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Telomerase, as a potential biomarker for early cancer diagnostics and therapies, has attracted considerable interests concerning its detection and monitoring. Herein, we develop a novel method for sensitive detection of telomerase activity by designing a gold nanoparticles/graphene oxide (AuNPs/GO) probe. The AuNPs were functionalized with a telomerase substrate (TS) primer and a 6-carboxy-fluorescein (FAM)-modified complementary DNA (P1). In the absence of telomerase, P1 exists in the random-coiled conformation, and the fluorescence resonance energy transfer (FRET) from FAM to AuNPs and GO results in efficient fluorescence quenching. In the presence of telomerase, the multiple hybridization between TS extension products and P1 leads to the conformation transition of P1 from single-stranded DNA to double-stranded rigid structure, and thus the FRET process can be prevented with the efficient fluorescence recovery. The metal enhanced fluorescence (MEF) effect between FAM and AuNPs can further effectively enhance the fluorescence of FAM, and thus the sensitivity and specificity of telomerase detection can be remarkably improved. It is worth mentioning that the proposed strategy does not need to design complex hairpin structure and allows the measurement of telomerase activity in three crude cell extracts equivalent to 7 HeLa cells, 8 A549 cells and 8 L929 cells in 1 h. In addition, the present sensing platform can be applied to inhibitor screening, in situ telomerase imaging, and intracellular drug delivery. Image 1 • The metal enhanced fluorescence effect can be regulated to generate significant fluorescence enhancement. • Weak background fluorescence can be realized via efficient fluorescence resonance energy transfer. • Telomerase activity down to 7 HeLa cells can be sensitively detected. • The method facilitates cellular imaging, inhibitor screening and drug delivery. [ABSTRACT FROM AUTHOR]

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]

Determination of hydrogen peroxide (H 2 O 2 ) with high sensitivity and selectivity in living cells is a challenge for evaluating the diverse roles of H 2 O 2 in the physiological and pathological processes. In this work, we present novel surface enhanced Raman scattering (SERS) nanosensors, 4-carboxyphenylboronic acid (4-CA) modified gold nanoparticles (Au NPs/4-CA), for sensing H 2 O 2 in living cells. The nanosensors are based on that the H 2 O 2 -triggered oxidation reaction with the arylboronate on Au NPs would liberate the phenol, thus causing changes of the SERS spectra of the nanosensors. The results show the nanosensors feature higher selectivity for H 2 O 2 over other reactive oxygen species, abundant competing cellular thiols and biologically relevant species, as well as excellent sensitivity with a low detection limit of 80 nM, which fulfills the requirements for detection of H 2 O 2 in a biological system. In addition, the SERS nanosensors exhibit long term stability against time and pH, and high biocompatibility. More importantly, the presented nanosensors can be successfully used for monitoring changes of H 2 O 2 levels within living biological samples upon oxidative stress, which opens up new opportunities to study its cellular biochemistry. [ABSTRACT FROM AUTHOR]