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We present a report on the electrochemical kinetics and sensing studies conducted on a flexible ITO-PET transducer, fabricated with a new nanocomposite of L-cysteine coated iron oxide nanoparticles (LCys@Fe3O4 NPs) and multi-wall carbon nanotubes (MWCNT), for the first time. Synthesized via the wet-chemical co-precipitation method, the LCys@Fe3O4 NPs exhibit a pure cubic phase. A nanocomposite of these LCys@Fe3O4 NPs are prepared via dispersion in chitosan (CS) solution along with MWCNT, and further drop-casted onto a low-cost, flexible ITO-PET sheet. The fabricated CS-MWCNT-LCys@Fe3O4/ITO-PET electrode shows a higher surface roughness, compared to either MWCNT or LCys@Fe3O4 modified electrode counterpart. The CS-MWCNT-LCys@Fe3O4 nanocomposite exhibits a twofold enhancement of the peak anodic voltammetric current, and a tenfold decrease in the charge transfer resistance, as compared to the LCys@Fe3O4 nanoparticles. Additionally, a mathematical model is devised to evaluate the kinetic parameters (ks, α & DFe(II)) of the redox species K4[Fe(CN)6]/K3[Fe(CN)6] on the CS-MWCNT-LCys@Fe3O4/ITO-PET surface, confirming a quasi-reversible electron transfer process. We couple this transducer with an immunosandwich format to facilitate rapid and ultrasensitive electrochemical measurement of protein biomarkers. Proof-of-concept is carried out by measuring the SARS-CoV-2 spike glycoprotein on the biofunctionalized Ab1/CS-MWCNT-LCys@Fe3O4/ITO-PET immunoelectrodes within a wide linear range (1 pg mL-1-1 μg mL-1). The immunoelectrode encompasses a limit of detection of 0.932 pg mL-1, and a sensitivity of 0.499 μA pg−1 mL cm−2. Thus, CS-MWCNT-LCys@Fe3O4 presents a new and excellent nanocomposite for biosensing application, while the Ab1/CS-MWCNT-LCys@Fe3O4/ITO-PET immunoelectrode can serve as an efficient, flexible, and cost-effective biosensing platform which can further be utilised to fabricate point-of-care biosensors. |
