Enzymatic bioelectrocatalysis involves the application of enzymes to facilitate the conversion of chemical to electrical energy. This approach has been widely applied in the fields of biosensing, biofuel cells, and to a lesser degree the synthesis of fine chemicals. While direct electrochemical communication between the enzymes and electrodes is generally preferable, it is often the case that efficient electron transfer rates can only be achieved when redox mediators are employed to shuttle electrons reversibly from the redox site of the enzyme to the electrode interface. Unfortunately, there still exist many oxidoreductases for which no effective exogenous mediator is known. This may be due to insufficient understanding of the role that molecular structure of the mediator plays in determining its ability to facilitate electron transfer to a given enzyme. Consequently, selection and/or design of novel redox mediators remains a challenge that is often accomplished using a “guess and check” approach to maximize electron transfer rates. Developing a rapid, and convenient method of predicting the role played by other structural and chemical features beyond redox potential of a mediator is an important goal in advancing mediated bioelectrocatalysis. This talk will describe our recent efforts in identifying structure - function relationships of redox mediators that control efficient electron transfer rates. I will highlight results from stopped-flow spectrophotometry experiments which review the nature of electron transfer events between quinone redox couples in altering bioelectrocatalytic activity.

The electrochemical hydrogenation (ECH) of bio-mass derived compounds is an attractive alternative to traditional thermochemical hydrogenation (TCH) methods that are used in the U.S. chemical and petroleum industries to produce value-added fuels and chemicals. TCH uses high pressures and temperatures, along with an external source of hydrogen gas typically produced via methane reformation; these requirements make it an energy intensive process. ECH has the advantages of operating near ambient conditions and sourcing the participating hydrogen from the aqueous electrolyte solution, resulting in reduced energy costs and CO₂ emissions compared to TCH. The applied potential provides an additional parameter for controlling selectivity, which makes ECH more suitable to handle the wide chemical variability of biomass-derived feedstocks.

Metal hydride species have proven to be a crucial chemical motif across chemical disciplines. As the key intermediate in electrocatalytic hydrogen evolution by molecular catalysts, understanding how metal hydrides are formed and how they react has allowed the design of more efficient electrocatalysts. Independently to the field electrocatalysis, metal hydride species have been critical for organometallic catalysis as reagents for hydrogen atom transfer (HAT), in particular the activation of alkenes to a diverse array of hydrofunctionalization products. Recently, these two fields have been explicitly linked via the emergence of electrocatalytic hydrogen atom transfer (e-HAT); utilizing primarily Cobalt based catalysts (salen and bipyridine) members of the NSF Center for Synthetic Organic Electrochemistry (CSOE) have shown that in situ electro-generated cobalt hydride species can catalyze highly sought-after organic transformations of alkenes, such as alkene isomerizations and enantioselective hydrocyanation reactions. However, from an electrochemical perspective these reactions remain poorly understood, severely limiting the design of new hydrofunctionalization reactions. Here, cyclic voltametric studies of Co(salen) provide a sorely needed mechanistic framework to understand these multi-step electrocatalytic reactions. Using model homolytic reactions we establish rate constants for cobalt hydride formation as well as a relationship between hydride donor ability and alkene activation. Hammett analysis of a series of modified salen ligands shows changes in the rate determing step, suggesting tunability in future organic electrosynthetic reactions. Finally, we detect key off-cycle intermediates that inhibit catalytic turnover and suggest further optimization in yield and enantioselectivity selectivity are possible. In summary, we contend that these mechanistic studies provide an important template for studying complex, multistep organic reactions from the perspective of traditional molecular electrocatalysis as developed by Jean-Michel Savéant.

The detrimental effects of CO₂ emissions from fossil fuels and the decreasing cost of electricity have accelerated interest in electrochemical synthesis. Electro-organic synthesis offers a sustainable and cost-effective pathway for chemical manufacturing. This method has the potential to minimize greenhouse gas emissions, enhance reaction selectivity, and replace hazardous chemical reagents with electric current.

Reduction of carbon dioxide has as main objective the production of useful organic compounds and fuels - renewable fuels - in which solar energy would be stored. Molecular catalysts can be employed to reach this goal, either in photochemical or electrochemical (or combined) contexts. They may in particular provide excellent selectivity thanks to easy tuning of the electronic properties at the metal and of the ligand second and third coordination sphere. Recently it has been shown that such molecular catalysts may also be tuned for generating highly reduced products such as methanol and methane, leading to new exciting advancements.

This work aims to design a high sensitivity and selectivity biosensor based on the electrochemistry of single impacts onto ultramicroelectrode (UME) to detect and identify various bacterial strains. The main objective is to establish a unique electrochemical signature for each bacterial cell through the individual impact event signal on the surface of the UME [1, 2]. First, we focus on the detection of well-known electroactive Gram-negative bacteria such as Shewanella oneidensis in order to be able to selectively detect these different single cells. In this case, the strategy currently used is to record a chronoamperometric curve in an aqueous potassium phosphate buffer (pH = 7.4) solution containing a redox probe at an UME polarized at the oxidation or reduction potential of the electrochemical active aqueous species and to observe a “current step” when one bacterium impacts the UME, corresponding to a “blocking effect” [3] (Figure A). The response signal expected from single bacterium collision may also be a “current spike” corresponding to either the own electrochemical activity of the bacterium toward the redox probe and the UME applied potential or a “bouncing effect” of the bacterium which does not stick onto UME surface (Figure B).

Electrochemistry plays a major role in immunosensor development because of its higher sensitivity, simplicity, portability, and rapidity compared to more common enzymatic, fluorescent and radioactive labelling methods. Silver nanoparticles (AgNPs) have been identified as potential electrochemical labels for such immunoassays. Characterizing the composition, size, shape, and surface modifications of the AgNP is important to achieve expected analytical performance of the bio assay. Here we are interested in studying the effect of nanoparticle shape towards the electrochemical detection of a metallo-immunoassay using Au-Ag galvanic exchange (GE) reaction followed by anodic stripping voltammetry. We observe that during GE between electrogenerated Au³⁺ and the Ag labels, a thin shell of Au forms on the surface of the NP and prevent further exchange. This shell is more porous when GE proceeds on silver nanocubes (AgNCs) compared to spherical silver nanoparticles (sAgNPs), and therefore, more exchange occurs when using AgNCs. More interestingly, optimizing the ratio of the two types of AgNP labels, we could able to decrease the LOD of a biological assay designed to detect a heart failure biomarker (NT-proBNP) without compromising the dynamic range compared to using either of the two labels independently. This made it possible to achieve the clinically relevant range for NT-proBNP analysis used by physicians for heart failure risk stratification.

A SARS-CoV-2 rapid detection technology employed commercially available test strips similar to the blood glucose test strips were developed with a detection time of 30 sec and the sensitivity as good as polymerase chain reaction (PCR). The analytical specificity of this technology was also investigated by testing the cross-reactivity and microbial interference on this biosensor platform using FDA suggested 31 different contaminants. Variants of SARS-CoV-2 have mutated along with the worldwide spread of the pandemic. Currently, the most common detection methods are PCR and lateral flow tests. The former takes more than an hour to obtain results and the latter has difficulty detecting the virus at low concentrations (for cycling threshold values, CT values, >25 to 27). Therefore, the demand for a fast, cost-effective, and low detection limit testing method has been significantly increased. In this work, 60 human saliva samples with 30 positive and 30 negative were collected and tested with PCR for SARS-CoV-2 prior to using our disposable strips. For this technology, the test strip was connected to the gate electrode of the MOSFET on the printed circuit board that serves to amplify signals. A synchronous double-pulsed bias voltages (around 1 ms) were sent to both the drain and gate of the MOSFET. The resulting change in drain waveforms was converted to digital readings and compared with cycling threshold (Ct) values of human samples to assess this sensor technology. The result signifies that positive human samples with a range of Ct values from 17.8 to 40 can be differentiated, along with proving none of those high-risk organisms would hinder the sensitivity of our system. Which demonstrated the potential of this system to be developed into a cost-effective and point-of-care rapid detection for SARS-CoV-2.