A systematic study of the influence of nanoelectrode dimensions on electrode performance and the implications for electroanalysis and sensing

Abstract

Micron resolution photolithography has been employed to make microsquare nanoband edge electrode (MNEE) arrays with reproducible and systematic control of the crucial dimensional parameters, including array element size and spacing and nanoelectrode thickness. The response of these arrays, which can be reproducibly fabricated on a commercial scale, is first established. The resulting characteristics (including high signal and signal-to-noise, low limit of detection, insensitivity to external convection and fast, steady-state, reproducible and quantitative response) make such nanoband electrode arrays of real interest as enhanced electroanalytical devices. In particular, the nanoelectrode response is presented and analysed as a function of nanometre scale electrode dimension, to assess the impact and relative contributions of previously postulated nanodimensional effects on the resulting response. This work suggests a significant contribution of migration at the band edges to mass transfer, which affects the resulting electroanalytical response even at ionic strengths as large as 0.7 mol dm(-3) and for electrodes as wide as 50 nm. For 5 nm nanobands, additional nanoeffects, which are thought to arise from the fact that the size of the redox species is comparable to the band width, are also observed to attenuate the observed current. The fundamental insight this gives into electrode performance is discussed along with the consequent impact on using such electrodes of nanometre dimension.

Impedimetric measurement of DNA–DNA hybridisation using microelectrodes with different radii for detection of methicillin resistant Staphylococcus aureus (MRSA)

“…It is reassuring and satisfying that these photolithographically fabricated microelectrodes showed the expected response prior to chemical modification and mecA detection experiments. Reductions in current observed immediately upon reversing the bias can be attributed to parasitic capacitances from microfabricated structures 26 . Figure 2B presents a microscope image of an r = 25 µm electrode (diameter = 50 µm) and shows a platinum disc defined by the silicon nitride insulating layer.…”

Wafer level characterisation of microelectrodes for electrochemical sensing applications

“…Under the presented conditions, the current is mass transport controlled by the diffusion of analyte to the electrode and reaches a steady state current (i L ). This current can be quantified using [13], [14],…”

Functionalised microscale nanoband edge electrode (MNEE) arrays: the systematic quantitative study of hydrogels grown on nanoelectrode biosensor arrays for enhanced sensing in biological media

“…The MNEE array design, fabrication procedures and geometries are detailed elsewhere 12,13 and shown below (Fig. 1).…”

“…This indicates increased gelator density, and is consistent with the previously predicted and observed enhanced currents for microsquare versus microdisc electrodes, due to enhanced square corner diffusion and reaction. 13,15 It is interesting that SEM images taken at t ¼ 5 s also indicate such enhanced xerogel corner density (Fig. S2 †).…”

“…Note that Table S1 in the ESI † contains the values for the fits of these data to the appropriate limiting case for the general equivalent circuit (inset). Also note that this is an extension of the established MNEE equivalent circuit, 13 with an additional Warburg element to account for within hydrogel diffusion. All fits give relatively low fit values (with c 2 < 0.156).…”