Solid-state optical detection of amino acids

The spectrophotometric properties of porphyrins are altered upon interaction with nucleic acids, proteins, and amino acids. Meso-tetra (4-sulphonatophenyl) porphyrin (TPPS) immobilized as a monolayer onto a cellulose film exhibits an absorbance peak in the Soret region at 421 nm. The interaction of the porphyrin with arginine, glycine, histidine and serine induces blue shifts in the Soret spectrum with absorbance losses at 422, 427, 427, and 421/427 nm, respectively, and the appearance of new peaks at 410/415, 412, 414, and 412 nm, respectively. The intensity of the Soret spectral change is proportional to the log of amino acid concentration. The detection limit with immobilized porphyrin for the above amino acids is 30, 20, 30 and 60 nM, respectively. These results suggest the possibility to develop a solid-state optically based selective and sensitive sensor of different l-amino acids.