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Based on the controlled aggregation of quantum dots (QDs), a valid, reliable, and label-free fluorescence turn-on strategy is established for the detection of alkaline phosphatase activity. The aqueous solution of anionic QDs exhibits intense fluorescence. However, the addition of cationic polymer (poly-1) significantly quenched the fluorescence of the QDs via their induced aggregation. While short 3'-phosphorylated DNA (DNA-P) could not be extended by terminal deoxynucleotidyl transferase (TdT) and therefore, fluorescence of the QDs was recovered negligibly. The effective elimination of phosphate group of DNA-P in the presence of alkaline phosphatase (ALP) produced 3'-OH termini and the resulting DNA could be sufficiently extended by TdT. The presence of greater binding strength between the elongated DNA and poly-1 is very crucial to compete with the poly-1/QDs aggregates and release the QDs. Turned-on fluorescence emission is observed due to the efficient release of the QDs. A novel strategy for alkaline phosphatase detection is therefore established. Our method is quite sensitive and selective, as low as 0.1 mU/mL ALP can be easily detected., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Abstract Proteases, as one of the most significant kind of digestive enzymes, are closely related to a variety of physiological processes and diseases. Herein, a black phosphorus nanosheets (BPs) based sensitive fluorometric method for protease detection and inhibitor screening is proposed. The aqueous solution of perylene probe (probe 1) displays a strong fluorescence. BPs, as novel discovered two-dimensional (2D) materials, can adsorb probe 1 through electrostatic interactions, which causes fluorescence quenching of probe 1. Histone can control the interactions between the perylene probe and BPs, which can be further regulated by the introduction of a protease. Thus, the protease activity can be monitored by detecting the fluorescence intensity changes of probe 1. The method is label free, sensitive and selective. As low as 1 ng/mL trypsin can be easily detected. Graphical abstract fx1 Highlights • Black phosphorus nanosheets were used as the quencher for a fluorometric assay. • A label-free method for protease detection and inhibitor screening. • Histone controlled interactions between a perylene probe and black phosphorus nanosheets were used for signal transduction. • No covalent modifications were needed, and the assay is simple, sensitive and selective. [ABSTRACT FROM AUTHOR]

In this work, a fluorescence turn-on method for copper(II) detection is reported. A molecular beacon (MB) was designed as a template. Cu 2+ was reduced to Cu + in the presence of a reductant (ascorbic acid). Two short single-stranded oligonucleotides one was labeled with a 5′-alkyne and the other with 3′-azide group, proceeded a template-dependent chemical ligation through the Cu(I)-catalyzed azide-alkyne cycloaddition. The newly generated click-ligated long chain oligonucleotide, which was complementary to the MB, opened the MB hairpin structure and resulted in a turn on fluorescence. The increase in fluorescence intensity is directly proportional to the amount of Cu 2+ added to the assay solution. The present assay is quite sensitive and allows the detection of 2 nM Cu 2+ . The described assay also exhibits high selectivity over other metal ions. [ABSTRACT FROM AUTHOR]

The development of sensitive and efficient analytical methods for multiple biomarkers is crucial for cancer screening at early stage. MicroRNAs (miRNAs) are a kind of biomarkers with diagnostic potential for cancer. However, the ultrasensitive and logical analysis of multiple miRNAs with simple operation still faces some challenges. Herein, a photonic crystal (PC)-enhanced fluorescence biosensor with logic gate operation based on one-pot cascade amplification DNA circuit was developed for enzyme-free and ultrasensitive analysis of two cancer-related miRNAs. The fluorescence biosensor was performed by biochemical recognition amplification module (BCRAM) and physical enhancement module (PEM) to achieve logical and sensitive detection. In the BCRAM, one-pot cascade amplification circuit consisted of the upstream parallel entropy-driven circuit (EDC) and the downstream shared catalytic hairpin assembly (CHA). The input of target miRNA would trigger each corresponding EDC, and the parallel EDCs released the same R strand for triggering subsequent CHA; thus, the OR logic gate was obtained with minimization of design and operation. In the PEM, photonic crystal (PC) array was prepared easily for specifically enhancing the fluorescence output from BCRAM by the optical modulation capabilities; meanwhile, the high-throughput signal readout was achieved by microplate analyzer. Benefiting from the integrated advantages of two modules, the proposed biosensor achieved ultrasensitive detection of two miRNAs with easy logic gate operation, obtaining the LODs of 8.6 fM and 6.7 fM under isothermal and enzyme-free conditions. Hence, the biosensor has the advantages of high sensitivity, easy operation, multiplex and high-throughput analysis, showing great potential for cancer screening at early stage. [Display omitted] • An ultrasensitive fluorescence biosensor integrated cascade DNA circuit and PC. • OR logic gate with minimized design and operation was used for two-miRNA analysis. • The whole cascade DNA circuit was one-pot, enzyme-free and isothermal. • High-throughput signal readout was achieved with PC array and microplate analyzer. [ABSTRACT FROM AUTHOR]

The development of a simple and effective method for the highly sensitive and selective discrimination of proteins is a subject of enormous interest. Herein, we report the construction of a novel fluorescence detection method based on a perylene probe for the highly efficient discrimination of multiple proteins. Single-stranded DNA (ssDNA) could induce aggregation of the perylene probe which caused quenching of probe fluorescence. After the addition of a protein, the protein could interact with the ssDNA-probe assembly complex with "turn-on" or further "turn-off" fluorescence response. A sensor array was designed based on the above phenomena which could realize the successful discrimination of proteins with 100% accuracy of cross validation. Nine representative proteins were successfully recognized. Moreover, it was observed that a protein could induce characteristic effect on the DNA-probe assembly with varying pH of assay buffer. Thus, different proteins showed unique fluorescence response towards assay buffers having different pH values. The assay buffer pH was then utilized as a sensing channel. Based on Linear Discriminant Analysis (LDA) nine proteins were successfully discriminated at the nanomolar concentration with 100% accuracy of cross validation. Furthermore, the sensor array also demonstrated differentiation of the nine proteins regardless of their concentration. The developed sensor array could also detect the proteins with great precision in human urine sample at a quite low concentration, which suggests its practical applicability for analysis of biological fluids. Fluorescence sensor array based on DNA induced PeryProbe self-assembly. Image 1 • A fluorescence sensor array is developed for the discrimination of proteins. • Negatively charged ssDNA induced self-assembly of the perylene probe. • The array was based on the different interactions between the protein and the ssDNA-PeryProbe assembly complex. • The array could discriminate proteins regardless of their concentration. • The array was applied to discriminate proteins in human urine samples. [ABSTRACT FROM AUTHOR]