Advanced Security Printing Enabled by Biomass-Derived Multicolor Anti-Counterfeiting Fluorescent Carbon Dot Ink with Multimodal Applications

Advanced Security Printing Enabled by Biomass-Derived Multicolor Anti-Counterfeiting Fluorescent Carbon Dot Ink with Multimodal Applications | 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 Advanced Security Printing Enabled by Biomass-Derived Multicolor Anti-Counterfeiting Fluorescent Carbon Dot Ink with Multimodal Applications Tingting Cai, Yifan Zhao, Tingyu Zhang, Yun Yang This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6547577/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 18 Jul, 2025 Read the published version in Microchimica Acta → Version 1 posted 9 You are reading this latest preprint version Abstract One of the most pressing challenges in fluorescence-based anti-counterfeiting technology is the development of multi-color fluorescent materials that simultaneously satisfy the stringent requirements of high security, cost-effectiveness, and environmental sustainability. Biomass-derived fluorescent carbon dots (CDs) are characterized by their low cost, non-toxicity, and tunable multicolor fluorescence, making them ideal candidates for developing multicolor fluorescent inks with multi-level anti-counterfeiting capabilities. In this study, N-doped tricolor CDs were synthesized via a solvothermal method using orange juice, lemon juice, and banana leaves as biomass precursors. These CDs exhibited distinct blue, green, and blue-red dual-emission fluorescence, with their structure-property relationships and luminescence mechanisms systematically investigated through comprehensive characterization techniques. A glycerol-based tricolor fluorescent ink system was developed, enabling multilayered information encryption under UV/visible light dual-mode through integrated processes such as handwriting, screen printing, and stamping. Furthermore, flexible sensing films were fabricated by incorporating CDs into polyvinyl alcohol (PVA) matrices. Remarkably, the CDs-embedded films exhibited significantly enhanced electrical signal responses during mechanical sensing. This work not only provides a novel strategy for high-value utilization of biomass resources but also opens innovative pathways for developing intelligent anti-counterfeiting materials and flexible electronic devices. Biomass-derived carbon dots Fluorescent ink Multiple anti-counterfeiting flexible sensing Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Introduction In the context of rapidly advancing technology, the proliferation of counterfeit products and information breaches has posed severe challenges to national image building, corporate brand protection, and consumer rights safeguarding. Optical anti-counterfeiting technologies, leveraging the intuitive reliability of human color perception, have emerged as a critical research frontier. Among these, fluorescent anti-counterfeiting strategies demonstrate exceptional security advantages through material-specific color variations under natural and UV light. Current fluorescent systems include transition metal complexes, inorganic semiconductors, chalcogenide-based quantum dots, metal halide perovskites, metal-organic frameworks, and lanthanide-doped upconversion nanoparticles [ 1 – 4 ] . While these materials exhibit high photoluminescence quantum yields and broad emission spectra, they suffer from complex synthesis, high costs, insufficient brightness, and environmental concerns [ 5 , 6 ] . Crucially, most methods rely on monochromatic emission, limiting anti-counterfeiting capacity and code complexity against professional decryption. Thus, developing cost-effective, eco-friendly multicolor fluorescent materials with high security remains a pivotal challenge. Carbon dots (CDs) have recently gained prominence due to their unique advantages including low toxicity, excellent solvent dispersibility, high yield, tunable stable luminescence, and photobleaching resistance,which are ideal for anti-counterfeiting [ 7 , 8 ] . Unlike conventional fluorescent materials, CDs offer emission wavelength tunability through precursor selection and synthesis optimization [ 5 , 9 ] . Multi-color coupling further enhances security. Biomass-derived CDs are particularly promising for two reasons. One is that biomass precursors (e.g., fruit peels, juice, leaves, flowers) are abundant, eco-friendly, and biodegradable [ 10 , 11 ] , crucial for consumer-safe applications. Moreover, their inherent heteroatom richness enables self-doping [ 12 ] , yielding CDs with distinct tunable properties. Thus, biomass-derived multicolor CDs present significant potential for multi-level anti-counterfeiting through ink formulation and signal superposition. In this work, blue, green, and red-emitting CDs were synthesized via one-step solvothermal treatment of lemon, orange, and banana leaf biomass. A glycerol-based multiphase ink system was developed to suppress non-radiative energy transfer between multicolor CDs, significantly enhancing fluorescence stability. The ink demonstrated multilevel anti-counterfeiting through handwriting, screen printing, and stamping. Furthermore, flexible polyvinyl alcohol (PVA) films embedded with CDs exhibited enhanced electromechanical responses, with CD incorporation boosting electrical signal intensity during mechanical sensing. This study not only advances biomass valorization but also provides interdisciplinary solutions for next-generation optical-sensing anti-counterfeiting technologies and smart interactive systems. 1. Experimental 1.1 Reagents Urea, anhydrous ethanol, glycerol, and polyvinyl alcohol (PVA) (analytical grade) were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Fresh lemons and oranges were procured from a local fruit market, while banana leaves were harvested from the greenhouse botanical garden. Deionized water was prepared by the laboratory ultrapure water system. 1.2 Instruments Transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HR-TEM) images were observed on a JEM-F200 transmission microscope (JOEL, Japan). Fourier transform infrared spectra (FT-IR) were obtained on a Nicolet iS20 spectrometer with KBr spheres (Thermo Fisher Scientific, USA). X-ray photoelectron spectroscopy (XPS) spectra were obtained on an X-ray photoelectron spectrometer (ESCALAB 250, Thermo Fisher Scientific, USA). The UV–vis absorption spectra were recorded with UV–vis spectrophotometer ( UV-3600Plus, SHIMADZU, Japan ). Fluorescence spectra measurements were performed on the FLS1000 spectrofluorometer (Edinburgh Instruments Ltd., UK). 1.3 Preparation of N-doped carbon dots As shown in Fig. 1 , fresh lemon juice (20 mL) was mixed with absolute ethanol (10 mL) and urea (0.05 g) in a beaker. After ultrasonic dispersion for 15 min, the homogeneous mixture was transferred into a Teflon-lined stainless steel autoclave and heated at 190°C for 6 h in a preheated oven. The resulting brown transparent solution was cooled to room temperature, filtered through a 0.22 µm microporous membrane, and dialyzed (1000 Da) to remove small organic molecules. The purified product was freeze-dried to obtain brown powdery B-CDs.​ With identical synthetic procedures, G-CDs were prepared by replacing lemon juice with fresh orange juice (20 mL) while maintaining all other reaction conditions. To obtain the R-CDs, fresh banana leaves were air-dried for one week and ground into powder. The precursor mixture of banana leaf powder (2 g), ethanol (30 mL), and urea (0.05 g) were ultrasonicated for 30 min before hydrothermal treatment at 200°C for 8 h. After identical purification steps, the red-emitting R-CDs were obtained by lyophilization. 1.4 Preparation of N-Doped CDs inks The three prepared CDs solutions (post-dialysis) were separately mixed with glycerol at different volume ratios and thoroughly homogenized by magnetic stirring to obtain the CDs inks with distinct emission colors. The inks were loaded into empty pen refills by a micropipette for writing on multiple textures. Furthermore, these inks were integrated with traditional anti-counterfeiting techniques, including screen printing and sealing, enabling large-scale production of security patterns on diverse substrates such as non-fluorescent cellulose paper, kraft paper, and the flexible PVA films. 1.5 Preparation of Carbon Dots/PVA Composite Films​ 1 g of polyvinyl alcohol was added to 49 mL of deionized water, and the solution was heated and stirred at 90 ° C for 2.5 h until clear and transparent. 0 mg, 1 mg, 2 mg, and 3 mg carbon dots were mixed with 10 mL PVA aqueous solution at 60 ℃ and 500 rpm for 10 min. After mixing, the mixture was poured into the silicone mold, placed at 4 ℃ for 12 h, then removed, and dried in a constant temperature drying oven at 80 ℃ for 4 h to obtain the film. 2. Results and Discussion The TEM images of B-CDs、G-CDs、 R-CDs samples are shown in Fig. 2 a-c. As revealed, all CDs particles exhibit spherical morphology with monodisperse distribution and negligible aggregation. Statistical analysis of particle sizes demonstrates diameters of 4.6 ± 0.3 nm (B-CDs), 5.3 ± 0.4 nm (G-CDs), and 2.4 ± 0.2 nm (R-CDs), indicating significantly larger size for B-CDs and G-CDs compared to R-CDs. Furthermore, high-resolution TEM images in the inset display well-defined lattice fringes of B-CDs, G-CDs, and R-CDs with the interplanar spacing of 0.21 nm, corresponding to the (100) graphene plane in CDs [ 13 ] . In the FT-IR spectrum of CDs in Fig. 2 d-f, the strong and wide absorption peak at 3300–3700 cm − 1 are attributed to the stretching vibration of N‒H and -OH, especially for B-CDs and G-CDs. The double peaks at 1620–1710 cm − 1 are assigned to -NH 2 and N-C = O. These results reveal that the N element from carbamide have been chemically bonded with the CDs during the solvothermal process of B-CDs and G-CDs. For R-CDs, the peak at 3300–3700 cm − 1 are unconspicuous, indicating a lower content of N‒H and -OH [ 14 , 15 ] . The strong and sharp double peaks at 2850 and 2930 cm − 1 ,which is a character absorption of symmetric and asymmetric stretching vibration of C-H [ 16 ] , is prominent for R-CDs. The peaks located in 1360–1460 and 1050–1170 cm − 1 demonstrating the diversity oxygen-containing functional groups in the CDs samples [ 17 ] . X-ray photoelectron spectroscopy (XPS) analysis revealed the surface chemical composition of the as-prepared carbon dots (CDs), with survey spectra showing characteristic peaks for C 1s (284 eV), N 1s (398 eV), and O 1s (530 eV) in Fig. 3 a. Quantitative analysis indicated varying elemental contents, with R-CDs exhibiting the highest carbon content (83.4%) but lowest nitrogen doping (1.72%), while B-CDs and G-CDs showed comparable nitrogen contents (4.66% and 4.08%, respectively). In the N 1 s spectrum of B-CDs and G-CDs, the three bands at around 399.3, 400, and 401.5 eV indicated the presence of amino N, pyrrolic N, and graphitic N (Fig. 3 b-c).The C 1s spectrum of B-CDs and G-CDs were deconstructed into four peaks, namely, C-C/C-H, C = N, C-O, and C = O at 284.4, 285.6, 286.5 and 288 eV respectively (Fig. 3 d-e). R-CDs has the highest content of carbon element, so the C1s peak intensity is the largest, and the C-C and C-H bond content is the highest. The three peaks of O 1s spectrum around 531.0, 532.1, and 533.0 eV correspond to -C = O, -OH, and -C-O, respectively [ 18 , 19 ] , indicating the existence of oxygen-containing functional groups such as hydroxyl and carboxyl groups with high density on the surface of the CDs. The fluorescence spectra and ultraviolet-visible (UV–vis) absorption of CDs were systematically investigated at room temperature. As illustrated in Fig. 4 a-c, the three-dimensional (3D) fluorescence spectra of CDs under different excitation wavelengths were obtained. For B-CDs (Fig. 4 a), the emission peak exhibited a significant red shift as the excitation wavelength increased from 320 to 420 nm, with the maximum emission intensity observed in the range of 450–480 nm. Similarly, G-CDs displayed red-shift characteristics with an emission peak centered around 540 nm. Notably, R-CDs revealed two distinct emission centers (Fig. 4 c). The photoluminescence spectra exhibited dual emission peaks at 470 nm (blue fluorescence) and 660 nm (red fluorescence), indicating unique blue-red dual-emission properties. The aqueous solution of B-CDs exhibited a clear absorption peak at 280 nm, indicating the n-π* transitions of the sp 2 aromatic domains. Additionally, the weak absorption peak at 219 nm could be attributed to the π-π* transition of the C = C bond within the internal structure of CDs [ 14 , 15 ] . The optimal wavelengths of excitation (purple line) and emission (blue line) were at 390 and 465 nm, with a Stokes shift of 75 nm [ 20 ] .Combined with the structural analysis, it can be inferred that the C-N/C-O bonds in the C 1s spectrum may promote exciton radiative recombination by providing lone pair electrons. This process leads to the formation of a surface defect state while simultaneously passivating the nonradiative recombination centers on the surface of CDs. The UV absorption spectrum of G-CDs exhibits a strong absorption peak near 278 nm, which can be ascribed to the n-π* transition of the aromatic C = O group. Additionally, a broad absorption band in the range of 310–500 nm is observed, attributed to the presence of nitrogen atoms with lone pair electrons that facilitate the formation of the n − π* electronic configuration, thereby inducing a red shift in the absorption spectrum [ 15 , 16 ] . As depicted in Fig. 3 b, the excitation spectrum scan reveals an optimal excitation wavelength of approximately 450 nm, with the corresponding emission peak located at 512 nm, exhibiting green fluorescence and a Stokes shift of 62 nm. Structural analysis suggests that the conjugated carbonyl or imine groups associated with the C = O/C = N bonds extend the π-electron conjugation system, enhancing the red shift of the fluorescence emission wavelength. Furthermore, the deprotonation of N-H bonds contributes to the passivation of surface defects, effectively reducing non-radiative recombination. As shown in Fig. 4 f, the R-CDs solution exhibited significant characteristic absorption peaks at 280 nm, 319 nm, 415 nm, and 656 nm. The absorption peaks at 280 nm and 319 nm were attributed to the π→π* electron transition of the C = C bond and the n→π* electron transition of the C = O bond in nanocarbon, respectively. Meanwhile, the absorption peaks at 415 nm and 656 nm were ascribed to the n→π* electron transitions of the C = O and C = N bonds within the chlorophyll-derived porphyrin structure [ 21 ] . Furthermore, the excitation and emission fluorescence spectra of R-CDs (Fig. 4 f) revealed that this carbon dot solution possesses dual-emission characteristics. Specifically, the emission peak at 475 nm exhibited a red shift with increasing excitation wavelength, demonstrating excitation-dependent behavior. Conversely, the emission peak at 660 nm was independent of the excitation wavelength and remained stable during the excitation wavelength scan from 310 to 350 nm. The two emission peaks at 470 nm and 660 nm corresponded to the optimal excitation wavelengths of 370 nm and 410 nm, respectively. As confirmed by prior XPS characterization, the nitrogen deficiency is mechanistically consistent with the dual-emission behavior, which arises from the competitive radiative recombination pathways between chlorophyll-derived porphyrin π→π* transitions and carbohydrate-based surface state emissions. To improve the applicability of the prepared carbon dots (CDs) for writing and printing purposes, they were formulated into fluorescent inks. The effects of mixing CDs solutions with varying proportions of thickeners, specifically glycerol, were systematically examined. It was found that mixing CDs solutions with glycerol at ratios of 1:1 and 1:2 yielded fluorescent inks with distinct concentrations and viscosities, demonstrating superior fluorescence performance suitable for creating diverse types of anti-counterfeiting marks via writing or printing. To enhance the efficiency and convenience of producing anti-counterfeiting marks, this study assessed the anti-counterfeiting efficacy of three methods: fluorescent pen cores, anti-counterfeiting stamps, and screen printing. The CDs solution was mixed with glycerol and loaded into empty pen refills to fabricate fluorescent ink pens (Fig. 5 a), which exhibited bright blue, green, and red fluorescence under 365 nm UV irradiation. When writing "LLU" on non-fluorescent paper, the text was invisible under sunlight but clearly visible as tricolor fluorescent characters under 365 nm UV light (Fig. 5 b). Figures 5 c-d demonstrate the writing effects on aluminum fiber cloth, showing distinct "CDs PL light" and "Snow" patterns. Figure 5 e presents the writing performance of B-CDs ink on nitrile gloves, where "Take care" and a lightning symbol became clearly visible under UV light. Figure 5 f displays the "LLU" pattern on PVA flexible film, indicating the potential application of these fluorescent pen cores for marking and anti-counterfeiting purposes on organic flexible films. Based on these experiments, it is evident that the fluorescent pen core can be effectively applied to various substrates and achieve superior anti-counterfeiting performance. It is suitable not only for manual writing but also for anti-counterfeiting purposes in packaging, printing, trademarks, tickets, certificates, and other valuable items. Compared with fluorescent writing pens, stamps and screen printing technology demonstrate significant efficiency advantages in anti-counterfeiting processing, enabling the mass production of industrial-grade anti-counterfeiting labels and wide application in the preparation of anti-counterfeiting labels for food and beverages, pharmaceuticals, intellectual property protection, financial security, and public safety. As shown in Fig. 6 a, carbon dot solutions can directly replace traditional inks for the production of anti-counterfeiting stamps or the printing of hidden patterns by adapting to stamping and screen printing processes. Figures 6 b-d systematically demonstrate the practical application effects of the two technologies. By comparing the pattern features under different lighting conditions, it is found that the patterns show low contrast and blurred details under sunlight (Fig. 6 b). While under 365 nm ultraviolet light excitation, the fluorescence emission characteristics of carbon dots make the patterns clearly visible, with significantly improved visual resolution. Specifically, the cartoon rabbit-shaped stamp based on green and red carbon dot modification in Fig. 6 b can achieve three-color fluorescence imaging with sharp boundaries and excellent anti-counterfeiting performance. Further research shows that the fluorescence ink prepared by combining a volume ratio of 1:2 green fluorescent carbon dot solution (G-NCDs) with glycerol, combined with the screen printing process on non-fluorescent paper, forms a dragon-shaped pattern (Fig. 6 c) that shows a high saturation and strong contrast fluorescence response under ultraviolet light. In addition, Fig. 6 d compares the imaging differences of fluorescent stamps and red official stamps on non-fluorescent toilet paper: the former appears nearly colorless under natural light, but can display high-resolution school emblems and the words "Carbon Group" under ultraviolet excitation. The above experiments fully verify the application potential of carbon dot ink in stamp fluorescence imaging and screen printing. In addition, given the ability of CDs to retain fluorescence when used for writing on flexible films, the incorporation of B-CDs into PVA flexible films as sensing materials was investigated. The CDs/PVA composite served as the friction layer material in the assembly of the sensor device. Aluminum electrodes were employed as the conductive electrodes, with a silicone ring acting as the spacer layer, and the outer surface was encapsulated using polyimide (Fig. 7 a). The sensor demonstrated regular electrical signals based on the principle of single-electrode triboelectric response. As illustrated in Fig. 7 b, under actual operating conditions, variations in pressure caused the CDs/PVA films on either side of the spacer to repeatedly contact and separate from the aluminum electrode. This cyclic process intermittently generated triboelectric current [ 22 – 24 ] . The testing was carried out with the triboelectric sensor testing system in Figure S4. The results presented in Fig. 7 c indicated that the incorporation of CDs enhanced the electrical response performance of the film. Specifically, as the concentration of CDs increased, the peak voltage of the film also increased, exhibiting an approximately linear relationship. When varying amounts of CDs (0, 1, 2, and 3 mg) were added to 50 mL of a 2% PVA solution, the response voltage progressively increased from 0.2 V to 2.5 V, 7.5 V, and 12.5 V, achieving a 62.5-fold enhancement. The response voltage in response revealed that as the applied external force increased, the device exhibited larger response voltages and currents (Fig. 7 d). More importantly, the voltage response of this sensor exhibits a linear relationship with increasing pressure, thereby enabling its application in the quantitative sensing of motion, gestures, vocalization, and other related phenomena. Combining the previous structural and component representations, it can be inferred that CDs can be uniformly incorporated into the polymer matrix for their small size and excellent dispersibility. Therefore, numerous interfaces were introduced into the composite material and thereby promoting various interfacial polarization phenomena [ 23 , 25 , 26 ] . This contributes to an increase in the relative dielectric constant of the polymer composite material and the surface charge density, significantly improving the overall sensing performance of triboelectric nanogenerator (TENG)-based sensors [ 27 ] . The amino (-NH₂) groups present at the terminals of O-CDs act as effective electron-donating moieties, enhancing the surface charge density of triboelectric materials [ 28 ] . Additionally, CDs can function as crosslinkers via non-covalent interactions, simultaneously increasing the crosslinking density and accelerating the film-forming rate of polyvinyl alcohol (PVA) films [ 29 , 30 ] . 3 Conclusions Three types of nitrogen-doped fluorescent carbon dot (CD) inks were synthesized via a solvothermal method using lemon juice, orange juice, chlorophyll powder, urea, and anhydrous ethanol as raw materials for anti-counterfeiting applications. Specifically, B-CDs emit blue fluorescence with optimal excitation and emission wavelengths at 390 nm and 460 nm, respectively; G-CDs exhibit green fluorescence with optimal excitation and emission wavelengths at 450 nm and 540 nm, respectively; R-CDs display red fluorescence with dual-emission characteristics, having optimal excitation wavelengths at 380 nm and 390 nm, and emission peaks at 470 nm and 660 nm. Studies indicate that the size, surface functional groups, and N-doping form of the three CDs directly influence their fluorescence emission wavelengths. By mixing CDs with thickeners, three-color fluorescent inks were successfully developed. These inks demonstrate significant ultraviolet-induced fluorescence effects in applications such as pen writing, seal stamping, and screen printing. Furthermore, when these inks are used in double or triple superposition, they exhibit excellent multi-level anti-counterfeiting performance, offering broad application prospects in areas such as packaging anti-counterfeiting printing, printer-based printing, and anti-counterfeiting seals. Additional research reveals that combining these inks with PVA flexible films enables force sensing, where the response electrical signal exhibits a clear linear relationship with both the doping concentration of CDs and the magnitude of applied external force. This highlights their substantial potential for dual-mode fluorescence-force sensing applications. Declarations Ethical approval This research did not involve human or animal samples. Conflict of interest The authors declare no competing interests. Funding This work was supported by The Fundamental Research Program of Shanxi Province (No. 202303021212284,), Key research and development projects for the introduction of high-level scientific and technological talents in Lyuliang City (2024RC25), The Science and Technology Plan Project of Lyuliang (No. 2023GXYF06), Teaching Reform and Innovation Programs of Higher Education Institutions in Shanxi (J20231330). Author Contribution Tingting Cai and Yifan Zhao carried out the experiment and analysis, while wrote the main manuscript text. Tingyu Zhang and Yun Yang provide suggestions to the manuscript. All authors reviewed the manuscript. 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Supplementary Files SI.docx Cite Share Download PDF Status: Published Journal Publication published 18 Jul, 2025 Read the published version in Microchimica Acta → Version 1 posted Editorial decision: Revision requested 21 May, 2025 Reviews received at journal 21 May, 2025 Reviews received at journal 15 May, 2025 Reviewers agreed at journal 11 May, 2025 Reviewers agreed at journal 09 May, 2025 Reviewers invited by journal 08 May, 2025 Editor assigned by journal 06 May, 2025 Submission checks completed at journal 06 May, 2025 First submitted to journal 28 Apr, 2025 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. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6547577","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":455008910,"identity":"3e9bf26e-bdbc-4714-b848-b3cabfa0ce99","order_by":0,"name":"Tingting Cai","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA8UlEQVRIie3RMWuDQBTA8SeCLtJbX0hIv8LtHfpVlEBcHJxKhkZ0OZdKV79GNkeDkC43F8dzydTBjG59J4VOUcdC7w+nh9yPBx6AyfQns1Lw6eXQTqlYf/FnSZbSGSRic58vInoMET0IFxGWN7nqqmPysM4/Dz5vgLkRh6G6T1AGWRrID3Q28qXVZPX2xa1C3iccNBEXdDDaj4S3EbctMUFY90tiTZ5nCY5TXomEFxin4AzBtsvKQNQrgZFNfyz0UF7jczFB2HuoboNI2GMZdn1/eNqyfHdSwwT5qaHljZfi6Uc9CwASWq5acNBkMpn+Y9/XTlIZoCD+5QAAAABJRU5ErkJggg==","orcid":"","institution":"Lyuliang University","correspondingAuthor":true,"prefix":"","firstName":"Tingting","middleName":"","lastName":"Cai","suffix":""},{"id":455008912,"identity":"d43aa167-999f-430a-a7a1-e4b266c4b106","order_by":1,"name":"Yifan Zhao","email":"","orcid":"","institution":"Lyuliang University","correspondingAuthor":false,"prefix":"","firstName":"Yifan","middleName":"","lastName":"Zhao","suffix":""},{"id":455008914,"identity":"66c02e98-dc56-41bd-9885-39a827576860","order_by":2,"name":"Tingyu Zhang","email":"","orcid":"","institution":"Lyuliang University","correspondingAuthor":false,"prefix":"","firstName":"Tingyu","middleName":"","lastName":"Zhang","suffix":""},{"id":455008917,"identity":"5b38952a-10cf-4e84-952f-24e8f53c22e4","order_by":3,"name":"Yun Yang","email":"","orcid":"","institution":"Lyuliang University","correspondingAuthor":false,"prefix":"","firstName":"Yun","middleName":"","lastName":"Yang","suffix":""}],"badges":[],"createdAt":"2025-04-28 11:53:22","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6547577/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6547577/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s00604-025-07334-3","type":"published","date":"2025-07-18T16:05:35+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":82619635,"identity":"b71cbb01-ff94-454d-b6ed-c568dce6e658","added_by":"auto","created_at":"2025-05-13 12:09:05","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":113513,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic illustration of biomass-derived carbon dots synthesis​\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6547577/v1/709a965de78c798332ad40a9.jpg"},{"id":82619667,"identity":"4b5a54e3-6f1d-47a9-b8c8-402f116174ff","added_by":"auto","created_at":"2025-05-13 12:09:07","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":188756,"visible":true,"origin":"","legend":"\u003cp\u003eStructural and optical characterization of B-CDs, G-CDs, R-CDs:(a-c) TEM images with corresponding HRTEM insets (scale bars: 5 nm), and photoluminescence under 365 nm UV excitation;(d-f) Fourier-transform infrared (FT-IR) spectra showing functional group fingerprints.\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6547577/v1/11ca44cb501bff224e965992.jpg"},{"id":82619637,"identity":"6e5861bc-87ac-42b6-81b7-4799080243c1","added_by":"auto","created_at":"2025-05-13 12:09:05","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":90979,"visible":true,"origin":"","legend":"\u003cp\u003e(a) XPS survey spectra of B-CDs, G-CDs, and R-CDs. High-resolution N 1s spectrum of (b) B-CDs and (c) G-CDs. High-resolution C 1s spectrum of (d)B-CDs, (e)G-CDs and (f)R-CDs.\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6547577/v1/19dc7e87ea4a34e9b54db925.jpg"},{"id":82619636,"identity":"f21900ee-f79f-40b7-94af-2a72a8a1025b","added_by":"auto","created_at":"2025-05-13 12:09:05","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":120241,"visible":true,"origin":"","legend":"\u003cp\u003ePL spectral mapping of (a) B-CDs, (b) G-CDs, and (c) R-CDs under varying excitation wavelengths.\u003c/p\u003e\n\u003cp\u003eUV-vis absorption, excitation, and emission spectra for (d) B-CDs, (e) G-CDs, and (f) R-CDs.\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6547577/v1/763159d06210dc20e53887dd.jpg"},{"id":82619670,"identity":"bbc91c15-da0f-4a0b-8691-54ff920214b2","added_by":"auto","created_at":"2025-05-13 12:09:07","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":79787,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Three ink pens under sunlight and 365 nm UV illumination with B-CDs, G-CDs, and R-CDs. The PL performance of CDs ink on (b) non-fluorescent paper towels, (c-d) aluminum fiber cloth, (e) nitrile gloves, (f) the surface of polyvinyl alcohol (PVA) film.\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6547577/v1/c3effce035e304a74adb56c6.jpg"},{"id":82622128,"identity":"41478f6c-1a2f-4841-bb3a-8472362120f6","added_by":"auto","created_at":"2025-05-13 12:25:07","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":84494,"visible":true,"origin":"","legend":"\u003cp\u003eApplication of three types of CDs ink. (a) Schematic representation of CDs integration in seal fabrication and screen printing. (b) Comparative visualization of cartoon seal, triple-fluorescent script, screen-printed dragon, and official seals under solar illumination versus 365 nm ultraviolet irradiation.\u003c/p\u003e","description":"","filename":"6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6547577/v1/6a7e0f429d74a5b9f1d932e5.jpg"},{"id":82619663,"identity":"6c1cee9d-01c1-4d78-9130-ce917b7569da","added_by":"auto","created_at":"2025-05-13 12:09:06","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":73554,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Schematic illustration of the assembly structure for the B-CDs/PVA sensor device. (b) Diagram depicting the charge movement during a single force application cycle.(c) Response voltage as a function of different B-CDs concentrations.(d) Response voltage under various applied forces.\u003c/p\u003e","description":"","filename":"7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6547577/v1/09db7d3977df8bbdd65f8346.jpg"},{"id":88506075,"identity":"08c40dbd-6b3c-4906-b15d-e8c4e5709af3","added_by":"auto","created_at":"2025-08-07 07:30:30","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1225166,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6547577/v1/599e1a22-8d54-4373-9f0e-a064e106f338.pdf"},{"id":82619634,"identity":"19e747ed-267c-491e-a07d-4e8db0030729","added_by":"auto","created_at":"2025-05-13 12:09:05","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":1267347,"visible":true,"origin":"","legend":"","description":"","filename":"SI.docx","url":"https://assets-eu.researchsquare.com/files/rs-6547577/v1/e3751d6efddab39456ed2787.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Advanced Security Printing Enabled by Biomass-Derived Multicolor Anti-Counterfeiting Fluorescent Carbon Dot Ink with Multimodal Applications ","fulltext":[{"header":"Introduction","content":"\u003cp\u003eIn the context of rapidly advancing technology, the proliferation of counterfeit products and information breaches has posed severe challenges to national image building, corporate brand protection, and consumer rights safeguarding. Optical anti-counterfeiting technologies, leveraging the intuitive reliability of human color perception, have emerged as a critical research frontier. Among these, fluorescent anti-counterfeiting strategies demonstrate exceptional security advantages through material-specific color variations under natural and UV light. Current fluorescent systems include transition metal complexes, inorganic semiconductors, chalcogenide-based quantum dots, metal halide perovskites, metal-organic frameworks, and lanthanide-doped upconversion nanoparticles\u003csup\u003e[\u003cspan additionalcitationids=\"CR2 CR3\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]\u003c/sup\u003e. While these materials exhibit high photoluminescence quantum yields and broad emission spectra, they suffer from complex synthesis, high costs, insufficient brightness, and environmental concerns\u003csup\u003e[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]\u003c/sup\u003e. Crucially, most methods rely on monochromatic emission, limiting anti-counterfeiting capacity and code complexity against professional decryption. Thus, developing cost-effective, eco-friendly multicolor fluorescent materials with high security remains a pivotal challenge.\u003c/p\u003e \u003cp\u003eCarbon dots (CDs) have recently gained prominence due to their unique advantages including low toxicity, excellent solvent dispersibility, high yield, tunable stable luminescence, and photobleaching resistance,which are ideal for anti-counterfeiting\u003csup\u003e[\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]\u003c/sup\u003e. Unlike conventional fluorescent materials, CDs offer emission wavelength tunability through precursor selection and synthesis optimization\u003csup\u003e[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]\u003c/sup\u003e. Multi-color coupling further enhances security. Biomass-derived CDs are particularly promising for two reasons. One is that biomass precursors (e.g., fruit peels, juice, leaves, flowers) are abundant, eco-friendly, and biodegradable\u003csup\u003e[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]\u003c/sup\u003e, crucial for consumer-safe applications. Moreover, their inherent heteroatom richness enables self-doping\u003csup\u003e[\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]\u003c/sup\u003e, yielding CDs with distinct tunable properties. Thus, biomass-derived multicolor CDs present significant potential for multi-level anti-counterfeiting through ink formulation and signal superposition.\u003c/p\u003e \u003cp\u003eIn this work, blue, green, and red-emitting CDs were synthesized via one-step solvothermal treatment of lemon, orange, and banana leaf biomass. A glycerol-based multiphase ink system was developed to suppress non-radiative energy transfer between multicolor CDs, significantly enhancing fluorescence stability. The ink demonstrated multilevel anti-counterfeiting through handwriting, screen printing, and stamping. Furthermore, flexible polyvinyl alcohol (PVA) films embedded with CDs exhibited enhanced electromechanical responses, with CD incorporation boosting electrical signal intensity during mechanical sensing. This study not only advances biomass valorization but also provides interdisciplinary solutions for next-generation optical-sensing anti-counterfeiting technologies and smart interactive systems.\u003c/p\u003e"},{"header":"1. Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e1.1 Reagents\u003c/h2\u003e \u003cp\u003eUrea, anhydrous ethanol, glycerol, and polyvinyl alcohol (PVA) (analytical grade) were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Fresh lemons and oranges were procured from a local fruit market, while banana leaves were harvested from the greenhouse botanical garden. Deionized water was prepared by the laboratory ultrapure water system.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003e1.2 Instruments\u003c/h3\u003e\n\u003cp\u003eTransmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HR-TEM) images were observed on a JEM-F200 transmission microscope (JOEL, Japan). Fourier transform infrared spectra (FT-IR) were obtained on a Nicolet iS20 spectrometer with KBr spheres (Thermo Fisher Scientific, USA). X-ray photoelectron spectroscopy (XPS) spectra were obtained on an X-ray photoelectron spectrometer (ESCALAB 250, Thermo Fisher Scientific, USA). The UV\u0026ndash;vis absorption spectra were recorded with UV\u0026ndash;vis spectrophotometer ( UV-3600Plus, SHIMADZU, Japan ). Fluorescence spectra measurements were performed on the FLS1000 spectrofluorometer (Edinburgh Instruments Ltd., UK).\u003c/p\u003e\n\u003ch3\u003e1.3 Preparation of N-doped carbon dots\u003c/h3\u003e\n\u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, fresh lemon juice (20 mL) was mixed with absolute ethanol (10 mL) and urea (0.05 g) in a beaker. After ultrasonic dispersion for 15 min, the homogeneous mixture was transferred into a Teflon-lined stainless steel autoclave and heated at 190\u0026deg;C for 6 h in a preheated oven. The resulting brown transparent solution was cooled to room temperature, filtered through a 0.22 \u0026micro;m microporous membrane, and dialyzed (1000 Da) to remove small organic molecules. The purified product was freeze-dried to obtain brown powdery B-CDs.​\u003c/p\u003e \u003cp\u003eWith identical synthetic procedures, G-CDs were prepared by replacing lemon juice with fresh orange juice (20 mL) while maintaining all other reaction conditions.\u003c/p\u003e \u003cp\u003eTo obtain the R-CDs, fresh banana leaves were air-dried for one week and ground into powder. The precursor mixture of banana leaf powder (2 g), ethanol (30 mL), and urea (0.05 g) were ultrasonicated for 30 min before hydrothermal treatment at 200\u0026deg;C for 8 h. After identical purification steps, the red-emitting R-CDs were obtained by lyophilization.\u003c/p\u003e\n\u003ch3\u003e1.4 Preparation of N-Doped CDs inks\u003c/h3\u003e\n\u003cp\u003eThe three prepared CDs solutions (post-dialysis) were separately mixed with glycerol at different volume ratios and thoroughly homogenized by magnetic stirring to obtain the CDs inks with distinct emission colors. The inks were loaded into empty pen refills by a micropipette for writing on multiple textures. Furthermore, these inks were integrated with traditional anti-counterfeiting techniques, including screen printing and sealing, enabling large-scale production of security patterns on diverse substrates such as non-fluorescent cellulose paper, kraft paper, and the flexible PVA films.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003e1.5 Preparation of Carbon Dots/PVA Composite Films​\u003c/h3\u003e\n\u003cp\u003e1 g of polyvinyl alcohol was added to 49 mL of deionized water, and the solution was heated and stirred at 90 ° C for 2.5 h until clear and transparent. 0 mg, 1 mg, 2 mg, and 3 mg carbon dots were mixed with 10 mL PVA aqueous solution at 60 ℃ and 500 rpm for 10 min. After mixing, the mixture was poured into the silicone mold, placed at 4 ℃ for 12 h, then removed, and dried in a constant temperature drying oven at 80 ℃ for 4 h to obtain the film.\u003c/p\u003e\n"},{"header":"2. Results and Discussion","content":"\u003cp\u003eThe TEM images of B-CDs、G-CDs、 R-CDs samples are shown in Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea-c. As revealed, all CDs particles exhibit spherical morphology with monodisperse distribution and negligible aggregation. Statistical analysis of particle sizes demonstrates diameters of 4.6 ± 0.3 nm (B-CDs), 5.3 ± 0.4 nm (G-CDs), and 2.4 ± 0.2 nm (R-CDs), indicating significantly larger size for B-CDs and G-CDs compared to R-CDs. Furthermore, high-resolution TEM images in the inset display well-defined lattice fringes of B-CDs, G-CDs, and R-CDs with the interplanar spacing of 0.21 nm, corresponding to the (100) graphene plane in CDs\u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e13\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eIn the FT-IR spectrum of CDs in Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ed-f, the strong and wide absorption peak at 3300–3700 cm\u003csup\u003e− 1\u003c/sup\u003e are attributed to the stretching vibration of N‒H and -OH, especially for B-CDs and G-CDs. The double peaks at 1620–1710 cm\u003csup\u003e− 1\u003c/sup\u003e are assigned to -NH\u003csub\u003e2\u003c/sub\u003e and N-C = O. These results reveal that the N element from carbamide have been chemically bonded with the CDs during the solvothermal process of B-CDs and G-CDs. For R-CDs, the peak at 3300–3700 cm\u003csup\u003e− 1\u003c/sup\u003e are unconspicuous, indicating a lower content of N‒H and -OH\u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e15\u003c/span\u003e]\u003c/sup\u003e. The strong and sharp double peaks at 2850 and 2930 cm\u003csup\u003e− 1\u003c/sup\u003e,which is a character absorption of symmetric and asymmetric stretching vibration of C-H\u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e16\u003c/span\u003e]\u003c/sup\u003e, is prominent for R-CDs. The peaks located in 1360–1460 and 1050–1170 cm\u003csup\u003e− 1\u003c/sup\u003e demonstrating the diversity oxygen-containing functional groups in the CDs samples\u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e17\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eX-ray photoelectron spectroscopy (XPS) analysis revealed the surface chemical composition of the as-prepared carbon dots (CDs), with survey spectra showing characteristic peaks for C 1s (284 eV), N 1s (398 eV), and O 1s (530 eV) in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea. Quantitative analysis indicated varying elemental contents, with R-CDs exhibiting the highest carbon content (83.4%) but lowest nitrogen doping (1.72%), while B-CDs and G-CDs showed comparable nitrogen contents (4.66% and 4.08%, respectively). In the N 1 s spectrum of B-CDs and G-CDs, the three bands at around 399.3, 400, and 401.5 eV indicated the presence of amino N, pyrrolic N, and graphitic N (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eb-c).The C 1s spectrum of B-CDs and G-CDs were deconstructed into four peaks, namely, C-C/C-H, C = N, C-O, and C = O at 284.4, 285.6, 286.5 and 288 eV respectively (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ed-e). R-CDs has the highest content of carbon element, so the C1s peak intensity is the largest, and the C-C and C-H bond content is the highest. The three peaks of O 1s spectrum around 531.0, 532.1, and 533.0 eV correspond to -C = O, -OH, and -C-O, respectively\u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e19\u003c/span\u003e]\u003c/sup\u003e, indicating the existence of oxygen-containing functional groups such as hydroxyl and carboxyl groups with high density on the surface of the CDs.\u003c/p\u003e\u003cp\u003eThe fluorescence spectra and ultraviolet-visible (UV–vis) absorption of CDs were systematically investigated at room temperature. As illustrated in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ea-c, the three-dimensional (3D) fluorescence spectra of CDs under different excitation wavelengths were obtained. For B-CDs (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ea), the emission peak exhibited a significant red shift as the excitation wavelength increased from 320 to 420 nm, with the maximum emission intensity observed in the range of 450–480 nm. Similarly, G-CDs displayed red-shift characteristics with an emission peak centered around 540 nm. Notably, R-CDs revealed two distinct emission centers (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ec). The photoluminescence spectra exhibited dual emission peaks at 470 nm (blue fluorescence) and 660 nm (red fluorescence), indicating unique blue-red dual-emission properties.\u003c/p\u003e\u003cp\u003eThe aqueous solution of B-CDs exhibited a clear absorption peak at 280 nm, indicating the n-π* transitions of the sp\u003csup\u003e2\u003c/sup\u003e aromatic domains. Additionally, the weak absorption peak at 219 nm could be attributed to the π-π* transition of the C = C bond within the internal structure of CDs\u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e15\u003c/span\u003e]\u003c/sup\u003e. The optimal wavelengths of excitation (purple line) and emission (blue line) were at 390 and 465 nm, with a Stokes shift of 75 nm\u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e20\u003c/span\u003e]\u003c/sup\u003e.Combined with the structural analysis, it can be inferred that the C-N/C-O bonds in the C 1s spectrum may promote exciton radiative recombination by providing lone pair electrons. This process leads to the formation of a surface defect state while simultaneously passivating the nonradiative recombination centers on the surface of CDs.\u003c/p\u003e\u003cp\u003eThe UV absorption spectrum of G-CDs exhibits a strong absorption peak near 278 nm, which can be ascribed to the n-π* transition of the aromatic C = O group. Additionally, a broad absorption band in the range of 310–500 nm is observed, attributed to the presence of nitrogen atoms with lone pair electrons that facilitate the formation of the n − π* electronic configuration, thereby inducing a red shift in the absorption spectrum\u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e16\u003c/span\u003e]\u003c/sup\u003e. As depicted in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eb, the excitation spectrum scan reveals an optimal excitation wavelength of approximately 450 nm, with the corresponding emission peak located at 512 nm, exhibiting green fluorescence and a Stokes shift of 62 nm. Structural analysis suggests that the conjugated carbonyl or imine groups associated with the C = O/C = N bonds extend the π-electron conjugation system, enhancing the red shift of the fluorescence emission wavelength. Furthermore, the deprotonation of N-H bonds contributes to the passivation of surface defects, effectively reducing non-radiative recombination.\u003c/p\u003e\u003cp\u003eAs shown in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ef, the R-CDs solution exhibited significant characteristic absorption peaks at 280 nm, 319 nm, 415 nm, and 656 nm. The absorption peaks at 280 nm and 319 nm were attributed to the π→π* electron transition of the C = C bond and the n→π* electron transition of the C = O bond in nanocarbon, respectively. Meanwhile, the absorption peaks at 415 nm and 656 nm were ascribed to the n→π* electron transitions of the C = O and C = N bonds within the chlorophyll-derived porphyrin structure\u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e21\u003c/span\u003e]\u003c/sup\u003e. Furthermore, the excitation and emission fluorescence spectra of R-CDs (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ef) revealed that this carbon dot solution possesses dual-emission characteristics. Specifically, the emission peak at 475 nm exhibited a red shift with increasing excitation wavelength, demonstrating excitation-dependent behavior. Conversely, the emission peak at 660 nm was independent of the excitation wavelength and remained stable during the excitation wavelength scan from 310 to 350 nm. The two emission peaks at 470 nm and 660 nm corresponded to the optimal excitation wavelengths of 370 nm and 410 nm, respectively. As confirmed by prior XPS characterization, the nitrogen deficiency is mechanistically consistent with the dual-emission behavior, which arises from the competitive radiative recombination pathways between chlorophyll-derived porphyrin π→π* transitions and carbohydrate-based surface state emissions.\u003c/p\u003e\u003cp\u003eTo improve the applicability of the prepared carbon dots (CDs) for writing and printing purposes, they were formulated into fluorescent inks. The effects of mixing CDs solutions with varying proportions of thickeners, specifically glycerol, were systematically examined. It was found that mixing CDs solutions with glycerol at ratios of 1:1 and 1:2 yielded fluorescent inks with distinct concentrations and viscosities, demonstrating superior fluorescence performance suitable for creating diverse types of anti-counterfeiting marks via writing or printing. To enhance the efficiency and convenience of producing anti-counterfeiting marks, this study assessed the anti-counterfeiting efficacy of three methods: fluorescent pen cores, anti-counterfeiting stamps, and screen printing.\u003c/p\u003e\u003cp\u003eThe CDs solution was mixed with glycerol and loaded into empty pen refills to fabricate fluorescent ink pens (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ea), which exhibited bright blue, green, and red fluorescence under 365 nm UV irradiation. When writing \"LLU\" on non-fluorescent paper, the text was invisible under sunlight but clearly visible as tricolor fluorescent characters under 365 nm UV light (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003eb). Figures \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ec-d demonstrate the writing effects on aluminum fiber cloth, showing distinct \"CDs PL light\" and \"Snow\" patterns. Figure \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ee presents the writing performance of B-CDs ink on nitrile gloves, where \"Take care\" and a lightning symbol became clearly visible under UV light. Figure \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ef displays the \"LLU\" pattern on PVA flexible film, indicating the potential application of these fluorescent pen cores for marking and anti-counterfeiting purposes on organic flexible films. Based on these experiments, it is evident that the fluorescent pen core can be effectively applied to various substrates and achieve superior anti-counterfeiting performance. It is suitable not only for manual writing but also for anti-counterfeiting purposes in packaging, printing, trademarks, tickets, certificates, and other valuable items.\u003c/p\u003e\u003cp\u003eCompared with fluorescent writing pens, stamps and screen printing technology demonstrate significant efficiency advantages in anti-counterfeiting processing, enabling the mass production of industrial-grade anti-counterfeiting labels and wide application in the preparation of anti-counterfeiting labels for food and beverages, pharmaceuticals, intellectual property protection, financial security, and public safety. As shown in Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003ea, carbon dot solutions can directly replace traditional inks for the production of anti-counterfeiting stamps or the printing of hidden patterns by adapting to stamping and screen printing processes. Figures \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003eb-d systematically demonstrate the practical application effects of the two technologies. By comparing the pattern features under different lighting conditions, it is found that the patterns show low contrast and blurred details under sunlight (Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003eb). While under 365 nm ultraviolet light excitation, the fluorescence emission characteristics of carbon dots make the patterns clearly visible, with significantly improved visual resolution. Specifically, the cartoon rabbit-shaped stamp based on green and red carbon dot modification in Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003eb can achieve three-color fluorescence imaging with sharp boundaries and excellent anti-counterfeiting performance. Further research shows that the fluorescence ink prepared by combining a volume ratio of 1:2 green fluorescent carbon dot solution (G-NCDs) with glycerol, combined with the screen printing process on non-fluorescent paper, forms a dragon-shaped pattern (Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003ec) that shows a high saturation and strong contrast fluorescence response under ultraviolet light. In addition, Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003ed compares the imaging differences of fluorescent stamps and red official stamps on non-fluorescent toilet paper: the former appears nearly colorless under natural light, but can display high-resolution school emblems and the words \"Carbon Group\" under ultraviolet excitation. The above experiments fully verify the application potential of carbon dot ink in stamp fluorescence imaging and screen printing.\u003c/p\u003e\u003cp\u003eIn addition, given the ability of CDs to retain fluorescence when used for writing on flexible films, the incorporation of B-CDs into PVA flexible films as sensing materials was investigated. The CDs/PVA composite served as the friction layer material in the assembly of the sensor device. Aluminum electrodes were employed as the conductive electrodes, with a silicone ring acting as the spacer layer, and the outer surface was encapsulated using polyimide (Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003ea). The sensor demonstrated regular electrical signals based on the principle of single-electrode triboelectric response. As illustrated in Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003eb, under actual operating conditions, variations in pressure caused the CDs/PVA films on either side of the spacer to repeatedly contact and separate from the aluminum electrode. This cyclic process intermittently generated triboelectric current\u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e22\u003c/span\u003e–\u003cspan class=\"CitationRef\"\u003e24\u003c/span\u003e]\u003c/sup\u003e. The testing was carried out with the triboelectric sensor testing system in Figure S4. The results presented in Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003ec indicated that the incorporation of CDs enhanced the electrical response performance of the film. Specifically, as the concentration of CDs increased, the peak voltage of the film also increased, exhibiting an approximately linear relationship. When varying amounts of CDs (0, 1, 2, and 3 mg) were added to 50 mL of a 2% PVA solution, the response voltage progressively increased from 0.2 V to 2.5 V, 7.5 V, and 12.5 V, achieving a 62.5-fold enhancement. The response voltage in response revealed that as the applied external force increased, the device exhibited larger response voltages and currents (Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003ed). More importantly, the voltage response of this sensor exhibits a linear relationship with increasing pressure, thereby enabling its application in the quantitative sensing of motion, gestures, vocalization, and other related phenomena.\u003c/p\u003e\u003cp\u003eCombining the previous structural and component representations, it can be inferred that CDs can be uniformly incorporated into the polymer matrix for their small size and excellent dispersibility. Therefore, numerous interfaces were introduced into the composite material and thereby promoting various interfacial polarization phenomena\u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e26\u003c/span\u003e]\u003c/sup\u003e. This contributes to an increase in the relative dielectric constant of the polymer composite material and the surface charge density, significantly improving the overall sensing performance of triboelectric nanogenerator (TENG)-based sensors\u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e27\u003c/span\u003e]\u003c/sup\u003e. The amino (-NH₂) groups present at the terminals of O-CDs act as effective electron-donating moieties, enhancing the surface charge density of triboelectric materials\u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e28\u003c/span\u003e]\u003c/sup\u003e. Additionally, CDs can function as crosslinkers via non-covalent interactions, simultaneously increasing the crosslinking density and accelerating the film-forming rate of polyvinyl alcohol (PVA) films \u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e30\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e"},{"header":"3 Conclusions","content":"\u003cp\u003eThree types of nitrogen-doped fluorescent carbon dot (CD) inks were synthesized via a solvothermal method using lemon juice, orange juice, chlorophyll powder, urea, and anhydrous ethanol as raw materials for anti-counterfeiting applications. Specifically, B-CDs emit blue fluorescence with optimal excitation and emission wavelengths at 390 nm and 460 nm, respectively; G-CDs exhibit green fluorescence with optimal excitation and emission wavelengths at 450 nm and 540 nm, respectively; R-CDs display red fluorescence with dual-emission characteristics, having optimal excitation wavelengths at 380 nm and 390 nm, and emission peaks at 470 nm and 660 nm. Studies indicate that the size, surface functional groups, and N-doping form of the three CDs directly influence their fluorescence emission wavelengths. By mixing CDs with thickeners, three-color fluorescent inks were successfully developed. These inks demonstrate significant ultraviolet-induced fluorescence effects in applications such as pen writing, seal stamping, and screen printing. Furthermore, when these inks are used in double or triple superposition, they exhibit excellent multi-level anti-counterfeiting performance, offering broad application prospects in areas such as packaging anti-counterfeiting printing, printer-based printing, and anti-counterfeiting seals. Additional research reveals that combining these inks with PVA flexible films enables force sensing, where the response electrical signal exhibits a clear linear relationship with both the doping concentration of CDs and the magnitude of applied external force. This highlights their substantial potential for dual-mode fluorescence-force sensing applications.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003cstrong\u003eEthical approval\u003c/strong\u003e \u003cp\u003eThis research did not involve human or animal samples. Conflict of interest The authors declare no competing interests.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eThis work was supported by The Fundamental Research Program of Shanxi Province (No. 202303021212284,), Key research and development projects for the introduction of high-level scientific and technological talents in Lyuliang City (2024RC25), The Science and Technology Plan Project of Lyuliang (No. 2023GXYF06), Teaching Reform and Innovation Programs of Higher Education Institutions in Shanxi (J20231330).\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eTingting Cai and Yifan Zhao carried out the experiment and analysis, while wrote the main manuscript text. Tingyu Zhang and Yun Yang provide suggestions to the manuscript. All authors reviewed the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThe authors would like to thank the Shiyanjia Lab (www. shiya njia. com) for the TEM, XPS, and FT-IR analysis.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eMAO X, ZHAO X, HU H, et al. Hydrophobic Carbon Dots with Aggregation-Induced Emission for Multistage Anticounterfeiting [J]. ACS Applied Nano Materials, 2023, 6(21): 20346-20354.\u003c/li\u003e\n\u003cli\u003eMUTHAMMA K, SUNIL D, SHETTY P. Carbon dots as emerging luminophores in security inks for anti-counterfeit applications - An up-to-date review [J]. Applied Materials Today, 2021, 23.\u003c/li\u003e\n\u003cli\u003eSIMOES R, RODRIGUES J, NETO V, et al. Carbon Dots: A Bright Future as Anticounterfeiting Encoding Agents [J]. Small, 2024, 20(28): e2311526.\u003c/li\u003e\n\u003cli\u003eZHANG H, SUN L, GUO X, et al. 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Small, 2023, 19(31): e2204365.\u003c/li\u003e\n\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":"microchimica-acta","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"miac","sideBox":"Learn more about [Microchimica Acta](https://link.springer.com/journal/604)","snPcode":"604","submissionUrl":"https://submission.springernature.com/new-submission/604/3","title":"Microchimica Acta","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Biomass-derived carbon dots, Fluorescent ink, Multiple anti-counterfeiting, flexible sensing","lastPublishedDoi":"10.21203/rs.3.rs-6547577/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6547577/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eOne of the most pressing challenges in fluorescence-based anti-counterfeiting technology is the development of multi-color fluorescent materials that simultaneously satisfy the stringent requirements of high security, cost-effectiveness, and environmental sustainability. Biomass-derived fluorescent carbon dots (CDs) are characterized by their low cost, non-toxicity, and tunable multicolor fluorescence, making them ideal candidates for developing multicolor fluorescent inks with multi-level anti-counterfeiting capabilities. In this study, N-doped tricolor CDs were synthesized via a solvothermal method using orange juice, lemon juice, and banana leaves as biomass precursors. These CDs exhibited distinct blue, green, and blue-red dual-emission fluorescence, with their structure-property relationships and luminescence mechanisms systematically investigated through comprehensive characterization techniques. A glycerol-based tricolor fluorescent ink system was developed, enabling multilayered information encryption under UV/visible light dual-mode through integrated processes such as handwriting, screen printing, and stamping. Furthermore, flexible sensing films were fabricated by incorporating CDs into polyvinyl alcohol (PVA) matrices. Remarkably, the CDs-embedded films exhibited significantly enhanced electrical signal responses during mechanical sensing. This work not only provides a novel strategy for high-value utilization of biomass resources but also opens innovative pathways for developing intelligent anti-counterfeiting materials and flexible electronic devices.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e","manuscriptTitle":"Advanced Security Printing Enabled by Biomass-Derived Multicolor Anti-Counterfeiting Fluorescent Carbon Dot Ink with Multimodal Applications","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-05-13 12:08:45","doi":"10.21203/rs.3.rs-6547577/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-05-22T03:49:19+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-05-22T01:19:38+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-05-15T07:06:41+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"326314341790064919709375635067379216096","date":"2025-05-12T01:02:59+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"79373810058792420377871997750728294639","date":"2025-05-09T06:35:30+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-05-08T21:10:27+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-05-07T00:04:25+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-05-07T00:02:56+00:00","index":"","fulltext":""},{"type":"submitted","content":"Microchimica Acta","date":"2025-04-28T11:44:33+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"microchimica-acta","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"miac","sideBox":"Learn more about [Microchimica Acta](https://link.springer.com/journal/604)","snPcode":"604","submissionUrl":"https://submission.springernature.com/new-submission/604/3","title":"Microchimica Acta","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"ba923508-5629-4fb1-9c74-1979f2b562de","owner":[],"postedDate":"May 13th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-08-07T07:12:41+00:00","versionOfRecord":{"articleIdentity":"rs-6547577","link":"https://doi.org/10.1007/s00604-025-07334-3","journal":{"identity":"microchimica-acta","isVorOnly":false,"title":"Microchimica Acta"},"publishedOn":"2025-07-18 16:05:35","publishedOnDateReadable":"July 18th, 2025"},"versionCreatedAt":"2025-05-13 12:08:45","video":"","vorDoi":"10.1007/s00604-025-07334-3","vorDoiUrl":"https://doi.org/10.1007/s00604-025-07334-3","workflowStages":[]},"version":"v1","identity":"rs-6547577","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6547577","identity":"rs-6547577","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}