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42161-GB5
Nanoparticle Platforms for Controlled Adsorption and Behavior in Protein Monolayer Electrochemistry

Michael Leopold, University of Richmond

Protein monolayer electrochemistry (PME) is a strategy for studying fundamental interactions of biomolecules at interfaces and involves the attachment of proteins to synthetic surfaces called self-assembled monolayers (SAMs) in order to study their adsorption and electroactivity.  Unfortunately, PME has certain limitations including a lack of molecular-level control over interactions at the protein/surface interface.  In PME, proteins experience a range of surface environments and display non-ideal electrochemistry.  We proposed a novel, alternative platform for PME using specialized nanoparticles called Monolayer-Protected Clusters (MPCs).  MPCs are targeted because their properties can be easily tailored to exhibit specific and diverse molecular-level properties, including hydrophobic, coulombic, and interfacial flexibility properties – important factors for effective protein adsorption.  Our hypothesis was that MPCs can be engineered, tethered to a surface, and used to promote and control the immobilization and behavior of proteins.

As the main project of my group during the duration of this grant, this research has been both successful and popular with undergraduates in my lab.  At the time of this final report to ACS, seven undergraduate researchers have worked on this project over the course of three summer sessions and six semesters.  In all the cases, students participated in research for multiple semesters and in several instances, the students stayed for multiple summer sessions of research as well.  Their hard work culminated earlier this year with the publication of our results in the J. Am. Chem. Soc. [2008, 130, 1649].  More importantly, research became a part of these student’s daily lives and even inspired three of them to stay beyond graduation as post-baccalaureates to complete their portions of the project.  In my opinion, the “ownership” showed by these students and the demonstrated ability to apply themselves to a problem as an independent scientists are the true signs of a successful research program for undergraduates.   

Research on this project served as a significant experience for the development and education of my students as well as representing a major milestone in my own career.  The JACS publication became my seventh publication in six years and a centerpiece of my recent promotion to associate professor.  For the students, their research experience inspired four of the students to pursue further education in the sciences at graduate programs while other students bound for medical schools gained significant self-confidence, a sense of responsibility, and an enhanced problem solving ability that should serve them well in that environment.  All of the students on this project have presented at least once at local symposia or regional/national meetings of the ACS, including one student that presented his work on this project at three national meetings over the course of his career at the University of Richmond.  The research experience for one of my students inspired her to pursue and be granted a Fulbright Scholarship to study and work with Professor Israel Rubinstein in Israel.    

As for the research itself, significant understanding of MPCs as protein adsorption platforms was achieved.  Our previous progress report showed that the background signal is highly dependent on the architecture of the MPC film.  In the second year of our study, we focused our attention on the electron transfer signal from adsorbed protein and showed that rational design of individual MPCs translated into greater molecular level control at the protein adsorption interface while still generating well-defined voltammetry. The third phase of our study and the focus of the past year was the investigation to see if MPC platforms are able to provide a more uniform distribution of adsorption sites over a large area of a substrate. Surface heterogeneity induces non-ideality in electrochemical response, usually manifested in full-width-half-maximum (FWHM) values for the voltammetric peaks that exceed the ideal value of 90 mV for proteins at SAMs (typically >120 mV).  Our experiments show that MPC platforms are able to control interfacial chemistry at a molecular level, negating topographical heterogeneity, and providing a more uniform adsorption environment with FWHM values between 90-100 mV.  Another striking impact of our work for the ACS-PRF program over the past year is that it became the basis for additional research proposals that have been written for the National Science Foundation and that will be written for ACS-PRF (December).  Preliminary results on the next phase of our work, focusing on the kinetics of ET for protein at MPC films, appear very promising and have already garnered the interest of several new research students in my group.  We remain extremely grateful to the ACS-PRF for helping us achieve both significant results of interest to the scientific community as well as fostering invaluable research experiences for undergraduates at the University of Richmond. 

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