The spectrophotometric properties of porphyrins are altered upon interaction with nucleic acids, proteins, and amino acids. TPPS immobilized as a monolayer onto a cellulose film exhibits an absorbance peak in the Soret region. The interaction of the porphyrin with the follwing amino acids arginine, glycine, histidine and serine induces blue shifts in the Soret that enables us to quantify and identify these amino acids in the nM scale. The interaction of PCP with the following porphyrins and metaloporphyrins TPPS, Zn-TPPS, TPPS1, C1TPP, C4TPP, Cu-C4TPP in solution induces a red shift in the...