Spectral response of BV2+ towards various spiked amino acids in human plasma upon irradiation. Absorption spectra of solutions of BV2+ (20 mM) in human blood plasma and 0.5 M Tris buffer (pH 7.0) spiked with 1.5 µM Hcy (dashed line) and 500 µM amino acids (solid lines = L-Ala, Arg, Gln, Met, Ser, Thr & Phe). Plasma (10% v/v) was added to an argon-saturated solution of viologen, amino acids and buffer and irradiated for 15 min using a Reptisun™ lamp.