A practical point-of-care sandwich enzyme-linked immunosorbent assay (ELISA) microchip remains elusive. A concave area on the undersurface of a microchannel was formed by nanosecond pulse laser ablation and its utility for a microfluidic system based on capillary-driven flow supporting such a microchip was determined. Ablation using a 193 nm wavelength, 1.76 J∙cm−2 UV laser modified the surface of poly(methyl methacrylate), providing a surface amenable for antibody immobilization. A concave microchannel 10 µm deep and 260 µm in diameter allowed both successful antibody microdeposition and complete reagent replacement required for a practical ELISA microchip. Quantitative analysis of concentrations of procollagen-type I carboxy-terminal propeptide (PICP) using this microchannel showed a linear relationship at PICP concentrations between 0–600 ng·ml−1, which is adequate for clinical estimation of PICP concentrations in the blood.