Optical immunosensor for quantifying C-telopeptide fragments of type II collagen as an osteoarthritis biomarker in urine

Abstract

A fluorescence-based biosensor for measuring the quantity of C-telopeptide fragments of type II collagen (CTX-II) was developed as an osteoarthritis biomarker in urine. During osteoarthritis progression, joint components such as cartilage collagen are degraded by collagenase-protease and secreted into the serum as CTX-II. To detect CTX-II in urine (uCTX-II) having structural heterogeneity, conventional sandwich format assay does not provide sufficient accuracy. As an alternative, a competitive immunoassay was developed for the quantification of uCTX-II, which uses antibody-conjugated fluoro-microbeads to generate an optical signal. After preparing the biosensing surface, the uCTX-II sample and antibody-optical probe conjugates were reacted on the PEG4-EKGPDP exposed biosensing surface. The optical probes competed with the uCTX-II in the sample for binding to the immobilized PEG4-EKGPDP. This assay was able to detect uCTX-II concentrations between 200 ng/mmol (corrected value vs. creatinine) and 1,400 ng/mmol, encompassing the clinical detection ranges required for osteoarthritis diagnosis. The competitive immunoassay developed for uCTX-II detection was rapid and exhibited good correlation with conventional ELISA methods. This novel competition assay is a promising tool for the diagnosis and monitoring of osteoarthritis using urine samples.