Biosensing of Cardiac Biomarkers Using Single Polyaniline Nanowires

Abstract

In this thesis, we explore innovative methods of fabricating single polymer nanowires and applying the fabricated single polymer nanowires for biosensors. The fabrication of single polymer nanowire was carried out via electrochemical deposition growth method, which deposits ionized molecules in a pre-patterned nanochannel between two Au electrodes and forms a nanowire. For biosensing application, we employ polyaniline (PANI) in this research since it has advantages of biocompatibility, easy synthesis, and broad range of electrical conductivity. The single PANI nanowires-based biosensor show high sensitivity and good sensing reliability due to the high surface to volume ratio and single nanowires. Using the fabricated single PANI nanowires, the biosensors were developed to detect cardiac biomarkers such as myoglobin (Myo), cardiac troponin I (cTnI), creatine kinase-MB (CK-MB), and B-type natriuretic peptide (BNP). The single PANI nanowires are functionalized by surface immobilization method that was developed in our laboratory using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and N-Hydroxysuccinimde (NHS) to attach monoclonal antibodies (mAbs) of biomarkers without pre-chemical or physical treatments. Lastly, microfluidic devices including channels and solution infusion/withdrawal system were integrated on the biosensor in order to develop an all-in-one biosensor. Our single PANI nanowire-based biosensor is unique in terms of the functionalization on specific area; the mAbs are immobilized on the only surface of PANI nanowires because PANI has superior biocompatibility to mAbs unlike SiO2 layer or Au electrodes. This advantage reduces functionalization steps comparing to inorganic nanowire biosensors and frees the interfered signals from non-nanowire areas. In addition, the microfluidic channel helps achieving stable electrical signals, high sensitivity, safe sample handling, and minimal damage of nanowire. The integrated single PANI nanowire biosensors with microfluidic devices detect very low concentrations of Myo (100 pg/mL), cTnI (250 fg/mL), CK-MB (150 fg/mL), and BNP (50 fg/mL) with good specificity. The remarkable specificity value in cardiac biomarker sensing is over 106 fold, that the specificity value is defined as the ratio of [the highest concentration of non-specific protein showing ignorable or non-response signal] to [the lowest concentration of specific protein showing significant signal change], in the test of bovine serum albumin (BSA) or other cardiac markers. The single PANI nanowire biosensors have shown linear sensing profiles along different concentration from hundreds fg/mL to tens ng/mL depending on the mAbs of the specific biomarkers, and exhibit fast response in a few minutes satisfying reference values of Myo, cTnI, CK-MB, and BNP to diagnose heart failure and determine the patient’s stage of disease