A MALDI-MS sensing chip prepared by non-covalent assembly for quantitation of acid phosphatase

A novel sensing chip was designed for MALDI-MS quantitation of acid phosphatase (ACP). The ACP sensing chip was constructed through non-covalent interaction of streptavidin and biotin for the assembly of biotinylated peptide substrate on biotinylated polyethylene-glycol (PEG) modified indium-tin oxide (ITO) slide. In the presence of ACP, the peptide substrate was dephosphorylated under acidic condition to generate a new mass signal. The quantitative assay of ACP was achieved with the mass signal ratio of product to the sum of product and left peptide substrate. Under optimal detection conditions, the ratio was linearly correlated with the concentration of ACP in the range of 0.05-12 g/L with a detection limit (LOD) of 0.04 g/L. The designed ACP sensing chip has been used to analyze ACP in complex clinical samples, which exhibited high selectivity, good repeatability, and admirably anti-interference ability. This work further demonstrates the concept of MS sensing and the application of MALDI-MS in quantitative analysis, and provides a convenient method for the quantitation of proteases in clinical diagnosis.