Structure-switching electrochemical aptasensors use a redox reporter-labelled aptamer in a self-assembled monolayer formed on a gold electrode, to detect specific target molecules. Arrays of individually addressable microelectrodes enable the simultaneous detection of multiple analytes. However, the selective modification of individual electrodes within a microelectrode array poses a challenge for fabricating biosensing surfaces such as electrochemical aptasensors. Since gold electrodes are typically placed into a solution containing thiols for adsorption to the electrode surface, the close spacing of the gold microelectrodes within the array, means it is difficult to separately incubate each electrode in the desired aptamer solution. In this work, a method was developed to produce a symmetrically arranged microelectrode array of tunable electrode number, size and spacing. The individual electrode surfaces were selectively modified using controlled adsorption and desorption of different aptamers to enable the simultaneous detection of multiple analytes. The use of multiple aptasensors with cross-selectivity, in an array, allowed improved specificity of the method. The sizescale of the array will allow localized measurements of specific analytes, although increasing the microscopic surface area is required to accommodate a greater number of probes adsorbed on the surface to maximize the sensor signal. This was achieved using electrodeposition of gold, using a pulsed waveform to maintain a small electrode footprint. The gold morphology of deposited electrodes was shown to affect the formation of the sensor monolayer, which manifested in changes to the probe number density, magnitude of signal change in response to analyte and apparent binding affinity.

Electrochemical aptasensor arrays for selective detection of analytes

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