Abstract
We report the microfabrication and characterization of gold microband electrodes on silicon using standard microfabrication methods, i.e., lithography and etching techniques. A two-step electrodeposition process was carried out using the on-chip platinum reference and gold counter electrodes, thus incorporating glucose oxidase onto a platinum-modified, gold microband electrode with an o-phenylenediamine and ß-cyclodextrin mixture. The as-fabricated electrodes were studied using optical microscopy, scanning electron microscopy, and atomic force microscopy. The two-step electrodeposition process was conducted in low sample volumes (50 µL) of both solutions required for biosensor construction. Cyclic voltammetry and electrochemical impedance spectroscopy were utilised for electrochemical characterization at each stage of the deposition process. The enzymatic-based microband biosensor demonstrated a linear response to glucose from 2.5–15 mM, using both linear sweep voltammetry and chronoamperometric measurements in buffer-based solutions. The biosensor performance was examined in 30 µL volumes of fetal bovine serum. Whilst a reduction in the sensor sensitivity was evident within 100% serum samples (compared to buffer media), the sensor demonstrated linear glucose detection with increasing glucose concentrations (5–17 mM).
Highlights
The fabrication of silicon-based electrodes is valuable for the development of miniaturized electrochemical biosensors, as various electrode designs, dimensions, and configurations can be fabricated on a compact electroanalytical device [1,2]
Whilst studies have explored both mediator-free glucose detection and the use of o-PD modified microelectrodes towards glucose sensing, here, we demonstrate the amperometric deposition of a mixture of ß-cyclodextrin, o-phenylenediamine (o-PD), and glucose oxidase on to an ultramicroband electrode using the on-chip Pt reference (RE) and Au counter (CE) electrodes
The single band sensors demonstrated excellent intra-chip reproducibility, as a RSD of less than 0.1% was determined between both the steady state oxidation and reduction currents for n = 5 WE’s in 1 mM FcCOOH, at a scan rate of 50 mVs−1. This indicated that the on-chip RE and CE were effective for electrochemical measurements
Summary
The fabrication of silicon-based electrodes is valuable for the development of miniaturized electrochemical biosensors, as various electrode designs, dimensions, and configurations can be fabricated on a compact electroanalytical device [1,2]. We describe a single gold band electrode that is 45 μm in length, 1 μm in width, and has a height of ~80–90 nm. This specific type of electrode is commonly referred to as an ultramicroelectrode, as it has at least one dimension that is less than a number of micrometers [11,12]. In the case of glucose detection, one potential advantage of using ultra-microelectrodes is that they benefit from radial mass transport, and the sensors developed are not limited by local oxygen diffusion at the electrode surface, unlike their larger macro-electrode analogues [21]. The use of o-PD has been widely investigated for both the immobilization of glucose oxidase on to electrodes [23,24,25]
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