Understanding and controlling complex modified electrochemical interfaces using novel measurements and model systems

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The pandemic has highlighted the many unmet, or partially met, needs in society and in healthcare. The availability of effective, simple, accurate and sensitive bio-sensing capacities was realized as a critical part of the strategy for dealing with the pandemic and ensuing healthcare challenge going forward and for future challenges. Biosensors developed using electrochemical detection and measurement form an important part of the portable sensor ecosystem. They require sophisticated modification of the electrode surface so as to specifically detect the analyte of interest in complex media. Challenges in preparing these sensors for commercialization are many, but inevitably involve the modification and stability of the electrode surface, the quality of the surface modification and the characteristics of the underlying substrate. Understanding the interfacial characteristics at the molecular level while under measurement conditions (e.g., in buffer or in-situ) is required, though only a few techniques exist and more are needed. Surface analysis while in buffer is difficult and requires many complimentary approaches to achieve an unbiased result. Insight into the conditions of the surface-based probe or sensor transducer when in buffer, before or after binding the target is important for tailoring the design and surface engineering for the specific analytical need. Developing new in-situ surface analysis methods for characterizing real sensors will advance sensor development and commercialization. This research programme uses our unique in-situ fluorescence microscopy spectroelectrochemical methodology to study modified electrode surfaces and addresses many of the challenges above. The substrate used is a single crystal bead electrode that contains the complete stereographic triangle which provides access to all forms of the arrangement of the atoms that make up the underlying substrate. This electrode provides a unique insight into sensors that are typically prepared on poly-crystalline gold substrates (e.g., have a random variety of surface structures like grains separated by high energy grain boundaries). Understanding the role of these structural features has proven critical for improving sensor stability and sensing performance. The distribution and organization of the adsorbed molecules will be explored by developing single molecule optical methods. This will enable study of the local environment of the adsorbate, kinetics of single molecule recognition and the distribution of analyte binding efficiency. Advanced in-situ surface characterization will direct new methods for preparing the sensor surface achieving control over density, local environment and distribution of the adsorbates. This will improve sensor stability and performance. These results will be used to engineer surfaces to enable new detection modalities which will combine electrochemical and fluorescence methods in a dual detection scheme.