Functionalization of a PC-TIR Biosensor for Label-Free cTnI Antigen Detection

Damaged myocardial cells release specific biomarkers, such as cardiac troponin I (cTnI) antigen, into the bloodstream. Sensitive detection of the cardiac biomarkers is a vital component for early detection of myocardial infarctions and drug-induced cardiotoxicity screenings. In this study, a compact standalone biosensing system was developed based on a Photonic-Crystal structure in a Total-Internal-Reflection (PC-TIR) configuration for label-free detection of cardiac biomarkers. To functionalize the PC-TIR sensor, (3-aminopropyl)triethoxysilane (APTES), carboxymethyl-dextran (CM-dextran), and 3-(triethoxysilyl)propylsuccinic anhydride (TESPSA) were immobilized on the sensing surface. These biochemical pathways were then tested to investigate and compare their binding affinity towards cTnI antibody and, ultimately, their ability to detect cTnI antigen. Additionally, cTnI antigen detection was investigated utilizing UV immobilization of Amino- and PolyT-modified aptamers on an APTES, (3-mercaptopropyl)trimethoxysilane (MPTMS) modified, and unmodified sensor surfaces. The cTnI antibody, Amino-modified aptamer, and Poly-T-modified aptamer running buffer's ionic strength and pH were then optimized to improve the binding affinity between antibodies/aptamers and their respective functionalized surfaces. After proper functionalization with either cTnI antibody or Amino- and Poly-T modified aptamers, the bioassays were evaluated for their respected capabilities to detect for cTnI antigen.