<p>Biological thiols (biothiols), such as cysteine (Cys), glutathione (GSH), and homocysteine (Hcy) are essential for maintaining life activities, and their abnormal concentrations are closely associated with various diseases. We developed a dual-mode sensor using synergistically passivated CsPbBr₃ quantum dots (QDs). By introducing the ligand sodium dodecyl sulfate (SDS) into CsPbBr₃ QDs and combining the specific recognition ability of 5,5’-dithiobis-(2-nitrobenzoic acid) (DTNB) toward thiol groups (–SH), a dual-mode detection system was constructed. In the presence of biological thiols, the –SH group reacts with DTNB to generate 2-nitro-5-thiobenzoic acid (TNB). A discernible color change of the solution from light green to yellow, along with fluorescence quenching of the CsPbBr₃@SDS QDs, was observed. This is attributed to the inner-filter effect (IFE), which is initiated by the overlap of the TNB absorption spectrum with the excitation spectrum of the QDs. This enables the dual-mode detection of target analytes via fluorescence and colorimetric signals. The sensor demonstrates high sensitivity toward Cys, GSH, and Hcy, with detection limits as low as 2.63 µM, 3.09 µM, and 2.15 µM, respectively, along with a wide linear range. The sensor also exhibits excellent selectivity and anti-interference capabilities. This work provides an effective strategy for biothiol detection, showing promising application prospects in biomedical diagnosis and environmental monitoring.</p> Graphical abstract <p></p>