Fluorescent Carbon Dots: Aggregation-Induced Emission Enhancement, Application as probe for CN - and Cr 2 O 7 -2 , sensing strips and bio-imaging agent

Fluorescent Carbon Dots: Aggregation-Induced Emission Enhancement, Application as probe for CN - and Cr 2 O 7 -2 , sensing strips and bio-imaging agent | 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 Fluorescent Carbon Dots: Aggregation-Induced Emission Enhancement, Application as probe for CN - and Cr 2 O 7 -2 , sensing strips and bio-imaging agent Madhuri Bhatt, Shreya Bhatt, Gaurav Vyas, Ishan Raval, Anshu Kumar, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3808914/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 17 Feb, 2024 Read the published version in Journal of Fluorescence → Version 1 posted 7 You are reading this latest preprint version Abstract Fluorescent carbon dots (Trp-CDs) were prepared using tryptophan as precursor and were characterized on the basis of elemental analysis, powder-XRD, IR, Raman spectroscopy, 13 C-NMR, UV-Vis, fluorescence and TEM. Trp-CDs exhibit poor fluorescence in 100% water but showed strong Aggregation Induced Emission (AIE) in ethanol and higher alcohols. The anion sensing study of Trp-CD revealed that it selectively detects CN − and Cr 2 O 7 − 2 and from fluorescence quenching titration study, quenching constant, LOD and range of detection were evaluated. The emission life-time of Trp-CD before and after addition of CN − and Cr 2 O 7 − 2 were measured, the decay curve before addition of anion was best fitted with a bi-exponential function with life-time of τ1 2.79 ns (10.74%) and τ2 18.93 ns (89.26%). The mechanistic study revealed that for CN − , the fluorescence quenching is due to its interaction with protons attached to surface functional groups and for Cr 2 O 7 − 2 , it is due to inner filter effect (IFE). Sensing strips were prepared by coating Trp-CDs onto various solid surfaces including agarose films and were used for detection of CN − and Cr 2 O 7 − . Trp-CD was found to be nontoxic and biocompatible and used as staining agent for Artemia and Bacteria ( Bacillus Subtilis , Pseudomonas ) and detection of CN − and Cr 2 O 7 − . Carbon dots Aggregation-induced emission Cyanide sensing Chromium(IV) sensing Bio-imaging Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Introduction The fluorescent carbon dots are emerging as potential material for sensing of cations and anions and also for bioimaging [ 1 – 5 ]. Several fundamental phenomena are reported for the origin of fluorescence in carbon dots, it has also been reported that the fluorescence property can be amplified applying different methodologies. One of such methods is Aggregation Induced Emission (AIE), which involves assembly of particles making changes in the fluorescence property [ 6 – 9 ]. AIE has been observed in organic small molecules (OSMs) as well as in photoluminescent nanoparticles (PLNPs) [ 10 , 11 ]. Aggregation of PLNPs depend on the functional groups on the surface of the nanoparticles and surrounding environmental conditions such as solvents, pH, ionic strength etc. [ 12 ]. In carbon dots, AIE enhancement is mainly due to solvent-induced or cation-induced aggregation of the dots [ 13 – 15 ]. This property of carbon dots/nanoparticles can be effectively used for the developments of probes for ion recognition. In the present study, the carbon dots prepared exhibited fluorescence enhancement due to AIE and it selectively detects CN − and Cr 2 O 7 − 2 . Cyanide (CN − ) is one of the most toxic anion [ 16 , 17 ]. In human body it binds cytochrome c oxidase that causes the inhibition of oxygen transport to mitochondria, resulting in hypoxia and eventually death [ 18 , 19 ]. CN − contamination in environment is mainly due to industrial processes such as herbicide synthesis, gold-extraction, paper, textiles, plastic manufacturing etc. [ 20 – 22 ]. CN − is also found in some natural sources, it is present in seeds of several fruits, certain plants and in some food stuffs [ 23 , 24 ]. Another extremely toxic ion is Cr(VI)/Cr 2 O 7 − 2 , industrial activities such as preservation of wood, textile dyeing, leather tanning, electroplating and metal finishing processes release hexavalent chromium Cr(VI), which contaminates with water and soil creating environmental pollution [ 25 – 27 ]. According to the World Health Organization (WHO), the maximum permissible level of CN − in drinking water is 0.20 ppm and that of Cr(VI) is 0.10 ppm [ 28 ]. Therefore, detection of CN − and Cr(VI)/Cr 2 O 7 − 2 in aqueous media is critically important. There are several instrument based analytical techniques for detection/estimation of these ions, however, most of these methods require expensive instruments, involve tedious sample preparation process, sometime amount of sample and limit of detection become a matter of concern [ 28 – 31 ]. Alternatively, colorimetric and fluorometric methods of detection are increasing rapidly because of its simplicity, low cost and fast detection process [ 32 – 34 ]. In these methods, as sensing materials, discrete molecules [ 34 – 36 ], composite materials [ 37 , 38 ], nanoparticles [ 39 – 42 ], carbon dots [ 43 , 44 ] etc., which exhibit colour and UV-vis/fluorescence spectral changes in presence of CN − and/or Cr(VI) have been used. The interaction of the guest ion with the sensing material results changes in optical properties of the sensor due to energy/electron transfer process involved in the event. In recent time, fluorescent carbon dots have emerged as a new class of sensing material for detection of metal ions and anions, particularly Cr(VI) and CN − in aqueous media [ 44 – 46 ]. In addition to the sensing of analytes, the use of carbon dots for bio-imaging is also growing rapidly [ 45 , 46 ]. The application of carbon dots as sensors as well as bio-imaging agent is becoming popular because of its simple method of preparation from mostly inexpensive precursors. Herein, a simple and eco-friendly method for preparation of fluorescent carbon dots using tryptophan as precursor and its application for sensing of toxic ions such as CN − and Cr 2 O 7 − 2 and as bio-imaging agent is reported. The carbon dots (Trp-CD) prepared exhibited poor fluorescence in water but in ethanol and higher alcohols it showed strong Aggregation Induced Emission (AIE) and selectively detected CN − and Cr 2 O 7 − 2 among a large number of anions used in this study. Trp-CD was also used for preparation of sensing strips by coating it onto solid surfaces and the strips with agarose films were used for detection of CN − and Cr 2 O 7 − in aqueous media. The Trp-CD is found to be non-toxic and biocompatible and it is used as bioimaging agent for Artemia and Bacteria for detection of CN − and Cr 2 O 7 − 2 in live whole invertebrates and Bacteria. Materials and Methods Chemicals L-Tryptophan was purchased from Spectrochem (Mumbai, India). All tetrabutylammonium salts of the anions were purchased from Alfa Aesar (Johnson Matthey Company). Potassium dichromate was purchased from Merck. Sodium cyanide was purchased from sigma Aldrich. All reagents used were of analytical grade and were used as received without further purification. Instrumentation Elemental analysis (C, H, and N) were performed on a model Vario Micro CUBE elemental analyzer. Fluorescence spectra were recorded on Edinburgh Instrument’s fluorescence spectrometer and UV/Vis spectra were recorded on a CARY 500 scan Varian spectrophotometer. Infrared spectra were recorded on a Perkin-Elmer spectrum GX FT-system using KBr pellets. Powder-XRD was recorded on a PANalytical instrument, model: Empyrean using Cu Kα radiation, NMR spectra were recorded on model Avance II 500 Bruker FT-NMR instrument. Raman spectra were recorded on a Horiba Scientific model LabRAM HR Evolution Raman Spectrometer. TEM images was recorded on a JEOL, model JEM 2100 transmission electron microscope (200 Kv). Preparation of carbon dots (Trp-CD) In a typical experiment, tryptophan (1 g) was heated in air furnace at 200 0 C for 3 h and then allowed to cool to room temperature. The carbonious material thus obtained was stirred in ethanol (250 mL) for 24 h at room temperature. The mixture was then centrifuged at 7000 rpm for 10 min to remove large particles. The resulting supernatant was filtered through a cellulose acetate syringe filter (pore size of 0.2 µm). Dark orange solution of purified Trp-CD thus obtained was dried by rotary evaporation. After drying, the purified Trp-CD was obtained as a brownish powder. Ion-selectivity study Interaction of the Trp-CD with various anions was investigated with the aid of fluorescence spectroscopy. To perform this experiment, stock solution of Trp-CD was prepared by adding 13.8 mg of the Trp-CD in ethanol-water mixture (10:90, 100 mL). 1 mL of Trp-CD solution (0.138 mg/mL) was then treated with 1 mL solution of the tetrabutylammonium salts of the anions such as F − , Cl − , Br − , I − , H 2 PO 4 − , ClO 4 − , NO 3 − , BF 4 − , CH 3 COO − , CN − and HSO 4 − and potassium salt of Cr 2 O 7 − 2 dissolved in deionized water (2 x 10 − 4 M). During fluorescence study, the effective concentration of the anions was 1x10 − 4 M and the fluorescence spectra of the resulting solutions were recorded after 1 min of incubation time. For fluorometric titration with CN − and Cr 2 O 7 − 2 , the incremental amounts of the solutions containing CN − and Cr 2 O 7 − 2 were added into the solution of Trp-CD and fluorescence spectra were recorded after 1 min of incubation time. To investigate interference from other anions, the solutions of other anions (50 µM) were added into the solution containing CN − (20 µM) and Cr 2 O 7 − 2 (20 µM), and fluorescence spectra of the resulting solutions were recorded under the same experimental conditions. For interference study, the excited wavelength was set at 380 nm (with slit width of 4 nm) and the fluorescence intensity at 450 nm was recoded for all of the measurement. Determination of concentration of Trp-CD by mass extinction coefficient measurement The concentration of Trp-CD was determined using mass extinction coefficient measurement. The mass extinction coefficient of Trp-CD has been calculated considering the absorbance at the first absorption peak position using the Lambert − Beer’s law, A = ε CL , where A is the absorbance at the position of the first excitation absorption peak of Trp-CD, C is the mass concentration (g/L) of Trp-CD, L is the path length (cm) of the radiation beam used for recording the absorption spectrum. In this case, L was fixed at 1 cm, ε is the mass extinction coefficient of Trp-CD (L g − 1 cm − 1 ). The concentration of Trp-CD solution calculated was 0.069 mg mL − 1 with A = 0.1101 and ε = 1.595. Determination of quantum yield (QY) Quantum yield (QY) of the Trp-CD was determined following the published procedure [ 47 ]. QY was calculated by taking the ratio of the integrated photoluminescence (PL) intensities (excited at 380 nm) and the absorbance value (at 380 nm) of Trp-CD using quinine sulphate as a reference, which was dissolved in 0.1 M H 2 SO 4 (QY, 54%). The quantum yield was calculated using the following equation: Ø = Ø' × (A'/A) × (F/F') × (η 2 / η' 2 ) Where Ø is the QY of the testing sample, F is the testing sample’s emission intensity, η is the refractive index (1.33 for water), and A is absorbance. The prime symbol (′) refers to the reference dye of known QY. To minimize reabsorption effects, absorption was always kept below 0.05 at the excitation wavelength. Preparation of agarose gel based sensing strips Agarose powder (0.5 g) was dispersed in 50 mL ethanol-water (5:45 mL) and was autoclaved at 180 0 C for 30 min to ensure the complete dissolution of agar powder. Subsequently, by cooling this agarose powder containing solution to room temperature, agarose gel was formed. For making the sensing strips, the film was cut into a rectangular shape and immersed in solution of Trp-CD, after 5 min, the film was removed from the solution and air-dried. The film based strip containing Trp-CD was then exposed to aqueous solution of anions. After 5 min, the strip was removed from the aqueous solution, air-dried at room temperature and the changes in colour was noted. Toxicity study of Trp-CD towards Artemia To study the toxicity of Trp-CD, Artemia cysts (650–700 mg in 500 mL autoclaved sea water) were allowed to hatch overnight with vigorous aeration under visible light. Shortly after complete hatching, approximately 50 Artemia were added in each tube (in 10 mL aqueous solution). Two sets of tubes (in triplicate) were arranged. Artemia were allowed to nurture for 24 h in absence (control) and presence of Trp-CD and next day mortality were counted to check the toxicity of Trp-CD towards Artemia . Artemia incubation and imaging Under visible light (20 lux) and at vigorous aeration Artemia cysts were captured. Different concentrations of CN − (1 µM) and Cr 2 O 7 − 2 (1 µM) in 10 mL of water were used. Artemia were incubated to these anions solutions initially for 2 h at 25°C and then the free anions which were present in the solution was removed through centrifugation (repeated twice to avoid any background colour). Artemia were then exposed to Trp-CD taken in ethanol-water (10:90% v/v). Nearly 150 numbers of Artemia were added in each tube. After completion of the incubation, they were washed with water and then the individual Artemia was mounted on a glass slide and monitored through a fluorescent microscope. Tubes containing just Trp-CD were also used to get control image. Results and Discussion Synthesis and characterization of Trp-CD Nitrogen rich tryptophan was used as carbon source for the preparation of carbon dots following an eco-friendly procedure without use of any harmful acids, salts and drastic conditions. Tryptophan powder converted into carbonaceous material (CM) by heating in air (ashing) at 200 º C for 3h (Fig. 1 ). During heating, reactions such as dehydration, polymerization, carbonization, condensation between the amino and carboxylic groups of tryptophan took place and carbonaceous material was obtained. This carbonaceous material having oxygen and nitrogen containing functional groups, exhibited almost non-fluorescent behaviour (Fig. S1 , SI). These carbonaceous material was further treated with ethanol and purified following the procedure described in the Experimental Section, which yielded brownish carbon dots (Trp-CD). The carbon dots thus obtained were characterized on the basis of analytical, spectroscopic and microscopic analysis. The elemental analysis of Trp-CD revealed that it contains C, 75.48, H, 3.70 and N, 13.49%, the remaining 7.3% (by calculation) is expected to be oxygen. The data suggest that Trp-CD contains functional groups containing C, H, N and O on to the surface of the carbon particles. It has been further confirmed by FT-IR study, the IR spectrum of which, shown in Fig. 2a, exhibits a strong band at 3408 cm − 1 , which is due to –OH/NH functional groups. The band at 1620 cm − 1 is assigned to ν(C = O) and the other bands in the region 1200 to 1350 cm − 1 are due to C-N and C-O containing moieties [ 46 ]. The IR data therefore suggests the presence of amide/acid/OH groups on the surface of the carbon dots. The 13 C NMR spectrum of Trp-CD was recorded in solid state and shown in Fig. 2b. It exhibits broad and overlapped signals for carbon mainly in three regions, 50–75, 110–140 and 170–200 ppm, which in general are the region for aliphatic, aromatic, amide and carboxylic acid carbon atoms, respectively. The amide and carboxylic carbon atoms with inter-/intramolecular interaction may appear in the low field region. Therefore, the 13 C NMR spectrum supports the presence of amide, carboxylic acid and carbonyl groups on the surface of the carbon dots [ 48 ]. The powder X-ray diffraction (PXRD) pattern for the Trp-CD was recorded and shown in Fig. 2c. It may be noted that the PXRD pattern of the Trp-CD exhibits at broad peak at 25.88 degree with increment in interlayer spacing of 4.12 Å, the enhancement in interlayer spacing in purified Trip-CD could be attributed to the more oxygen-containing groups are incorporated on the surface of the carbon dots [ 49 ]. The Raman spectrum of Trp-CD is shown in Fig. 2d. The D band at 1350 cm − 1 represents the sp 3 -hybridized carbon, and the G band at 1560 cm − 1 is associated with the sp 2 carbon atoms, which is consistent to the observation noted in 13 C NMR [ 50 ]. Ethanol induced aggregation of Trp-CD and enhancement of fluorescence UV-Vis and fluorescence properties of Trp-CD As The study on optical properties of Trp-CD was carried out in water-ethanol, the UV-vis absorption and fluorescence spectra of Trp-CD were recorded and shown in Figs. 5a and 5b. In UV-vis absorption spectrum (Fig. 5a), the Trp-CD exhibits a peak at 217 nm which is attributed to n- π * transition. The other peak at 290 nm and a broad shoulder around 345 nm with high energy tail in visible region are observed and they are attributed to π - π * transition and Mie scattering caused by nano size particles, respectively [ 47 ]. On excitation at 380 nm, the fluorescence spectrum of Trp-CD shows a strong peak at 452 nm with a Stokes shift of 72 nm (Fig. 5b). Like many fluorescent carbon dots, the Trp-CD also exhibits an excitation-dependent photo luminescence behaviour. When excitation wavelength is increased stepwise by 20 nm from 300 to 480 nm, emission intensity of Trp-CD was increased first with red shift in emission maxima, reached to a maximum intensity with excitation at 380 nm and then the intensity was gradually decreased (Fig. 5c). In order to determine the emission life-time, the time-resolved fluorescence decay curve of Trp-CD was measured at room temperature (Fig. 5d). The decay curve thus obtained for Trp-CD could be best fitted with a bi-exponential function with life-time of τ1 2.79 ns (10.74%) and τ2 18.93 ns (89.26%) with χ2 1.05. The bi-exponential emission is believed to be corresponding to the energy gap and surface state transitions [ 52 , 53 ]. The quantum yield (QY) of the Trp-CD was also measured in ethanol-water (10:90) using quinine sulphate as a reference and was found to be 9% of the reference material. Effect of pH on fluorescence intensity of Trp-CD Effect of pH on fluorescence intensity of Trp-CD was also studied. It showed pH dependent fluorescence intensity, with increasing pH the intensity of the fluorescence band was gradually decreased (Fig. S2, SI). It may be noted that the decrease in intensity in the pH range 3 to 5 is not so significant but after that fluorescence intensity decreased rapidly with increasing pH. At lower pH, the increased concentration of H + facilitates protonation of surface decorated groups such as amide, amine etc., enhancing the electronic conjugation in Trp-CD, which probably induces enhancement in fluorescence intensity. At higher pH, such an effect is absent, instead deprotonation might have taken place causing restricted proton transfer in conjugated carbon system resulting in quenching of fluorescence intensity [ 54 ]. Interaction of Trp-CD with anions This observation suggests strong interaction of these two anions with the nanoparticles. The change in fluorescence intensity and corresponding fluorescence change under UV light is shown in Fig. 6 b. For the determination of binding constant with anions and to evaluate LOD, fluorescence titration of Trp-CD with incremental addition of CN − and Cr 2 O 7 − 2 (0.1 µM to 0.6 mM) was carried out following the procedure described in the Experimental Section and the fluorescence change is shown in Figs. 7a and 7c. The quenching constant was calculated using the Stern − Volmer equation, (F 0 /F) = 1 + Ksv [Q] [ 55 ], where F 0 is the initial fluorescence intensities of Trp-CD, F is the fluorescence intensities upon addition of the anions, [Q] is the concentration of the anions and Ksv is the quenching constant. The plot of [(F 0 /F) – 1] against concentration of anion is shown in Figs. 7b and 7d and the linear section is shown as inset of these Figures. The Ksv thus calculated for CN − is 4.595 × 10 3 M − 1 and LOD obtained is 0.7 µM and for Cr 2 O 7 − 2 Ksv is 5.364 × 10 3 M − 1 and LOD obtained is 3.2 µM. The linear range for CN − is from 0.1µM to 0.4 mM with R 2 = 0.992 and for Cr 2 O 7 − 2 the range is 3.3 µM to 0.16 mM with R 2 = 0.993, therefore, quantification can be done if the concentration is in this range. Mechanism of anion sensing The surface of Trp-CD is decorated with different amide and amine containing functional groups, which are mainly responsible for interaction with CN − /Cr 2 O 7 − 2 . Strong electron withdrawing CN − can easily interact with the protons of different functional groups, which restricts the electron flow within the cluster resulting in quenching in emission intensity. An analogues experiment was carried out with increasing the pH of the solution by adding TBA-OH, which also resulted in quenching in emission intensity (Fig. S3, SI) supporting the proposed mechanism [ 54 , 56 ]. The UV-Vis spectra upon addition of CN − did not exhibit any noticeable change (Fig. S4, SI), indicating that it is a surface phenomenon [ 57 ]. The decay profile of the emission life-time measurement exhibited a change from bi-exponential to tri-exponential with life-time of 0.079, 3.78 and 13.81 ns and χ 2 = 1.08 (Fig. S5, SI). On the basis of these information, a schematic representation of the proposed mechanism of CN − interaction is shown in Fig. 8a. Interestingly, for Cr(VI) the situation is different because of the presence of strong bands of Cr 2 O 7 − 2 in the visible and UV regions. The excitation (380 nm) and emission (450 nm) bands of Trp-CD are overlapped significantly with the absorption bands of Cr 2 O 7 − 2 in the UV-Vis region. This overlapping favoured the inner filter effect (IFE) rather than surface state interaction. The Cr 2 O 7 − 2 ion shields the excitation light of Trp-CD and absorb the emission light from Trp-CD (Fig. 8b) [ 52 ]. Absorption of emission light restricts the fluorescence enhancement and quenched the emission intensity. The decay profile of the emission life-time measurement exhibited a bi-exponential with 2.5 and 16.25 ns life-time and χ 2 = 1.01 (Fig. 8c). A schematic representation showing the interaction of Cr 2 O 7 − 2 with the Trp-CD is shown in Fig. 8d. Interference study Interference study for CN − and Cr 2 O 7 − in presence of other anions were carried out following the method described in the Experimental Section. The bar diagram showing the fluorescence intensity of Trp-CD in presence of CN − and a mixture of CN − and other anions (2.5 times molar excess) is shown in Fig. 9a and similar plot for Cr 2 O 7 − 2 is shown in Fig. 9b. It may be noted that for CN − , there is slight decrease in emission intensity when Cr 2 O 7 − was added and a slight increase in intensity when SO 4 2− was added. For Cr 2 O 7 − , some quenching is noted when CN − was added with Cr 2 O 7 − 2 anion, which is expected because both CN − and Cr 2 O 7 − interact with the Trp-CD. However, presence of Cr 2 O 7 − can be confirmed initially by yellow colour of the solution and finally by UV-Vis absorption spectrum, which exhibits a strong band in the visible region (~ 400 nm). Application of Trp-CD Application of Trp-CD as sensing strips The fluorescent Trp-CD was coated on various solid surface for preparation of fluorescent sensing material in solid state. The solid surfaces used were waste wooden strips, agarose based gel, filter paper etc., as shown in Fig. S6 (SI). For practical application as sensing material, agar-agar based fluorescent film was prepared following the procedure described in the Experimental Section, the films under day light and UV light is shown in Fig. S7 (SI). The film based strip containing Trp-CD was then immersed into aqueous solution of anions, after 5 min it was removed from the solution and air-dried. the changes under UV light is shown in Fig. 10. The figure suggests that the film based sensor can be effectively used for the detection of CN − and Cr 2 O 7 − 2 up to 5 ppm of ion concentration. Toxicity study and application as staining agent for Aterima and Bacteria The toxicity study of Trip-CD was carried out following the procedure, described in the Experimental Section and found to be nontoxic. Highly fluorescent, nontoxic and biocompatible nature of these carbon dots made it a potential material for biological application and has been applied as staining agent for Aterima and Bacteria (Bacillus subtilis and pseudomonas bacteria) using different wavelength. Aterima and bacteria were incubated to the solutions CN − and Cr 2 O 7 − following the procedure described in the Experimental Section and their microscopic images were recorded with excitation at different wavelength in the regions blue, green and red and the microscopic images are shown in Fig. 11. Artemia and bacteria containing CN − and Cr 2 O 7 − were then exposed to Trp-CD taken in ethanol-water (10:90%, v/v) and in presence of CN − and Cr 2 O 7 − , the highly fluorescent Trp-CD get quenched, as shown in Fig. 12 . The Trp-CD can penetrate into artemia and bacteria and can detect these anions by quenching the fluorescence of Trp-CD because of its interaction with CN − and Cr 2 O 7 − . Conclusions Fluorescent carbon dots (Trp-CDs) were prepared by a simple eco-friendly technique using tryptophan as precursor and were characterized on the basis of analytical, spectroscopic and microscopic techniques. Trp-CDs exhibited poor fluorescence in 100% water but it showed strong fluorescence in ethanol and higher alcohols, which is attributed to Aggregation Induced Emission (AIE) enhancement. Trp-CD selectively detected CN − and Cr 2 O 7 − ions by fluorimetric method without interference from any other anions used in this study. Fluorescence titration with incremental addition of CN − and Cr 2 O 7 − were also carried out and from the data quenching constant, LOD and linear range of detection are evaluated. The emission life-time determination before and after addition of CN − and Cr 2 O 7 − exhibited a bi-exponential decay curve with life-time of τ1 2.79 and τ2 18.93 ns (before addition of anion). The study on mechanism of interaction revealed that for CN − , the quenching in emission intensity is due to its interaction with the protons associated with functional groups on to the surface and for Cr 2 O 7 − , it is due to inner filter effect (IFE). The Trp-CD was used as coating material and the agar-agar based fluorescent film strips prepared was used for detection of CN − and Cr 2 O 7 − . Trp-CD was also used as staining agent for Artemia and Bacteria ( Bacillus Subtilis , Pseudomonas ) and it penetrated into Artemia and Bacteria to detect CN − and Cr 2 O 7 − . Declarations Acknowledgements CSIR-CSMCRI Registration No. is 217/2023. P. P. Gratefully acknowledges CSIR for the financial support in the form of CSIR-Emeritus Scientist Scheme (CSIR-ES Scheme No. 21(1046)/18/EMR-II). S. Bhatt (CSIR Award No.: 31/28(0240)/2018-EMR-I) and G. Vyas (CSIR- Award No.: 31/28(0238)/2018-EMR-I) acknowledge CSIR for awarding the Senior Research Fellowship. A. Kumar (Award No. 19-06/2011(i)EU-IV) gratefully acknowledges UGC for awarding the Research Fellowship (JRF and SRF). All the authors acknowledge CSIR-CSMCRI for providing research facilities and partial research expense related to this work. We thank Dr. G. R. Bhadu, for recording TEM and Laiya Riddhi P. for XRD, V. Agrawal for recording IR spectra, V. Bakani for elemental analysis and Raman spectra. We thank AESD&CIF for additional analytical support. Compliance with Ethical Standards Funding Details of funding received is incorporated in the Acknowledgement. Availability of data and materials The online version of this article (https://doi.org/.......) contains supplementary material, which is available to authorized users. Conflict of Interest There are no conflicts to declare. References Ji C, Zhou Y, Leblanc RM, Peng Z (2020) Recent developments of carbon dots in biosensing: A review. ACS Sens 5:2724–2741 Sharma A, Das J (2019) Small molecules derived carbon dots: synthesis and applications in sensing, catalysis, imaging, and biomedicine. Nanobiotechnol, 17:Article No. 92 Sharma V, Singh SK, Mobin SM (2019) Bioinspired carbon dots: from rose petals to tunable emissive nanodots. 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Supplementary Files SIJFluorescence.docx TableofContentJfluorescence.docx Cite Share Download PDF Status: Published Journal Publication published 17 Feb, 2024 Read the published version in Journal of Fluorescence → Version 1 posted Editorial decision: Revision requested 03 Jan, 2024 Reviews received at journal 03 Jan, 2024 Reviewers agreed at journal 29 Dec, 2023 Reviewers invited by journal 28 Dec, 2023 Submission checks completed at journal 28 Dec, 2023 Editor assigned by journal 28 Dec, 2023 First submitted to journal 26 Dec, 2023 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. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-3808914","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":264259629,"identity":"4162e2e2-6ce4-44e9-a01f-37254fc196e1","order_by":0,"name":"Madhuri Bhatt","email":"","orcid":"","institution":"CSIR-Central Salt and Marine Chemicals Research Institute, G. B. Marg","correspondingAuthor":false,"prefix":"","firstName":"Madhuri","middleName":"","lastName":"Bhatt","suffix":""},{"id":264259631,"identity":"42b0c1a2-b8e3-4608-80ab-18ab3211a133","order_by":1,"name":"Shreya Bhatt","email":"","orcid":"","institution":"CSIR-Central Salt and Marine Chemicals Research Institute, G. B. Marg","correspondingAuthor":false,"prefix":"","firstName":"Shreya","middleName":"","lastName":"Bhatt","suffix":""},{"id":264259635,"identity":"fc1455e0-a189-4297-a0bd-fa8a88a73ad1","order_by":2,"name":"Gaurav Vyas","email":"","orcid":"","institution":"CSIR-Central Salt and Marine Chemicals Research Institute, G. B. Marg","correspondingAuthor":false,"prefix":"","firstName":"Gaurav","middleName":"","lastName":"Vyas","suffix":""},{"id":264259636,"identity":"a61fb3e9-9488-4241-8be3-8ff9eb59613e","order_by":3,"name":"Ishan Raval","email":"","orcid":"","institution":"CSIR-Central Salt and Marine Chemicals Research Institute, G. B. Marg","correspondingAuthor":false,"prefix":"","firstName":"Ishan","middleName":"","lastName":"Raval","suffix":""},{"id":264259638,"identity":"212f5446-c6b7-4f92-a709-24ca59f310db","order_by":4,"name":"Anshu Kumar","email":"","orcid":"","institution":"CSIR-Central Salt and Marine Chemicals Research Institute, G. B. Marg","correspondingAuthor":false,"prefix":"","firstName":"Anshu","middleName":"","lastName":"Kumar","suffix":""},{"id":264259640,"identity":"e12f7086-f096-486b-a64b-c8bf95b5ab31","order_by":5,"name":"Parimal Paul","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAtklEQVRIiWNgGAWjYLCCBxUQ+gDxWhLOkKwlsY14tQwM5tLNzyQS59nZ67affXiAoeKeXQMhLZZzjplJJG5LTtx2Jt3gAMOZ4mSCWgxuJIC0HEgwu8HGcICxLSGZoMMMbqR/k0icc8CeFC05QFsaDjBug2qxI6jFcs6ZYouEYyC/pDEcSDiTkEBQi7l0+8YbH2rs7M2OH2P+8KEiwZ6wwySQeUArEhtI0wIEhG0ZBaNgFIyCEQcAHtw/kaViIccAAAAASUVORK5CYII=","orcid":"","institution":"CSIR-Central Salt and Marine Chemicals Research Institute, G. B. Marg","correspondingAuthor":true,"prefix":"","firstName":"Parimal","middleName":"","lastName":"Paul","suffix":""}],"badges":[],"createdAt":"2023-12-26 16:44:13","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3808914/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3808914/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s10895-024-03602-2","type":"published","date":"2024-02-17T15:01:11+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":49093233,"identity":"193781d0-7a44-496c-a1e6-e9ac8332b0ea","added_by":"auto","created_at":"2024-01-03 02:11:36","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":81448,"visible":true,"origin":"","legend":"\u003cp\u003eSynthetic route for Trp-CD.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-3808914/v1/3e72809d6a0400a6bbec112c.png"},{"id":49092401,"identity":"efabedfd-e5f1-4fb8-add4-4c0fcd0a4a6d","added_by":"auto","created_at":"2024-01-03 02:03:36","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":421950,"visible":true,"origin":"","legend":"\u003cp\u003e(a) FT-IR spectrum, (b) \u003csup\u003e13\u003c/sup\u003eC NMR (solid state) spectrum, (c) powder X-ray diffraction and (d) Raman Shift of Trp-CD.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-3808914/v1/8e53425420a2908ca5acb0a0.png"},{"id":49092398,"identity":"032cb27a-f91e-4bb4-8535-5d807836a0d2","added_by":"auto","created_at":"2024-01-03 02:03:36","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":674449,"visible":true,"origin":"","legend":"\u003cp\u003e(A) Fluorescence spectral changes of Trp-CD upon incremental addition of ethanol, (B) plot of fluorescence intensity as a function of concentration of ethanol, (C) schematic presentation showing aggregation of Trp-CD in presence of ethanol, (D) fluorescence spectral change upon addition of different alcohols and (E) fluorescent changes of Trp-CD in presence of methanol (1), ethanol (2), isopropanol (3), butanol (4), pentanol (5), hexanol (6), heptanol (7) and octanol (8).\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-3808914/v1/b60aec9a405b67b5d9cc24bd.png"},{"id":49093235,"identity":"5a53d414-a99f-41df-83cf-3b3eeca3126a","added_by":"auto","created_at":"2024-01-03 02:11:36","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":313705,"visible":true,"origin":"","legend":"\u003cp\u003eTEM image of Trp-CD in (a) 100 % water and (b) 100 % ethanol.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-3808914/v1/87913ede6a22ba2ac81f6f98.png"},{"id":49092400,"identity":"54805ad7-aaf5-42cc-b1f1-5aab3d139d6a","added_by":"auto","created_at":"2024-01-03 02:03:36","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":425601,"visible":true,"origin":"","legend":"\u003cp\u003e(a) UV-Vis spectrum, (b) fluorescence spectrum with excitation at 380 nm, (c) fluorescence emission spectra recorded under different excitation wavelengths with 20 nm increments from 300 to 500 nm and (d) time-resolved fluorescence decay and fitting curves for Trp-CD recorded in ethanol-water.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-3808914/v1/0fc5cc99a2e2ee9968a2eeb6.png"},{"id":49092404,"identity":"0b723c92-d320-4702-8466-3e4a6f13e50f","added_by":"auto","created_at":"2024-01-03 02:03:36","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":228653,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Fluorescence spectra of Trp-CD in presence of different anion (20 µM), (b) bar diagram showing the change in fluorescence intensity upon addition of different anions and (c) corresponding fluorescence changes under UV light.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-3808914/v1/d3c61aefb5e3315bc579058a.png"},{"id":49093703,"identity":"d750f04c-fe64-4120-ad06-bc04cca3e845","added_by":"auto","created_at":"2024-01-03 02:19:36","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":346258,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Fluorescence titration of Trp-CD\u003cstrong\u003e \u003c/strong\u003eupon addition of incremental amount of CN\u003csup\u003e-\u003c/sup\u003e (0.02 µM to 0.18 mM), (b) plot of [(F\u003csub\u003e0\u003c/sub\u003e/F) – 1] as a function of the concentration of CN\u003csup\u003e-\u003c/sup\u003e, inset: linear plot, (c) fluorescence titration of Trp-CD\u003cstrong\u003e \u003c/strong\u003eupon addition of incremental amount of Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u003csup\u003e-2\u003c/sup\u003e (0.02 µM to 0.18 mM) and (d) plot of [(F\u003csub\u003e0\u003c/sub\u003e/F) – 1] as a function of the concentration of Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u003csup\u003e-2\u003c/sup\u003e, inset: linear plot.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-3808914/v1/33d8a7c0ae79864e5e9709e3.png"},{"id":49092410,"identity":"2d46798d-d819-4fe7-90f8-4d640c768f06","added_by":"auto","created_at":"2024-01-03 02:03:36","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":339319,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Schematic representation of the interaction of CN\u003csup\u003e-\u003c/sup\u003e with Trp-CD, (b) The overlapping excitation and emission bands of Trp-CD with the absorption bands of Cr(VI), (c) decay profile of the emission life-time of Trp-CD upon addition of Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u003csup\u003e-2\u003c/sup\u003e and (d) schematic representation of the interaction of Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u003csup\u003e-2\u003c/sup\u003e with Trp-CD.\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-3808914/v1/0127ff91c980d1f5e8495bf4.png"},{"id":49093237,"identity":"978e81a1-d29b-4ddb-b030-1310fbbae21a","added_by":"auto","created_at":"2024-01-03 02:11:36","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":142581,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Bar diagram showing the fluorescence intensity of Trp-CD and the same after addition of CN\u003csup\u003e-\u003c/sup\u003e\u0026nbsp; and a mixture of CN\u003csup\u003e-\u003c/sup\u003e and other anions used in this study and (b) bar diagram showing the fluorescence intensity of Trp-CD and the same after addition of Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u003csup\u003e-2\u003c/sup\u003e and a mixture of Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u003csup\u003e-2\u003c/sup\u003e and other anions.\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-3808914/v1/4eeff98bc5f38199607ba83b.png"},{"id":49092406,"identity":"3bb7b7fa-108c-4204-ad4b-4cd5d4d08fc0","added_by":"auto","created_at":"2024-01-03 02:03:36","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":194085,"visible":true,"origin":"","legend":"\u003cp\u003eAgarose based film strip for CN\u003csup\u003e-\u003c/sup\u003e and Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u003csup\u003e-2\u003c/sup\u003e sensing at 5 ppm.\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-3808914/v1/7b9cdd0ef73aff99352e3cf6.png"},{"id":49093236,"identity":"ee917245-a769-4b8a-83f1-04055c1bc566","added_by":"auto","created_at":"2024-01-03 02:11:36","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":407268,"visible":true,"origin":"","legend":"\u003cp\u003eFluorescent microscopic images of \u003cem\u003eArtemia \u003c/em\u003e(a, b, c), bacteria (bacillus subtilis, d, e, f) and pseudomonas (g, h, i) under excitation in different wavelength (excitation 330-385 nm, blue) (excitation at 395-475 nm, green) (excitation at 395-475 nm, red).\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-3808914/v1/a072fafaaef7d819e7d398cd.png"},{"id":49093238,"identity":"25e1cba0-1016-4b62-8d48-1528b481b353","added_by":"auto","created_at":"2024-01-03 02:11:36","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":195809,"visible":true,"origin":"","legend":"\u003cp\u003eFluorescent microscopy images of \u003cem\u003eArtemia\u003c/em\u003e in (a) absence and (b) presence of CN\u003csup\u003e-\u003c/sup\u003e and that in (c) absence and (d) presence of Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u003csup\u003e-2\u003c/sup\u003e.\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-3808914/v1/00da8e17d7e22974eec8bcd0.png"},{"id":51323093,"identity":"e3c23df9-9298-49e8-8dc3-5e2280ec1fe1","added_by":"auto","created_at":"2024-02-19 15:14:59","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3676690,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3808914/v1/78e16cb4-8326-44f4-adc9-acaf0eadd369.pdf"},{"id":49092409,"identity":"2ade1723-2d78-4836-8375-d468b6431b3a","added_by":"auto","created_at":"2024-01-03 02:03:36","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":1382284,"visible":true,"origin":"","legend":"","description":"","filename":"SIJFluorescence.docx","url":"https://assets-eu.researchsquare.com/files/rs-3808914/v1/a4e43f53034dbf84ee054377.docx"},{"id":49092405,"identity":"51a2655d-601f-4bba-9f04-c29cc3f32f5c","added_by":"auto","created_at":"2024-01-03 02:03:36","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":259845,"visible":true,"origin":"","legend":"","description":"","filename":"TableofContentJfluorescence.docx","url":"https://assets-eu.researchsquare.com/files/rs-3808914/v1/853b40fea700e9b2abbb60d0.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Fluorescent Carbon Dots: Aggregation-Induced Emission Enhancement, Application as probe for CN - and Cr 2 O 7 -2 , sensing strips and bio-imaging agent","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe fluorescent carbon dots are emerging as potential material for sensing of cations and anions and also for bioimaging [\u003cspan additionalcitationids=\"CR2 CR3 CR4\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Several fundamental phenomena are reported for the origin of fluorescence in carbon dots, it has also been reported that the fluorescence property can be amplified applying different methodologies. One of such methods is Aggregation Induced Emission (AIE), which involves assembly of particles making changes in the fluorescence property [\u003cspan additionalcitationids=\"CR7 CR8\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. AIE has been observed in organic small molecules (OSMs) as well as in photoluminescent nanoparticles (PLNPs) [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Aggregation of PLNPs depend on the functional groups on the surface of the nanoparticles and surrounding environmental conditions such as solvents, pH, ionic strength etc. [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. In carbon dots, AIE enhancement is mainly due to solvent-induced or cation-induced aggregation of the dots [\u003cspan additionalcitationids=\"CR14\" citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. This property of carbon dots/nanoparticles can be effectively used for the developments of probes for ion recognition. In the present study, the carbon dots prepared exhibited fluorescence enhancement due to AIE and it selectively detects CN\u003csup\u003e\u0026minus;\u003c/sup\u003e and Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eCyanide (CN\u003csup\u003e\u0026minus;\u003c/sup\u003e) is one of the most toxic anion [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. In human body it binds cytochrome c oxidase that causes the inhibition of oxygen transport to mitochondria, resulting in hypoxia and eventually death [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. CN\u003csup\u003e\u0026minus;\u003c/sup\u003e contamination in environment is mainly due to industrial processes such as herbicide synthesis, gold-extraction, paper, textiles, plastic manufacturing etc. [\u003cspan additionalcitationids=\"CR21\" citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. CN\u003csup\u003e\u0026minus;\u003c/sup\u003e is also found in some natural sources, it is present in seeds of several fruits, certain plants and in some food stuffs [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Another extremely toxic ion is Cr(VI)/Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, industrial activities such as preservation of wood, textile dyeing, leather tanning, electroplating and metal finishing processes release hexavalent chromium Cr(VI), which contaminates with water and soil creating environmental pollution [\u003cspan additionalcitationids=\"CR26\" citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. According to the World Health Organization (WHO), the maximum permissible level of CN\u003csup\u003e\u0026minus;\u003c/sup\u003e in drinking water is 0.20 ppm and that of Cr(VI) is 0.10 ppm [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTherefore, detection of CN\u003csup\u003e\u0026minus;\u003c/sup\u003e and Cr(VI)/Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e in aqueous media is critically important. There are several instrument based analytical techniques for detection/estimation of these ions, however, most of these methods require expensive instruments, involve tedious sample preparation process, sometime amount of sample and limit of detection become a matter of concern [\u003cspan additionalcitationids=\"CR29 CR30\" citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. Alternatively, colorimetric and fluorometric methods of detection are increasing rapidly because of its simplicity, low cost and fast detection process [\u003cspan additionalcitationids=\"CR33\" citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. In these methods, as sensing materials, discrete molecules [\u003cspan additionalcitationids=\"CR35\" citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e], composite materials [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e], nanoparticles [\u003cspan additionalcitationids=\"CR40 CR41\" citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e], carbon dots [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e] etc., which exhibit colour and UV-vis/fluorescence spectral changes in presence of CN\u003csup\u003e\u0026minus;\u003c/sup\u003e and/or Cr(VI) have been used. The interaction of the guest ion with the sensing material results changes in optical properties of the sensor due to energy/electron transfer process involved in the event. In recent time, fluorescent carbon dots have emerged as a new class of sensing material for detection of metal ions and anions, particularly Cr(VI) and CN\u003csup\u003e\u0026minus;\u003c/sup\u003e in aqueous media [\u003cspan additionalcitationids=\"CR45\" citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e]. In addition to the sensing of analytes, the use of carbon dots for bio-imaging is also growing rapidly [\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e, \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e]. The application of carbon dots as sensors as well as bio-imaging agent is becoming popular because of its simple method of preparation from mostly inexpensive precursors.\u003c/p\u003e \u003cp\u003eHerein, a simple and eco-friendly method for preparation of fluorescent carbon dots using tryptophan as precursor and its application for sensing of toxic ions such as CN\u003csup\u003e\u0026minus;\u003c/sup\u003e and Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e and as bio-imaging agent is reported. The carbon dots (Trp-CD) prepared exhibited poor fluorescence in water but in ethanol and higher alcohols it showed strong Aggregation Induced Emission (AIE) and selectively detected CN\u003csup\u003e\u0026minus;\u003c/sup\u003e and Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e among a large number of anions used in this study. Trp-CD was also used for preparation of sensing strips by coating it onto solid surfaces and the strips with agarose films were used for detection of CN\u003csup\u003e\u0026minus;\u003c/sup\u003e and Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e in aqueous media. The Trp-CD is found to be non-toxic and biocompatible and it is used as bioimaging agent for \u003cem\u003eArtemia\u003c/em\u003e and \u003cem\u003eBacteria\u003c/em\u003e for detection of CN\u003csup\u003e\u0026minus;\u003c/sup\u003e and Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e in live whole invertebrates and \u003cem\u003eBacteria.\u003c/em\u003e\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eChemicals\u003c/h2\u003e \u003cp\u003eL-Tryptophan was purchased from Spectrochem (Mumbai, India). All tetrabutylammonium salts of the anions were purchased from Alfa Aesar (Johnson Matthey Company). Potassium dichromate was purchased from Merck. Sodium cyanide was purchased from sigma Aldrich. All reagents used were of analytical grade and were used as received without further purification.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eInstrumentation\u003c/h2\u003e \u003cp\u003eElemental analysis (C, H, and N) were performed on a model Vario Micro CUBE elemental analyzer. Fluorescence spectra were recorded on Edinburgh Instrument\u0026rsquo;s fluorescence spectrometer and UV/Vis spectra were recorded on a CARY 500 scan Varian spectrophotometer. Infrared spectra were recorded on a Perkin-Elmer spectrum GX FT-system using KBr pellets. Powder-XRD was recorded on a PANalytical instrument, model: Empyrean using Cu Kα radiation, NMR spectra were recorded on model Avance II 500 Bruker FT-NMR instrument. Raman spectra were recorded on a Horiba Scientific model LabRAM HR Evolution Raman Spectrometer. TEM images was recorded on a JEOL, model JEM 2100 transmission electron microscope (200 Kv).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003ePreparation of carbon dots (Trp-CD)\u003c/h2\u003e \u003cp\u003eIn a typical experiment, tryptophan (1 g) was heated in air furnace at 200\u003csup\u003e0\u003c/sup\u003eC for 3 h and then allowed to cool to room temperature. The carbonious material thus obtained was stirred in ethanol (250 mL) for 24 h at room temperature. The mixture was then centrifuged at 7000 rpm for 10 min to remove large particles. The resulting supernatant was filtered through a cellulose acetate syringe filter (pore size of 0.2 \u0026micro;m). Dark orange solution of purified Trp-CD thus obtained was dried by rotary evaporation. After drying, the purified Trp-CD was obtained as a brownish powder.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eIon-selectivity study\u003c/h2\u003e \u003cp\u003eInteraction of the Trp-CD with various anions was investigated with the aid of fluorescence spectroscopy. To perform this experiment, stock solution of Trp-CD was prepared by adding 13.8 mg of the Trp-CD in ethanol-water mixture (10:90, 100 mL). 1 mL of Trp-CD solution (0.138 mg/mL) was then treated with 1 mL solution of the tetrabutylammonium salts of the anions such as F\u003csup\u003e\u0026minus;\u003c/sup\u003e, Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e, Br\u003csup\u003e\u0026minus;\u003c/sup\u003e, I\u003csup\u003e\u0026minus;\u003c/sup\u003e, H\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e, ClO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e, NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e, BF\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e, CH\u003csub\u003e3\u003c/sub\u003eCOO\u003csup\u003e\u0026minus;\u003c/sup\u003e, CN\u003csup\u003e\u0026minus;\u003c/sup\u003e and HSO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e and potassium salt of Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e dissolved in deionized water (2 x 10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e M). During fluorescence study, the effective concentration of the anions was 1x10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e M and the fluorescence spectra of the resulting solutions were recorded after 1 min of incubation time. For fluorometric titration with CN\u003csup\u003e\u0026minus;\u003c/sup\u003e and Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, the incremental amounts of the solutions containing CN\u003csup\u003e\u0026minus;\u003c/sup\u003e and Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e were added into the solution of Trp-CD and fluorescence spectra were recorded after 1 min of incubation time. To investigate interference from other anions, the solutions of other anions (50 \u0026micro;M) were added into the solution containing CN\u003csup\u003e\u0026minus;\u003c/sup\u003e (20 \u0026micro;M) and Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e (20 \u0026micro;M), and fluorescence spectra of the resulting solutions were recorded under the same experimental conditions. For interference study, the excited wavelength was set at 380 nm (with slit width of 4 nm) and the fluorescence intensity at 450 nm was recoded for all of the measurement.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eDetermination of concentration of Trp-CD by mass extinction coefficient measurement\u003c/h2\u003e \u003cp\u003eThe concentration of Trp-CD was determined using mass extinction coefficient measurement. The mass extinction coefficient of Trp-CD has been calculated considering the absorbance at the first absorption peak position using the Lambert\u0026thinsp;\u0026minus;\u0026thinsp;Beer\u0026rsquo;s law, \u003cem\u003eA\u003c/em\u003e\u0026thinsp;=\u0026thinsp;ε\u003cem\u003eCL\u003c/em\u003e, where A is the absorbance at the position of the first excitation absorption peak of Trp-CD, C is the mass concentration (g/L) of Trp-CD, L is the path length (cm) of the radiation beam used for recording the absorption spectrum. In this case, L was fixed at 1 cm, ε is the mass extinction coefficient of Trp-CD (L g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). The concentration of Trp-CD solution calculated was 0.069 mg mL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e with A\u0026thinsp;=\u0026thinsp;0.1101 and ε\u0026thinsp;=\u0026thinsp;1.595.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eDetermination of quantum yield (QY)\u003c/h2\u003e \u003cp\u003eQuantum yield (QY) of the Trp-CD was determined following the published procedure [\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e]. QY was calculated by taking the ratio of the integrated photoluminescence (PL) intensities (excited at 380 nm) and the absorbance value (at 380 nm) of Trp-CD using quinine sulphate as a reference, which was dissolved in 0.1 M H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e (QY, 54%). The quantum yield was calculated using the following equation:\u003c/p\u003e \u003cp\u003e\u0026Oslash; = \u0026Oslash;' \u0026times; (A'/A) \u0026times; (F/F') \u0026times; (η\u003csup\u003e2\u003c/sup\u003e / η'\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003cp\u003eWhere \u0026Oslash; is the QY of the testing sample, F is the testing sample\u0026rsquo;s emission intensity, η is the refractive index (1.33 for water), and A is absorbance. The prime symbol (\u0026prime;) refers to the reference dye of known QY. To minimize reabsorption effects, absorption was always kept below 0.05 at the excitation wavelength.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003ePreparation of agarose gel based sensing strips\u003c/h2\u003e \u003cp\u003eAgarose powder (0.5 g) was dispersed in 50 mL ethanol-water (5:45 mL) and was autoclaved at 180\u003csup\u003e0\u003c/sup\u003eC for 30 min to ensure the complete dissolution of agar powder. Subsequently, by cooling this agarose powder containing solution to room temperature, agarose gel was formed. For making the sensing strips, the film was cut into a rectangular shape and immersed in solution of Trp-CD, after 5 min, the film was removed from the solution and air-dried. The film based strip containing Trp-CD was then exposed to aqueous solution of anions. After 5 min, the strip was removed from the aqueous solution, air-dried at room temperature and the changes in colour was noted.\u003c/p\u003e \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e \u003ch2\u003eToxicity study of Trp-CD towards Artemia\u003c/h2\u003e \u003cp\u003eTo study the toxicity of Trp-CD, \u003cem\u003eArtemia\u003c/em\u003e cysts (650\u0026ndash;700 mg in 500 mL autoclaved sea water) were allowed to hatch overnight with vigorous aeration under visible light. Shortly after complete hatching, approximately 50 \u003cem\u003eArtemia\u003c/em\u003e were added in each tube (in 10 mL aqueous solution). Two sets of tubes (in triplicate) were arranged. \u003cem\u003eArtemia\u003c/em\u003e were allowed to nurture for 24 h in absence (control) and presence of Trp-CD and next day mortality were counted to check the toxicity of Trp-CD towards \u003cem\u003eArtemia\u003c/em\u003e.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eArtemia incubation and imaging\u003c/h2\u003e \u003cp\u003eUnder visible light (20 lux) and at vigorous aeration \u003cem\u003eArtemia\u003c/em\u003e cysts were captured. Different concentrations of CN\u003csup\u003e\u0026minus;\u003c/sup\u003e (1 \u0026micro;M) and Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e (1 \u0026micro;M) in 10 mL of water were used. \u003cem\u003eArtemia\u003c/em\u003e were incubated to these anions solutions initially for 2 h at 25\u0026deg;C and then the free anions which were present in the solution was removed through centrifugation (repeated twice to avoid any background colour). \u003cem\u003eArtemia\u003c/em\u003e were then exposed to Trp-CD taken in ethanol-water (10:90% v/v). Nearly 150 numbers of \u003cem\u003eArtemia\u003c/em\u003e were added in each tube. After completion of the incubation, they were washed with water and then the individual \u003cem\u003eArtemia\u003c/em\u003e was mounted on a glass slide and monitored through a fluorescent microscope. Tubes containing just Trp-CD were also used to get control image.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results and Discussion","content":"\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\n \u003ch2\u003eSynthesis and characterization of Trp-CD\u003c/h2\u003e\n \u003cp\u003eNitrogen rich tryptophan was used as carbon source for the preparation of carbon dots following an eco-friendly procedure without use of any harmful acids, salts and drastic conditions. Tryptophan powder converted into carbonaceous material (CM) by heating in air (ashing) at 200 \u003csup\u003e\u0026ordm;\u003c/sup\u003eC for 3h (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e). During heating, reactions such as dehydration, polymerization, carbonization, condensation between the amino and carboxylic groups of tryptophan took place and carbonaceous material was obtained. This carbonaceous material having oxygen and nitrogen containing functional groups, exhibited almost non-fluorescent behaviour (Fig. \u003cspan class=\"InternalRef\"\u003eS1\u003c/span\u003e, SI). These carbonaceous material was further treated with ethanol and purified following the procedure described in the Experimental Section, which yielded brownish carbon dots (Trp-CD). The carbon dots thus obtained were\u003c/p\u003e\n \u003cp\u003echaracterized on the basis of analytical, spectroscopic and microscopic analysis. The elemental analysis of Trp-CD revealed that it contains C, 75.48, H, 3.70 and N, 13.49%, the remaining 7.3% (by calculation) is expected to be oxygen. The data suggest that Trp-CD contains functional groups containing C, H, N and O on to the surface of the carbon particles. It has been further confirmed by FT-IR study, the IR spectrum of which, shown in Fig.\u0026nbsp;2a, exhibits a strong band at 3408 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which is due to \u0026ndash;OH/NH functional groups. The band at 1620 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is assigned to \u0026nu;(C\u0026thinsp;=\u0026thinsp;O) and the other bands in the region 1200 to 1350 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are due to C-N and C-O containing moieties [\u003cspan class=\"CitationRef\"\u003e46\u003c/span\u003e]. The IR data therefore suggests the presence of amide/acid/OH groups on the surface of the carbon dots.\u003c/p\u003e\n \u003cp\u003eThe \u003csup\u003e13\u003c/sup\u003eC NMR spectrum of Trp-CD was recorded in solid state and shown in Fig. 2b. It exhibits broad and overlapped signals for carbon mainly in three regions, 50\u0026ndash;75, 110\u0026ndash;140 and 170\u0026ndash;200 ppm, which in general are the region for aliphatic, aromatic, amide and carboxylic acid carbon atoms, respectively. The amide and carboxylic carbon atoms with inter-/intramolecular interaction may appear in the low field region. Therefore, the \u003csup\u003e13\u003c/sup\u003eC NMR spectrum supports the presence of amide, carboxylic acid and carbonyl groups on the surface of the carbon dots [\u003cspan class=\"CitationRef\"\u003e48\u003c/span\u003e]. The powder X-ray diffraction (PXRD) pattern for the Trp-CD was recorded and shown in Fig.\u0026nbsp;2c. It may be noted that the PXRD pattern of the Trp-CD exhibits at broad peak at 25.88 degree with increment in interlayer spacing of 4.12 \u0026Aring;, the enhancement in interlayer spacing in purified Trip-CD could be attributed to the more oxygen-containing groups are incorporated on the surface of the carbon dots [\u003cspan class=\"CitationRef\"\u003e49\u003c/span\u003e]. The Raman spectrum of Trp-CD is shown in Fig.\u0026nbsp;2d. The D band at 1350 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e represents the sp\u003csup\u003e3\u003c/sup\u003e-hybridized carbon, and the G band at 1560 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is associated with the sp\u003csup\u003e2\u003c/sup\u003e carbon atoms, which is consistent to the observation noted in \u003csup\u003e13\u003c/sup\u003eC NMR [\u003cspan class=\"CitationRef\"\u003e50\u003c/span\u003e].\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\n \u003ch2\u003eEthanol induced aggregation of Trp-CD and enhancement of fluorescence\u003c/h2\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e\n \u003ch2\u003eUV-Vis and fluorescence properties of Trp-CD\u003c/h2\u003e\n \u003cp\u003eAs The study on optical properties of Trp-CD was carried out in water-ethanol, the UV-vis absorption and fluorescence spectra of Trp-CD were recorded and shown in Figs. 5a and 5b. In UV-vis absorption spectrum (Fig. 5a), the Trp-CD exhibits a peak at 217 nm which is attributed to n- \u0026pi; \u003csup\u003e*\u003c/sup\u003e transition. The other peak at 290 nm and a broad shoulder around 345 nm with high energy tail in visible region are observed and they are attributed to \u0026pi; - \u0026pi; \u003csup\u003e*\u003c/sup\u003e transition and Mie scattering caused by nano size particles, respectively [\u003cspan class=\"CitationRef\"\u003e47\u003c/span\u003e]. On excitation at 380 nm, the fluorescence spectrum of Trp-CD shows a strong peak at 452 nm with a Stokes shift of 72 nm (Fig.\u0026nbsp;5b). Like many fluorescent carbon dots, the Trp-CD also exhibits an excitation-dependent photo luminescence behaviour. When excitation wavelength is increased stepwise by 20 nm from 300 to 480 nm, emission intensity of Trp-CD was increased first with red shift in emission\u003c/p\u003e\n \u003cp\u003emaxima, reached to a maximum intensity with excitation at 380 nm and then the intensity was gradually decreased (Fig. 5c). In order to determine the emission life-time, the time-resolved fluorescence decay curve of Trp-CD was measured at room temperature (Fig. 5d). The decay curve thus obtained for Trp-CD could be best fitted with a bi-exponential function with life-time of \u0026tau;1 2.79 ns (10.74%) and \u0026tau;2 18.93 ns (89.26%) with \u0026chi;2 1.05. The bi-exponential emission is believed to be corresponding to the energy gap and surface state transitions [\u003cspan class=\"CitationRef\"\u003e52\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e53\u003c/span\u003e]. The quantum yield (QY) of the Trp-CD was also measured in ethanol-water (10:90) using quinine sulphate as a reference and was found to be 9% of the reference material.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec16\" class=\"Section2\"\u003e\n \u003ch2\u003eEffect of pH on fluorescence intensity of Trp-CD\u003c/h2\u003e\n \u003cp\u003eEffect of pH on fluorescence intensity of Trp-CD was also studied. It showed pH dependent fluorescence intensity, with increasing pH the intensity of the fluorescence band was gradually decreased (Fig. S2, SI). It may be noted that the decrease in intensity in the pH range 3 to 5 is not so significant but after that fluorescence intensity decreased rapidly with increasing pH. At lower pH, the increased concentration of H\u003csup\u003e+\u003c/sup\u003e facilitates protonation of surface decorated groups such as amide, amine etc., enhancing the electronic conjugation in Trp-CD, which probably induces enhancement in fluorescence intensity. At higher pH, such an effect is absent, instead deprotonation might have taken place causing restricted proton transfer in conjugated carbon system resulting in quenching of fluorescence intensity [\u003cspan class=\"CitationRef\"\u003e54\u003c/span\u003e].\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec17\" class=\"Section2\"\u003e\n \u003ch2\u003eInteraction of Trp-CD with anions\u003c/h2\u003e\n \u003cp\u003eThis observation suggests strong interaction of these two anions with the nanoparticles. The change in fluorescence intensity and corresponding fluorescence change under UV light is shown in Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003eb. For the determination of binding constant with anions and to evaluate LOD, fluorescence titration of Trp-CD with incremental addition of CN\u003csup\u003e\u0026minus;\u003c/sup\u003e and Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e (0.1 \u0026micro;M to 0.6 mM) was carried out following the procedure described in the Experimental Section and the fluorescence change is shown in Figs. 7a and 7c. The quenching constant was calculated using the Stern\u0026thinsp;\u0026minus;\u0026thinsp;Volmer equation, (F\u003csub\u003e0\u003c/sub\u003e/F)\u0026thinsp;=\u0026thinsp;1\u0026thinsp;+\u0026thinsp;Ksv [Q] [\u003cspan class=\"CitationRef\"\u003e55\u003c/span\u003e], where F\u003csub\u003e0\u003c/sub\u003e is the initial fluorescence intensities of Trp-CD, F is the fluorescence intensities upon addition of the anions, [Q] is the concentration of the anions and Ksv is the quenching constant. The plot of [(F\u003csub\u003e0\u003c/sub\u003e/F) \u0026ndash; 1] against concentration of anion is shown in Figs.\u0026nbsp;7b and 7d and the linear section is shown as inset of these Figures. The Ksv thus calculated for CN\u003csup\u003e\u0026minus;\u003c/sup\u003e is 4.595 \u0026times; 10\u003csup\u003e3\u003c/sup\u003e M\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and LOD obtained is 0.7 \u0026micro;M and for Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e Ksv is 5.364 \u0026times; 10\u003csup\u003e3\u003c/sup\u003e M\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and LOD obtained is 3.2 \u0026micro;M. The linear range for CN\u003csup\u003e\u0026minus;\u003c/sup\u003e is from 0.1\u0026micro;M to 0.4 mM with R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.992 and for Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e the range is 3.3 \u0026micro;M to 0.16 mM with R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.993, therefore, quantification can be done if the concentration is in this range.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec18\" class=\"Section2\"\u003e\n \u003ch2\u003eMechanism of anion sensing\u003c/h2\u003e\n \u003cp\u003eThe surface of Trp-CD is decorated with different amide and amine containing functional groups, which are mainly responsible for interaction with CN\u003csup\u003e\u0026minus;\u003c/sup\u003e/Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. Strong electron withdrawing CN\u003csup\u003e\u0026minus;\u003c/sup\u003e can easily interact with the protons of different functional groups, which restricts the electron flow within the cluster resulting in quenching in emission intensity. An analogues experiment was carried out with increasing the pH of the solution by adding TBA-OH, which also resulted in quenching in emission intensity (Fig. S3, SI) supporting the proposed mechanism [\u003cspan class=\"CitationRef\"\u003e54\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e56\u003c/span\u003e]. The UV-Vis spectra upon addition of CN\u003csup\u003e\u0026minus;\u003c/sup\u003e did not exhibit any noticeable change (Fig. S4, SI), indicating that it is a surface phenomenon [\u003cspan class=\"CitationRef\"\u003e57\u003c/span\u003e]. The decay profile of the emission life-time measurement exhibited a change from bi-exponential to tri-exponential with life-time of 0.079, 3.78 and 13.81 ns and \u0026chi;\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;1.08 (Fig. S5, SI). On the basis of these information, a schematic representation of the proposed mechanism of CN\u003csup\u003e\u0026minus;\u003c/sup\u003e interaction is shown in Fig. 8a.\u003c/p\u003e\n \u003cp\u003eInterestingly, for Cr(VI) the situation is different because of the presence of strong bands of Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e in the visible and UV regions. The excitation (380 nm) and emission (450 nm) bands of Trp-CD are overlapped significantly with the absorption bands of Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e in the UV-Vis region. This overlapping favoured the inner filter effect (IFE) rather than surface state interaction. The Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e ion shields the excitation light of Trp-CD and absorb the emission light from Trp-CD (Fig. 8b) [\u003cspan class=\"CitationRef\"\u003e52\u003c/span\u003e]. Absorption of emission light restricts the fluorescence enhancement and quenched the emission intensity. The decay profile of the emission life-time measurement exhibited a bi-exponential with 2.5 and 16.25 ns life-time and \u0026chi;\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;1.01 (Fig.\u0026nbsp;8c). A schematic representation showing the interaction of Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e with the Trp-CD is shown in Fig. 8d.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec19\" class=\"Section2\"\u003e\n \u003ch2\u003eInterference study\u003c/h2\u003e\n \u003cp\u003eInterference study for CN\u003csup\u003e\u0026minus;\u003c/sup\u003e and Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e in presence of other anions were carried out following the method described in the Experimental Section. The bar diagram showing the fluorescence intensity of Trp-CD in presence of CN\u003csup\u003e\u0026minus;\u003c/sup\u003e and a mixture of CN\u003csup\u003e\u0026minus;\u003c/sup\u003e and other anions (2.5 times molar excess) is shown in Fig. 9a and similar plot for Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e is shown in Fig. 9b. It may be noted that for CN\u003csup\u003e\u0026minus;\u003c/sup\u003e, there is slight decrease in emission intensity when Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e was added and a slight increase in intensity when SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e was added. For Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e, some quenching is noted when CN\u003csup\u003e\u0026minus;\u003c/sup\u003e was added with Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e anion, which is expected because both CN\u003csup\u003e\u0026minus;\u003c/sup\u003e and Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e interact with the Trp-CD. However, presence of Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e can be confirmed initially by yellow colour of the solution and finally by UV-Vis absorption spectrum, which exhibits a strong band in the visible region (~\u0026thinsp;400 nm).\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eApplication of Trp-CD\u003c/strong\u003e\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec20\" class=\"Section2\"\u003e\n \u003ch2\u003eApplication of Trp-CD as sensing strips\u003c/h2\u003e\n \u003cp\u003eThe fluorescent Trp-CD was coated on various solid surface for preparation of fluorescent sensing material in solid state. The solid surfaces used were waste wooden strips, agarose based gel, filter paper etc., as shown in Fig. S6 (SI). For practical application as sensing material, agar-agar based fluorescent film was prepared following the procedure described in the Experimental Section, the films under day light and UV light is shown in Fig. S7 (SI). The film based strip containing Trp-CD was then immersed into aqueous solution of anions, after 5 min it was removed from the solution and air-dried. the changes under UV light is shown in Fig.\u0026nbsp;10. The figure suggests that the film based sensor can be effectively used for the detection of CN\u003csup\u003e\u0026minus;\u003c/sup\u003e and Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e up to 5 ppm of ion concentration.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec21\" class=\"Section2\"\u003e\n \u003ch2\u003eToxicity study and application as staining agent for Aterima and Bacteria\u003c/h2\u003e\n \u003cp\u003eThe toxicity study of Trip-CD was carried out following the procedure, described in the Experimental Section and found to be nontoxic. Highly fluorescent, nontoxic and biocompatible nature of these carbon dots made it a potential material for biological application and has been applied as staining agent for Aterima and Bacteria \u003cem\u003e(Bacillus subtilis and pseudomonas bacteria)\u003c/em\u003e using different wavelength. Aterima and bacteria were incubated to the solutions CN\u003csup\u003e\u0026minus;\u003c/sup\u003e and Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e following the procedure described in the Experimental Section and their microscopic images were recorded with excitation at different wavelength in the regions blue, green and red and the microscopic images are shown in Fig. 11. Artemia and bacteria containing CN\u003csup\u003e\u0026minus;\u003c/sup\u003e and Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e were then exposed to Trp-CD taken in ethanol-water (10:90%, v/v) and in presence of CN\u003csup\u003e\u0026minus;\u003c/sup\u003e and Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e, the highly fluorescent Trp-CD get quenched, as shown in Fig. \u003cspan class=\"InternalRef\"\u003e12\u003c/span\u003e. The Trp-CD can penetrate into artemia and bacteria and can detect these anions by quenching the fluorescence of Trp-CD because of its interaction with CN\u003csup\u003e\u0026minus;\u003c/sup\u003e and Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"Conclusions","content":"\u003cp\u003eFluorescent carbon dots (Trp-CDs) were prepared by a simple eco-friendly technique using tryptophan as precursor and were characterized on the basis of analytical, spectroscopic and microscopic techniques. Trp-CDs exhibited poor fluorescence in 100% water but it showed strong fluorescence in ethanol and higher alcohols, which is attributed to Aggregation Induced Emission (AIE) enhancement. Trp-CD selectively detected CN\u003csup\u003e\u0026minus;\u003c/sup\u003e and Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e ions by fluorimetric method without interference from any other anions used in this study. Fluorescence titration with incremental addition of CN\u003csup\u003e\u0026minus;\u003c/sup\u003e and Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e were also carried out and from the data quenching constant, LOD and linear range of detection are evaluated. The emission life-time determination before and after addition of CN\u003csup\u003e\u0026minus;\u003c/sup\u003e and Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e exhibited a bi-exponential decay curve with life-time of τ1 2.79 and τ2 18.93 ns (before addition of anion). The study on mechanism of interaction revealed that for CN\u003csup\u003e\u0026minus;\u003c/sup\u003e, the quenching in emission intensity is due to its interaction with the protons associated with functional groups on to the surface and for Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e, it is due to inner filter effect (IFE). The Trp-CD was used as coating material and the agar-agar based fluorescent film strips prepared was used for detection of CN\u003csup\u003e\u0026minus;\u003c/sup\u003e and Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e. Trp-CD was also used as staining agent for \u003cem\u003eArtemia\u003c/em\u003e and Bacteria (\u003cem\u003eBacillus Subtilis\u003c/em\u003e, \u003cem\u003ePseudomonas\u003c/em\u003e) and it penetrated into \u003cem\u003eArtemia\u003c/em\u003e and Bacteria to detect CN\u003csup\u003e\u0026minus;\u003c/sup\u003e and Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCSIR-CSMCRI Registration No. is 217/2023. P. P. Gratefully acknowledges CSIR for the financial support in the form of CSIR-Emeritus Scientist Scheme (CSIR-ES Scheme No. 21(1046)/18/EMR-II). S. Bhatt (CSIR Award No.: 31/28(0240)/2018-EMR-I) and G. Vyas (CSIR- Award No.: 31/28(0238)/2018-EMR-I) acknowledge CSIR for awarding the Senior Research Fellowship.\u0026nbsp;A. Kumar (Award No. 19-06/2011(i)EU-IV)\u0026nbsp;gratefully acknowledges UGC for awarding the Research Fellowship (JRF and SRF).\u0026nbsp;All the authors acknowledge CSIR-CSMCRI for providing research facilities and partial research expense related to this work. \u0026nbsp;We thank Dr. G. R. Bhadu, for recording TEM and Laiya Riddhi P. for XRD, V. Agrawal for recording IR spectra, V. Bakani for elemental analysis and Raman spectra. We thank AESD\u0026amp;CIF for additional analytical support.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompliance with Ethical Standards\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eDetails of funding received is incorporated in the Acknowledgement.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe online version of this article (https://doi.org/.......) contains supplementary material, which is available to authorized users.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of Interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThere are no conflicts to declare.\u0026nbsp;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eJi C, Zhou Y, Leblanc RM, Peng Z (2020) Recent developments of carbon dots in biosensing: A review. 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Nanoscale 5:5514\u0026ndash;5518\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"journal-of-fluorescence","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jofl","sideBox":"Learn more about [Journal of Fluorescence](https://www.springer.com/journal/10895)","snPcode":"10895","submissionUrl":"https://submission.nature.com/new-submission/10895/3","title":"Journal of Fluorescence","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Carbon dots, Aggregation-induced emission, Cyanide sensing, Chromium(IV) sensing, Bio-imaging","lastPublishedDoi":"10.21203/rs.3.rs-3808914/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3808914/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eFluorescent carbon dots (Trp-CDs) were prepared using tryptophan as precursor and were characterized on the basis of elemental analysis, powder-XRD, IR, Raman spectroscopy, \u003csup\u003e13\u003c/sup\u003eC-NMR, UV-Vis, fluorescence and TEM. Trp-CDs exhibit poor fluorescence in 100% water but showed strong Aggregation Induced Emission (AIE) in ethanol and higher alcohols. The anion sensing study of Trp-CD revealed that it selectively detects CN\u003csup\u003e\u0026minus;\u003c/sup\u003e and Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e and from fluorescence quenching titration study, quenching constant, LOD and range of detection were evaluated. The emission life-time of Trp-CD before and after addition of CN\u003csup\u003e\u0026minus;\u003c/sup\u003e and Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e were measured, the decay curve before addition of anion was best fitted with a bi-exponential function with life-time of τ1 2.79 ns (10.74%) and τ2 18.93 ns (89.26%). The mechanistic study revealed that for CN\u003csup\u003e\u0026minus;\u003c/sup\u003e, the fluorescence quenching is due to its interaction with protons attached to surface functional groups and for Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, it is due to inner filter effect (IFE). Sensing strips were prepared by coating Trp-CDs onto various solid surfaces including agarose films and were used for detection of CN\u003csup\u003e\u0026minus;\u003c/sup\u003e and Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e. Trp-CD was found to be nontoxic and biocompatible and used as staining agent for \u003cem\u003eArtemia\u003c/em\u003e and \u003cem\u003eBacteria\u003c/em\u003e (\u003cem\u003eBacillus Subtilis\u003c/em\u003e, \u003cem\u003ePseudomonas\u003c/em\u003e) and detection of CN\u003csup\u003e\u0026minus;\u003c/sup\u003e and Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e.\u003c/p\u003e","manuscriptTitle":"Fluorescent Carbon Dots: Aggregation-Induced Emission Enhancement, Application as probe for CN - and Cr 2 O 7 -2 , sensing strips and bio-imaging agent","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-01-03 02:03:31","doi":"10.21203/rs.3.rs-3808914/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-01-03T12:51:23+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-01-03T08:25:17+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"a924bcea-6d85-4e0d-b6fa-efd88dd7de52","date":"2023-12-29T07:36:18+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2023-12-28T21:05:14+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2023-12-28T09:43:05+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2023-12-28T09:43:05+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Fluorescence","date":"2023-12-26T16:33:33+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-fluorescence","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jofl","sideBox":"Learn more about [Journal of Fluorescence](https://www.springer.com/journal/10895)","snPcode":"10895","submissionUrl":"https://submission.nature.com/new-submission/10895/3","title":"Journal of Fluorescence","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"64fb258e-081f-4731-8517-b6417a67469c","owner":[],"postedDate":"January 3rd, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-02-19T15:10:12+00:00","versionOfRecord":{"articleIdentity":"rs-3808914","link":"https://doi.org/10.1007/s10895-024-03602-2","journal":{"identity":"journal-of-fluorescence","isVorOnly":false,"title":"Journal of Fluorescence"},"publishedOn":"2024-02-17 15:01:11","publishedOnDateReadable":"February 17th, 2024"},"versionCreatedAt":"2024-01-03 02:03:31","video":"","vorDoi":"10.1007/s10895-024-03602-2","vorDoiUrl":"https://doi.org/10.1007/s10895-024-03602-2","workflowStages":[]},"version":"v1","identity":"rs-3808914","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3808914","identity":"rs-3808914","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}