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We present a fluorescence turn-on and colorimetric dual-readout sensing system for the sensitive detection of alkaline phosphatase (ALP) activity via self-assembled gold nanoclusters (AuNCs) based on fluorescence resonance energy transfer (FRET). The positively charged polyallylamine hydrochloride (PAH)-crosslinked AuNCs (PAH-AuNCs) with aggregation-induced enhancement (AIE) characteristics can electrostatically adsorb the negatively charged 2, 6-dichlorophenolindophenol (DCIP). Thus, the fluorescence of PAH-AuNCs can be significantly quenched by the occurrence of FRET from PAH-AuNCs to DCIP. However, the reduction reaction of DCIP from blue to colourless by L -ascorbic acid (AA) which is generated by the ALP catalyse hydrolysis of 2-Phospho- L -ascorbic acid (AAP) disturbs the FRET between PAH-AuNCs to DCIP. The quenched PAH-AuNCs fluorescence can be recovered efficiently. The strategy of first creating AIE-enhanced PAH-AuNCs, followed by the effective FRET manipulation, is an important contribution to the sensitive detection of ALP. More importantly, the distinct colorimetric signal change can be used to visually distinguish the presence of ALP. More importantly, the distinct colorimetric signal change can be used to visually distinguish the presence of ALP. Good linear relationships of fluorescence and colorimetric sensing towards ALP were obtained in the range from 0.5 to 100 U/L, and the detection limits were 0.2 U/L and 0.5 U/L, respectively. In addition, the proposed FRET sensing system was applied to the detection of ALP in human serum samples with satisfactory results. The simple and efficient sensing approach proposed here has the potential to promote the development of chemo/biodetection methods using fluorescence and colorimetric dual-readout.

Glutathione (GSH) serves several vital biological functions and its abnormal levels are associated with many diseases. Simple and sensitive methods capable of detecting GSH are desired for better understanding the mechanism of diseases. In this work, a label-free MnO2 nanosheets assisted aggregation-induced emission (AIE)-silica nanospheres (SiO2 NPs) nanoprobe for fluorescent "turn-on" detection of GSH with high sensitivity was reported for the first time. The anionic tetraphenylethylene derivative 3 (TPE3) was synthesized and employed as the AIE-active probe, which can be aggregated on the uncoated amino-functionalized SiO2 NPs to form AIE-SiO2 NPs and emitted strong fluorescence. Negatively charged MnO2 nanosheets were employed as both positive charge protectors for amino-functionalized SiO2 NPs and recognition units for GSH. The presence of GSH could selectively reduce MnO2 nanosheets to Mn2+, thus releasing the amino-functionalized SiO2 NPs and exposure its positive charges. Accordingly, the TPE3 could be aggregated on the exposured amino-functionalized SiO2 NPs to form AIE-SiO2 NPs and emitted strong fluorescence. The proposed assay is simple, fast, low cost, and highly sensitive with a detection limit of 200nM for GSH. The assay was further applied in human serum samples for the detection of GSH with satisfactory results, demonstrating its promising application in practical biological samples.

Using sterculia lychnophora seeds as precursors for the first time, fluorescent carbon dots (CDs) were synthesized by simple hydrothermal treatment. The quantum yield of as-synthesized CDs was 6.9% by using quinine sulfate as the reference. The fluorescence of CDs could be effectively quenched by a MnO2 nanosheet based on fluorescence resonance energy transfer (FRET). Ascorbic acid (AA) could reduce MnO2 to Mn2+ and result in the destruction of the MnO2 nanosheets, which could induce the fluorescence recovery of the CDs. In particular, alkaline phosphatase (ALP) could bio-catalyze acid 2-phosphate (AAP) hydrolysis to AA. Here, an efficient fluorescence probe based on a CDs-MnO2 nanosheet for rapid and selective detection of ALP was reported for the first time. Excellent performance for the detection of ALP was observed with high sensitivity and a detection limit of 0.4U/L owing to the low background. The detection of ALP in human serum was conducted with satisfactory results, demonstrating its potential applications in clinical diagnosis.

This study demonstrates a novel and convenient ratiometric fluorescent method for the detection of alkaline phosphatase (ALP) activity. Amino-functionalized mesoporous silica nanoparticle-gold nanoclusters (MSN-AuNCs) nanocomposites were integrated with o-phenylenediamine (OPD) to form a ratiometric fluorescence nanoplatform. The presence of ALP induced the generation of quinoxaline (QX) derivative which called 3-(dihydroxyethyl)furo[3,4-b]quinoxaline-1-one (DFQ) with strong fluorescence emission at 450 nm, while the orange-red fluorescence of MSN-AuNCs at 580 nm was slightly quenched. Meanwhile, an obvious fluorescence color change from orange-red to purple and finally to blue can be observed by naked eyes with the increasing of ALP concentration. Therefore, employing the fluorescence emission of DFQ at 450 nm as the reporter signal and the fluorescence emission of MSN-AuNCs at 580 nm as a reference signal, a sensitive ratiometric detection method for ALP was developed. Quantitative detection of ALP activity in the linear range from 0.2 to 80 U/L with a detection limit of 0.1 U/L can be realized in this way, which endows the assay with high sensitivity enough for practical detection of ALP in human serum samples.

Glutathione (GSH) serves several vital biological functions and its abnormal levels are associated with many diseases. Simple and sensitive methods capable of detecting GSH are desired for better understanding the mechanism of diseases. In this work, a label-free MnO

Using sterculia lychnophora seeds as precursors for the first time, fluorescent carbon dots (CDs) were synthesized by simple hydrothermal treatment. The quantum yield of as-synthesized CDs was 6.9% by using quinine sulfate as the reference. The fluorescence of CDs could be effectively quenched by a MnO

The ultrasensitive monitoring of glucose with a fast and accurate method is significant in potential therapeutics and optimizes protein biosynthesis. Incorporation of enzyme into matrix is considered as promising candidates for constructing highly sensitive glucose-responsive systems. In this study, three-dimensional poly(acrylic acid) brushes-nanospherical silica (PAA-nano silica) with high amplification capability and stability were used to covalently immobilize bienzymes for cascade enzymatic catalysis. The major advantages of PAA-nano silica-bienzyme co-incorporation is that the enzymes are proximity distribution, and such close confinement both minimized the diffusion of intermediates among the enzymes in the consecutive reaction and improve the utilization efficiency of enzymes, thereby enhancing the overall reaction efficiency and specificity. Thus, this present bienzymatic biosensor shows robust signal amplification and ultrasensitivity of glucose-responsive properties with a detection limit of 0.04μM.

A stable zirconium (Ⅳ)-based metal organic frameworks (UIO-67) material possessing good chemical, thermal and water stability was synthesized and applied as a sorbent for the dispersive solid phase extraction (DSPE) of 8 plant growth regulators (PGRs) in fruit samples. Fluorescence labeling combined with high performance liquid chromatography fluorescence detection (HPLC-FLD), was used to quantify the target analytes. Characterization of the UIO-67 material was performed by X-ray diffraction(XRD) and scanning electron microscopy (SEM). The experimental parameters, such as amount of UIO-67, type and volume of eluting solvent, adsorption and desorption time, were optimized. Under the optimized conditions, good linearity was observed in the range of 10–1000 pmol/mL with R 2 >0.9989. The limits of detection and limits of quantification were in the range of 0.21–0.57 ng/mL and 0.81–1.91 ng/mL, respectively. The intra-day and inter-day precisions (based on the relative standard deviation, n =3) of the PGR derivatives were under 3.1% and 5.3% respectively and the accuracies of the method for the PGRs were in the range from 89.3% to 102.3%. The developed method was successfully applied to analyze PGRs residues in fruit samples. The proposed method is proved to be simple, environment-friendly and inexpensive and it is feasible to directly use UIO-67 as sorbent to extract targets by varying conditions.

Platinum nanoparticles (PtNPs) attached to glass slide surface was successfully prepared by using a simple in situ chemical reduction method. In this method, a approximately 10nm gold layer was first sputtered uniformly onto the glass slide surface, PtNPs could be grown directly on the gold layer by immersing the glass slide into the grown solution containing H(2)PtCl(4) and ascorbic acid. The gold layer sputtered uniformly serves as "seed" for the following growth of PtNPs and high dense of PtNP modified film can be prepared. Control experiment without the gold layer found no obvious formation of PtNPs indicating the importance of the "seed". The electrocatalytic effect of the PtNP film was investigated with the detection of hydrogen peroxide and for the fabrication of biosensors. Glucose oxidase was selected and directly electrodeposited onto the PtNPs modified surface. The resulting biosensor has a fast response time (10s) with wide linear range (5x10(-6) to 2x10(-2)). The fabrication method is simple, convenient and can be used for the mass fabrication of biosensors. The present preparation method of PtNPs modified film could be used for the preparation of other metal nanoparticle and find electrochemical applications as well as for optical uses.