Professor Michael C. Leopold of the University of Richmond is supported by the Analytical and Surface Chemistry Program in the Division of Chemistry to conduct research leading to the development of chemically modified gold nanoparticles assembled onto conducting surfaces, known as monolayer-protected clusters (MPCs), and to use this platform as a functional electrode component for protein monolayer electrochemistry to probe the electron transfer properties of immobilized redox proteins, while preserving their biological function. Experiments will be conducted to study the role of the core size and functionality of the MPCs, and the dependence of electron transfer rates on distance through the MPCs. Understanding of the interactions and charge transfer properties of proteins with these substrates will lead to a better realization of the potential of MPCs in many applications in bioanalytical chemistry leading to the development of miniaturized biosensors. This research will involve undergraduate students in an undergraduate institution in modern research methods and train them in state-of-the-art instrumentation.
," Funding: $255,000 from 2/15/2009-1/31/2013. As nanomaterials continue to emerge in both the scientific field and in products of everyday life, fundamental understanding of their structures, interconnection, and functionality continues to be an important goal of research. The primary focus of our NSF funded project was to investigate gold nanoparticle (NP) film assemblies as an adsorption platform/interface for adsorbing proteins that are electrochemically active – fundamental bioanalytical chemistry related to important future medical applications. The merger of such proteins with and man-made materials is a significant foundation for future sensor development, including real-time, implantable sensors for the continuous monitoring of clinically relevant species (e.g., glucose for diabetics or lactate for sepsis diagnosis) as well as general biocompatible materials. We proposed the use of electrodes modified with a film ensemble of colloidal gold NPs as an alternative platform for fundamental studies of this nature. In 2008, we introduced the use of non-aqueous NP films as a protein adsorption platform publishing our findings in the J. Am. Chem. Soc.. That work became the premise of the NSF proposal (CHE-0847145) which proposed specific experiments performed exclusively by undergraduates and aimed at a greater understanding of the NP film as this type of interface. Our model system, blue copper azurin protein (Az) adsorbed to NP films, was used study different aspects of the NP film platform related to signal-to-noise (S/N), the most significant intellectual merit of our efforts described below. At traditional interfaces, protein electrochemical signals, crucial to their incorporation in sensors, was distance limited, a property negatively affecting S/N. Our analysis of Az at NP film assemblies (Figure 1) resulted in relative distance independence of the electrochemical signal, up to distances 20 times greater than adsorption platforms without NPs, work published in Langmuir (2010). As part of this study, we utilized a novel cross-sectional TEM imaging technique that we published in J. Visualized Experiments (2011) to independently measure the thickness of our NP film assemblies. This student-directed video documentation of our procedures will benefit future research as a training video, saving valuable time and resources. Another important aspect of our work with S/N issues within these NP systems is differentiating the analytical signal from the background noise, a property we found to be dependent on interparticle linkages within the NP film. We explored this aspect of the protein at NP films using alternative electrochemical techniques known for their ability to discriminate against background noise (J. Electroanal. Chem. (2011)). Other undergraduate researchers established that the NP film assemblies provided interfaces for protein adsorption that were homogeneous, a property resulting in more uniform electrochemical signals which we visualized using atomic force microscopy. These findings were published in the J. Colloid and Interface Science (2010). Our success with these fundamental studies prompted our efforts to expand to alternative aqueous NPs, such as gold nanoshells and silver nanotriangles as well as optical sensing NP films described in work published in Thin Solid Films (2010) and J. Materials Science (2011) where we were able to establish the relative importance of electronic communication within the NP assembly. Collectively these fundamental studies enabled the final stage of our research, preliminary studies using NP networks as a functional component of an actual sensor. The viability of the NP networks in this capacity was shown with the successful incorporation of NPs within a silica platform as part of glucose sensor. Findings related to this were recently published in Analytical Chemistry (2013) and Langmuir (2013) and set the stage for future study of NP assisted sensing schemes. The Broader Impacts during the NSF (CHE-0847145)-supported period since 2009 revolved around the targeted and intensive training/mentoring of undergraduates in science and a partnership with the Math Science Innovation Center of Richmond working with teachers/students (grades 6-12) to introduce nanotechnology into their science curricula, including 7 presentations to these audiences. This NSF grant has allowed for the involvement of 13 undergraduates including 8 female students, a traditionally underrepresented group in chemistry. These students performed well over 50 semesters or summers of research activity that resulted in 8 published research papers featuring over 21 undergraduate coauthors. Five of these students choose to become post-baccalaureate researchers and laboratory managers, a remarkable achievement of a tiered mentoring system where more-experienced students take responsibility of teaching less-experienced students. The most significant broader impact of this funding has been the immersion of students into all aspects of scientific research including conception of an idea, independent experimentation and data analysis, as well as writing results for publication – an experience that has led these undergraduate to prestigious national awards and highly ranked graduate and medical schools.
