Regina Ragan - US grants

ABSTRACT
Proposal Number: CTS-0642217
Principal Investigator: Regan, Regina
Affiliation: University of California-Irvine
Proposal Title: SGER: Fabrication and Optimization of Highly Ordered Assemblies of Metallic Nanowire and Nanocrystal Arrays

Intellectual Merit:

The fabrication of noble metal nanostructures immobile on Si substrates via self-assembly with feature sizes less than 10 nm and more notable inter-particle spacing on the order of nanometers via a self-assembled template is unique to this proposal. This experimental study is combined with ab initio structural calculations of interfaces involved in phase aggregation that leads to nanostructure formation. Theory and experiment are combined in order to optimize structure and to apply these principles to obtain a variety of structures and vary material in the structure. Characterization of optical properties of nanostructures will be addressed to demonstrate the feasibility of using these structures in surface plasmon resonance biological sensors. Metal nanoparticles with diameters much less than the wavelength of light and narrow inter-particle spacing have strong near field coupling due to a local enhancement of the electromagnetic field around these particles. Thus, in order to achieve maximum enhancement to the electromagnetic signal, the inter-particle spacing should be on the order of nanometers. By using self-assembly, the feature size, 8 nm, and inter-particle spacing achievable, ~10 nm, is smaller than that obtained with electron beam lithography and the throughput is much higher.

Broader Impacts:

The approach proposed uses self-assembly as a low-cost method to fabricate nanostructure arrays composed of noble metal nanocrystals and nanowires. The development and fundamental understanding of fabricating large-areas of uniformly-sized ensembles of noble metal nanocrystals and nanowires and investigating an efficient readout method will foster the emergence of low-cost and highly sensitive biosensing devices in addition to other applications such as transport of electromagnetic energy along metallic nanowires, and catalysis. This proposal will support the training of undergraduate and graduate students in a highly interdisciplinary area of science. Interest and experience in science and engineering will also be fostered via curriculum development, computer simulations and experimental data from this project incorporated in undergraduate and graduate courses.

National Science Foundation - Division of Chemical &Transport Systems Particulate & Multiphase Processes Program (1415)

Proposal Number: 0731349
Principal Investigators: Ragan, Regina
Affiliation: University of California Irvine
Proposal Title: Fabrication and Optimization of Highly Ordered Assemblies of Metallic Nanowire and Nanoparticle Arrays

Metal/rare earth disilicide core-shell nanostructure arrays on silicon substrates that have high density in addition to uniform size and shape will be designed, modeled, and characterized for incorporation into biosensor systems. Although noble metal nanostructures have demonstrated extraordinary capacity for single molecule detection limits in biosensors, one of the most significant challenges to technological developments that capitalize on their unique properties is the fabrication of arrays with monodisperse size, shape and high density using a low cost and high throughput technique. Recently, the principal investigator has developed a unique ultralarge scale compatible fabrication process for dense (~1011 cm-2) ordered arrays of monodisperse Pt and Au coreshell nanostructures on Si substrates. Physical vapor deposition of Pt and Au atoms on self-assembled nanowire templates followed by reactive ion etching produces noble metal/rare earth disilicide core-shell nanostructure arrays with mean particle diameter of less than 10 nm, a narrow size distribution, <1 nm, and inter-particle spacing of ~ 10 nm without lithography.
. Fabrication: Preliminary results demonstrate that the proposed synthesis route produced both Pt and Au nanostructures on self-assembled rare earth disilicide nanowires on Si(001) substrates. This successful fabrication technique will thus be applied to fabricate Ag and other metal core-shell structures in order to tune optical responses in different frequency range.
. Theory: Theoretical calculations of surface atomic structures of self-assembled templates, their interfaces with the Si(001) surface, and noble metal atom aggregation on nanowire template surfaces will be performed. The goal is to understand assembly mechanisms in order to optimize structure and make our process translatable to other material systems.
. Characterization: Atomic level resolution of surface structures and electronic states will be investigated by STM and spectroscopy.
Intellectual Merit: Metal nanostructures with diameters much less than the wavelength of light and narrow interparticle spacing have strong near field coupling due to a local enhancement of the electromagnetic field around these particles. We will address fundamental questions in this context: 1) how the arrangement of nanostructures in arrays affects signal enhancements; and 2) how to effectively pattern nanostructures over a large surface. Fabrication of monodisperse metal nanostructures in array format on Si substrates using microelectronic processing methods and combining self- assembly with lithography is unique to this proposal. Through the self-assembly process, the feature size, 8 nm, and inter-particle spacing achievable, ~10 nm, are smaller than that obtained with electron beam lithography and the throughput is much higher; thus unique optical properties can be attained. The synergistic theoretical and experimental studies will allow efficient and rational optimization and eventually massive production of nanostructures for biosensor applications.
Broader Impact: Innovative and high-throughput fabrication techniques of nanostructure arrays are significant for many emerging technologies such as nanocatalysis, spintronics, quantum computing and optochemistry. This proposed fundamental study will pave the way for successful fabrication of high density, uniformly dispersed, nanostructure arrays optimized for biosensor applications. Our proposed fabrication technique is apparently translatable for other applications and affords the possibility to scale to large areas for massive production due the compatibility with current semiconductor manufacturing technology. This proposal will also support the continued training of high school, undergraduate and graduate students through research opportunities and outreach activities.

ECCS-0709481

Intellectual Merit: Artificial bacterial cell membranes are to be chemically assembled on patterned gold surfaces. Protein diffusion and the resulting membrane structures will be evaluated to verify that the laboratory platform mimics properties of cell membranes. The fabricated membranes will then serve as a test platform to study pore formation due to interactions between bactericidal proteins and membrane surfaces. Pore formation will be measured by an ion current that results across the membrane when a pore is formed. The toxicity of antimicrobial proteins will be determined by cell-based cytotoxicity assays and related to electrochemical properties. Patterning of membranes structures in array format will be also be developed for high-throughput studies of protein-membrane interactions.

Broader Impacts: This project involves the fabrication of a laboratory platform for use in the identification of the next generation of antibiotics in response to increasing bacterial resistance to current antibiotics. Pore formation due to assembly of proteins on cell surfaces that occurs under natural circumstances is a mechanism for killing bacterial cells while leaving mammalian cells intact. The development of artificial cell membrane arrays will allow for rapid screening of potential bactericidal agents as well as studies of drug delivery mechanisms across cell membranes. Both graduate and undergraduate students will perform research to gain advanced analytical training in interdisciplinary research. The research activities and results will also be used as case studies in the investigators' undergraduate courses in order to educate a larger pool of students in interdisciplinary research.

The Analytical and Surface Chemistry Program of the Division of Chemistry will support the CAREER development plan of Regina Ragan of the Department of Chemical Engineering and Materials Science at the University of California, Irvine on the project titled "A fundamental study of biological/inorganic interfaces: understanding mechanisms for probing biomolecular interactions using nanostructures." This project aims to understand how material interfaces affect device behavior of electronic measurement platforms that measure interactions between biological molecules. Professor Ragan and her students will utilize scanning probe microscopy integrated with fluorescence microscopy to characterize systems with molecular scale resolution. It is expected that the fundamental knowledge gained from these studies will lead to devices with enhanced performance for drug discovery and environmental monitoring. Professor Ragan will also provide advanced analytical training for high school students at a local high school that serves a predominantly Hispanic student body in order to increase and retain the number of students from under represented groups attending UC Irvine in science, engineering and mathematics.

The objective of this research project is to develop versatile methods for self-organization of metal nano-architectures where colloidal solutions of metal nanoparticles are assembled on self-organized chemical domains using covalent nanoparticle-substrate interactions. The assembly process to be developed allows for control of nanoparticle size, composition and shape, number of nanoparticles assembled in a cluster as well as array architecture. The chemical domain diameter to nanoparticle diameter ratio will be investigated as a means to control the cluster size. A balance between capillary and double layer forces yields molecular scale separations between nanoparticles in clusters that is important to yield enhanced optical fields. The inter-particle spacing and cluster size will be varied to tune resonances and local enhancement of optical fields. Models for investigating local and collective resonances in clustered or arrayed nanoparticles will be developed, including the local density of states, and extinction and absorption coefficients.

None of the standard nanoscale lithographic techniques such as focused ion-beam, electron beam and nano-imprint lithography, are easily translated into large-area production that is needed to transform proof of concepts into commercial products. In contrast, guided self-organization is designed here to be inexpensive and scalable to large-area production. Facile, large-area synthesis of ordered arrays of metal nanostructures will enable or enhance performance in several critical technologies. Partnerships with industrial and government laboratories are included to test metal nanosystems in sensor, laser and detector applications. For example, plasmonic nanoparticle clusters will be used to lower detection limits in optical based sensors that is needed in both biomedical applications and in explosive agent detection. The research program will also directly contribute to the education of graduate and undergraduate students through hands-on laboratory experience in a field that is at the forefront of modern research. Outreach activities will include integrating local high school students in research activities to increase science, technology, engineering, and math enrollment of underrepresented groups.

With this award from the Chemistry Major Research Instrumentation (MRI) Program and co-funding from the Chemistry Research and Facilities (CRIF) Program, Professor John Hemminger from University of California Irvine and colleagues Regina Ragan, Matthew Law, Reginald Penner and Daniel Munn will acquire a combined X-ray photoelectron spectrometer (XPS) and scanning Auger microprobe (SAM). The proposal is aimed at enhancing research and education at all levels, especially in areas such as (a) XPS and Auger electron spectroscopy (AES) depth profiling, SAM, and UPS studies of solar cell absorbers and device stacks; (b) characterization of metal oxide and metal chalcogenide nanocrystals for photocatalysis; (c) ultraviolet photoelectron spectroscopy (UPS), XPS and AES depth profiling studies; (d) manganese dioxide nanowires for ultra-high capacity and rate capabilities for lithium cathodes; (e) correlating surface functionalization and transport properties of single-walled carbon nanotubes; and (f) dynamics of thermally-grown oxides in power generation and propulsion materials.

X-ray photoelectron spectrometers are used for chemical analysis. The XPS technique quantitatively measures elemental composition, empirical formula, chemical state and electronic state of the elements in a given material. A sample is irradiated with a beam of monochromatic X-rays and the kinetic energies of the resulting photoelectrons are measured and related to specific elements. XPS often plays a crucial role in defining the system under study. The technique requires the use of ultra-high vacuum conditions. In Auger electron spectroscopy, energetic electrons emitted from an excited atom are analyzed to provide information on surfaces. The work to be carried out by these investigators represents a wide array of systems requiring surface characterization. The instrumentation will be used in research activities and also for research training and education of a large number of students from diverse backgrounds.

In the sector of medical diagnostic, there is an emerging set of data showing that volatile metabolites provide a signature of infectious and disease states. For instance, biomarkers for cystic fibrosis have been found in patients? saliva and lung cancer biomarkers have been found in a patient's breath. A facile method with trace detection limits would benefit not only diagnosis but also point-of-care evaluations. In the automotive industry, there is concern with detection limit and quantitative real time monitoring of nitrous oxide. To address these challenges, this team proposes the surface enhanced Raman scattering (SERS) sensors that are low-cost, scalable to large areas, with low detection limits.

An innovative method has been developed for fabricating self-organized clusters of metal nanoparticles on diblock copolymer thin films as surface enhanced Raman scattering (SERS)-active structures. Sensors based on SERS provide a molecular fingerprint of molecules near the surface though issues of reproducibility and cost have limited technological impact. The developed method reproducibly produces size controlled nanoparticle clusters with nanometer scale inter-particle spacing and represents a significant advancement in scaling, cost and point-to-point reproducibility in sensor performance. The team has theoretically and experimentally identified key geometric properties desirable for performance as optical sensors.

Nanoarchitectures with subwavelength-sized metallic building blocks arranged on surfaces manipulate light matter interactions. These nanoengineered materials basically lay the foundation for a new, engineered way of controlling light, and pave the way for novel functional devices, unattainable with conventional optics benefitting applications including sensing, energy, imaging, and light guiding. Yet the lack of scalability for large-scale and low-cost production of these nanoarchitectures limits impact. This Scalable NanoManufacturing (SNM) research program will provide disruptive manufacturing solutions to create nanoarchitectures embedded in micron scale surface to foster a breakthrough in scalable fabrication. The investigators will work closely with an industrial advisory board to tailor research that addresses scientific studies to the benefit of a broad range of technology sectors that includes medical and industrial diagnostic systems to optical communications as well as the precision manufacturing equipment needed to achieve the goal of scalable nanomanufacturing. The research program is closely integrated with a diverse educational plan and robust industry outreach that is designed to train students (high school to graduate level, STEM educators/learners and industry practitioners) to be future leaders in science and technology to benefit innovation and strengthen manufacturing in the United States. This plan includes creation of movies and demonstrations in collaboration with the UC Irvine School of Education "From Lab to Lesson Plan" that train high school teachers from the Mathematics Engineering Science Achievement (MESA) program serving underrepresented students in Science, Technology, Engineering, and Math (STEM). Undergraduate students will be recruited from The Louis Stokes for Minority Participation in STEM, a statewide initiative funded by the National Science Foundation, to train a diverse group of students in advanced research activities. Interdisciplinary training will be provided for graduate students involving fundamental science and engineering as well as technological applications and scientific communication.

Synergistic experimental and theoretical studies involve understanding driving forces that direct assembly of nanoparticles from colloidal solution into predefined surface patterns, physical mechanisms of direct writing of periodic and aperiodic nanowire arrangements using elecromechanical spinning technology, and needed precision in process control. These studies when integrated with existing lithographic techniques will produce multi-length scale complex architectures using high throughput manufacturing methods that afford tunable properties at infrared and optical frequencies while retaining low cost. Test bed applications of these systems include sensors exhibiting low detection limits over large areas, non-linear optical devices, and optical antennas and actuators to demonstrate the benefit to technological applications. Advancements to the research field will be threefold: 1) studies of fundamental mechanisms in nanofabrication will allow researchers to conceive new and robust nanofabrication methods that will benefit research beyond optics, 2) the understanding of defect tolerance in the development of optically responsive surfaces and optomechanical systems will provide guidelines for geometric tolerances in nanomanufacturing, and 3) new insights into the physical mechanism of multi-length scale electromagnetic interactions will improve understanding of novel light-matter interactions and produce improved functionalities for future optical devices.

Cell metabolites are small molecules used or produced by cells and are direct indicators of the cellular state, function, and health. Metabolomic analyses is the characterization of cellular metabolites, and it is key to our understanding of cell function. Current metabolomic methods include mass spectrometry and nuclear magnetic resonance, techniques which require large, expensive instruments and long times for analysis. Here, an alternative approach is to use integrated optical sensing devices to detect the chemical fingerprints of metabolic changes within cells on the time scale of minutes. These devices will fingerprint bacterial metabolites involved in stress responses-a basic component of bacterial survival in dynamic conditions. As part of this work, scientific questions about the relationship between the molecular scale architecture of optical sensors and the ability to differentiate metabolite response in the resulting data will be answered. The demonstration and characterization of this sensing platform will also involve the rapid collection of large data sets and the application of automated big data analysis software to interpret complex sensor signals. Results from these studies will inform understanding of bacterial behavior in diverse habitats ranging from medical infections and industrial contamination to probiotics in human health and agriculture, and microbial interactions influencing nutrient cycling in the environment. The principal investigators and students will engage in an annual two-week summer outreach program for a diverse group of high school students - ASPIRE: Access Student Program to Inspire, Recruit, and Enrich. Graduate, undergraduate and high school students will learn how to define, analyze and solve research problems and communicate results that focus on the importance of metabolomics in health and the environment and the importance of technology innovation.

Practical nanophotonic sensing platforms will provide a new lens for examining dynamic biological function. Control of surface-enhanced Raman scattering sensor architectures and surface chemistry will be investigated to design sensitive receptors that both enable the rapid collection of large data sets and differentiation of metabolite fingerprints in complex biological media. Measurements of phonon-plasmon coupling will inform of chemical interactions between functionalized sensor surfaces and metabolites of interest. Machine learning algorithms will be further developed that are best suited to accurately analyze the large volume of vibrational spectra generated as part of these studies. Libraries of microbial metabolic fingerprints and methods for analysis of spectral information will be disseminated. The fundamental studies of nanophotonic device architecture, nanoparticle surface chemistry, and machine learning analysis of complex Raman spectra will then be utilized for the detection of metabolic fingerprints associated with stress response in polymicrobial bacterial communities. Metabolic changes associated with bacterial stress responses to antimicrobials and inter-species interactions will be measured to develop new methods to understand how to control, nurture, and mitigate various microbe-host interactions-a key application area of the investigated sensing technologies. High throughput detection of the bacterial stress response is important for screening antimicrobial treatments for bacterial contamination in medical and industrial settings. Similarly, metabolic markers of bacterial stress can be used as indicators of the presence of chemicals of interest in the environment, such as heavy metals or toxic organic compounds. In both cases, the ability to quickly and accurately detect stress-induced metabolic changes in bacteria is a critical technological challenge uniquely addressed by this nanophotonic sensing platform.

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.

Nontechnical Abstract: The Materials Research Science and Engineering Center (MRSEC) at the University of California, Irvine (UCI) builds on UCI?s strengths in multidisciplinary science and engineering research to establish a major research hub for materials discovery and innovation in the Southern California academe-industry eco-system. The primary mission of this MRSEC is to establish foundational knowledge in materials science by developing new classes of materials that offer unique and broad functionalities. The MRSEC comprises two Interdisciplinary Research Groups (IRGs), each working in close collaboration to address Grand Challenges in national defense and human health. The first IRG aims to create materials which exhibit unprecedented physical properties, such as the ability to withstand extreme environments having applications in national defense. The second IRG team is addressing dynamic, responsive soft materials that are in essence living electronic materials serving as an interface with living systems for healthcare applications. Through seed projects, the UCI MRSEC engages new participants in exciting new research directions. It attracts a diverse group of scientists, including women, underrepresented minority groups, and persons with disabilities, from across the nation and trains future leaders at all academic and professional levels to address critical societal challenges. This MRSEC?s integrated activities?including novel materials research, partnerships with industry and national laboratories, entrepreneurial innovation, career development, and mentorship?are enabling a transformative long-term impact on fundamental science, advanced applications, and workforce development.

Technical Abstract: The UCI MRSEC combines an experimental, computational, and theoretical framework pursuing atomic- and molecular-level design and control of structure and dynamic response through two Interdisciplinary Research Groups (IRGs). IRG 1 investigates the atomic-level structure, chemistry, thermodynamics, and kinetics of interfaces in an emerging class of Complex Concentrated Materials (CCMs) that exhibit exceptional properties such as high strength, ultra-low thermal conductivity, and extremely large dielectric constants. Understanding their structure-property relationships guides design and processing of next-generation structural and functional materials. IRG 2 investigates dissipative self-assembly strategies to understand fundamental charge-matter interactions, with the goal to produce supramolecular ?living? materials. Development of conductive active materials, where assembly is fueled by chemical, electrical, and other stimuli, provides the intellectual framework for a new class of living electronic materials for bio-interfaces and biological computing. The research team leverages state-of-the-art electron microscopy facilities within the Irvine Materials Research Institute and pursues instrumentation innovations to characterize atomic-scale structure and dynamic properties. Multifaceted education, outreach, and collaborations with industry, national laboratories, and nonprofit organizations allow this MRSEC to achieve significant, long-term impact with the targeted scientific advances. This impact includes technological innovation, workforce development, and boosting of the regional and national economy. Synergistic activities provide holistic training of diverse junior scientists at all stages, from K-12, undergraduate, and graduate students to postdoctoral scholars and untenured faculty, further fostering inclusive excellence in STEM.

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.