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.

Due to their unique properties, polythiophene and other conductive polymers have become the subject of intensive research and are promising substrate materials for innovative and trendsetting applications. To this day, boron trifluoride diethyl etherate (BFEE) is the preferred solvent for the electropolymerization of thiophene, although it does not allow for reproducible film qualities due to its decomposition under ambient conditions. We therefore want to equip the reader with a starter kit for the electropolymerization of high-quality polythiophene films from stable solvents and a simple yet efficient method to remove the deposited films from the electrodes for their reuse. By drying the working solution prior to its utilization, and by adding a Lewis acid catalyst, films that display enhanced electron transfer and a smooth surface topography can be obtained, which can both be beneficial for the analytic performance of a subsequently built biosensor.

Biosensors offer exciting opportunities for various clinical applications and constitute a rapidly growing research branch due to new generations of bioreceptors, transducers, and biomaterials with versatile characteristics, such as conductive polymers. Polythiophene is a prominent example of conducting polymers and convinces with excellent conductivity and stability—and is yet barely used for the construction of biosensors. We want to address the fundamental lack of straightforward fabrication procedures for bioreceptor immobilization platforms based on polythiophene. We investigate the literature-known monomer 3-thiopheneacetic acid and present our newly developed method for electrochemical coupling of the linker p-aminobenzoic acid to deposited polythiophene films. Aminated bioreceptors can subsequently be immobilized via EDC/NHS click chemistry. Films were electropolymerized and modified by chronopotentiometry, characterized by electrochemical impedance spectroscopy, surface-enhanced Raman spectroscopy, as well as energy-dispersive X-ray spectroscopy. Both of the presented methods allow for the fabrication of functionalized polythiophene thin films of high conductivity and good reproducibility while convincing with their ease in synthesis.