Carbon nanofiber-based electrochemical biosensing of miRNA: Deeper insights through modelling and experiments

The development of ultrasensitive biosensing techniques for miRNA detection can be achieved through the integration of improved functional materials such as the use of carbon-based nanomaterials. Electrochemical biosensors are particularly promising platforms because of their high sensitivity, rapid response, and potential for miniaturization. Literature reports use of such advance materials towards the ultrasensitive detection; however, the discoveries are predominantly based on experimental trial-and-error. There are no reports on the structure-function relationship of these novel materials aiding to enhanced sensitivity. In this context, we explored carbon nanofiber as a nanomaterial to modify our electrode surface, resulting in atto-molar sensitivity, explained through the mechanistic understanding of the transport phenomenon and electrochemistry resulting in the reaction on such surfaces. We modelled the system physics in detail using COMSOL Multiphysics software, and presented a parametric estimation delineating the effect of important parameters such as exchange current density and electrical double layer capacitance. Our system achieved a limit of detection of 9.42 aM, a limit of quantification of 31.41 aM, and a sensitivity of 1.63 × 10¹⁶ μA/(mM·cm²) in buffer solution for the detection of miRNA-21. This study presents two significant breakthroughs over current literature: (a) an improved sensing utilizing our CNF-based electrodes (b) a comprehensive mechanistic understanding of the charge transfer event in these devices. The aforementioned protocol will facilitate improved design of such devices while simultaneously minimising the time and resources required for establishing the experimental systems relevant to each use case.