A ratiometric fluorescence platform based on WS2 QDs/CoOOH nanosheet system for α-glucosidase activity detection.

In this study, we have constructed a ratiometric fluorescence sensor for sensitive sensing of α-glucosidase activity based on WS2 QDs/ CoOOH nanosheet system. In this system, as an oxidase-imimicking nanomaterial, CoOOH nanosheet could convert o-phenylenediamine into 2,3-diaminophenazine (DAP), which had a high fluorescence emission at 575 nm. The DAP subsequently could quench the fluorescence of WS2 QDs via the inner filter effect (IFE). L-Ascorbic acid-2-O-α-D-glucopyranose could be hydrolyzed by α-glucosidase to yield ascorbic acid. CoOOH nanosheet can be converted to Co2+ ions by ascorbic acid, leading to the fluorescence decrease of DAP and the fluorescence recovery of WS2 QDs. Therefore, a novel ratio fluorescence sensing strategy was established for α-glucosidase detection based on WS2 QDs/CoOOH nanosheet system. This WS2 QDs/CoOOH nanosheet system has a low detection limit of 0.009 U/mL for α-Glu assay. The proposed strategy succeeded in detecting α-Glu in human serum samples.

A bond energy transfer based difunctional fluorescent sensor for Cys and bisulfite.

In living cells, cysteine (Cys) and bisulfite are involved in many important physiological processes. Their unbalance in vivo would lead to multiple diseases. So, it is vital to develop difuntional sensor for Cys and bisulfite. As we known, cysteine could metabolized into bisulfite by the metabolic processes of cysteine in the animal level. Therefore, we designed and synthesized a mitochondria-targeted long-wavelength ratio fluorescence sensor Z2 for Cys and bisulfite simultaneous detection. Z2 exhibitted excellent selectivity, good anti-interference, fast response and low detection limit. The sensor exhibited obviously two channels fluorescence response for Cys and bisulfite orderly. Z2 is widely used for imaging Cys and bisulfite in MCF-7 cells, zebrafish, and mice, and successfully imaging Cys metabolism in these livings. We hope this bifunctional ratio fluorescence sensor Z2 will be a useful tool to monitor Cys and SO2 levels in living systems.

A FRET-based ratiometric fluorescent probe to detect cysteine metabolism in mitochondria.

As an important biothiol in living cells, cysteine is closely related to oxidative damage in living organisms. Sulfite from cysteine metabolism in living cells plays a crucial role in maintaining homeostasis in an organism, and the unbalance of sulfite in vivo would lead to multiple diseases. Thus the development of a new fluorescent probe for cysteine metabolism is needed urgently in mitochondria which are the main place of cysteine metabolism. Herein we construct a novel targeting mitochondria fluorescent probe CP-K based on the FRET mechanism to visualize sulfite in living MCF-7 cells. Probe CP-K displays a large Stokes shift of 150 nm, a low detection limit (26.3 nM) and "naked eye" detection after the addition of HSO3-. Importantly, it is appropriate for imaging the endogenous sulfite from cysteine metabolism in living cells.