Highly Specific Detection of ONOO- Using SiQDs Synthesized from Oxidized Tripeptides

Next, we compared the optical properties of SiQDs synthesized from catechol (SiQDs-Cat) and melanin-like (SiQDs-(K/L-P)ox) precursors. As is evident from Figure 3a, SiQDs-(K/L-P)ox has a superior fluorescence intensity and a wider emission range when compared to SiQDs-Cat. Upon the addition of ONOO-, both (K/L-P)ox and SiQDs-(K/L-P)ox display obvious fluorescence quenching, while SiQDs-Cat remains unaffected. This indicates that SiQDs-(K/L-P)ox synthesized from oxidized tripeptides are highly specific for the detection of ONOO-. A PL intensity diagram of SiQDs-(K/L-P)ox excited by excitation light with wavelength range of 300-420 nm is shown in Figure S7, which demonstrates the excellent stability of the maximum emission peak of the SiQDs-(K/L-P)ox at 480 nm. The Zeta potential of SiQDs-(K/L-P)ox, as displayed in Figure 3b, is negative, which is different from (K/L-P)ox and SiQDs-Cat. This could be attributed to acidic group dissociation from L-Phe occurring on the surface of SiQDs-(K/L-P)ox. The electronegativity of the solution further indicates that the probe is more easily oxidized by ONOO-.