Thiol-containing biomolecules, such as cysteine (Cys), homocysteine (Hcy), glutathione (GSH), play crucial roles in maintaining
biological systems. For example, elevated levels of Hcy have been implicated as an independent risk factor for tumor invasion and
metastasis. Being associated with a wide variety of cancer progressions, there is a significant interest in looking for the fluorescent detection
of such thiol species (Cys, Hcy, and GSH) in cancer cells. Various thiol-specific probes have been developed on the basis of different
strategies. This review focuses on recent contributions for the fluorescent or colorimetric sensors for thiol-containing amino acids,
with special emphasis on the design and application of novel fluorophores for detecting thiol-containing amino acids with higher sensitivity.