Cysteine (Cys) is well-known to be an important biothiol and related to many diseases. However, the in situ trapping of endogenous Cys is still handicapped by a lack of straightforward methods combined with long-wavelength emission and high-performance response. In this work, we described the rational design strategy of cyanine-based near-infrared (NIR) probes for the rapid detection of mitochondrial Cys in living cells and mice. We focus on how to improve the response rate via regulating the electron density of the recognition units in probes. The obtained three probes all displayed remarkable fluorescence enhancement at 780 nm. From screening the obtained probes, it was found that the probe Cy-S-diOMe with electron-donating recognition unit displayed the fastest response rate, the lowest detection limit, and the highest signal-to-noise ratio. More importantly, Cy-S-diOMe was successfully applied to monitor Cys in tumor-bearing mice (within merely 5 min). This paradigm by modulation of the response rate in the cyanine dyes provides a promising methodology for the design of high-performance cyanine-based NIR probes.
Keywords: cyanine; cysteine; fluorescent probe; in vivo imaging; near infrared; rapid response.