Evaluation of a New CA15-3 Protein Assay Method: Optical Protein-Chip System for Clinical Application

Carbohydrate antigen 15-3 (CA15-3) is frequently measured as a breast cancer marker test. Here we describe a novel type of optical biosensor system, the optical protein chip (OPC), to detect CA15-3 in serum.The complex formed by interaction between an antibody molecule and its corresponding antigen can be detected on a silicon substrate by an optical sensor, as described in previous reports (1)(2). For processing and modification of the silicon substrate surface, silicon wafers were cut into ∼2 × 0.7 cm rectangles and made hydrophilic by immersion in an acidic peroxide solution (300 mL/L H2O2–980 mL/L H2SO4; 1:3 by volume) and light shaking in a shaker for 30 min. The solution not only removed contaminants from the silicon surface but also increased the number of silanol groups on the surface. The hydrophilic surfaces were rinsed in distilled water 3 times and in absolute ethanol 3 times, then incubated in a mixture of 3-aminopropyltriethoxysilane and ethanol (1:15 by volume) and shaken lightly in a shaker for 2 h. The liquid was then removed, and the silicon wafers were rinsed in absolute ethanol 3 times and in phosphate-buffered saline (PBS) buffer 3 times. The wafers were then placed in a mixture of glutaraldehyde and PBS (1:10 by volume), shaken lightly in a shaker for 1 h, and finally, washed in PBS buffer 3 times and left in a beaker with PBS buffer until use. Through the reaction of glutaraldehyde with 3-aminopropyltriethoxysilane, Fc regions of the antibody molecules were covalently immobilized on the chip surfaces.Protein chip preparation and detection included the following steps: (a) CA15-3-specific monoclonal antibody (Biodezign) was concentrated to 0.1 g/L, and then 20 μL of CA15-3 solution …