A new fluorescent turn-on probe for the rapid optical sensing of thiols has been designed and synthesized. The probe displays high on/off signal ratios and high selectivity towards thiols. The potential of the probe as a biosensor for thiols was demonstrated by imaging of thiols in living cells.

An ICT-based fluorescent turn-on probe for hydrogen sulfide with high selectivity has been designed and synthesized. It exhibits up to 62-fold switch-on response toward H₂S at given concentrations and can detect H₂S in living cells with high sensitivity.

Unveiling the detailed roles of glutathione (GSH) in chemoresistance necessitates a reliable assay for its detection in intact live specimens. Herein, by taking advantage of the susceptibility of electron-poor C_sp²–S_sufinyl bond to GSH nucleophilic attack, we developed a naphthalimide–sulfoxide based fluorogenic probe (Na-8) applicable for tracking endogenous GSH fluctuation in live cells. Na-8 features a high degree of sensitivity towards GSH as demonstrated by its utmost 2200-fold fluorogenic response. As a proof of concept, Na-8 has been applied to image GSH in liver cancer HepG2 cells with the normal L02 cell counterparts serving as a control, and elevated GSH level was observed in HepG2 in contrast to L02. Further experiments showed that this elevated GSH level was involved in doxorubicin-resistance but not in cisplatin-resistance. Noteworthy, monitoring GSH change in HepG2 and L02 cells in response to doxorubicin treatment revealed that while normal cells showed a burst of GSH in adaption to doxorubicin treatment, no significant change was detected in HepG2 cells, suggesting that HepG2 cells have been preconditioned by their intrinsic oxidative stress which confers drug-resistance. Given the observed sensitivity and spatiotemporal resolution, Na-8 should hold promise for future study on the detailed roles of GSH in drug-resistance.

A novel fluorescent sensor, 1,4-bis(2-(quinolin-8-yloxy)acetyl)piperazine (DQS), utilizing an 8-hydroxyquinoline scaffold was designed and synthesized. DQS shows good water solubility, high selectivity and excellent sensitivity for detecting Sn⁴⁺ and PO₄ ³⁻. It exhibits a reversible on-off type fluorescence response with alternate addition of tin(IV) and the phosphate anion under aqueous conditions.