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er and indicated that the gelatin coating did not affect its crystallinity. Scanning electron microscopy (SEM) analysis revealed a reduction in the nanoparticle diameter after the calcination of the precursor, indicating the formation of the oxide. The formation of a gelatin layer around Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er was evidenced by SEM, suggesting that cross-linking with GA reduced the size of the nanoparticles. Luminescence spectroscopy for Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er exhibited characteristic Yb\u003csup\u003e3+\u003c/sup\u003e/Er\u003csup\u003e3+\u003c/sup\u003e UC emission peaks, and it was observed that the coating process did not alter the photophysical properties of the material, although it affected the emission intensities. Relaxometric characterization of the gelatin-coated systems (Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin) indicated an increase in relaxivity, especially for \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e, suggesting a greater interaction of gelatin with water molecules and the potential to enhance contrast in MRI applications. In addition, Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er and Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin NPs were viable in biological applications, as observed in the cytotoxicity analysis, where it was observed that Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er and Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin NPs had no cytotoxic effect on healthy cells, presenting cellular viability above 90%. In summary, the compound Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin2_GA was chosen as the most promising nanoparticle to continue the planned applications. These results pave the way for future research and clinical applications, where this functionalized nanosensor can be used in biomedical therapy and diagnosis.\u003c/p\u003e "},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eCredit authorship contribution statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eJ. F. S., Lima:\u0026nbsp;\u003c/strong\u003eConceptualization, Methodology, Investigation, Writing - original draft.\u003cstrong\u003e\u0026nbsp;G. N. S. A., Oliveira:\u0026nbsp;\u003c/strong\u003eMethodology - relaxometry.\u003cstrong\u003e\u0026nbsp;D. K. D. N., Santos:\u0026nbsp;\u003c/strong\u003eMethodology - Cell viability.\u003cstrong\u003e\u0026nbsp;G. A. L., Pereira:\u0026nbsp;\u003c/strong\u003eConceptualization, Investigation - relaxometry - review \u0026amp; editing.\u003cstrong\u003e\u0026nbsp;R. S. Viana:\u0026nbsp;\u003c/strong\u003eConceptualization, Methodology, Writing - review \u0026amp; editing, Supervision.\u003cstrong\u003e\u0026nbsp;S. A., J\u0026uacute;nior:\u0026nbsp;\u003c/strong\u003eWriting - review \u0026amp; editing, Supervision.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDeclaration of Competing Interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research has received support from the Coordena\u0026ccedil;\u0026atilde;o de Aperfei\u0026ccedil;oamento de Pessoal de N\u0026iacute;vel Superior - Brasil (CAPES), the Conselho Nacional de Desenvolvimento Cient\u0026iacute;fico e Tecnol\u0026oacute;gico - Brasil (CNPq), and the Funda\u0026ccedil;\u0026atilde;o de Amparo \u0026agrave; Pesquisa do Estado de Alagoas (FAPEAL; grant no. DCR2022051000008).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors thank the Optics and Nanoscopy Group (GON-IF-UFAL) and Earth Rare Laboratory (BSTR -UFPE) for the optical measurements. R.S.V gratefully acknowledged the FAPEAL/PDCTR/CNPq program for a scholarship (grant no. DCR2022051000008).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eLi H, Wang X, Huang D, Chen G (2020) Recent advances of lanthanide-doped upconversion nanoparticles for biological applications. Nanotechnology, 31(7):072001.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang D, Peng R, Liu W, Donovan M J, Wang L, Ismail I, Li J, Li J, Qu F, Tan W (2021) Engineering DNA on the Surface of Upconversion Nanoparticles for Bioanalysis and Therapeutics. American Chemical Society Nano. 15(11):17257\u0026ndash;17274.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi X, Wang J, Yu Z, Lou X, Zhang C, Jia X, Jia G (2021) Well-defined Gd(OH)CO\u003csub\u003e3\u003c/sub\u003e, Gd\u003csub\u003e2\u003c/sub\u003eO(CO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u0026middot;H\u003csub\u003e2\u003c/sub\u003eO, and Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e compounds with multiform morphologies and adjustable particle sizes: Synthesis, formation process, and luminescence properties. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 624:126834.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAnsari A A, Parchur A K, Chen G (2022) Surface modified lanthanide upconversion nanoparticles for drug delivery, cellular uptake mechanism, and current challenges in NIR-driven therapies. Coordination Chemistry Reviews, 457:214423.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBloembergen N (1959) Solid state infrared quantum counters. Physical Review Letters, 2(3):84\u0026ndash;85.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHlav\u0026aacute;ček A, Farka Z, Mickert M J, Kostiv U, Brandmeier, J C, Hor\u0026aacute;k D, Skl\u0026aacute;dal P, Foret F, Gorris H H (2022) Bioconjugates of photon-upconversion nanoparticles for cancer biomarker detection and imaging. Nature Protocols, 17:1028\u0026ndash;1072.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDong H, Sun L-D, Yan C-H (2015) Energy transfer in lanthanide upconversion studies for extended optical applications. Chemical Society Reviews, 44(6):1608\u0026ndash;1634.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLingeshwar Reddy K, Balaji R, Kumar A, Krishnan V (2018) Lanthanide Doped Near Infrared Active Upconversion Nanophosphors: Fundamental Concepts, Synthesis Strategies, and Technological Applications. Small, 14:1\u0026ndash;27.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGai S, Yang P, Wang D, Li C, Niu N, He F, Li X (2011) Monodisperse Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Ln (Ln\u0026thinsp;=\u0026thinsp;Eu\u003csup\u003e3+\u003c/sup\u003e, Tb\u003csup\u003e3+\u003c/sup\u003e, Dy\u003csup\u003e3+\u003c/sup\u003e, Sm\u003csup\u003e3+\u003c/sup\u003e, Yb\u003csup\u003e3+\u003c/sup\u003e/Er\u003csup\u003e3+\u003c/sup\u003e, Yb\u003csup\u003e3+\u003c/sup\u003e/Tm\u003csup\u003e3+\u003c/sup\u003e, and Yb\u003csup\u003e3+\u003c/sup\u003e/Ho\u003csup\u003e3+\u003c/sup\u003e) nanocrystals with tunable size and multicolor luminescent properties. 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Dalton Transactions 44(36):16081\u0026ndash;16090.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"upconversion, glutaraldehyde, relaxometry, coating, bioimaging.","lastPublishedDoi":"10.21203/rs.3.rs-3961971/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3961971/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eT he present study aimed to develop a theranostic nanoprobe for application. This nanoprobe is composed of upconversion nanoparticles (NPs) coated with gelatin. Initially, erbium-ytterbium co-doped gadolinium oxide (Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er) was synthesized using the homogeneous precipitation technique. The Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er particles were coated with gelatin (Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin) using the desolvation method. Four syntheses were conducted with different gelatin concentrations and the use of glutaraldehyde (GA) as a cross-linking agent. The characterization of the nanoprobe included structural, relaxometric, luminescent, and cytotoxicity analyses. The results indicate that cross-linking with GA reduces the size of the NPs, suggesting a greater compaction of the gelatin chains. It was observed that the gelatin coating increases the concentration of water molecules near the NPs through hydrogen bonding interactions and modulates their diffusion time near the paramagnetic center, influencing the decrease in proton relaxation time. On the other hand, cross-linking with GA restricts the mobility of water molecules, by all relaxivity values were found to be higher than those of commercial contrast agents. The luminescent data showed that although the spectral emission profile of upconversion between Yb\u003csup\u003e3+\u003c/sup\u003e and Er\u003csup\u003e3+\u003c/sup\u003e ions did not change compared to the oxide, the emission intensity ratio (I\u003csub\u003eR\u003c/sub\u003e/I\u003csub\u003eG\u003c/sub\u003e) decreased with coating, and the emission in the green region is generated by the absorption of three photons, while the emission in the red region is generated by the absorption of two photons. It was also observed that Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er and Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:Yb/Er@Gelatin NPs had no cytotoxic effect on healthy cells, with cell viability above 90%. The developed nanoprobe showed interesting luminescent and relaxometric properties, making it a promising tool for optical and magnetic bioimaging.\u003c/p\u003e","manuscriptTitle":"Design and Characterization of Gelatin-Coated Upconversion Nanoparticles: Insights into Structural, Relaxometric, Luminescent, and Cytotoxic Properties","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-02-27 00:35:23","doi":"10.21203/rs.3.rs-3961971/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"b966d781-d466-4471-ad4e-197e132fe49e","owner":[],"postedDate":"February 27th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-08-22T01:49:06+00:00","versionOfRecord":[],"versionCreatedAt":"2024-02-27 00:35:23","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-3961971","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3961971","identity":"rs-3961971","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}