Jon Camden, Ph.D. - US grants

This CAREER award by the Chemical Measurement and Imaging (CMI) program supports Professor Jon Camden at the University of Tennessee Knoxville to develop surface nonlinear spectroscopy as a analytical method for probing the two-photon properties of molecules, surface adsorbate structure, and ultrasensitive detection. A method for measuring absolute SEHRS enhancement factors is presented and subsequently utilized to elucidate the respective roles of chemical and electromagnetic enhancements in SEHRS. The wavelength dependent nature of the molecule-plasmon coupling and of resonance enhanced hyper-Raman will provide information on the complex interplay of molecular excited states important in two-photon processes. Detailed comparisons between experiment and theory are pursued, which will benchmark new electronic structure methods for the calculation of nonlinear molecular properties. The studies will demonstrate SEHRS to be a powerful, routinely applicable, and ultrasensitive analytical tool. Further, this work will provide the basis for future studies of surface-enhanced nonlinear spectroscopy.

In addition to the scientific objectives of this proposal, the PI seeks to increase the number of high-school students pursuing Science, Technology, Engineering, and Mathematics (STEM) majors in college. The PI will collaborate to provide curricular enrichment to local public high-schools through the creation of ASPIRE teams (Aspiring Scientists Participating in Research and Education). ASPIRE teams will deliver hands-on laboratory experiments to local high school classrooms once a month during the regular school year, for a total of six activities. The activities are aligned to meet the requirements of Tennessee State curriculum and introduce students to the properties of nanoscale materials. Regular assessments are used to refine the activities and gauge their impact.

With support from the Chemical Measurement and Imaging Program in the Division of Chemistry, Professors Camden and Svarovsky of the University of Notre Dame will undertake a study of the analytical applications of the surface-enhanced hyper-Raman scattering (SEHRS) effect and implement a student-driven program to monitor the concentration of uranium in ground water sources. SEHRS is a technique provide unique information about molecules adsorbed on a surface. The success of this work has the potential to impact a wide range of studies, especially the geometry of a molecule adsorbed on a surface differs in complex environments. It can also make a difference in deep-tissue imaging. Furthermore, Professors Camden and Svarovsky and their groups also work on ways to reduce the cost of SEHRS spectrometers, making SEHRS accessible to a wide range of researchers and analytical problems. Students working in these two labs have a great opportunity to learn different skills through collaboration. As a way to engage a new and national K-12 audience in outreach efforts, Professors Camden and Svarovsky also plan to work with the University of Notre Dame's Center for STEM Education together and launch a new Citizen Science project called U-Watch. The program will bring the benefits of surface-based spectroscopy research supported by this grant to a broad audience and could identify potentially dangerous levels of contamination, such as uranium, in ground water drinking sources.

In this work, SEHRS is used to provide information that is not available via other techniques. New methods for single-molecule SEHRS are used to probe nanoparticle-adsorbate interactions at the level of single molecules in complex chemical environments. SEHRS nanoparticles also serve as a platform for near-infrared and short-wave-infrared (SWIR) (0.8-2.5 Pm) sensing, imaging, and authentication. The Notre Dame groups also plan to develop the characterization methods needed to pursue the rational design of SWIR tags and apply them to deep-tissue imaging studies. A comparison of SEHRS and surface-enhanced Raman spectroscopy (SERS) shows that SEHRS can be more sensitive than SERS in certain situations. Lastly, they explore the potential for hand-held, field-portable devices capable of recording SEHRS spectra with continuous-wave lasers. Through the supported research, the groups will demonstrate SEHRS as a powerful and practical analytical approach to ultrasensitive detection, imaging, and the elucidation of surface structure and environment.

In this project, funded by the Macromolecular, Supramolecular, and Nanochemistry program of the Chemistry Division, Professors Jon Camden and Marya Lieberman of the University of Notre Dame and Professor David Jenkins of the University of Tennessee are developing robust, reusable, and highly specific nanoparticles for ultrasensitive detection of chemical species in complex biological and chemical systems. To meet this challenge, special and unique chemical modification of the surface of these nanoparticles is done. After modification of the surfaces, these particles can be applied to serve as sensors for specific molecules. This effort is also focusing on devising new methods of analysis that can be used in low-resource environments and drug testing. The highly collaborative nature will benefit students working in these labs. The success of this research has the potential to impact a wide range of sensor applications such as imaging cells, detecting trace contaminants, and analyzing samples outside of a laboratory setting.

The unique optical properties of plasmonic nanoparticles and plasmonic assemblies has driven an explosion of new sensing and imaging modalities over the past several decades. The wide-reaching impact of functionalized metallic nanostructures is evidenced by studies which range from fundamental research to commercial applications. In this work, a transformative functionalization approach based on N-heterocyclic carbenes is employed for surface-enhanced Raman spectroscopy (SERS). This collaborative effort specifically targets a regenerative sensor for hydrogen peroxide and an in vitro pH sensor with expanded range. Additionally, procedures are established that make NHC functionalized films and colloids available to a non-specialist audience by proposing a "one-pot" synthesis of modified surfaces from conventional imidazoliums. These demonstrations will showcase how effective this new technology is for the broader chemical sensing community.

Nontechnical Description: This collaborative and interdisciplinary project brings together both experimentalists and theorists to explore advanced optical materials and devices. This is accomplished using new materials processing methods, advanced characterization techniques, and state-of-the-art theoretical/computational models. The materials and devices have practical applications such as improved solar energy conversion, chemical sensors, and faster as well as higher data storage capacity for computing. The project explores new material combinations and architectures to optimize the way different frequencies of light can be harnessed and manipulated. Advanced materials processing methods are developed to create complex two-dimensional and three-dimensional arrangements of these optical materials. One goal of the project is to train both graduate and undergraduate students to function in a collaborative and interdisciplinary environment. To accomplish this, the graduate students work closely with the collaborating institutions which cross-cut several research areas: materials synthesis (materials science and engineering), materials characterization (chemistry), and theory/simulation (chemistry and applied mathematics). Undergraduate students are impacted by the development of a new multi-institutional and interdisciplinary design project.

Technical Description: The overarching goal of this activity is to study new plasmonic materials and architectures for advanced optical and metamaterial concepts with a broad spectral tunability across the visible and near-IR. This goal is realized via the execution of three overarching objectives. The first objective comprises a systematic study of the synthesis, characterization, and theory/modeling of Au-Al, Ag-Al binary, and Au-Ag-Al ternary alloys with the goal of correlating the materials nanostructure to the fundamental optical properties and full plasmonic spectrum. The second objective aims to rationally design, synthesize, and characterize innovative 2D plasmonic nanoarchitectures that incorporate multi-material dimer/oligomer systems, templated substrates that induce asymmetric dielectric coupling, and advanced lithographic/focused ion beam nanomachining for pushing the limits of small size/narrow gaps. The third objective seeks understanding of the far- and near-field optical properties of new 3D plasmonic nanoarchitectures synthesized via focused electron beam induced processing. These objectives are accomplished via a highly collaborative and multi-disciplinary approach which brings together distinctive expertise in the areas of thin film and nanoscale synthesis and characterization, optical and electron-beam plasmon spectroscopy, and advanced theory/simulation of optical- and electron-induced localized surface plasmon resonance phenomena. The multidisciplinary program provides a unique learning experience for both undergraduate and graduate student participants. Additionally, a new multi-disciplinary and multi-institutional design project extends this experience to other undergraduate students at all three participating institutions.

With the support of the Macromolecular, Supramolecular, and Nanochemistry Program in the Division of Chemistry, Dr. David Jenkins of the University of Tennessee and Drs. Jon Camden and Gina Navoa Svarovsky of the University of Notre Dame explore the use of N-heterocyclic carbenes (NHCs) chemistry for the surface modification of gold nanoparticles. Gold nanoparticles, which are typically stabilized by charged molecules such as citrate or monolayers with thiol anchoring groups, are used in wide-ranging chemical, biological, and environmental technologies but use is limited by the inherent instability of the nanoparticles in water. Drs. Jenkins and Camden are identifying ways to overcome this limitation by using NHC ligands. To do so, they are using a top-down method that involves the initial coordination of these ligands to coinage metal ions before being transferred to gold nanoparticle surfaces. They are using a variety of characterization tools to evaluate this chemistry and to better understand what NHC ligands promote enhanced stability of the functionalized gold nanoparticles. Drs. Jenkins, Camden, and Svarovsky are pursuing a Teaching Fellows Residency program to create an immersive research experience in the research laboratories and a Student Engagement in Authentic Science (SEAS) program that engages middle school students with original scientific data.

The research involves the synthesis, characterization, and transfer of metal NHC complexes to gold nanoparticle surfaces, the characterization of the resulting bonding and close packing of a library of NHC ligands on gold nanoparticles, and the subsequent evaluation of NHC-functionalized gold stability and longevity. All of these studies utilize a top-down approach wherein the gold nanoparticles are functionalized after isolated coinage metal NHC complexes have formed in solution. This universal, top-down strategy is expected to be broadly applicable to gold nanoparticles of varying shapes and sizes. This approach has the potential to overcome limitations associated with bottom-up functionalization steps where each individual reaction is typically optimized for a specific system. Gold nanoparticles functionalized with heterocyclic carbenes hold promise in the quest to overcome challenges faced by conventional surface chemistries.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.