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The emergence of stimuli-responsive fluorescence anti-counterfeiting technology has garnered increasing attention in the era of intelligent internet. Smart fluorescent hydrogels combine the characteristics of luminous materials with the unique structure of hydrogels, offering the potential for dynamic reversible erasing and multi-tiered data encryption. In this work, a fluorescent hydrogel was constructed by zeolitic imidazolate framework-8 loaded with fluorescein and then mixed with polyvinyl alcohol hydrogel, sodium carboxymethyl cellulose and borax, which could be used for image hiding in visible light. The reversible bonds cross-linked fluorescent hydrogel was stretchable and self-healing with a three-dimensional network structure. The hydrogel presented bright green fluorescence under 365 nm UV light, which was quenched by adding copper ions. Meanwhile, the imprint of the hydrogel could be cleared by L-Cysteine and repeatedly recorded information many times. The alkali-induced shape memory capability was further utilized to achieve multi-tiered data encryption by deforming it to a 3D-specific shape through folding. The rewritable and multi-dimensional encrypted hydrogel is expected to improve data security and reduce resource consumption. The synthesis, storage of information and the prevention of counterfeiting of PVA/B/CMC/ZIF-8@Flu hydrogel. [Display omitted] • Fluorescein-encapsulated ZIF-8 and a fluorescent hydrogel were synthesized by a simple one-pot method. • The hydrogel is multi-functional with stretchability, self-repairing, antibacterial activity and water resistance. • The hydrogel is capable of storing information through Cu2+ quenching the fluorescence for anti-counterfeiting. • L-Cysteine restores the fluorescence of this hydrogel, enabling erasable information storage. [ABSTRACT FROM AUTHOR]

With the emergence of numerous food safety problems, rapid and accurate detection of histamine in food spoilage remains a challenge. To this end, we developed a simple design and easy synthesis of fluorescein-based probe FCHO to achieve specific and rapid (<1 s) quantitative detection of histamine through "imine formation" reaction. Significant enhanced fluorescence signal in response to histamine enabled our probe with high sensitivity as low as 51 nM. Utilizing the visualized fluorescence color changes of the probe as histamine increasing, we combined it with paper-based test chip to construct a color-resolved and highly selective recognition system. In addition, our proposed probe has been successfully used to visually imaging histamine changes in fish samples. Finally, for the first time, we have proved it possesses reliable ability to directly in situ imaging the distribution of histamine in whole spoiled fish. Thus, our strategy will provide great potential for monitoring food spoilage. [Display omitted] • Simple design of fluorescein-based probe for histamine detection via one-step synthesis. • Rapid response (<1 s) and quantitative determination of histamine as low as 51 nM. • Monitoring histamine levels in food samples with specificity, accuracy, and simplicity. • Combination of the probe with paper-based chip for point-of-care testing. • In situ visually imaging the distribution of histamine in the whole spoiled fish. [ABSTRACT FROM AUTHOR]

In this study, a novel fluorescent nanoprobe (ZIF-90@FSS) was constructed using a zeolite imidazolium ester skeleton (ZIF-90) incorporating sodium fluorescein within its porous structure. Notably, this nanoprobe exhibited regular fluorescence "off" detection performance of Fe3+ in actual samples and living cells. The concentration range of 0–150 ng/mL exhibited a lowest detection limit of 0.26 ng/mL. A nanofiber paper-based platform (VL78/ZIF-90@FSS) was further developed by coupling the prepared nanoprobe to a multi-dimensional fiber paper via C N bonds, enabling rapid visual white light colorimetric and fluorescence imaging of Fe3+ within 2 min. The constructed nanoprobe and its paper-based detection platforms demonstrated a stable recovery range in tap water, beer, and soy sauce samples during spiking-recovery assessments. The recovery rates ranged from 98.46 % to 108.24 % for the nanoprobe and from 91.75 % to 108.71 % for the nanofiber paper-based platform. Therefore, the developed nano-fluorescent sensor and paper-based nanofiber sensing platform offer a promising strategy for the visual detection of Fe3+, while also presenting novel and valuable methods to investigate the regulatory mechanisms of Fe3+ in living cells. [Display omitted] • A novel fluorescent nanoprobe ZIF-90@FSS and paper-based nanofiber platform VL78/ZIF-90@FSS were developed. • ZIF-90@FSS and VL78/ZIF-90@FSS exhibit dynamic sensing and real-time imaging of Fe3+ in living cells and actual samples. • ZIF-90@FSS achieved fluorescence "off" detection of Fe3+ based on fluorescence energy transfer and absorption competition. • The ZIF-90@FSS nanoprobe exhibited rapid detection in vitro and spatiotemporal resolution for Fe3+ imaging in vivo. [ABSTRACT FROM AUTHOR]

The freshness of sea food has always been the focus of attention from consumers, and food-safety issues are in urgent need of efficient approaches. A HOF-based ratiometric fluorescence probe (HOF-FITC/Eu) featuring superior amine-response, offers the real-time and visual detection of seafood freshness. Via intermolecular hydrogen bond interaction to form hydrogen-bonded organic frameworks (HOFs), which serve as a structural basis for the conjugate loading of pH-sensitive fluorescein (5-FITC) and coordination doping of lanthanide Eu 3+ . Amine vapors stimulate the dual-wavelength (525 nm and 616 nm) characteristic fluorescence of HOF-FITC/Eu with an inverse trend, resulting in an increase of the ratio of I 525 to I 616 accompanied by a distinct color transition from red to green. Prepared HOF-FITC/Eu featuring sensitive red-green color change characteristics of amine response are readily dripped into composite films of filter paper through integrated smartphone and 254 nm UV lamp as mobile observation devices to on-site monitor the freshness of raw fish and shrimp samples. The intelligent food probe HOF-FITC/Eu opens a novel material assembly type for fluorescence sensing and a potential pathway for other functional materials in the field of investigational food., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Solid-phase fluorescence excitation-emission matrix (SPF-EEM) spectroscopy has potential for non-extractive, non-destructive, and non-contact analytical measurements of powder and solid-state samples, as well as front-face EEM spectroscopy for suspensions of high optical density. However, as there is no unified measurement method for SPF spectroscopy, comparing samples measured in different research fields is difficult. Therefore, this study designs a cell that can be created by a 3D printer and examines reproducibility on measuring fluorescent powders. The developed cell is applied to proteins (ovalbumin, BSA, gliadin, gluten, powdered collagen, casein), amino acids (tryptophan, tyrosine, and phenylalanine), soybean ingredients (daidzein, and genistein), and fluorescent chemicals (rhodamine B, fluorescein sodium salt, pyrene, and quinine sulfate dihydrate) and their spectra are compared with those in the solution states. When samples are refilled into the cell three times, the cell exhibits high reproducibility in terms of fluorescence peak wavelength and intensity. The solid proteins exhibit peaks attributed to the fluorescent amino acid residues, and broad peaks which are not detected for the proteins in the solution states. Powdered rhodamine B and fluorescein sodium salt do not exhibit fluorescence, possibly due to the inner-filter effect (IFE). Some non-colored molecules also exhibit loss of fluorescence or a remarkable difference between the solid and solution states, possibly due to the interaction of the fluorescent structure with the surrounding local environment, similar to the solvent effect, which is possibly affected by the molecular proximity, three-dimensional structure, and moisture absorption capacity., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Antibiotics are one of the emerging contaminants in water, which have a great impact on ecosystems and human health. It has been challenging to simultaneously realize low-cost, rapid, highly sensitive and selective detection of antibiotics with conventional methods. Here, we report luminescent chemosensors for detecting antibiotics in water, based on metal-organic framework (MOF), i.e., zeolitic imidazolate framework-8 (ZIF-8), loaded with rhodamine B (RhB) and fluorescein disodium salt (FSS) dyes. Compared with ZIF-8, the fluorescence signals of RhB@ZIF-8 and FSS@ZIF-8 were significantly improved and presented ultrahigh sensitivity to nitrofurans (NFAs) and tetracyclines (TCs) with fluorescence quenching and fluorescence enhancement in water, respectively. The unique structures and properties of RhB@ZIF-8 and FSS@ZIF-8 lead to outstanding sensitivities in antibiotic detection. For instance, the RhB@ZIF-8 sensor shows the lower limit of detection (LOD) of 0.26 μM to nitrofurantoin (NFT), 0.47 μM to nitrofurazone (NFZ), 0.11 μM to tetracycline (TC), and 0.14 μM to oxytetracycline (OTC); while the FSS@ZIF-8 sensor shows the LOD of 0.31 μM to NFT, 0.35 μM to NFZ, 0.17 μM to TC, and 0.16 μM to OTC. In addition, NFT and TC were also successfully detected by FSS@ZIF-8 in water from real water environment. The results indicate that dye@MOF-based luminescent composites are favorable for antibiotic detection, presenting great potentials in water quality monitoring. Image 1 • The MOF-based luminescent sensors were developed to detect antibiotics in water. • Sensors showed high sensitivity and selectivity to nitrofurans and tetracyclines. • Sensors showed good stability and recyclability in aqueous environment. • Detection mechanisms of fluorescence quenching/enhancement were presented. [ABSTRACT FROM AUTHOR]

In this study, we have designed and synthesized a novel 'AND' logic based fluorescence probe,1-(3′,6′-bis((tert-butyldiphenylsilyl)oxy)-3-oxospiro (isoindoline-1,9′-xanthen)-2-yl)-3-phenylthiourea (FPSi), for the rapid (3 min) simultaneous detection of F− and Hg2+ in DMSO/H 2 O solution (7:3, v/v). The FPSi probe, synthesized over three steps starting from commercially available fluorescein, was constructed by attaching tert-butyldiphenylsilyl and thiosemicarbazide (as the specific identification groups for F− and Hg2+) to the skeleton of fluorescein, respectively. FPSi produced no fluorescence response towards the addition of F− or Hg2+ separately. However, when the probe was exposed to a solution containing both F− and Hg2+, there was a significant yellow-green fluorescence. FPSi demonstrated an excellent selectivity towards both F− and Hg2+ in the presence of interfering substances. The results of TOF-MS-EI analysis indicated that the response of FPSi towards F− and Hg2+ was mainly aroused by the F− promoted cleavage of Si–O bond, and Hg2+ triggered an irreversible desulfurization reaction leading to the spiral ring opening. Furthermore, the FPSi probe has been successfully used to detect F− and Hg2+ ions in tap water and cropland soil. Image 1 • A fluorescein-based chemosensor was synthesized. • The sensor is an efficient AND-logic probe for detecting Hg2+ and F−. • It can turn on the fluorescence in the coexisting solution of Hg2+ and F−. • The response of the probe towards Hg2+ and F− is rapid. [ABSTRACT FROM AUTHOR]

Abstract Cysteine (Cys) plays an important role in both maintaining intracellular redox homeostasis and regulating protein structure and function, developing fluorescence probes for monitoring Cys selectively and sensitively is thereby highly needed for understanding its pathophysiological significance. Herein we designed a new fluorescent probe (FRCA) composed of a julolidine-fluorescein-based hybrid as the fluorescence reporter and an acrylate moiety as the Cys response site. It manifested the following advantage: a turn-on fluorescence response at 567 nm when excited at 538 nm in phosphate buffer solution, rapid discrimination of Cys from other biothiols (glutathione and homocysteine) and cysteine-containing bovine serum albumin by virtue of its different second order rate constants with them, and a very low detection limit of 39.2 nM. Through a combination of mass spectrum analysis and density functional theory calculation we further identified its sensing mechanism to Cys as suppression of photo-induced electron transfer quenching. Additionally, this probe was successfully used to imagine Cys in HepG2 cells. Graphical abstract fx1 Highlights • FRCA exhibits a turn-on red fluorescence response in PBS for sensing Cys. • FRCA can rapidly distinguish Cys from other biothiols, various amino acids and BSA. • FRCA is highly sensitive to sense Cys with a very low detection limit of 39.2 nM. • FRCA has been successfully applied for selective imaging Cys in HepG2 cells. [ABSTRACT FROM AUTHOR]

Abstract Facing the problem of a growing number of analyses, the need for using simple equipment appears. Smartphone-based optical detection is one of the most widely applied ideas nowadays. A personal device such as a smartphone equipped with a camera is affordable even in the source-limited places. After a simple modification, providing the light source of both defined properties and orientation, a smartphone may become an efficient analytical device. In this work we present a uniform methodology of such a modification, offering a complete hand-held device for fluorometric measurements. Inducing the fluorescence of the tested analytes was done by ordinary light-emitting diodes, and phone camera was used as a detector. Then the obtained images were analyzed using the RGB colour model to get proper calibration curves. The demonstration of the system performing with the use of fluorescein preceded the examples of determination of quinine, rhodamine B, riboflavin and calcein in real-life circumstances. Example determinations of the calcium ions in mineral water and riboflavin in alcoholic beverages are provided. The results obtained with the designed device are fully comparable to the ones obtained with the conventional fluorometric equipment. The presented systems allow determination of all the investigated analytes with satisfactory detection limits, in some cases down to ppb levels. Thanks to the use of LEDs, the system could be adapted for both measuring and inducing fluorescence in different analytes, characterized by various excitation wavelengths. Graphical abstract fx1 Highlights • Portable smartphone system for determination of the fluorogenic substances is demonstrated. • The analytical performance of the set up was compared to the conventional fluorimeter equipment. • Data were analyzed using the RGB model, and the results were explained according to the CMOS characteristic and sensitivity. • The practical usefulness of the system in different scenarios using real samples was confirmed. [ABSTRACT FROM AUTHOR]

Abstract A thermometer-type visual sensor for glutathione (GSH) sensing was developed with stimulus-responsive fluorescent hydrogel which was obtained by using 5, 6-bicarboxylic fluorescein crossli'nked partly ammoniated polyacrylamide. Various experimental parameters such as the particle size of hydrogel, buffer solution and swelling time were optimized. It is accessible to measure the volume change of hydrogel with the sensor by reading the graduation on a pipette like thermometer with naked eye. The concentration of the GSH depended on the volume in a certain range as the signal. Satisfactory agreements between the sensor and HPLC results for atuomolan tablet assays indicated the capability of the thermometer-type sensors for the analysis of real samples. These findings proved the utility of stimulus-responsive, intelligent hydrogel and the suitability of thermometer-style visual sensor design for quantitative assays. Graphical abstract 5,6-dicarboxylic fluorescein (5,6-DCF) cross-linked amine-functionalized polyacrylamide (PAM) hydrogel for volumetric response to glutathione. Photographic images of the hydrogel sensor and its responses to glutathione which can be quantitatively distinguished like a thermometer-style by the naked eye. fx1 Highlights • A thermometer-type sensor with convenience, smartness, low-cost versions was developed with stimuli-responses of hydrogel. • The sensor undergoes volume response to glutathione, which enables naked-eye detection by reconstructed pipette. • The challenge for the difficulty of measuring hydrogel volume changes became easy. • Our design stands out visual detection without instruments or power sources. [ABSTRACT FROM AUTHOR]

Abstract Fluorescein has been found as an efficient visible-light-induced oxidase mimic and its catalytic performance is group-dependent. Herein, a facile colorimetric strategy for β-galactosidase (β-gal) was developed using fluorescein di β-D-galactopyranoside (FDG) as a probe based on the analyte induced change in oxidase mimicking activity of fluorescein derivatives. FDG doesn't possess any visible-light-induced oxidase activity and can generate fluorescein and fluorescein mono β-D-galactopyranoside (FMG) in the presence of β-gal. The in situ generated fluorescein and FMG possess high oxidase-like activities under visible-light illumination and could catalyze the oxidation of 3, 3′, 5, 5′-tetramethylbenzidine (TMB) upon short irradiation by light-emitting diode (LED) lamp. Thus, the β-gal activity can be selectively detected in linear range from 0.10 to 12.9 μg mL−1 with a limit of detection (LOD) of 0.04 μg mL−1. We further integrated with the visual detection of α-fetoprotein antigen (AFP) based on the corresponding colorimetric signal induced by β-gal-linked colorimetric immunoassay, a LOD of 0.08 ng mL−1 could be achieved. Significantly, our proposed assay provides a facile sensing platform based on the change in enzyme mimicking activity induced by analytes. In addition, this optical method works without complex synthesis procedure and efficiently avoids participation of unstable H 2 O 2 as an oxidant. Therefore, the present work not only shows the excellent assay performance in β-gal and tumor biomarker detection, but also opens up a new avenue for its application in practical optical sensing. Graphical abstract A new optical method for β-galactosidase (β-gal) was developed using fluorescein di β-D-galactopyranoside (FDG) as a probe based on the oxidase mimicking activity of fluorescein and integrated with the detection of tumor biomarkers such as α-fetoprotein antigen (AFP) based on the corresponding colorimetric signal induced by β-gal-linked colorimetric immunoassay. fx1 Highlights • A new optical method by mediated catalytic activity of fluorescein derivatives with target. • A facile colorimetric strategy for β-gal detection has been established. • β-gal-linked colorimetric immunoassay enabled simple detection of AFP. • The sensing system uses commercial LED lamp as the illumination. [ABSTRACT FROM AUTHOR]

A novel ratiometric fluorescence nanoprobe was developed to detect tryptophan enantiomers with high selectivity and sensitivity. Fluorescein (FL) was doped into SiO 2 nanoparticles with little dye leakage, acting as an internal reference signal. The chiral center of L-histidine (L-His) was introduced by partially replacing the carboxyl on the surface of SiO 2. The response signal of Eu3+ was coordinated with carboxyl to obtain the FL@SiO 2 -Eu/His nanoprobe. The nanoprobe shows enantioselective luminescence responses for tryptophan enantiomers. The red emission of Eu3+ can be effectively quenched by the tryptophan enantiomers, but the quenching efficiency is different due to the different interactions with the chiral recognition sites. The fluorescence intensity ratio (I 613 / I 515) shows excellent linearity with tryptophan enantiomers in the range of 0–100 μM (R 2 > 0.99). The limit of detection (LOD) is 1.0 μM and 1.3 μM for L-tryptophan (L-Trp) and D-tryptophan (D-Trp), respectively. The FL@SiO 2 -Eu/His nanoprobe shows good selectivity and specific recognition in serum actual samples. In addition, the nanoprobe can realize visual detection under UV light due to the obvious color change. This work provides an innovative idea for the development of new probes in the detection field. [Display omitted] • A ratiometric fluorescence nanoprobe was developed to detect tryptophan enantiomers. • Fluorescein was doped into SiO 2 nanoparticles, acting as internal reference signal. • Eu3+ was as responsive signal and L-His was introduced as the chiral center. • The quenching efficiency of the nanoprobe was different to tryptophan enantiomers. [ABSTRACT FROM AUTHOR]

Microfluidic-based analyses of single-cell dynamics in response to dynamic biochemical signals are emerging as pivotal approaches for investigating the effects of extracellular microenvironmental biochemical factors on cellular structure, function, and behavior. However, current devices often fail to consistently apply identical dynamic biochemical signals to trapped cells. In this study, we introduce a novel radially distributed single-cell trapping microfluidic array, designed to quantitatively and consistently apply identical biochemical stimulating signals to each trapped cell. Numerical simulations were employed to optimize microchannel geometry, enhancing trapping efficiency while minimizing signal distortion. Experimental validation demonstrated the trapping success rate and the single-cell trapping efficiency exceeding 99% and 85%, respectively. The microarray's capability to deliver identical dynamic biochemical stimulating signals, with various waveforms, to each unit was confirmed through fluorescein transport tests. Furthermore, we examined the intracellular calcium dynamics of U-2 OS human osteosarcoma cells in response to dynamic ATP signals, observing both single-peak calcium responses and calcium oscillations, which were modelled by a second-order system with a natural frequency of 1.6 mHz. Overall, our proposed microfluidic array offers a robust and valuable framework for advancing the understanding of single-cell dynamics. [Display omitted] • A single-cell-trapping microarray capable of delivering identical biochemical stimulating signals to trapped cells for cellular dynamics analysis was presented. • The trapping efficiency and the ability of loading biochemical stimulating signals were numerically and experimentally validated. • Intracellular calcium dynamics of U-2 OS cells in response to various ATP stimulations were investigated. • The intracellular calcium signaling dynamics can be characterized by the second-order system. [ABSTRACT FROM AUTHOR]

Abstract Fluorescein and its derivatives, including 4′,5′–dibromofluorescein, 2′,7′–dichlorofluorescein and 2′,4′,5′,7′–tetrabromofluorescein can be employed as efficient coreactants for luminol reaction. Under an alkaline condition they reacted with luminol to produce measureable chemiluminescence (CL) in the absence of any extra–oxidant. Cobalt ion (Co2+) significantly enhanced the CL emission of the reaction. The CL emission was strongly dependent on the concentration of carbonate buffer used; higher concentration of carbonate buffer provided more intense CL emission. The system had two emission peaks locating at 425 nm and 535 nm, respectively. With 4′,5′–dibromofluorescein as the coreactant for luminol reaction, a new CL method was developed for the detection of Co2+. The procedure allowed the linear detection of Co2+ in the range of 5–1000 nmol/L. The limit of detection (LOD) and limit of quantitation (LOQ) were 1.8 nmol/L and 5.0 nmol/L, respectively. The intra–day precision (n = 11) and inter–day precision (n = 3) was 3.2% and 4.7% for replicated measurements of 0.2 μmol/L Co2+ solution. The method was successfully applied to the determination of Co2+ in blue silica gel samples. Graphical abstract fx1 Highlights • Fluorescein and its derivatives can directly react with luminol to produce CL. • Co2+ ion enhanced the CL emission significantly. • High concentration of carbonate buffer provided more intense CL emission. • The system had two emission peaks at 425 nm and 535 nm, respectively. • A highly sensitive method was developed for CL detection of Co2+. [ABSTRACT FROM AUTHOR]

Abstract A novel and highly sensitive method for detection of microRNA (miRNA) was developed by integration of T7 exonuclease-triggered amplification and cationic conjugated polymer (CCP) biosensing. First, a fluorescein-labeled probe was designed with the complementary sequence to the target miRNA. When target miRNA was absent in the solution, the fluorescence probe interacted with CCP through the strong electrostatic interactions, leading to the highly efficient fluorescence resonance energy transfer (FRET) from CCP to fluorescein. In the presence of target miRNA, the probe hybridized with the miRNA to form DNA/miRNA duplex hybrids. Then, T7 exonuclease digested cyclically the fluorescence probes in hybrids and triggered the enzyme amplification reaction, generating a large number of single nucleotides. Owing to the weak electrostatic interaction between CCP and the single nucleotide, the FRET from CCP to fluorescein would not take place, which effectively reduced the background and significantly enhanced the sensitivity and the dynamic range of miRNA detection. The linear range of the assay was 0.2–100 pM and the detection limit 0.08 pM was 58 times lower than that of the endonuclease-based assay. The method is simple, cost-effective, and with no need for the sophisticated instrument, and has broad application prospects for miRNA detection and early diagnosis. Graphical abstract fx1 Highlights • A highly sensitive, specific, and homogeneous method for detection of microRNA. • Integration of T7 Exo-triggered amplification and conjugated polymer biosensing. • Mononucleotide digestion products of T7 Exo effectively reduces the background. • The method is simple, cost-effective, and without sophisticated instrument. [ABSTRACT FROM AUTHOR]

Pi class glutathione S-transferase (GSTP1) is highly expressed in various cancerous cells and pre-neoplastic legions, where it is involved in apoptotic resistance or metabolism of several anti-tumour chemotherapeutics. Therefore, GSTP1 is a marker of malignant and pre-malignant cells and is a promising target for visualization and drug development. Here we demonstrate that fluorescein diacetate (FDA), a fluorescent probe used for vital staining, is a fluorescently activated by esterolytic activity of human GSTP1 (hGSTP1) selectively among various cytosolic GSTs. Fluorescence activation of FDA susceptible to GST inhibitors was observed in MCF7 cells exogenously overexpressing hGSTP1, but not in cells overexpressing hGSTA1 or hGSTM1. Inhibitor-sensitive fluorescence activation was also observed in several cancer cell lines endogenously expressing GSTP1, suggesting that GSTP1 is involved in FDA esterolysis in these cells. Among the FDA derivatives examined, FOMe-Ac, the acetyl ester of fluorescein O -methyl ether, was found to be a potential reporter for GSH-dependent GSTP1 activity as well as for carboxylesterase activity. Since GSTP1 is highly expressed in various types of cancer cells compared to their normal counterparts, improving the fluorogenic substrates to be more selective to the esterolysis activity of GSTP1 rather than carboxylesterases should lead to development of tools for detecting GSTP1-overexpressing cancer cells and investigating the biological functions of GSTP1. [ABSTRACT FROM AUTHOR]

A simple, rapid, and ultrasensitive fluorescence strategy for adenosine triphosphate (ATP) detection was developed by using a FAM (carboxyfluorescein) labeled DNA (FAM-DNA). In this strategy, highly fluorescent FAM-DNA was used as a probe, and nanoceria (CeO 2 NPs) acted as an efficient quencher. FAM-DNA attached to the surface of nanoceria through the coordination between the phosphate group of DNA and NP surface, which induced complete quenching in the FAM-DNA fluorescence due to a photo induced electron transfer (PET) process. It was found that ATP can readily displace adsorbed DNA from nanoceria surface because of the stronger coordination ability of ATP with nanoceria, and the nanoceria-based competitive binding resulted in over 7-fold fluorescence enhancement. Over a wide range from 0.1 nM to 1.5 μM, a good linear relationship between the fluorescence intensity and the concentration of ATP was obtained and the detection limit was estimated to be as low as 54 pM. This method was successfully used to analyze ATP in a single drop of blood and human urine. [ABSTRACT FROM AUTHOR]

To improve the water-solubility of heavy-metal sensing materials, a modified fluorescein-based derivative, acryloyl fluorescein hydrazine (ACFH), was designed and developed by incorporating a non-hydrogen-bonding group into the conjugated molecule for weakening intermolecular hydrogen-bonding interactions. In neutral water environments, ACFH presented a fluorescence-enhancement performance at λ max =512 nm in the presence of Hg 2+ , which could be visualized by naked-eyes. Under the optimized conditions, the linear range of Hg 2+ detection was 1.0–100×10 −9 mol L −1 with a correlation coefficient of 0.9992 and a detection limit of 0.86×10 −9 mol L −1 . The recognition mechanism was confirmed to be a stable and irreversible 1:1 five-member ring complex between ACFH and Hg 2+ with a coordination constant of 3.36×10 9 . ACFH would possess a potential application in detecting Hg 2+ for biological assay with low cytotoxicity. [ABSTRACT FROM AUTHOR]

A novel water-soluble fluorescent probe FLS2 based on the thiooxofluorescein derivative has been firstly designed and synthesized. UV–vis absorption and fluorescence spectra studies showed that the FLS2 as a colorimetric and ratiometric fluorescent probe exhibited high selectivity and sensitivity towards Hg 2+ , which was mainly attributed to the special binding with the receptor unit accompanied with the spirolactam ring-opening progress. In addition, the probe FLS2 could be used as a naked-eye indicator for Hg 2+ with reversible response. It displayed approximate 37-fold fluorescent enhancement at 529 nm in the presence of only 2.0 equiv. Hg 2+ and the detection limit was calculated at about 39 nM. What's more, cellular imaging experiment revealed that the sensor had excellent biocompatibility and low cytotoxicity that could be utilized for monitoring Hg 2+ in living cells. [ABSTRACT FROM AUTHOR]

This work reports on the development of a novel methodology for bromide determination by combining headspace single-drop microextraction with microvolume fluorospectrometry. The method lies in the in situ generation of bromine, transfer of the volatile to the headspace and trapping/reaction onto a fluorescein-containing aqueous drop exposed to the gas phase. The decrease in the fluorescence intensity enabled the determination of bromide without dilution of the enriched microdrop. Experimental parameters influencing the performance of the method, namely, fluorescence parameters, extractant phase composition, bromine generation conditions and microextraction time, were evaluated and controlled. Under optimal conditions, an enrichment factor of 243 was attained. The limits of detection and quantification achieved under optimal conditions for bromide were found to be 1.4 and 4.4 µg L −1 , respectively. The intra-day repeatability, expressed as relative standard deviation, was 4.4% (n=6). Besides, the inter-day reproducibility, performed at four different days, was 7.1%. Finally, the developed method was successfully applied to the determination of bromide in different water samples, showing recovery values in the range of 95–110%, and validated against certified reference material BCR-611 (ground water, Br − low level). The proposed method represents a highly convenient approach for monitoring of bromide at very low concentrations. [ABSTRACT FROM AUTHOR]

2,4,6-Trinitrophenol (TNP, also called picric acid, PA) pose a large threat to environmental health, public safety and military security. Conjugated microporous polymers are emerging new fluorescence sensing materials for TNP. In this paper, we report the synthesis of two fluorescein containing conjugated microporous polymers (DTF and TTF) through the palladium catalyzed Sonogashira–Hagihara polycondensation reactions of tetraiodofluorescein sodium salt (TIFA) with 1,4-diethynylbenzene (DEB) or 1,3,5-triethynylbenzene (TEB). DTF and TTF are porous with the BET surface areas of 705 and 712 m 2 g −1 and exhibit high chemical and thermal stabilities. The formation of conjugated polymers with the incorporation of ethynyl groups leads to the fluorescent properties. The fluorescence quenching behaviors of DTF by nitroaromatic analytes in THF suspension are investigated. It is found that the fluorescence of DTF can be effectively quenched by 2,4,6-trinitrophenol over 2-nitrophenol (NP), 4-nitrotoluene (NT), nitrobenzene (NB), phenol (PhOH), p-dichlorobenzene (DClB) and 2,4-dinitrotoluene (DNT) with an SV constant of 2.08×10 3 L mol −1 and a detection limit of 7.22×10 −7 mol L −1 (0.165 mg L −1 ). In short, the DTF may be a new kind of fluorescence sensing material for detecting TNP. [ABSTRACT FROM AUTHOR]

Laser-induced fluorescence (LIF) detectors for low-micrometer and sub-micrometer capillary on-column detection are not commercially available. In this paper, we describe in details how to construct a confocal LIF detector to address this issue. We characterize the detector by determining its limit of detection (LOD), linear dynamic range (LDR) and background signal drift; a very low LOD (~70 fluorescein molecules or 12 yoctomole fluorescein), a wide LDR (greater than 3 orders of magnitude) and a small background signal drift (~1.2-fold of the root mean square noise) are obtained. For detecting analytes inside a low-micrometer and sub-micrometer capillary, proper alignment is essential. We present a simple protocol to align the capillary with the optical system and use the position-lock capability of a translation stage to fix the capillary in position during the experiment. To demonstrate the feasibility of using this detector for narrow capillary systems, we build a 2-μm-i.d. capillary flow injection analysis (FIA) system using the newly developed LIF prototype as a detector and obtain an FIA LOD of 14 zeptomole fluorescein. We also separate a DNA ladder sample by bare narrow capillary – hydrodynamic chromatography and use the LIF prototype to monitor the resolved DNA fragments. We obtain not only well-resolved peaks but also the quantitative information of all DNA fragments. [ABSTRACT FROM AUTHOR]

Acrylamide is a toxic species for human health, and is a Maillard reaction product which forms spontaneously in heat treatment process of foods. Therefore, a simple, fast and cost-effective method was developed for the indirect determination of acrylamide in processed foods particularly consumed by children. The method is based on ion–pairing of acrylamide with fluorescein (F 2− ) in presence of Ni(II) ions at pH 9.0, and then extraction of the formed ternary complex into micellar phase of poly(ethyleneglycol-mono- p -nonylphenylether) (PONPE 7.5) before analysis by flame atomic absorption spectrometry (FAAS). The ultrasonic-assisted cloud point extraction (UA-CPE) has been used for the preconcentration of acrylamide in the samples prior to its FAAS detection. The matrix matched calibration curve is linear in range of 0.3–150 µg kg −1 under optimal reagent conditions (1.75 mL of 0.1 mol L −1 ammonia buffer at pH 9.0, 2.2 mg L −1 Ni(II), 4.0×10 −4 mol L −1 F 2− , 0.4% (w/v) NH 4 Cl and 0.7% (v/v) PONPE 7.5) with sensitivity enhancement of 160-fold. The proposed method has been validated by assessment of the following parameters; the limits of detection (LOD) and quantification (LOQ) (0.08 µg kg −1 and 0.28 µg kg −1 , respectively) with a relative standard deviation (RSD%) lower than 6.3%, and extractive recovery higher than 95% for acrylamide spiked at levels of 5 and 25 µg kg −1 . The method was successfully applied to the indirect determination of acrylamide in the processed foods and two CRMs with satisfactory results. [ABSTRACT FROM AUTHOR]

A fluorescence turn-on assay was established for ALP (alkaline phosphatase) based on Cu2+ catalyzed Fenton-like reaction and Graphene Oxide (GO). GO was utilized to quench the fluorescence of fluorescein (FAM) labeled single strand DNA (F-DNA). ALP can remove the phosphate group in sodium ascorbyl phosphate (SAP), and convert it into reducing ascorbate. Highly reactive hydroxyl radicals (·OH) were generated in the presence of ascorbate and Cu2+ through the Fenton-like reaction. The reactive radicals generated in situ caused the cleavage of F-DNA into small fragments. When GO was added, the fluorescence emission of the sample without ALP was quenched and fluorescence emission recovered in the presence of ALP. The intensity of the recovered fluorescence was directly related to the concentration of ALP in the assay solution, and a sensitive and selective facile ALP assay is therefore established. Graphical abstractHighlights· An alkaline phosphatase assay was developed with high sensitivity and selectivity. · Graphene oxide was used for the efficient quenching of fluorescence dye labeled single stranded DNA. · The Cu2+ catalyzed Fenton-like reaction was utilized for the breakdown of dye labeled single stranded DNA. · The assay could also be used for the facile screening of ALP inhibitors. [ABSTRACT FROM AUTHOR]

The discovery of in-vitro systematic evolution of ligands by exponential enrichment (SELEX) process has considerably broaden the utility of aptamer as bio-recognition element, providing the high binding affinity and specificity against the target analytes. Recent research has focused on the development of structure switching signaling aptamer assay, transducing the aptamer- target recognition event into an easily detectable signal. In this paper, we demonstrate the development of structure switching aptamer assay for determination of aflatoxin M1 (AFM1) employing the quenching-dequenching mechanism. Hybridization of fluorescein labelled anti-AFM1 aptamer (F-aptamer) with TAMRA labelled complementary sequences (Q-aptamer) brings the fluorophore and the quencher into close proximity, which results in maximum fluorescence quenching. On addition of AFM1, the target induced conformational formation of antiparallel G-quadruplex aptamer-AFM1 complex results in fluorescence recovery. Under optimized experimental conditions, the developed method showed the good linearity with limit of detection (LOD) at 5.0ngkg-1 for AFM1. The specificity of the sensing platform was carefully investigated against aflatoxin B1 (AFB1) and ochratoxin A (OTA). The developed assay platform showed the high specificity towards AFM1. The practical application of the developed aptamer assay was verified for detection of AFM1 in spiked milk samples. Good recoveries were obtained in the range from 94.40% to 95.28% (n=3) from AFM1 spiked milk sample. Graphical abstractfx1Highlights· Structure switching aptamer assay for detection of aflatoxin M1 (AFM1). · Successfully investigated for detection of AFM1 in spiked milk samples. · Analytical performance of aptamer assay proves its applicability in milk analysis. · No complex milk sample preparation procedure. · Obtained recoveries were in the range of 94.40-95.28% (n=3). [ABSTRACT FROM AUTHOR]

TEV protease is of great importance for in vitro and in vivo site-specific cleavage of proteins. The proteolytic efficiency of TEV protease is often regulated by mutation of the substrate, which is irreversible and hard to be modulated. Herein, a facile and reversible method, based on phosphorylation in the substrate, is developed to regulate the cleavage capability of TEV protease. Phosphorylation at P3 tyrosine hinders the recognition of TEV protease to the substrate by using a robust fluorescent protease sensor. Moreover, the phosphate group can be easily removed by alkaline phosphatases for recovering the proteolytic efficiency of TEV protease. Additionally, 5(6)-carboxyfluorescein and pyrene have been used as high-efficiency mutual fluorophore-quencher pair in the peptide-based protease sensor for the first time, which provides a chance to simultaneously monitor the cleavage process in two respective fluorescence channels. Further studies indicated both dynamic and static components contributing to the mutual quenching system. The phosphorylation-regulated TEV protease proteolysis system can be used in conditional cleavage of protein or peptide tag. [ABSTRACT FROM AUTHOR]

Ubiquitin-binding domains (UBDs) are modular elements that bind non-covalently to the ubiquitin and ubiquitin chains. The preferences of UBDs for ubiquitin chains of specific length and linkage are central to their functions. We demonstrated that an artificial t andem h ybrid UBD (ThUBD) exhibits an unbiased high affinity to all ubiquitin chains and is a promising tool for global ubiquitination profiling research. In this study, we labeled fluorescein on the four cysteine residues in the N-terminal glutathione S-transferase (GST) tag of ThUBD, generating a fluorescein-labeled ThUBD (ThUBD-Flu) probe for direct polyubiquitination signal imaging and visualization. Compared to the canonical ubiquitin antibody method, the ThUBD-Flu is hyper-sensitive and accurate to detect ubiquitination signal. More importantly, the ThUBD-Flu probe provided, for the first time, a widely applicable, super-sensitive and unbiased technique for in situ detection of intracellular polyubiquitination signal through immunofluorescence staining, which was only achievable with recombinant fluorescence tag fused ubiquitin gene previously. We propose that ThUBD-Flu, combined with evolving microscopy technology, could serve as prototypes to track and trace cellular polyubiquitination signal in vivo. The ThUBD-Flu probe can temporally and spatially detect the in-situ poly-ubiquitination signal in a hyper-sensitive and unbiased way. [Display omitted] • The developed ThUBD-Flu probe could be used for direct polyubiquitination signal imaging and visualization. • The ThUBD-Flu showed high-performance for polyubiquitination signal detection with super-sensitivity and high accuracy. • The newly developed approach can temporally and spatially distinguish polyubiquitination signal imaging in situ cells. [ABSTRACT FROM AUTHOR]

Overuse of antibiotics posed a global threat to human health and the ecological environment. Efficient detection and control of antibiotic pollution demand novel sensory materials. Here, a dual-luminescent material FS@UIO66 was successfully synthesized by encapsulating fluorescent molecules (fluorescein sodium, FS) in UIO66 based on the in-situ encapsulation method. We found that the dual emission peaks of FS@UIO66 at 369 and 515 nm can be sensitively and synchronously quenched by tetracycline (TET). Interestingly, these two peak intensities were switched anisotropically by levofloxacin (LEV), in which the signal at 515 nm was enhanced. Photophysical analysis revealed that there may exist a competition and replenishment mechanism in the sensing processes. The ratiometric fluorescent feature was employed for rapid detection of TET and LEV, with detection limits of 0.2444 μM and 0.2808 μM for TET and LEV, respectively. The superior sensitivity, high selectivity, and excellent recyclability of FS@UIO66 in sensing TET and LEV were demonstrated in this work. In addition, TET and LEV were also successfully detected by FS@UIO66 in water from real water environment. The results indicate that FS@UIO66 composites are favorable for TET and LEV detection, presenting a great sensing platform for antibiotic detection. [Display omitted] • A dual-emission luminescent probe was synthesized by in-situ encapsulation. • We reported a ratiometric fluorescent platform for tetracycline and levofloxacin. • The platform has superior sensitivity, high selectivity, and a low detection limit. [ABSTRACT FROM AUTHOR]

We report a novel, selective and sensitive strategy for the sequentially “ON–OFF–ON” fluorescent detection of Cu 2+ and S 2− based on a fluorescein derivative, FL. The specific binding of FL towards Cu 2+ in aqueous and biological media led to the intensive green fluorescence quenching and a notable increase of the absorbance maximum at 480 nm. In the presence of S 2− , the intensity and overall pattern of the fluorescence emission and UV–vis spectra of FL–Cu 2+ ensemble were recovered since the abolishment of paramagnetic Cu 2+ . This displacement approach exhibited highly specificity, and sensitivity with detection limits of 3 nM for Cu 2+ and 150 nM for S 2− . The fluorescence “ON–OFF–ON” circle can be repeated to a minimum of 5 times by the alternative addition of Cu 2+ and S 2− , implying that FL is a renewable dual-functional chemosensor. The biocompatibility of FL toward breast carcinoma cells, MDA-MB-231 was confirmed by MTT assay. The reversible “ON–OFF–ON” fluorescent response of FL to Cu 2+ and S 2− in living system was further confirmed by confocal fluorescence imaging of living cells. The quantification of Cu 2+ and S 2− in single intact cell was realized by the flow cytometry analysis. [ABSTRACT FROM AUTHOR]

The design of a label-free aptamer for separation of recognition sequence from signal reporter is significant to ensure the high-efficiency affinity between aptamer and target. This work develops a label-free triple-helix aptamer (THA) as sensing platform for “signal-on” fluorescent detection of thrombin. THA was composed of aptamer sequence and help DNA 1 (H1), which contained the complementary sequence of hexachloro-fluorescein (HEX) labeled help DNA 2 (H2). The specific recognition event between aptamer and thrombin triggered the dismission of THA to release H1. The released H1 then reacted with the signal probe of H2/graphene oxide (GO) nanocomposite to form H1-H2 duplex, leading to the fluorescence recovery of H2 due to the detachment of H1-H2 duplex from the surface of GO. With employment of THA as a signal transducer and GO as a “superquencher”, this method shows a sensitive response to thrombin with a wide concentration range from 5 to 1200 nM. The limit of detection is 1.8 nM (S/N=3) with excellent selectivity. Considering the universality of THA, the proposed aptasensor would provide a platform for homogeneous fluorescent detection of a wide range of analytes. [ABSTRACT FROM AUTHOR]

Thiocyanate (SCN − ) is a small anion byproduct of cyanide metabolism. Several methods have been reported to measure SCN − above the micromolar level. However, SCN − is derived from many sources such as cigarettes, waste water, food and even car exhaust and its effect is cumulative, which makes it necessary to develop methods for the detection of trace SCN − . In this paper, a simple and ultrasensitive turn-on fluorescence assay of trace SCN − is established based on the fluorescence resonance energy transfer (FRET) between gold nanoparticles (AuNPs) and fluorescein. The detection limit is 0.09 nM, to the best of our knowledge, which has been the lowest detection LOD ever without the aid of costly instrumentation. The fluorescence of fluorescein is significantly quenched when it is attached to the surface of AuNPs. Upon the addition of SCN − , the fluorescence is turned on due to the competition action between SCN − and fluorescein towards the surface of AuNPs. Under an optimum pH, AuNPs size and concentration, incubation time, the fluorescence enhancement efficiency [( I F − I 0 )/ I 0 ] displays a linear relationship with the concentration of SCN − in the range of 1.0 nM to 40.0 nM. The fluorescein–AuNP sensor shows absolutely high selectivity toward SCN − than other 16 anions. The common metal ions, amino acids and sugars have no obvious interference effects. The accuracy and precision were evaluated based on the recovery experiments. The cost effective sensing system is successfully applied for the determination of SCN − in milk products and saliva samples. [ABSTRACT FROM AUTHOR]

Two aptasensors based on graphene oxide (GO) and molecular beacon were designed for the detection of L-tryptophan (L-Trp) using L-Trp aptamer (Trp3a-1). The fluorescein (FAM) labeled Trp3a-1 was absorbed by GO, which resulted in the fluorescence quenching, and exhibiting minimal background fluorescence. Upon the addition of L-Trp, Trp3a-1 was not absorbed quickly. This effect allows for a quantitative assay of L-Trp over the concentration range of 10–500 μM and with a detection limit of 6.84 μM. However, due to the unspecific adsorption of GO, the GO based aptasensor can׳t be applied in complex matrixes. In respect of molecular beacon based aptasensor, FRET between Trp3a-1 labeled with FAM and CS-Trp3a-1 labeled with BHQ-1(black hole quencher-1) which is partially complementary with the aptamer was used to detect L-Trp. L-Trp binding could induce the disassociation of CS-Trp3a-1, resulted in the enhancement of fluorescence in solution. With an excellent linear relationship in 10–500 μM and a detection limit of 6.97 μM in 25% serum, the aptasensor is expected to be improved for the detection of free L-Trp in other complex samples. [ABSTRACT FROM AUTHOR]

A ratiometric pH probe composed of a fluorescein moiety and an ionic near-infrared-emitting phosphorescent cyclometalated iridium(III) complex bis(6-(benzo[b]thien-2-yl)phenanthridinato)(4-(3-carboxypropyl)-4′-methyl-2,2′-bipyridine)iridium(III) was synthesized. With good cell permeability, the probe demonstrated a linear ratiometric response to the pH variation in the physiological range in HeLa cell assay. [ABSTRACT FROM AUTHOR]

DNA methylation plays an important role in many biological events and is associated with various diseases. Most traditional methods for detection of DNA methylation are based on the complex and expensive bisulfite method. In this paper, we report a novel fluorescence method to detect DNA and DNA methylation based on graphene oxide (GO) and restriction endonuclease HpaII. The skillfully designed probe DNA labeled with 5-carboxyfluorescein (FAM) and optimized GO concentration keep the probe/target DNA still adsorbed on the GO. After the cleavage action of HpaII the labeled FAM is released from the GO surface and its fluorescence recovers, which could be used to detect DNA in the linear range of 50 pM–50 nM with a detection limit of 43 pM. DNA methylation induced by transmethylase (Mtase) or other chemical reagents prevents HpaII from recognizing and cleaving the specific site; as a result, fluorescence cannot recover. The fluorescence recovery efficiency is closely related to the DNA methylation level, which can be used to detect DNA methylation by comparing it with the fluorescence in the presence of intact target DNA. The method for detection of DNA and DNA methylation is simple, reliable and accurate. [ABSTRACT FROM AUTHOR]

Abstract: Antisense oligonucleotides (ASOs) are often utilized to interfere with gene expression at mRNA level for cancer treatment. Here, we synthesized fluorescein doped silica nanoparticles (FSNPs) and coated them by polyethyleneimine (PEI) for carrying ASOs. Agarose gel electrophoresis proved that PEI/FSNPs could load ASOs by a weight ratio as high as 30:1. We tracked the delivery process of ASOs from the ASOs/PEI/FSNPs composites to HeLa cells in situ by the confocal laser scanning microscopy (CLSM) techniques, including nuclear staining and Z-axis scanning. We found the ASOs/PEI/FSNPs composites exhibited their biological effects at specific intracellular localization, and the fluorescence of the FSNPs showed the dynamic delivery process in the cells. [Copyright &y& Elsevier]

Viral infection has been one of the major health issues for human life. The real-time reverse transcription polymerase chain reaction (RT-PCR)-based detection has primarily been used for virus detection as a highly reliable procedure. However, it is a relatively long and multi-stage process. In addition, required skilled personnel and complex instrumentation presents difficulties in large scale monitoring efforts. Therefore, we report here a direct and fast detection method for CoV-2 genome as applied in the nose-throat swab samples without any further processing. The detection principle is based on fluorescein-loaded mesoporous silica nanoparticles capped by specific gene sequences probes immobilized on the surface of the nanoparticles. Upon hybridization with the target viral genome, the fluorescein molecules were released from the mesopores. Testing with synthetic oligonucleotides, the NSP12 gene-based detection resulted in a strong signal. Target detection time could be optimized to 15 min and the limit of detection was 1.4 RFU with 84% sensitivity with clinical samples (n = 43). [Display omitted] • A rapid biosensor for viruses. • Direct detection from nose-throat swab samples. • Detection time was 15 min. • Probe-gated silica nanoparticles were used to detect SARS-CoV-2 in clinical samples. [ABSTRACT FROM AUTHOR]

Abstract: The new approach to one-step derivatization of saccharide with 5-(((2-(carbohydrazino)methyl)thio)acetyl)-aminofluorescein (C356) was described. In this approach, high fluorescent C356 was applied to label saccharide to enhance the response of derivative saccharide and high sensitive capillary high performance liquid chromatography with laser-induced fluorescence (Capillary-HPLC-LIF) associated with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) was used to characterize C356 labeled saccharide. The effect of derivatization conditions was evaluated and discussed. The limit of detection (LOD) of neutral saccharide in our method attained the level of femtomolar. As a result, this method could be successfully applied to determine the structure of N-glycans of glycoprotein. [Copyright &y& Elsevier]

Abstract: Here we report a novel label-free fluorescent sensor for ultrasensitive detection of protamine and heparin based on the high quenching ability of gold nanoparticles to the fluorescence of fluorescein. The fluorescence was significantly quenched when fluorescein molecules were attached to the surface of gold nanoparticles by electrostatic interaction. Upon addition of protamine, the fluorescein molecules were detached from the surface of the gold nanoparticles due to the stronger adsorption of protamine on the surface of AuNPs, and resulting in the recovery of the fluorescein molecules fluorescence. Heparin is able to bind with Protamine specifically. In the presence of heparin, the interaction of heparin with protamine makes the AuNPs de-aggregate and the fluorescein molecules re-attach to the AuNPs, which lead to marked fluorescence quench again. By measuring the changes in the fluorescence of the fluorescein molecules, the concentration of protamine and heparin were sequentially determined. The linear response range was obtained over the concentration range from 0 to 0.8μg/mL and 4 to 1.6μg/mL with the low detection limit 0.0067μg/mL and 0.0013μg/mL for protamine and heparin, respectively. [Copyright &y& Elsevier]

Abstract: In this paper, we report a new strategy for detection of hydrogen peroxide and glucose using quantum dot (QD)-based fluorescence resonance energy transfer (FRET) and tyramide reaction. The principle of FRET is based on highly sensitive reaction of a carbocyanine dye (Cy5) labeled tyramide and hydrogen peroxide catalyzed by horseradish peroxidase (HRP), and the fluorescence spectrum of QDs (EX max 605nm) partially overlaps with the absorption bands of Cy5. We firstly conjugated HRP to QDs, and then demonstrated an efficient FRET between HRP conjugated QDs (as energy donors) and tyramide labeled Cy5 (as energy acceptors) due to the formation of Cy5-labeled HRP–QDs assemblies in the presence of H2O2. We observed that the fluorescence Cy5 depended linearly on the H2O2 concentration within a range of concentration from 10 to 100nM and the detection limit of this assay was 10nM. Based on the principle for determination of H2O2, we develop a new strategy for assay of glucose by coupling with glucose oxidase-mediated reaction. The established methods were successfully used for determination of glucose levels in human sera, and the results obtained were in good agreement with commercially available method. Our method is at least 1 order of magnitude more sensitive than in the commercially available method. More importantly, our method described here can be extended to other assay designs using different oxidase enzymes, energy donors and energy acceptors, such as near-infrared (NIR)-to-visible upconversion nanoparticles and silicon and carbon QDs. [Copyright &y& Elsevier]

Abstract: We studied the adsorption properties of organic and organic-inorganic films based on the dye calcein. Embedding of silver nanoparticles increases film sensitivity to some analytes (in particular, sensitivity to ethanol increases by about 30%). Both films demonstrate high sensitivity to water vapor, response of about 7000Hz for a quartz crystal microbalance sensor. Our investigations showed that essential restructuring of films and increase in their thickness occurs in the course of adsorption of water molecules. These changes are reversible: after drying, the sensor response reverts to zero and the film structure is fully restored. The value and reversibility of changes occurring because of adsorption processes at the surfaces of calcein and calcein−Ag films make these materials very promising for application not only in sensorics but also when developing nanoactuators as well. [Copyright &y& Elsevier]

Abstract: Herein, folic acid (FA) conjugated with AuNPs were introduced into the cancer cell imaging via the specific interaction between FA and the folate receptor on the cell surface. FA protected gold nanoparticles (AuNPs) was synthesized and labeled with fluorescein isothiocynate (FITC) to form the FITC–FA–AuNPs (FFANPs). As over-expressed folic acid receptor in some cancer cells and folic acid can specifically and selectively combine, the FFANPs can bind to the FR expressed on tumor cells such as HeLa cells (human epithelial cervical cancer) and CERF-CEM cells (T cell line, human acute lymphoblastic leukemia). As a result, cancer cell imaging can be achieved. To ascertain the FR target ability, it has been acquired by FR-targeted images using synthetic FFANPs. The formation of FITC–FA can be identified by MS. FCM was carried out to study the cell uptake of FFANPs. The cell toxicity (3-[4,5–dimethylthiazolyl–2]−2, 5-diphenyltetrazolium bromide, MTT) assay demonstrated that the FITC-labeled conjugate had only little effect on the cytotoxicity to the cells, which further proved the applicability of the method in tumor cell imaging. [Copyright &y& Elsevier]