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Highlights • Cancer-associated telomerase activity can be detected with QDs-SA biosensor. • The detection limit of telomerase can be down to 13 Hela cells and 9 A549 cells. • The QDs-SA biosensor allows intracellular telomerase tracking and imaging. • Inhibitor screening can be realized in vitro and in vivo. Abstract In order to overcome the shortcomings of traditional methods for telomerase activity detection of time-consuming and susceptibility to interferences in cell extracts, here, we develop a semiconductor quantum dots-streptavidin conjugates (QDs-SA)-based biosensor for sensitive detection of telomerase activity. In the absence of telomerase, the aggregation and thus the fluorescence quenching of QDs-SA can be observed in buffer solution due to charge shielding effect. In the presence of telomerase and biotin-dATP, QDs-SA will bind to telomerase elongation products due to the high affinity between the biotin and streptavidin, protecting the QDs-SA from aggregation and retaining their strong fluorescence. This sensor exhibited good fluorescence responses toward telomerase activity from HeLa cells in the range of 40–1000 cells with a detection limit of 13 cells or A549 cells within the linear range of 20–500 cells with a detection limit of 9 cells. Furthermore, the sensor can be used to efficiently monitor the evolution of telomerase activity in living cells, demonstrating great potential in tumor diagnosis and inhibitor drug screening. [ABSTRACT FROM AUTHOR]

A novel fluorescent probe, 2, 4-cyclohexanedione-1-propyl-pyrene (TAR), has been synthesized to research thioredoxin (Trx) disulfenylation and visualize the activity of Trx in cells. The turn-on fluorescence change was induced by combining the vicinal dithiol proteins with the spatially sensitive fluorescent signal of the pyrene excimer which emitted at 480 nm. Trx activity can be detected at nanomolar concentrations. Trx preference of TAR in vitro and in vivo was proved by fluorometric and confocal microscopic experiments. In addition, it could realize dynamic tracking of protein disulfenylation in situ with minimal disturbance to disulfenylated proteins and less perturbation with cellular function. We herein report the first turn-on fluorescent sensor for the selective detection of proximally disulfenylated protein sites, suitable for application in both aqueous solutions and in cells. [ABSTRACT FROM AUTHOR]

The instant and on-site detection of trace aqueous nitrite ions still remains a challenge for environmental monitoring and protection. In this work, we synthesized water-soluble striking fluorescent Cu nanoclusters (Cu NCs) by a green, simple, one-pot and stabilizer-free chemical reduction method. The fluorescence (FL) of the obtained Cu NCs can be selectively and efficiently quenched by the nitrite ions through the oxidation of Cu (0) atoms to Cu (I) in the core of Cu NCs. Under optimal conditions, two excellent linear relationships between the FL quenching degree of the Cu NCs and the concentrations of nitrite ions in the range of 0.0125–125 μM and 125–5000 μM with a low detection limit of 3.6 nM were obtained. More importantly, the portable paper-based sensor has been explored for visual detection of trace nitrite ions in aqueous solution by the appearance of different degrees of blue FL under a UV lamp. The very simple and effective strategy reported here should facilitate the development of portable and reliable FL chemosensors for nitrite ions in pollution control. [ABSTRACT FROM AUTHOR]