In this work, graphene interdigitated electrodes were fabricated using roll-to-roll flexographic printing of ball-milled graphene nanoplatelet (GNP)/ethyl cellulose (EC) ink. Photonic annealing on flexographic printed graphene-ethyl cellulose composite was used to partially remove the polymeric binder (i.e. EC) and produce vertically-aligned graphene (VAG) structures, which maximized the specific surface area of graphene for ultra-sensitive detection of algal toxin (i.e. MC-LR) in drinking water. A spray coating technique was employed to functionalize the biosensor in order to preserve the VAG structures. Prior to immobilization of MC-LR antibodies on the biosensor, a uniform coverage of APTES, which acted as an insulating self-assembly monolayer (SAM) for nonfaradaic electrochemical impedance spectroscopy (EIS) biosensors, was spray-coated onto the VAG. The effectiveness of the spray-coated APTES was studied using energy-dispersive x-ray spectroscopy (EDX) and cyclic voltammetry (CV) techniques. The change in phase from the non-faradic EIS measurement was obtained at a frequency of 167 mHz. At this frequency, an optimal response from the binding of antibody-antigen was observed at the VAG biosensors, which were subsequently tested at different MC-LR concentrations between 0.001 and 10 µg/L in PBS. The results showed a linear correlation established between the change in phase and logarithm of MC-LR concentration. The biosensor exhibited excellent sensitivity of 0.46 degree per decade and limit of detection (LoD) of 1.2 ng/L with good reproducibility, selectivity and stability. Finally, the VAG biosensor was validated using local tap water samples (Swansea, UK) and experienced minimal matrix effects from other factors, such as metal ions, in the water. Such low-cost, label-free, easy to use and ultra-sensitive VAG biosensor is ideal for large-scale early screening of contaminations in drinking water. The key results have been presented in three conferences and workshops:
• Invited presentation at UK-India Newton-Bhabha Fund RSC Researcher Links Workshop, IIT Bombay, Mumbai, India, 18th to 21st November 2019.
• Invited presentation at Xinghai Youth Scholar Forum, Dalian University of Technology, Dalian, China, 15th-17th May 2019.
• Oral Presentation at NANO.IL.2018 Jerusalem, Israel, 9th-11th October 2018.
Key research outcomes have also been published and submitted in two refereed journal papers:
• L, Wang, W. Zhang*, S. Samavat, D. Deganello, K. S. Teng, Vertically-aligned graphene biosensor prepared by photonic annealing for ultra-sensitive algal toxins detection in drinking water, Biosensor and Bioelectronics, submitted, 2020.
• W. Zhang*, M. B. Dixon, C. Saint, K. S. Teng, H. Furumai, Electrochemical biosensing of algal toxins in water: The current state-of-art, ACS Sensors, 2018, 3, 1233-1245.
