Sensitive and Site-Selective Determination of Phosphorylated Peptides with a Ratiometric Photoelectrochemical Strategy

Currently, the sensitive detection of phosphopeptides is greatly significant and necessary in the fields of medicinal and bioanalytical chemistry, and the main implementation is through a mass spectrometric (MS) method. However, MS methods are very complicated and expensive and are not capable of site-selective determination of phosphorylated amino acid residues. The exploration of a facile and reliable technique with high reproducibility that can both sensitively discriminate the normal and phosphorylated peptides and, more importantly, distinguish the different phosphorylated sites in peptides is highly desirable. Herein, we propose a ratiometric photoelectrochemical (PEC) strategy based on the totally opposite PEC response of phosphopeptides on rutile and anatase TiO₂-based photoelectrodes, which allows us to sensitively distinguish the nonphosphopeptides and phosphopeptides, to detect the concentrations of the phosphopeptides, and to recognize the phosphorylated residues in a site-selective sensing model. The ratiometric PEC strategy significantly minimizes the operation process, simplifies instrumentation, and has promising and wide applications in biology, analytical chemistry, and clinical diagnostics.