(a) Fluorescence responses of the newly developed probe MNDA (10 µM) to various amino acids in the green channel (including GSH, Hcy, Cys, Ala, DTT, Gln, Gly, His, Lys, Met, Pha and Ser, 100 µM each; excitation: 450 nm, slit widths: 3 nm, 3 nm). (b) Gradient titrations of MNDA with GSH in HEPES buffer solution. (c) Fluorescence responses of MNDA (10 µM) to various amino acids in the blue channel (including GSH, Hcy, Cys, Ala, DTT, Gln, Gly, His, Lys, Met, Pha and Ser, 100 µM each; excitation: 350 nm, slit widths: 1.5 nm, 3 nm); (d) Comparison of the sensing abilities of probes toward Hcy (excitation: 350 nm, slit widths: 1.5 nm, 3 nm).