Electrochemical sensing methods can provide reliable, fast, reagentless, sensitive and accurate detection of a range of analytes, and may be a more attractive approach than techniques such as mass spectrometry and chromatography detection, which often require additional sample preparation. Electrochemical biosensors are widely used for the detection of small and large biological molecules such as enzymes, neurotransmitters, and cancer biomarkers with high efficiency and the potential to be used as clinical point-of-care devices. Electrochemical, aptamer-based (E-AB) sensors, an emerging class of biosensors with high specificity, have been used to detect and quantify a wide range of biological and chemical analytes. E-AB sensors utilize a conformational change of an aptamer, induced by the presence of a target analyte, that alters the electron transfer efficiency between a redox molecule (e.g. methylene blue) appended to the distal end of the aptamer and the electrode surface. Currently, the few probes of this type that have been fabricated on the microscale required electrodeposited gold (Au) nanostructures to enhance the signal and stability of the sensor. However, the effects of Au morphology and size on sensor performance have not been studied. Here, to optimize the performance of E-AB sensors on the macro and microscales, electrodeposition was used to control the Au surface morphology. E-AB sensors were fabricated on electrodeposited surfaces, using an aptamer specific to adenosine triphosphate (ATP). While the increase in surface area led to an enhanced current response from the sensor, due to a greater number of redox labeled aptamers on the electrode surface, the aptamer probe packing densities were lower for more surfaces with more deposited gold. Moreover, the signal change (between no target molecule present and addition of target, ATP) also decreased with the more deposited surfaces. Scanning electron microscopy, surface roughness measurements, and electrochemical characterization were used to assess the morphology of electrodeposited electrode surfaces used for fabricating sensors, and it is expected that the resultant sensors would be useful for disposable macroscale biosensors and microscale electrodes that could be used for spatially resolved measurements.

Controlling electrodeposited gold morphology for the optimization of electrochemical, aptamer-based sensor performance

ACS Fall 2021

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