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Highlights • A reusable ratiometric fluorescent biosensor for Cys has been developed. • Cys in serum sample could be detected sensitively and selectively. • The sensing system could be reused time after time with excellent repeatability. • The ratiometric strategy could eliminate false positive and false negative results. • The sensing assay offers an effective "mix-then-test" way for Cys detection. Abstract Highly sensitive detection of cysteine is critical for early warning and diagnosis of cysteine-associated diseases. For the first time, herein, a reusable and ratiometric fluorescent biosensor with simple operation was developed for sensitive and rapid detection of Cys on the basis of configuration transformation of guanine-rich DNA (G-DNA). The sensing system is quite simple and consisted of G-DNA and Ag+ with NMM (N-methylmesoporphyrin IX) and terbium ion (Tb3+) as the two fluorescence probes. The Ag+ assists the G-DNA to keep its random single-strand structure (ssG-DNA), generating a distinct fluorescence of Tb3+ and a faint fluorescence of NMM. The analyte of cysteine (Cys) can strongly coordinate with Ag+, thus, the ssG-DNA is transferred into G-quadruplex (G4) configuration. The fluorescence of NMM is then outstandingly augmented, while the fluorescence of Tb3+ is significantly depressed. With the fluorescent intensity ratio of F NMM /F Tb as readout signal, the detection limit of the developed ratiometric fluorescent biosensor reaches as low as 4.1 nM, confirming the excellent sensitivity. After completing the Cys detection, Ag+ is further added to disrupt the G-quadruplex into random single-strand G-DNA, which restores the sensing system into the initial state. The reversible configuration change between G-quadruplex and single-stand G-DNA endows the as-developed sensing system with charming reusability for specific detection of Cys. The developed sensing assay is cost-effective and operated in an enzyme-free and label-free condition, providing a straightforward and effective "mix-then-test" strategy to meet the requirement for practical application in disease monitoring and diagnosis. [ABSTRACT FROM AUTHOR]

For the first time, a target (pathogenic bacterial gene)-induced logically reversible logic gate was constructed as an intelligent biosensor, which has one-to-one mapping functionality and can rapidly distinguish all information of the two targets, the presence of any target and the absence (or presence) of both of the targets, from the unique output signal pattern. [ABSTRACT FROM AUTHOR]

Since HCV and HIV share a common transmission path, high sensitive detection of HIV and HCV gene is of significant importance to improve diagnosis accuracy and cure rate at early stage for HIV virus-infected patients. In our investigation, a novel nanozyme-based bio-barcode fluorescence amplified assay is successfully developed for simultaneous detection of HIV and HCV DNAs with excellent sensitivity in an enzyme-free and label-free condition. Here, bimetallic nanoparticles, PtAu NPs , present outstanding peroxidase-like activity and act as barcode to catalyze oxidation of nonfluorescent substrate of amplex red (AR) into fluorescent resorufin generating stable and sensitive "Turn On" fluorescent output signal, which is for the first time to be integrated with bio-barcode strategy for fluorescence detection DNA. Furthermore, the provided strategy presents excellent specificity and can distinguish single-base mismatched mutant from target DNA. What interesting is that cascaded INHIBIT-OR logic gate is integrated with biosensors for the first time to distinguish individual target DNA from each other under logic function control, which presents great application in development of rapid and intelligent detection. [ABSTRACT FROM AUTHOR]