Novel cascade reaction-based fluorescent cyanine chemosensor for cysteine detection and bioimaging in living system

A ratiometric fluorescent probe with dual near infrared emission for in vivo ratio imaging of cysteine

Accurately detecting cysteine (Cys) in vivo is crucial for diagnosing Cys-related diseases. A novel ratiometric fluorescent probe featuring dual near-infrared emission is developed in this study for the in vivo ratio imaging of Cys. The probe comprises a hemicyanine organic small-molecule dye (HCy-CYS) with specific Cys recognition capabilities covalently coupled with carbon dots (CDs) synthesized using glutathione (GSH) as the carbon source (GCDs), forming a unique composite nanofluorescent probe (GCDs@CYS). The probe undergoes a specific reaction with acrylate upon the addition of Cys, converting HCy-CYS to HCy-OH. Consequently, the GCD fluorescence intensity at 685 nm gradually decreases, whereas that of HCy-OH at 720 nm progressively increases, yielding a ratiometric fluorescence signal. Notably, both emission wavelengths of the probe exceed 650 nm, thereby effectively mitigating the interference from background signals during cellular and in vivo imaging. Furthermore, the probe demonstrates high specificity for Cys, enabling its differentiation from homocysteine and GSH. The Cys concentration and fluorescence ratiometric intensity exhibit a strong linear correlation at 10-150 μM with a detection limit of 0.95 μM. These results indicate that the ratiometric fluorescent probe can serve as a valuable tool for monitoring Cys-related physiological or pathological processes.

An aqueous mediated ultrasensitive facile probe incorporated with acrylate moiety to monitor cysteine in food samples and live cells

A colorimetric probe TQA ((E)-4-(((8-(sec-butoxy)-2,3,6,7-tetrahydro-1H,5H-pyrido[3,2,1-ij]quinolin-9-yl)methylene)amino)benzylacrylate) possessing greater potent towards the sensing of cysteine was successfully synthesized and characterized. The aqueous soluble probe TQA detects Cys based on "ON-OFF" effect with excellent absorbance and emission properties. The probe TQA detects Cys up to its ultra-low level concentration of 1.5 nM and also quantifies the Cys up to 5.05 nM with the quicker response time of 140 s (2.3 min). In addition, the color change produced by the probe TQA on integrated with Cys was also identified easily via paper strip, cotton wool buds and RGB color picker app in smart mobiles. Further, the admirable selectivity and sensitivity of the probe TQA towards Cys extends its utility towards food samples and imaging of live HeLa cells.

Novel lysosome-targeted fluorescent molecular rotors based on a cyanine-like modular system and their application in living cells

Two novel fluorescence molecular rotors DpIn and NaIn were designed and synthesized involving of indolium units linked with meta-diphenol or ortha-naphthalenediol moiety, respectively. They underwent intramolecular charge transfer to form a cyanine-like modular system at a physiological pH. In glycerol aqueous solutions, the probe DpIn exhibited NIR strong emission (3-fold) at ca. 700 nm, while the probe NaIn displayed a turn-on emission (8-fold) with a larger Stokes shift (⊿λ ≈ 97 nm). The HeLa cell imaging experiments indicated probe DpIn and NaIn both exhibited excellent selectivity for staining intracellular lysosomes instead of mitochondria. ¹H NMR spectra revealed that more electrons were accumulated around benzene ring of indolium groups, which could be the evidence for its basic character leading to the lysosomes targeted staining. Furthermore, the probe NaIn proved to be an ideal lysosome-targeting tracer for monitor the changes of viscosity caused by stimuli in living cells.