The low specificity of the prostate-specific antigen (PSA) for early detection of prostate cancer (PCa) is a major issue worldwide. To overcome this problem, we developed a novel diagnostic biomarker, S2,3PSA%. PSA is a 34 kDa glycoprotein, which includes 8% of carbohydrates. The target structure of this assay system is sialic acid α2,3galactose residue of N-glycan on PSA. We developed a quantitative assay system using micro-Total Analysis Systems (μTAS method) based on micro-capillary electrophoresis. The μTAS system can utilize affinity-based separation involving noncovalent interaction between the immunocomplex of S2,3PSA and Maackia amurensis lectin to simultaneously determine concentrations of free PSA and S2,3PSA. Based on the results with clinical trial, S2,3PSA% was approved by the Japanese government as a diagnostic tool for PCa on Aug 22nd 2022 followed by health-insurance coverage on Feb 1st 2024.