ABSTRACT:We have developed a near-IR reversible fluorescent probe containing an organoselenium functional group that can be used for the highly sensitive and selective monitoring of peroxynitrite oxidation and reduction events under physiological conditions. The probe effectively avoids the influence of autofluorescence in biological systems and gave positive results when tested in both aqueous solution and living cells. Real-time images of cellular peroxynitrite were successfully acquired. P eroxynitrite (ONOO À ) performs as a strong oxidizing agent in physiological and pathological processes. 1À3 In vivo, abnormally high concentrations of ONOO À are formed from the fast reaction between nitric oxide (NO) and superoxide anion (O 2 À ), which requires no enzymatic catalysis. 4 The peroxynitrite anion is relatively stable, but the acid form (ONOOH) rapidly decays to nitrate. Although the half-life of ONOOH is ∼1 s at pH 7.40, 5 the oxidative species contributes to signal transduction, homeostasis regulation, and oxidative damage, which forms a unique biological oxidationÀreduction cycle indicating human health and disease.6 Therefore, the development of reversible detection technology for peroxynitrite would have important biomedical significance. In comparison with other technologies, fluorescence microscopy provides greater sensitivity, less invasiveness, and more convenience.7 Especially the use of near-IR (NIR) light (650À900 nm) allows deep penetration into tissues and efficaciously avoids the influence of bioautofluorescence. However, there exists a major obstacle to the design of novel fluorescent probes for ONOO À , namely, the nitro group, which is considered to be a strong quencher for fluorophores.3 To date, only a few fluorescent probes for ONOO À detection have been reported. 8 Thus, we anticipate widespread interest in a redoxreversible NIR fluorescent probe, which would exhibit much more value for visualizing cycles of redox signaling and stress caused by peroxynitrite.9 Here we report a redox-responsive NIR fluorescent probe for continuous monitoring of ONOO À . ONOO À is modulated by cellular antioxidant defense systems, 1,10 in which selenium (Se) plays an important role as the active site of the antioxidant enzyme glutathione peroxidase (GPx).11 GPx can catalyze the reduction of ONOO À by glutathione (GSH) via a unique ping-pong mechanism.12 Taking the advantage of this, we mimicked the catalytic cycle and developed an NIR fluorescent probe containing an organoselenium moiety that can be used for reversible peroxynitrite detection.As an overall strategy, cyanine (Cy), an NIR fluorescent dye with a high extinction coefficient, 13 was selected as a signal transducer, while 4-(phenylselenyl)aniline (PSe) was selected as a modulator because it can respond sensitively to ONOO À . 11,14Following the ping-pong mechanism, 12 we designed and synthesized a new NIR reversible fluorescent probe (Cy-PSe) for detection of ONOO À in living cells through a fast photoinduced electron transfer (PET) process. ...

In comparison with other biological detection technologies, fluorescence bioimaging technology has become a powerful supporting tool for intracellular detection, and can provide attractive facilities for investigating physiological and pathological processes of interest with high spatial and temporal resolution, less invasiveness, and a rapid response. Due to the versatile roles of hydrogen sulfide (H 2 S) in cellular signal transduction and intracellular redox status regulation, fluorescent probes for the detection of this third signalling gasotransmitter have rapidly increased in number in recent years. These probes can offer powerful means to investigate the physiological actions of H 2 S in its native environments without disturbing its endogenous distribution. In this feature article, we address the synthesis and design strategies for the development of fluorescent probes for H 2 S based on the reaction type between H 2 S and the probes. Moreover, we also highlight fluorescent probes for other reactive sulfur species, such as sulfane sulfurs and SO 2 derivatives.