Glutathione (GSH) is an important biological thiol, it performs significant biological functions such as serving an antioxidant which protect cells from oxidative stress by trapping free radicals which damage DNA and RNA. It is known that abnormal plasma levels of GSH have been linked to various human diseases. Therefore, the rapid, sensitive and highly selective detection of GSH is of great importance for investigating its functions in diseases diagnosis. Interestingly, we found in cetyl trimethylammonium bromide (CTAB) medium, the resorufin-based probe shows an extremely fast, highly selective response to GSH. The result indicates that this dye can be employed to detect GSH in biological samples such as human plasma. Cysteine (Cys) is another important biological thiol which is involved in a variety of significant cellur functions, including protein synthesis, detoxication, and metabolic process, etc. Abnormal levels of Cys are related to many diseases, such as slowed growth, Alzheimer's disease and cardiovascular disease. Thus, the detection and quantification of Cys in physiological media is of great importance. In this thesis, I am going to present two organic fluorescent probes (Resorufin-based probe and SNF probe) for the detection and quantification of Cys. In addition, we prove that they can directly quantify Cys in human plasma. The chemical mechanisms involved in the detection of Cys are discussed.