NANOscientific

Professor Michael V. Mirkin. Dept. of Chemistry, Queens College, NY, USA

Professor Mirkin, could you provide an overview of your current research at CUNY's Department of Chemistry?

Our research focuses on nano-electrochemistry, specifically using nanometer-sized electrochemical probes in conjunction with scanning probe microscopy techniques to explore various systems and processes at the nanoscale. These nano-electrochemical probes are highly versatile, allowing us to investigate a wide range of phenomena. For example, we can position the tip near the substrate surface to study charge transfer reactions occurring at a nanostructured solid/liquid interface. Alternatively, a tip can be inserted into a biological cell to probe intracellular processes with high spatial resolution. The flexibility and adaptability of these probes make them suitable for studying diverse samples, from nanoparticles to biological systems, providing unique insights into nanoscale behaviors.

You mentioned that nano-electrochemistry often needs to be combined with other techniques to provide a more complete picture. Can you elaborate on how integrating these methods enhances our understanding of nanoelectrochemical systems?

One of the most exciting developments in nanoelectrochemistry is the ability to combine it with other analytical techniques to gain a more comprehensive understanding of systems. Traditional electrochemical methods alone o¼en fall short, especially in providing detailed information about the chemical composition or atomic structure of materials. By integrating nano-electrochemistry with spectroscopy, one can learn more about local chemical environments, and by combining it with techniques like transmission electron microscopy (TEM), we can obtain atomic-scale structural information. This multidisciplinary approach allows researchers to create a more complete picture of the systems they study and tackle complex challenges, such as engineering catalytic sites on the nanoscale by correlating structural, chemical, and activity data.

What were the primary challenges in developing quantitative measurement techniques with scanning electrochemical microscopy (SECM), and how did you address these issues?

Developing quantitative measurement techniques based on scanning electrochemical microscopy (SECM) presented several significant challenges. One of the primary issues was ensuring that the measurements obtained with microelectrode and nanoelectrode probes were reliable and reproducible, especially when dealing with extremely small tips that are di’icult to visualize. Visualization typically requires advanced techniques like scanning electron microscopy (SEM) or TEM, but even with these, the in-situ positioning and characterization of probes remain complex. The fragility of these small, glasssealed electrodes adds another layer of di’iculty; unlike more robust atomic force microscopy (AFM) probes, SECM tips cannot physically contact surfaces without being damaged. Achieving reproducibility was also challenging because each nanoelectrode is manually cra¼ed and polished, requiring meticulous handling to ensure consistent results. Overcoming these obstacles involved developing better visualization methods, refining the fabrication process, and creating new strategies to interpret data accurately.

When conducting experiments at the nanoscale, what are the key di„iculties in visualizing and modeling these processes, and how do you overcome them to ensure accurate interpretation of data?

Modeling electrochemical processes at the nanoscale involves adapting standard electrochemical theories to the unique conditions presented by nanometer-sized probes. While the fundamental principles of di’usion-based theory still apply, modeling becomes more complex when dealing with probes smaller than 10 nanometers, where double-layer e’ects and electron tunneling come into play. As a small nanoelectrode approaches a conductive surface, tunneling can alter the expected outcomes, necessitating changes in theoretical approaches. Therefore, while the mathematics remains similar for larger nanoelectrodes, understanding what is being modeled is crucial, especially since direct visualization of these tiny systems is o¼en not possible. Accurate modeling requires a blend of computational tools and imaginative thinking to interpret the unseen dynamics of nanoscale systems.

Could you discuss a recent project from your lab that you found particularly novel or interesting, especially in how it advances our understanding of molecular electrocatalysis?

Traditionally, in molecular catalysis, the rate of a bimolecular catalytic reaction is thought to be independent of the applied electrical potential. We have recently developed voltage-driven electrocatalysis, in which a molecular catalyst is immobilized directly (i.e., without a spacer) on the electrode surface, and the applied potential drops on both sides of the attached molecule, driving both the oxidation/reduction of the molecular catalyst and the charge transfer between the catalyst and dissolved reactant species. The electrode potential contribution to the catalytic driving force allows a molecular catalyst to accelerate the rates of charge-transfer processes, which it normally would not be able to catalyze. This finding not only broadens the theoretical understanding of molecular electrocatalysis but also offers new pathways for designing more efficient catalytic systems.

While your research is primarily fundamental, are there any specific examples where your work in nanoscale electrochemistry has influenced or could influence real-world applications or technologies?

Although our primary focus is on fundamental science, some of our techniques have begun to find applications in real-world scenarios. For instance, SECM and its nanoscale variant, nano-SECM, are gaining traction in chemical and electrochemical engineering fields. Although my lab typically does not engage in industrial collaborations or direct application development, the foundational concepts we have developed are being adapted by engineers and applied researchers to solve practical problems in industry. This progression illustrates the potential of fundamental research to inspire technological innovations, even if the initial work was not directly aimed at application.

Looking to the future, what are some of the emerging challenges or research directions in nanoscale electrochemistry that you are excited to explore?

Looking ahead, our research aims to push the boundaries of what is possible in nanoscale electrochemistry by developing smaller, more precise, and more reliable probes. This goal includes expanding the range of materials and processes we can study, continually refining our techniques, and addressing the new challenges that arise as we push the limits of current technology. A recent focus area is studying photoelectrochemical processes on single semiconductor nanoparticles, which combines the challenges of nanoscale electrochemical measurements with the need for localized illumination. This emerging area requires both new technological developments and innovative approaches to study these complex systems. Our work is dynamic and evolves with each new discovery, driven by the unpredictability and excitement of scientific exploration.

Thank you, Professor Dr. Mirkin, for sharing your valuable insights and discussing your research with us.