3D Nanoscale Carbon Structure based Electrochemical Biosensors for Myoglobin and Glucose Detection

Abstract

Global prevalence of the diabetes mellitus reaches up to 8.5 % of the overall population. Diabetic patients are threatened by the risk of complex disease of diabetes and also increased risk of cardiovascular death. Abnormal glucose level in blood increases the risk of cardiovascular disease and cardiovascular death is the number one death cause among the diabetic patients. Acute myocardial infarction(AMI) is one of the main causes of the death by cardiovascular disease. In this thesis, we developed electrochemical biosensors for health monitoring in diabetics regarding myoglobin (cardiac biomarker for AMI detection) level in blood and glucose level in sweat. 3D nanoscale carbon structure based electrochemical biosensors are developed for the sensitive and selective detection of myoglobin and glucose. Low cost, reproducible wafer-level batch fabrication of 3D carbon structures was achieved by Carbon-MEMS process. In Carbon-MEMS, 3D photoresist structure was first patterned with controlled geometry using UV-lithography process. Then, pyrolysis process decomposed the patterned photoresist structure into conductive 3D carbon structure. During the decomposition, dramatic volume shrinkage (up to 90%) of the structure takes place and submicron scale carbon structures could be fabricated. We reported the development of an electrochemical redox cycling-based immunosensor using sandwich 3D triple electrode system. The triple electrodes consisting of a suspended carbon mesh and substrate-bound carbon interdigitated array (IDA) nanoelectrodes fabricated using C-MEMS. To complete an immunosensor a specific electrode was modified via the selective electrochemical reduction of aryl diazonium salts, and thus monoclonal antibody (mAb) could be immobilized on only suspended mesh electrode and the IDA electrodes were employed for the efficient redox-cycling of redox species (PAP/PQI). The developed redox cycling-based immunosensor with 3D triple electrode system successfully detected as low as ~0.4 pg/mL cMyo in human serum. And, the microchannel integration facilitated 8-fold better low limit of detection (LOD) as compare to bulk, preventing diffusion of PAP to the bulk solution. 3D porous carbon electrode with sponge-like edge structure was used for the development of the gold nanoparticle based non-enzymatic glucose sensor. Gold particle with small size and high density gives higher catalytic effect and it is required for the non-enzymatic glucose detection. Carbon electrode with sponge-like edge nanostructure enabled formation of small and dense gold nanoparticles (AuNPs) during thermal dewetting of thin gold film. Non-enzymatic glucose sensor fabricated with the nanostructure induced thin film dewetting method could show high sensitivity (4451.8 μA mM-1 cm-2 and low detection limit (0.35 μM). In sweat, there are interferences like ascorbic acid, uric acid, and etc. And, noise current signals from the interferences disturb the measurement of glucose. Here in, we proposed a novel selective detection method that fundamentally removes the interfering species itself. With microchannel integration of the glucose sensor, a simple electrochemical filtration technique based on the depletion effect in a confined solution was integrated into the electrochemical sensor to remove the interferences. Two types, in-situ and ex-situ, of electrochemical filtration methods were developed in this research. The microchannel integrated enzymatic glucose sensor showed 3-fold better sensitivity and low limit of detection (LOD) as compare to bulk, by reducing the interference effect.