Electrochemical Sensors for Flow-Enhanced Immunoassays and Flow Monitoring of Porous Materials

Abstract

Microfluidics enables a miniaturization of laboratory-scale biochemical analysis into a single chip. It has been actively developed and utilized in various biomedical diagnostic devices. Especially, lab-on-a-disc (LOD) and paper microfluidic system can serve as excellent candidates for point-of-care testing (POCT) because of several advantages including relatively simple fluid transfer mechanism, portable size of the device, fast analysis time, reduced cost, automated analysis steps and low consumption of test samples and reagents. In this thesis, electrochemical detection method has been implemented in two kinds of diagnostic devices. First, lab-on-a-disc integrated with screen-printed carbon electrodes (SPCEs) was developed for electrochemical detection of protein biomarkers, C-reactive protein. Compared to conventional optical detection, the electrochemical detection could provide enhanced sensitivity as well as significant cost reduction because it is not necessary to use optical grade plastic materials for the fabrication of the disc. In addition, we have developed electrochemical sensors for the measurement of the local fluid velocity based upon the fact that the electrochemical signal is proportional to the flow rate. As a proof of the concept experiment, we have used the electrochemical sensors for real time monitoring of the flow through porous materials, which can provide a practical tool to quantify the fluid velocity on the paper-based microfluidics. Based on chronoamperometric signals measurement using SPCEs, fluid transfer phenomena through various kinds of porous materials, geometries, absorption pads, and flow modifiers were evaluated. In conclusion, we have developed a cost-effective SPCEs-based electrochemical detection method and utilized not only for the immunoassays fully integrated on a disc but also to characterize fluid transfer behavior through the porous materials. The SPCEs can be utilized as a cost-effective sensor not only for the highly sensitive electrochemical detection for bioassays but also for the flow measurements in porous materials.