Immobilization Techniques for Aptamers on Gold Electrodes for the Electrochemical Detection of Proteins: A Review

Abstract

The development of reliable biosensing platforms plays a key role in the detection of proteins in clinically and environmentally derived samples for diagnostics, as well as for process monitoring in biotechnological productions. For this purpose, the biosensor has to be stable and reproducible, and highly sensitive to detect potentially extremely low concentrations and prevent the nonspecific binding of interfering compounds. In this review, we present an overview of recently published (2017–2019) immobilization techniques for aptamers on gold electrodes for the electrochemical detection of proteins. These include the direct immobilization of thiolated aptamers and the utilization of short linkers, streptavidin/biotin interaction, as well as DNA nanostructures and reduced graphene oxide as immobilization platforms. Applied strategies for signal amplification and the prevention of biofouling are additionally discussed, as they play a crucial role in the design of biosensors. While a wide variety of amplification strategies are already available, future investigations should aim to establish suitable antifouling strategies that are compatible with electrochemical measurements. The focus of our review lies on the detailed discussion of the underlying principles and the presentation of utilized chemical protocols in order to provide the reader with promising ideas and profound knowledge of the subject, as well as an update on recent discoveries and achievements.

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“…Additionally, backfilling with a short-chain thiol can fill the empty spots between probe molecules, encouraging the probe to orient uniformly and in an upright position. 32 This process can also displace any nonspecifically adsorbed molecules, including contaminants that might remain after cleaning.…”

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“…Finally, the solution was allowed to stand at room temperature for 5 min. Afterwards, 5 μL of aptamer solution was drop-casted onto the surface of the WE to immobilize the aptamer on the AuNPs via a self-assembled monolayer (SAM) ( Oberhaus et al 2020 ), which was spontaneously formed during incubation at 4 °C for 8 h. The aptamer-modified electrode was then gently rinsed with BB to remove non-bound aptamer. The Aptamer/AuNPs/SPCE was subsequently incubated with 1 mM of 6-mercapto-1-hexanol (MCH) + 10 mM PBS solution for 30 min at room temperature to displace the non-specific adsorption of the aptamers and to block the non-modified Au area to avoid pinhole formation.…”

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“…Ideally, bioreceptors are immobilized on the sensor in a stable, oriented, and reproducible way to enable a consistent sensor performance. Multiple linkers and various immobilization techniques for biosensors have been used in the past years: streptavidin–biotin interactions, electrodeposition, physisorption, and chemisorption (see, e.g., ref ( 111 )) are some of the examples. These immobilization techniques can provide dense and accessible monolayers of bioreceptors which are desired for more sensitive detection.…”