A novel fluorescent probe for selective labeling of histidine

A novel water-soluble fluorescent probe, 1-(2,3-epoxypropoxy)-2-phenylazo-8-acetylamino-naphthalene-3,6-disulfonic acid sodium salt (EPANS), was designed and synthesized by reacting epichlorohydrin with azophloxine, and its properties for labeling of histidine were studied. In alkaline media, EPANS reacted selectively with histidine rather than with other amino acids, causing a large decrease in fluorescence intensity and thereby allowing a selective detection of histidine without a tedious separation. The linear range was 4–500 (mu)M with a detection limit of 1 (mu)M (S/N=3). The proposed method has been successfully used to determine histidine in human serum. The obtained results were in good agreement with those given by using histidine–nickel complex adsorptive voltammetry.