Biosensing of Cardiac Biomarkers Using Single Polyaniline Nanowires

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

Materialization of single multicomposite nanowire: entrapment of ZnO nanoparticles in polyaniline nanowire

We present materialization of single multicomposite nanowire (SMNW)-entrapped ZnO nanoparticles (NPs) via an electrochemical growth method, which is a newly developed fabrication method to grow a single nanowire between a pair of pre-patterned electrodes. Entrapment of ZnO NPs was controlled via different conditions of SMNW fabrication such as an applied potential and mixture ratio of NPs and aniline solution. The controlled concentration of ZnO NP results in changes in the physical properties of the SMNWs, as shown in transmission electron microscopy images. Furthermore, the electrical conductivity and elasticity of SMNWs show improvement over those of pure polyaniline nanowire. The new nano-multicomposite material showed synergistic effects on mechanical and electrical properties, with logarithmical change and saturation increasing ZnO NP concentration

Detection of Cardiac Biomarkers Using Single Polyaniline Nanowire-Based Conductometric Biosensors

The detection of myoglobin (Myo), cardiac troponin I (cTnI), creatine kinase-MB (CK-MB), and b-type natriuretic peptide (BNP) plays a vital role in diagnosing cardiovascular diseases. Here we present single site-specific polyaniline (PANI) nanowire biosensors that can detect cardiac biomarkers such as Myo, cTnI, CK-MB, and BNP with ultra-high sensitivity and good specificity. Using single PANI nanowire-based biosensors integrated with microfluidic channels, very low concentrations of Myo (100 pg/mL), cTnI (250 fg/mL), CK-MB (150 fg/mL), and BNP (50 fg/mL) were detected. The single PANI nanowire-based biosensors displayed linear sensing profiles for concentrations ranging from hundreds (fg/mL) to tens (ng/mL). In addition, devices showed a fast (few minutes) response satisfying respective reference conditions for Myo, cTnI, CK-MB, and BNP diagnosis of heart failure and for determining the stage of the disease. This single PANI nanowire-based biosensor demonstrated superior biosensing reliability with the feasibility of label free detection and improved processing cost efficiency due to good biocompatibility of PANI to monoclonal antibodies (mAbs). Therefore, this development of single PANI nanowire-based biosensors can be applied to other biosensors for cancer or other diseases

Highly Flexible Touch Screen Panel Fabricated with Silver Nanowire Crossing Electrodes and Transparent Bridges

A capacitive-type touch screen panel (TSP) composed of silver nanowire (AgNW) crossing electrodes and transparent bridge structures was fabricated on a polycarbonate film The transparent bridge structure was formed with a stack of Al-doped ZnO (AZO) electrodes and SU-8 insulator. The stable and robust continuity of the bridge electrode over the bridge insulator was achieved by making the side-wall slope of the bridge insulator low and depositing the conformal AZO film with atomic layer deposition. With an extended exposure time of photolithography, the lower part of the SU-8 layer around the region uncovered by the photomask can be exposed enough to the UV light scattered from the substrate. This leads to the low side-wall slope of the bridge insulator. The fabricated TSP sample showed a large capacitance change of 22.71% between with and without touching. Our work supplies the technological clue for ensuring long-term reliability to the highly flexible and transparent TSP made by using conventional fabrication processesclose