Fluorescent Films Research Articles

Patterned Lead‐Free Double Perovskite/Polymer Fluorescent Piezoelectric Composite Films for Advanced Anti‐Counterfeiting

AbstractThe limitations of single fluorescent anti‐counterfeiting technologies necessitate the development of more sophisticated encryption methods to protect information and data. Traditional optical anti‐counterfeiting encryption techniques, which rely on light sources with varying wavelengths to identify information, are now insufficient to meet contemporary security demands due to their restricted response to a narrow range of wavelengths. In this study, the fabrication of patterned, lead‐free double perovskite (DP)/poly(vinylidene fluoride‐trifluoroethylene) (P(VDF‐TrFE)) fluorescent piezoelectric composite films (CFs) is reported. These CFs integrate the up‐conversion and down‐conversion photoluminescent properties of Cs2Na0.8Ag0.2BiCl6:Yb3+/Er3+ DP crystals with the piezoelectric properties of P(VDF‐TrFE) film, facilitating multi‐modal information protection. The fluorescent signals of different concealed information in CFs are observable under the excitation of 365 nm UV light and 980 nm infrared (IR) light. Additionally, external pressure applied at various locations on the CFs generates corresponding electrical signals, thereby providing triple‐layer encryption for protected information. A multifunctional anti‐counterfeiting device has been further developed by integrating patterned optical and electrical responses onto flexible CFs, achieving synergistic protection of information security in cross fields and bringing a significant advancement to the high‐level anti‐counterfeiting market.

A Fluorescent Polyvinyl Alcohol Film with Efficient Photodynamic Antimicrobial Performance Enabled by Berberine/Phytic Acid Salt for Food Preservation

AbstractFood packaging that impedes microbial growth and can be safely used is critical to attenuate food spoilage. Herein, a green berberine/phytate salt (BPA) is successfully synthesized and aggregated in polyvinyl alcohol (PVA) film to impart fluorescent and photodynamic antimicrobial properties. Compared to berberine hydrochloride (BHL), BPA exhibited stronger fluorescence because intramolecular motions and intermolecular π–π accumulation of BHL are restricted by phytic acid (PA). Molecular dynamics simulation indicate that aggregation of BHL and PA formed through electrostatic interactions in the PVA matrix due to the change of the binding energy during the drying process. With increasing BPA content, the films exhibited increased ultraviolet, water vapor, and oxygen barriers and fluorescent properties, but reduced tensile strength and elongation at break. After radiated, PVA‐BPA9 film showed the highest antimicrobial rates against Staphylococcus aureus, Escherichia coli, P. citrinum, and Aspergillus niger reached 100%, 100%, 86.14%, and 66.24%, respectively, due to the increased reactive oxygen species production. The total number of microbial colonies in cooked chicken and oranges packaged by PVA‐BPA9 film with irradiation ARE 87.54% and 29.21% of those by PVA film. The findings indicate a new and feasible strategy to obtain a green photodynamic‐mediated film for safe and effective food packaging.

Characterizing the photoluminescence of fluorescein-labeled cellulose in aqueous and alcohol solutions: influence of the cellulose backbone

Although many dyes have been introduced into cellulose, whether bound to its backbone or within a cellulose matrix, few studies have determined whether the backbone statically or dynamically quenches the photoluminescence of the dye. To advance cellulosic fluorescent films, the influence of the cellulose backbone on photoluminescence must be understood. We determined the fluorescence properties of fluorescein isothiocyanate (FITC) and fluorescein-labeled cellulose (FLC) in water and alcohol, including their quantum yields \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\boldsymbol{\\phi}_{\ extit{\ extbf{PL}}}$$\\end{document}, lifetimes \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\boldsymbol{\ au}}$$\\end{document}, and rates of radiative \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ extit{\ extbf{k}}}_{\ extit{\ extbf{r}}}$$\\end{document} and nonradiative \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ extit{\ extbf{k}}}_{\ extit{\ extbf{nr}}}$$\\end{document} decay. Dissolved FLC had a ~ 30× lower \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\boldsymbol{\\phi}_{\ extit{\ extbf{PL}}}$$\\end{document} than FITC, suggesting that incorporating FITC into the cellulose backbone remarkably reduces the fluorescence efficiency. The FLC solutions had a six-fold lower \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ extit{\ extbf{k}}}_{\ extit{\ extbf{r}}}$$\\end{document} than their FITC counterparts but a 10–20 times higher \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ extit{\ extbf{k}}}_{\ extit{\ extbf{nr}}}$$\\end{document}. Presumably, this was because the cellulose backbone interacted weakly with the fluorescein moieties, suggesting a quenching mechanism that can be termed quasi-static, corresponding to static quenching between the fluorescein moieties and cellulose backbone, in addition to the fluorescence quenching caused by the intramolecular nonradiative processes of fluorescein, as observed in conventional molecules. Using the Strickler‒Berg formula, we deduced the analytical radiative decay rate constants \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ extit{\ extbf{k}}}_{\ extit{\ extbf{r}}}^{\ extit{\ extbf{S.B.}}}$$\\end{document} and eventually estimated the number of very short-lived fluorescein moieties per single fluorescent fluorescein moiety, corresponding well with static quenching.

Photoluminescence color-tuning with polymer-dispersed fluorescent films containing two fluorinated diphenylacetylene-type fluorophores.

The development of organic light-emitting devices has driven demand for new luminescent materials, particularly after the 2001 discovery of aggregation-induced emission. This study focuses on fluorinated diphenylacetylene-based luminescent molecules, revealing that specific molecular modifications can enhance fluorescence and achieve a wide range of photoluminescence colors. A simple and effective luminescence color-tuning method is proposed to investigate the photoluminescence behavior of two-component polymer dispersion films blended with two types of fluorinated diphenylacetylenes, namely blue- and yellow- or red-fluorescent fluorinated diphenylacetylenes. It is confirmed that if blue and green-yellow or yellow fluorophores are blended in appropriate ratios, a binary blend with color coordinates (0.20, 0.32) can be achieved, which approaches the white point of pure white emission. These findings contribute to the development of effective lighting and display devices as new white-light-emitting materials.

Carbon Dots and Their Films with Narrow Full Width at Half Maximum Orange Emission.

To obtain carbon dots (CDs) with narrow full width at half maximum (FWHM) and long-wavelength emission, carbon sources with high conjugate sizes and abundant functional groups can be employed to synthesize CDs. In this study, orange-emissive carbon dots (OCDs) were synthesized with phloroglucinol and rhodamine B as precursors. When the molar ratio of them was 30:1, and ethanol was served as the solvent, OCDs with optimized emission wavelength at approximately 580 nm, an FWHM of 30 nm, and a quantum yield (QY) of 27.31% were obtained. Subsequently, the OCDs were incorporated into polyvinyl alcohol (PVA) to fabricate solid-state OCD/PVA fluorescent films, which exhibited an FWHM of 47 nm. The PVA matrix facilitated the dispersion of OCDs, thereby suppressing non-radiative energy transfer among the OCDs and enhancing luminescence efficiency. Consequently, compared with OCDs, the OCD/PVA film exhibited significant luminescent enhancement, and the QY of the composite film was increased to 84.74%. Moreover, OCD/PVA film showed good transmittance and thermal stability. This research offers a solid theoretical and experimental foundation for the potential applications of CDs in the field of solid-state lighting.

A pH-responsive fluorescent film with the smartphone-assistance for real-time and visual detection of food freshness

Monitoring food freshness is considerably important for food safety. In this study, a smart pH-responsive fluorescence hydroxypropyl methyl cellulose-κ-carrageenan-fluorescein isothiocyanate-NH2-CaAl2O4 (H-K-F-N) film was prepared. Taking synergetic advantage of the pH-dependent behavior of fluorescein isothiocyanate dye and the luminescence characteristics of calcium aluminate phosphor, the film exhibited a unique strong pH-responsive fluorescence with an exceptional linear relationship (correlation coefficient, R2 = 0.9993) across a wide pH rang of 2.0–12.0. Moreover, the H-K-F-N film, as a smart sensor, could be used to estimate the total volatile basic nitrogen and total viable count through fluorescence intensity based on the partial least squares regression model and support vector machine regression, respectively. Leveraging the relationship between the fluorescent image's digital signals and food freshness indicators, a smartphone-assisted system was developed. These results demonstrated that H-K-F-N film is promising for applications in intelligent food packaging and food safety monitoring.

Sensitive Detection and Visual Recognition of Jatrorrhizine Based on a Fluorescent Eu Coordination Polymer Probe

ABSTRACTBased on 4‐([2,2′:6′,2″‐terpyridin]‐4′‐yl) benzoic acid ligand (Htpba), a fluorescent lanthanide coordination polymer was successfully synthesized, namely, [Eu (tpba)3]n (1). The single‐crystal diffraction analysis shows that Eu3+ ions in complex 1 are alternately connected with tpba3− ligands to form a one‐dimensional chain structure, which further constitutes a three‐dimensional supramolecular architecture through the π···π interactions. Complex 1 demonstrated excellent stability of thermogravimetry; and displayed good fluorescence intensity in aqueous solution with a wide pH range. In this work, complex 1 was used as a fluorescence sensor for the detection of jatrorrhizine molecule (JAT). It was found that complex 1 had high sensitivity with the detection limit of 1.02 × 10−8 M, and simultaneously displayed specific selectivity and reutilization for the exploration of JAT molecule. The static quenching, the absorption competition, the electrostatic interactions, and the photo‐induced electron transfer process are responsible for the recognition mechanism of complex 1 with sensing JAT. It is worth mentioning that a fluorescent film based on complex 1 and a light‐emitting diode device coated with the powder of complex 1 were successfully fabricated, which could rapidly recognize JAT molecule with the naked eye further.

Fluorescent Nanocomposites of Cadmium Sulfide Quantum Dots and Polymer Matrices: Synthesis, Characterization, and Sensing Application

Fluorescent materials for sensing have gained attention for the visual detection of different substances as metals and pesticides for environmental monitoring. This work presents fluorescent nanocomposites in solution, film, and paper obtained without capping and stabilizing agents, coming from quantum dots of cadmium sulfide (CdS QDs) and anionic–cationic polymer matrices. Fluorescent films were formed by casting and fluorescent paper by impregnation from the solutions. The optical properties of CdS QDs in solution showed absorption between 418 and 430 nm and a maximum emission at 460 nm. TEM analysis evidenced particle size between 3 and 6 nm and diffraction patterns characteristic of CdS nanocrystals. Infrared spectra evidenced changes in the wavenumber in the fluorescent films. The band gap values (2.95–2.82 eV) suggested an application for visible transmitting film. Fluorescent solutions by UV-vis and fluorescence evidenced a chemical interaction with glyphosate standard between 1 and 100 µg/mL concentrations. The analysis of red, green, and blue color codes (RGB) evidenced a color response of the fluorescent paper at 10 and 100 µg/mL, but the fluorescent films did not show change. Nanocomposites of chitosan and pectin, in solution and on paper, exhibited a behavior “turn-on” sensor, while carboxymethylcellulose had a “turn-off” sensor. This methodology presents three fluorescent materials with potential applications in visual sensing.

Polymer-stabilized cholesteric liquid crystals with multi-state reversibility for applications in advanced smart adjustable anti-counterfeiting and energy-saving displays

The creation of an anti-counterfeiting material with reflection color, fluorescence, infrared imaging, and electrical property information will increase the level of anti-counterfeiting. However, the creation of such a material has proved to be extremely challenging. In this study, twin anti-counterfeiting labels with intelligently tunable patterns were obtained through a strategy of PMMA loaded chiral molecules via diffusing on the micrometer scale. In order to enhance anti-counterfeiting ability, the multi-mode intelligently modulated advanced anti-counterfeiting material was obtained through the strategy of introducing photo-isomerizing dithienylethene and infrared-shielding Cs0.33WO3 nanoparticles. This material can be reversibly converted into fluorescent, reflected colors, infrared, and electrical characteristic signals. The encrypted information is displayed with red fluorescence under UV light irradiation. Furthermore, the encrypted information can be reversibly displayed and erased under repeated stimulation by voltage and pressure, heating and cooling, UV, visible and near infrared (NIR) light. The aim of our work is to create a simple method to prepare complex patterns of structural and fluorescent color anti-counterfeiting films with the improved anti-counterfeiting capability. Based on this, the strategy of co-doping fluorescent molecules and photochromic molecules in liquid crystals combined with etching technology has realized a multiple anti-counterfeiting mode with a higher level of security. The advanced multiple anti-counterfeiting mode can output encrypted information of multiple states which will greatly improve the level of anti-counterfeiting. In terms of display, we obtained billboards with complex patterns, price intelligently tunable and full-color display by diffusion S5011 in liquid crystals, thus extending their application in the field of electronic shelf labels.

Ternary composite fluorescent films with tunable color and long lifetime based on efficient TS-FRET

Multi-color long-wavelength organic afterglow materials are of great significance in anti-counterfeiting, but their preparation is still challenging. In this paper, a series of room temperature phosphorescence (RTP) films were constructed with polyvinyl alcohol (PVA) as rigid matrix and 9,10-diaminophenanthrene (DAphe) as guest molecule. Surprisingly, by adjusting the doping content of DAphe, their RTP emission peak width could be adjusted accordingly, and the lifetime was up to 3.25 s. Their dopant content dependent and excitation wavelength dependent luminescence characteristics and theoretical calculation results indicated that the observed broad emission peaks of RTP might be attributed to multiple luminescence centers generated by the aggregation of guest molecules. Interestingly, by doping several suitable fluorescent dyes screened as energy acceptors, multi-color, long-lasting afterglow composite films from blue to red were obtained, achieving 0.42 s delayed fluorescence at 661 nm with a fluorescence quantum yield of 32.22 %. In addition, these adjustable afterglow materials had good molding processability, so several cryptographic patterns were achieved to demonstrate their good application prospects in advanced anti-counterfeiting technologies.

Wafer-level flexible carbon-based film for fluorescent display and optical information storage

Fluorescent materials have garnered significant interest in optical display and information storage fields for their vibrant and distinct color presentation. Extensive research has been conducted on carbon-based fluorescent materials owing to their environmental sustainability, versatility, and adjustable optical properties. However, it is difficult to integrate high-resolution fluorescent structure on various wafer-level substrate for abundant optical display and information storage. This study successfully fabricated wafer-level carbon-based fluorescent flexible film with ∼100 μm thick using a standardized “lithography + annealing” process. The sample demonstrates high fluorescence intensity with a peak at 603 nm and fluorescence lifetime of 0.3517 ns. When excited by light of 365 nm, 485 nm, and 525 nm wavelengths, the film displays yellow, green, and red, showcasing exceptional color tuning capability. This flexible film is portable and can be readily integrated with various substrates, offering significant technical and theoretical support for advancing carbon-based optical display and information storage technologies.

A novel fluorescent probe based on coumarin derivatives-grafted cellulose for specific detection of Fe3+ and its application

Fe3+ is one of the most important ions for maintaining the normal growth of plants and animals. However, imbalance and accumulation of Fe3+ can lead to serious damage to the environmental system. Hence, it is considerably crucial to monitor the concentration of Fe3+. In this paper, a high-performance fluorescent probe CA-NCC for specifically detecting Fe3+ was obtained by grafting cellulose acetate (CA) with coumarin derivative (NCC). The resulted probe displayed a bright blue fluorescence in THF solution and showed a distinct “turn-off” fluorescence response to Fe3+, while the small molecule compound NCC could not realize the detection of Fe3+. CA-NCC displayed excellent response performance to Fe3+ including excellent selectivity and sensitivity, rapid reaction time (2.5 min), wide pH detection range (6–11), and low detection limit (0.178 µM). More importantly, CA-NCC was successfully fabricated into fluorescent film based on the good processability of cellulose acetate, and achieved highly selective recognition of Fe3+ from various metal ions.

Fabrication of clickable bamboo-sourced cellulose nanofibrils for diverse surface modifications: Hydrophobicity and fluorescence functionalities

Surface functionalization of cellulose nanofibrils (CNF) is crucial for expanding their practical application. However, most functionalization processes are complicated and laborious. Herein, this work presents a facile surface engineering strategy to create a range of functionalized CNF via thiol-ene click reaction. Initially, clickable CNF was produced by grafting a compound with both carboxylate- and norbornene groups onto bamboo cellulose via norbornene-dicarboxylic anhydride esterification followed by homogenization. The introduction of negatively charged carboxylates facilitated nanofibrillation, resulting in CNF with a diameter of 3 nm and an aspect ratio of up to 600. The introduction of norbornenes enabled diverse functionalization of CNF through click reaction. Subsequently, hexadecanethiol successfully clicked with norbornene-grafting CNF, enhancing its hydrophobicity and dispersion in organic solvents. 7-mercapto-4-methyl coumarin was also able to click with norbornene-grafting CNF, yielding fluorescence-labeled CNF while maintaining excellent aqueous dispersibility. The fluorescence-labeled CNF was demonstrated to be utilized as an eco-friendly sensor for the detection of Fe3+ ions. Additionally, it could be converted into fluorescent films or intelligent inks suitable for anti-counterfeiting purposes. This study demonstrates that the proposed surface engineering strategy provides an effective approach for producing clickable CNF and fabricating cellulosic materials with diverse functionalities that meet the demands of various applications.

Multi-color emission composites of white carbon dots and dyes through inner filter effect

A series of multi-color carbon dot composites were obtained by transforming white carbon dots (WCDs) into three primary colors using the dyes' inner filter effect (IFE). WCDs were combined with three distinct dyes (methyl red, bromocresol green, and methylene blue), and three fluorescence colors (red, yellow, and blue) were obtained. The colors of the emitting light excited by the same UV light were similar to the colors of the respective dyes, and have a large Stokes shift. The presence of the IFE between WCDs and dyes was proved through a variety of methods, the analysis of the relationship between the UV of dyes and fluorescence spectra of WCDs, the excitation-emission matrix, as well as the comparison PL decay profiles of WCDs before and after dye addition. The Stern-Volmer quenching constant KSV exhibited no temperature dependence during the IFE process with increasing concentrations of dyes. The UV spectra of the mixture of WCDs and dyes were simply the sum of two individual components, which implies that there is no chemical interaction between WCDs and dyes. Since methyl red and bromocresol green are acid-base indicators, the fluorescence color of the carbon dot composite also changed continuously during the dilute NaOH solution titration process. In furtherment, distributing the binary system of “WCDs + dye” within poly (vinyl alcohol) (PVA), three colors fluorescent composite films of “WCDs / Dye / PVA” were produced successfully.

Efficient Redirection of Trapped Broad-Band Fluorescence from Substrates into Free Space Using c-Si Metasurfaces.

Fluorescent dye films on transparent substrates are essential for OLEDs, flexible displays, X-ray detection, and wireless optical communications. However, their efficiency is often hampered by fluorescence trapping due to total internal reflection (TIR) and waveguiding. This study tackles this longstanding challenge by reconceptualizing the integration of dye films with nanoantenna metasurfaces. Traditional methods involve directly spin-coating films onto c-Si metasurfaces on quartz substrates, resulting in edge luminescence and weak inner signals. We present a straightforward, adjustable approach by integrating dye films on the opposite side of quartz substrates, reaching a 2.5-fold photoluminescence enhancement and improving the uniformity of the emission compared to the conventional methods. These gains stem from redirecting a significant portion of leaked fluorescence light trapped inside the substrate into free space, surpassing TIR conditions through in-plane diffraction orders of the metasurfaces across the full RGB spectrum. Our findings facilitate the design of more efficient luminescent devices.

Proximity-induced FRET and charge-transfer between quantum dots and curcumin enable reversible thermochromic hybrid polymeric films.

This study introduces a novel strategy for developing reversible thermochromic fluorescent films by precisely controlling the nanoscale proximity of boron nitride quantum dots and curcumin molecules within a poly(3-hydroxybutyrate) matrix. The synergistic interaction and Förster resonance energy transfer between these fluorophores result in an energy transfer efficiency of ∼94%. This approach enables tunable color changes in response to temperature variations, governed by the segmental mobility of polymer chains. Practical applications of these films as temperature sensors for water bottles and electronic devices are demonstrated, highlighting their potential in temperature monitoring, smart packaging, and thermal management systems.

A ratiometric fluorescent electrospun film with high amine sensitivity and stability for visual monitoring of livestock meat freshness

Ratiometric fluorescent films with high amine sensitivity and stability were developed to monitor the freshness of beef and pork. Fluorescein isothiocyanate (FITC) and red carbon quantum dots (R-CQD) were used as the amine-responsive indicator and internal reference, respectively. The electrospun films prepared by immobilizing FITC and R-CQD complex (F-R) into polyvinylidene fluoride (PVDF) under 35 %, 55 % and 75 % of relative humidity (RH) were named F-R@PVDF-1, F-R@PVDF-2 and F-R@PVDF-3, respectively. In comparison, the F-R@PVDF-2 film exhibited the highest sensitivity to trimethylamine (TMA), demonstrating a limit of detection (LOD) value of 1.59 μM, and meanwhile high stability during storage with ΔE value of 1.99 after 14 days of storage at 4 °C. The F-R@PVDF-2 film also showed a significant fluorescent red-to-brown color change during meat freshness monitoring at 4 °C. Conclusively, this study reported a new ratiometric fluorescent film that can be used to track the freshness of meats in food packaging.

In-situ growing Eu-MOF on TEMPO-oxidized cellulose nanofibers to form fluorescent films for Fe3+ detection

Metal-organic frameworks (MOFs) are porous hybrid materials made of metal and organic linkers. Combining MOFs with polymers enhances their performance and addresses the issue of low stability. In this study, a uniform nanoscale Eu(III)-based metal-organic framework (Eu-MOF) was synthesized and grown in situ on TEMPO(2,2,6,6-tetramethylpiperidinyl-1-oxide)-oxidized cellulose nanofibrils (TOCNF), resulting in the formation of Eu-MOF@TOCNF fluorescence films through vacuum filtration. These films exhibited favorable mechanical properties, high transmittance, and stable fluorescence characteristics within the pH range of 3–11. The film produced the characteristic emission peak of Eu3+, recognized the selective quenching of Fe3+ within 0–100μM, and displayed an inverse relationship between fluorescence intensity at 616 nm and Fe3+ concentration. This approach holds significant promise for Fe3+ detection in solutions and offers a novel strategy for developing highly efficient optical sensors based on fluorescence specificity.

Red-emitting copper nanoclusters for ultrasensitive and selective detection of creatinine and its application in portable smartphone-based paper strips and polymer thin film

In this work, a quantitative paper-based sensor integrated with smartphone-application was developed using poly(sodium 4-styrenesulfonate) stabilized copper nanoclusters (PSS-CuNCs) as a fluorescence probe to detect creatinine (CRN). The surface morphology and optical properties of PSS-CuNCs were verified using UV–vis absorption, zeta-potential, photoluminescence, high resolution transmission electron microscopy (HR-TEM) and Fourier-transform infrared (FI-IR) and X-ray photoelectron (XPS) spectroscopy. PSS-CuNCs exhibited strong red fluorescence with the emission peak centered at 654 nm upon excitation at 390 nm. PSS-CuNCs was also used to determine CRN because of their excellent fluorescence properties. The fluorescence of PSS-CuNCs was quenched significantly by adding different concentrations of CRN, which mainly originated from the formation of ground state complexation. The PSS-CuNCs probe showed high sensitivity with a low limit of detection (LOD) of 2.48 nM and high selectivity even in the presence of other interfering analytes. This assay was also used to measure CRN in real samples. Additionally, test paper-based assay has been developed to detect CRN using smartphones. The developed assay provides a reliable, cost-effective, sensitive and portable on-site method to measure CRN levels by utilizing fluorescence color changes. Incorporation of PSS-CuNCs into poly(vinyl alcohol) resulted in the formation of fluorescent transparent polymer thin films with high photostability.

Static pressure response model of fluorescent pressure-sensitive film for underwater surface pressure measurement

The fluorescent pressure-sensitive film (FPSF) is a non-contact, deformation-based optical pressure sensor with high spatial resolution. The pressure response principle of FPSF is to convert pressure change into variations in fluorescent intensity through the deformation of fluorescent microspheres embedded within the film. To quantitatively analyze the pressure–deformation–intensity mechanism, a static pressure response model was established in this study. First, a finite element model was developed to predict the deformation of microspheres within the film under pressure. Second, the deformation-induced variation in fluorescent intensity was modeled with consideration of the light path blockage effect. The pressure calibration curve of the FPSF predicted by the proposed model was noted to be consistent with the experimental results of underwater calibration. In addition, the relationship between pressure sensitivity and the structural parameters of the FPSF were investigated using the pressure response model.