Peroxidase mimicking nanozyme catalyzed colorimetric immunosensor for detection of osteoporosis biomarker CTX-1

The present study introduces a colorimetric immunosensor for the detection of bone turnover biomarker C-terminal telopeptide of type I collagen (CTX-1), which is one of the prominent biomarkers in osteoporotic conditions. Elevated CTX-1 level increases the fracture risk to approximately 2-folds as compared to normal bone mineral density (BMD) level. This sensor is based on peroxidase-like activity of silver nanoparticles which have been derived from kitchen waste, using natural light from sun. After successful synthesis and careful characterisation of AgNPs, detection biochemistry was developed using 2,2-azino-bis −3-ethylbenzothiazoline-6-sulphonic acid (ABTS), which acts as a chromogenic substrate for peroxidase enzyme; AgNPs being demonstrating peroxidase like activity. AgNPs catalyses the oxidation of ABTS to for blue-green radical cation (ABTS •+ ), the reaction kinetics of which gets inhibited in presence of CTX-1, producing a measurable colorimetric response. The sensor showed a concentration dependent decrease in oxidized ABTS absorbance over a CTX-1 range of 1–100 ng/mL, with a limit of detection of 1.03 ng/mL with standard solutions and 1.54 ng /mL, in commercial human serum.The response is quantified by spectrophotometric analysis via redox-based signal change. The use of CTX-1 specific antibodies makes this immunosensor highly selective.