Development of Printable Graphene Electrochemical Biosensor for Environmental Monitoring and Medical Applications

Algal bloom is a type of harmful water pollution, which is mainly caused by the cyanobacteria or dinoflagellate that releases a variety of algal toxins into a water source. Among them, microcystins are often detected, of which microcystin-leucine-arginine (MC-LR) is known as one of the most toxic variants that has received a great amount of attention due to its serious consequences after ingestion such as irreversible organ damage or even death. Human cytomegalovirus (HCMV) is a type of herpes virus that can widely spread via mucous contact, resulting in many severe symptoms or even death especially for infants, pregnant women and immunocompromised patients if there is no timely diagnosis. Following these reasons, there is an urgent need to develop a commercially viable and sensitive monitoring system to reach a rapid identification on water quality or human health. This work mainly focuses on the development of vertically aligned graphene (VAG) electrodes through the novel use of flexographic printing and photonic annealing techniques for highly sensitive detection of biological targets using non-Faradaic electrochemical impedance spectroscopy (EIS). For the detection of MC-LR, the biosensor achieved an low limit of detection (LOD) of 1.2 ng/L via baseline method. In the baseline method, measurement was first performed using PBS. After that, measurement was then performed on antigen solution drop-casted on the biosensor. The biosensing response between PBS and antigen acquired at a specific frequency was dependent on the target concentration. The biosensor also exhibited excellent selectivity with high percentage of recovery (i.e., 91.8 %) and stability (i.e., 108.8 % and 99.4 % after one and three weeks, respectively). Moreover, similar good performance (i.e., 98.4%) was observed in tap water spiked with the antigen. As for the detection of CMV pp65-antigen, biosensing results showed a good linearity when tested on the control group (i.e., 0 ng/mL) up to 38,500 ng/mL of the antigen concentration using the same baseline measurement. The VAG biosensor showed a dynamic range of between 3.85 and 38,500 ng/mL for the detection of HCMV pp65-antigen, which matches with the clinically relevant range of 102 ~ 106 genomes/mL based on measurement performed on viral loaded urine samples using PCR technique. Measurements on the target concentration using the biosensor were also performed using a non-baseline method. In this method, only the antigen solution was used throughout the measurement, where the biosensing result was determined by the difference in the response recorded at the start of measurement and after a certain incubation duration at a specific frequency. In particular, the change in phase showed a strong correlation against the target concentration. The biosensing response for the control group (i.e., 0.38°±0.191°) up to 38,500 ng/mL (i.e., 2.26°±0.543°) antigen concentration was highly comparable to those (i.e., 0.16°±0.0854° for the control group and 2.21°±0.105° for 38,500 ng/mL) derived from the baseline method, implying the strong feasibility of the non-baseline testing.