Sandra J. Rosenthal, Ph.D. - US grants

This starter grant award of the Chemistry Division to Vanderbilt University supports the research of Professor Sandra J. Rosenthal. The theme of the research is the development of time-resolved scanning tunneling microscopy for the study of charge migration in novel optical and electronic materials. The initial material being studied is self-assembled monolayers composed of oligothiophene derivatives. Oligomers consisting of different numbers of the thiophene monomer are synthesized and the degree to which their ability to form ordered monolayers depends upon chain length explored with scanning probe microscopy. The oligothiophene systems are ideal candidates to be incorporated into a molecular transmission line to be used to demonstrate simultaneous picosecond time resolution and molecular spatial resolution of a time-resolved scanning tunneling microscope in the future. The research is a crucial step in a long-term research program for direct observation of both structure and function in novel materials, providing the information necessary to tailor new materials designed for specific device applications. The ability to design new conducting materials contributes to advances in the electronics industry.

This CAREER award to Dr. Sandra Rosenthal at Vanderbilt University is supported by the Advanced Materials Program in the Chemistry Division. The focus of the research is femtosecond fluorescence studies of charge transfer reactions in nanocrystal-based photovoltaic systems with the goal of exploiting quantum confinement in semiconducting nanocrystals to create high speed and efficiency photovoltaics. Specific ojectives are to determine and control the fate of photocreated electron-hole pairs in semiconducting nanocrystals, to determine the rate and mechanism of nanocrystal to C60 electron transfer, to determine the rate and mechanism of nanocrystal to polymer hole transfer, and to determine the ideal nanocrystal size for nanocrystal/C60/polymer-based photovoltaics. Fundamental issues to be addressed will be characterization of semiconductor nanocrystal surfaces at the atomic level and the role surface density of states plays in carrier relaxation and charge-transfer, ultrafast spectroscopy of charge-transfer in systems where a quantum confined semiconductor serves as a donor, and electron transfer in electroactive polymers. This research could impact and lead to commercially viable photovoltaic and optoelectronic devices.

Apart from involving undergraduates in the above research, the teaching component of the CAREER award will facilitate involvement of undergraduates in the Chemistry Department broadly through the establishment of integrated Analytical-Physical Chemistry labs and courses emphasizing use of advanced spectroscopic and surface microscopy instrumentation .

Cell surface receptors, ion channels and transporters are critical components of signaling and excitability in the nervous system and at target sites. As such they represent the majority of drug targets currently explored in the pharmaceutical industry. Currently the detection, quantitation and localization of membrane proteins is achieved largely using radiolabeled ligands or indirectly with antibody techniques. These approaches are limited due to the poor spatial resolution of radiotracer studies and the limited availability of surface domain-selective antibody probes for membrane proteins. In the proposed work a novel fluorescence labeling strategy using drug-conjugated nanocrystals will be developed. This method will enable the monitoring of protein trafficking in real time using fluorescence microscopy. This strategy will be tested using dopamine, norepinephrine and serotonin transporters as well as serotonin (5HT2) receptors. Phenyltropane-conjugated nanocrystals will be synthesized and their affinity for the transporters will be determined by tritiated dopamine, norepinephrine, and serotonin flux assays on transporter transfected cells. Phenylisopropylamine-nanocrystal conjugates will be synthesized and their ability to label 5HT2 receptors will be determined using competition binding and phosphoinositide hydrolysis assays in receptor transfected cells. Epifluorescence and confocal imaging will be used to determine whether the nanoconjugates provide suitable signal for detection of the transporters and receptors in nonpermeabilized cells. To follow transporter or receptor trafficking with fluorescence microscopy nanocrystal-labeled cells will be exposed to exogenus modulators known to cause internalizatioin and redistribution of cell surface transporters and receptors.

This grant supports the acquisition of an ultrashort-pulse, broadly tunable laser facility for the study of electron and phonon dynamics in micro- and nanostructured materials. The facility includes a titanium:sapphire oscillator, a regenerative amplifier for the oscillator, and a set of two optical parametric amplifiers that can be used by the oscillator-amplifier combination. The combined laser systems supply multiple streams of intense, coherent pulses over a wavelength range from ultraviolet to mid-infrared, with pulse duration of 100 fs, The unique experiments made accessible by the availability of this ultrafast laboratory will include: studies of electron-electron correlations, femtosecond dynamics of phase transitions, coherent phonon generation, spectral hole burning in nanostructures, optical spectroscopy of photosynthetic processes in biomimetic nanostructures, studies of fast nonradiative processes in semiconductors, and optical coherence tomography with sub-cellular resolution. The initial program involves researchers with substantial research funding carrying out studies on all of these topics. In addition to the co-investigators named in the proposal, scientists and engineers from several other schools and departments at Vanderbilt, Fisk and neighboring undergraduate institutions are expected to use the facility.

The project will enhance teaching, training and learning through an associated for-credit, two-week intensive training course in ultrafast spectroscopy taught by the co- investigators and associated post-doctoral scholars. This is necessary for effective use of the facility, but will also serve to enrich our graduate curriculum and provide a venue for recruitment of new users. Participation from underrepresented groups will be enhanced through the participation of faculty and students from Fisk University with whom many of the Vanderbilt co-PIs have established collaborative research arrangements. By making available this unique resource to qualified users, the ultrafast laser facility will significantly enhance the current infrastructure for research in Middle Tennessee. Broad dissemination of the results will be ensured not only through the usual scientific venues (conferences, workshops, seminars and colloquia), but also through Vanderbilt's Internet Webzine, Explorations, which is staffed by full-time professionals from the University's Division of News and Public Affairs. Benefits to society can be expected in fields ranging from biomedical engineering to semiconductor science.

The Vanderbilt-Fisk Interdisciplinary Program for Research and Education in the Nanosciences is a graduate level program focused on research and graduate student education associated with nanoscale science and engineering. This IGERT program combines the resources of Fisk University and Vanderbilt University in a unique university partnership. Students may enter Vanderbilt and earn a Ph.D., or enter Fisk University, earn a M.S., and then matriculate to the Vanderbilt Ph.D. The intellectual merit is associated with both the research goal - a fundamental and comprehensive approach to the nano-scale science and engineering; and the educational goal- a program, centered in interdisciplinary materials science, to train graduate students to be self-starters and self-learners. Educational and research goals are built on the extensive need for a true interdisciplinary approach required for modern materials science at the nano-scale level. The research theme is the creation, characterization and modeling of nano-structured materials. This is motivated by recent advances in lower dimensionality and creation of unique nanostructures, to access the realm of designed quantum confinement and to realize new materials properties. The educational component comprises a complete background in the interdisciplinary materials sciences which provide the underpinnings of nano-science and nano scale engineering, including current theory, modeling, and experimental practices. IGERT students will be prepared for the fast changing environment associated within nanotechnology. Features of the educational schedule include research rotations, internships, teaching assignments and specialized courses in interdisciplinary nano-science, literature retrieval and science ethics. The broader impact of this project lies in the very strong coupling between Fisk University (a M.S. granting HBCU) and Vanderbilt University. The IGERT is expected to be a significant factor in the cross-fertilization of these two institutions and the stimulation of under-represented groups to participate in nano-scale research and education. In addition we expect the educational aspects of the IGERT to provide a new concept in interdisciplinary education, tuned to the era of nano-scale science and engineering.

IGERT is an NSF-wide program intended to meet the challenges of educating U.S. Ph.D. scientists and engineers with the interdisciplinary background, deep knowledge in a chosen discipline, and the technical, professional, and personal skills needed for the career demands of the future. The program is intended to catalyze a cultural change in graduate education by establishing innovative new models for graduate education and training in a fertile environment for collaborative research that transcends traditional disciplinary boundaries. In this sixth year of the program, awards are being made to institutions for programs that collectively span the areas of science and engineering supported by NSF.

DESCRIPTION (provided by applicant): Receptor driven cellular behavior, ranging from signaling and excitability in neural activity to immune system response to disease invasion, represents an important class of functional nanobiostructures in biological systems. Receptors are uniquely suited to direct such processes due to their ability to sense the environment, through ligand binding, and their ability to transmit this signal to the cell interior via signal cascades. The goal of this proposal is the development of novel imaging tools and methods to establish a quantitative molecular level understanding of the function of biological receptors. Unfortunately, the study of these fundamental biological components is limited by currently available imaging tools such as radiolabeled ligands or indirect detection via antibodies. These approaches suffer due to the poor spatial resolution of radiotracer studies, the limited availability of surface-domain antibody probes for membrane proteins, the broad emission spectra of available fluorophores and their photochemical degradation. In this proposal, we will continue to develop our novel, non-isotopic, labeling strategy involving ligand-conjugated fluorescent nanocrystals (nanoconjugates). Specifically, we will: 1. Design, synthesize, and characterize novel nanoconjugate probes for imaging neural receptors. 2. Develop a molecular level understanding of nanoconjugate-receptor interactions. 3. Demonstrate dynamic imaging of neurotransmitter receptors in order to map their regulation and function. To accomplish these specific aims, we have assembled a multidisciplinary team including chemists, physicists, pharmacologists and neuroscientists. Completion of this grant will result in the development of a novel class of nanoconjugates based on highly fluorescent small-molecule and peptide conjugated CdSe/ZnS core shell nanocrystals. These probes will enable investigators in neuroscience and membrane biology to answer questions previously unanswerable due to the limitations of current methods. The nanoconjugates described herein present the opportunity for dynamic imaging of fundamental processes involving neural G protein-coupled receptors and transporter proteins. Such "real time" experiments will provide new insight into questions concerning the molecular details of these neuroreceptors, their trafficking and localization in response to external stimuli. Such results will provide new molecular level insights into neural processes such as depression, addiction and learning. Additionally, the nanoconjugates may serve as the basis for new drug discovery methods to identify unique drugs that target specific receptors previously implicated in neurological disorder.

Technical Abstract

The exploration of individual and freely suspended small particles in liquids is presently impaired by Brownian motion which makes a prolonged spectroscopic investigation difficult and for sub 100 nm scaled particles impossible. The proposed instrument will address this challenge through the development of a nanoparticle trap that is expected to allow the positioning, alignment and tracking of individual particles with diameters down to 10 nm. The instrument utilizes novel techniques for interferometric confocal particle detection with high sensitivity and bandwidth, and combines this with feedback controlled electrokinetic or mechanical manipulation of liquid flow in a microfluidic device. Spectroscopic characterization of trapped objects will initially be done using CW and time-resolved fluorescence measurements. The proposed instrument development will thereby provide an interdisciplinary team of researchers from Chemistry-, Pharmacology- and Physics Departments with a unique tool for spectroscopic exploration of individual micron or nano-scale objects in liquid environment. It is envisioned that this instrument may also be used as versatile tool for life sciences allowing prolonged investigation and tracking of viruses, bacteria or self-propelled organisms. The project is coupled to an educational component that consists of training of undergraduate and graduate students with the use of basic as well as advanced optical technologies.


Lay Abstract

As the exploration of the nano and micro-cosmos pushes towards new frontiers, challenges emerge that can prevent scientific progress in certain areas. One such challenge are the difficulties encountered with the investigation of individual sub-micron sized objects in liquids. This is due to Brownian motion which sends particles on a random path and makes prolonged investigation by spectroscopic or other means difficult if not impossible. The proposed instrument will help overcome such limitations through the development of a particle trap which will allow positioning, alignment and tracking of objects with diameters down to a few nanometers. This instrument is thereby expected to furnish an interdisciplinary team of researchers from Chemistry, Pharmacology and Physics Departments with a unique and versatile tool for spectroscopic investigations under previously inaccessible conditions. Moreover, it is envisioned that such an instrument may be used as a tool for life sciences, opening new horizons by allowing prolonged investigation and tracking of viruses, bacteria or self-propelled organisms. Research programs drawing on the use of this instrument are expected to benefit the discovery and development of more efficient materials for solid state light sources and better opto- or nanoelectronic devices for future electronic applications.

We propose an innovative pathway to the PhD for substantially broadening the participation of underrep-resented minorities in materials science, linking multiple NSF-funded materials research programs (CREST and REU) at the partnering institutions. The nucleus of this I3 will be the Fisk-Vanderbilt Masters-to-PhD Bridge program, with its strong track record of enabling students to earn a Master?s degree at Fisk as a stepping stone to the PhD program at Vanderbilt. Vanderbilt and Fisk are joined in this I3 by Dela-ware State University (DSU). Our program?s path to the PhD emphasizes research engagement and de-liberate mentorship by faculty at PhD-granting institutions to help students cross the aspirational and insti-tutional transitions.
We will directly address all of the I3 program goals. In so doing, with the I3 funding requested here we will enable at least 2 underrepresented minority graduate students toward the PhD in Materials Sci-ence each year, representing ~20 times the national institutional average. Over the 5 years of requested I3 support, this represents 10 individuals supported by I3 funding who will complete, or be on the path to-ward completing, the PhD. By itself this is a substantial, tangible result of our innovation and integration and a vital contribution to the STEM workforce.
Arguably even more important for the long-term sustained impact and institutionalization of this program, and the eventual expansion of our Masters-to-PhD Bridge model into additional STEM disci-plines, will be the foundation laid here for truly understanding how best to design the architecture of our model to ensure successful portability into new disciplinary and institutional contexts.
We will:
1.
Expand the Fisk-Vanderbilt Masters-to-PhD Bridge Program to include Materials Science. Key faculty have been identified as the ?bridge builders? following the model of the existing program in physics. Leveraging significant institutional support already in place, we will ex-pand and deepen the footprints of our NSF-funded CREST projects and enhance their sus-tainability.
2.
Extend the Bridge Program in partnership with Delaware State University. The resulting Fisk-Vanderbilt-DSU Masters-to-PhD Bridge Program will permit students to transition from the MS at Fisk to the PhD at Vanderbilt, from the MS at Fisk to the PhD at DSU, or from the MS at DSU to the PhD at Vanderbilt. The result will be increased synergy and collaboration across our NSF-funded CREST and REU programs, reducing the artificial boundaries that can so often impede student mobility across educational junctures.

Broadening Participation in Materials Science through Institutional Integration of a Masters-to-PhD Bridge Program at Fisk, Delaware State, and Vanderbilt Universities brings together NSF/EHR awards from the IGERT and CREST programs, as well as other work, around the I3 integrative themes for broadening participation, critical educational junctures, and the integration of research and education.

Cell surface receptors, ion channels, and transporters are critical components of signaling and excitability in the nervous system. As such, they represent the majority of drug targets currently being explored in the pharmaceutical industry. Basic studies have revealed that these proteins are nonuniformly distributed on neurons and targets and this distribution can be impacted by multiple signal transduction pathways and endogenous regulatory programs. Moreover, many drugs appear to alter the responsiveness, distribution and/or surface abundance of their protein targets following chronic occupancy. Currently, the detection, quantitation and localintion of membrane proteins is achieved largely using radiolabeled ligands or indirectly with antibody techniques. These approaches are limited due to the poor spatial resolution of radiotracer studies, the limited availability of surface domain-selective antibody probes for membrane proteins, the broad emission spectra of available fluorophores and their photochemical degradation. In this proposal we will continue to develop our novel, non-isotopic, labeling strategies with a principal focus on drug-conjugated fluorescent nanocrystals (nanoconjugates) that can permit the imaging and quantitative analysis of cell surface receptor and transporter proteins. Specifically we will: I. Synthesize improved nanocrystal probes. II. Establish dynamic imaging of the serotonin transporter protein. III. Develop pharmacological assays that exploit the unique properties of drug-conjugated nanocrystals. To accomplish these aims we have assembled an interdisciplinary team of chemists, microscopists, pharmacologists and neuroscientists. The experiments proposed here exploit the unique optical properties of fluorescent nanocrystals and cannot be performed with traditional organic fluorophores or fluorescent proteins. In this proposal nanotechnology interfaces with neuroscience in a way that advances both fields.

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).

This project will modernize the 10000 cleanroom facility in the Vanderbilt Institute of Nanoscale Science and Engineering (VINSE) core laboratory complex. This 1635 square foot cleanroom facility has been in continuous service since 2003. At present many faculty members and students are working on different research projects using this cleanroom facility including studies on solar energy conversion from electron field emission, thermal transport in carbon nanotubes, biosensor synthesis requiring e-beam lithography, and metal-insulator transitions that are modulated by optics. For the continued safe use of this cleanroom facility, it is in need of replacement of the following two essential components: 1) Toxic Gas Monitoring System (TGMS); and 2) HEPA filter fan units (FFU). This proposal is to replace the old TGMS unit with a new one, and make the cleanroom compatible to the current standards. The new TGMS unit is expected to detect all of the gases used or generated in a Semiconductor manufacturing facility.

Teaching, training and educational activities using the Vanderbilt Institute of Nanoscale Science and Engineering (VINSE) core laboratory complex are well defined and detailed in the proposal, and cleanroom facilities play a key role in these activities. In addition, the NSF supported IGERT program at Vanderbilt University with Fisk University provides opportunity for underrepresented minority students to be trained and educated using the VINSE Core Laboratory facilities. These facilities are also used by students and faculty members from Delaware State University for their education and research activities. Other outreach activities included nanoscience and nanotechnology programs for high school students through Vanderbilt Summer Academy.

The Vanderbilt Institute for Nanoscale Science and Engineering (VINSE) summer REU program will offer science and engineering undergraduate students the opportunity to work closely with faculty on research projects in the field of nanoscale science and engineering. VINSE faculty will provide REU students with an interdisciplinary research experience in an environment where physicists, chemists, biologists, and engineers collaboratively solve problems and create new scientific understanding. The overarching theme of the research is nano-materials innovation and fabrication for a wide range of applications from materials for drug delivery to efficient solar energy conversion. In nano-materials, the key structural features are about 1 thousandth of the width of a human hair.

Nanoscience and nanotechnology are based on the ability to synthesize, organize, characterize, and manipulate matter systematically at the nanoscale, creating uniquely functional materials which can be inorganic, organic or biological, or a hybrid of any two or more of these. Consequently, nanoscience and nanotechnology pose formidable challenges that cut across traditionally distinct disciplines. Clearly, to meet these demands, the training of future scientists and engineers in the broad field of nanotechnology is of paramount importance. The interdisciplinary nature of nanoscale science and engineering means it inherently involves all of the sciences and engineering, resulting in the need to train students at all levels in an interdisciplinary manner. This should include an appreciation for the way a solid grounding in the undergraduate major program prepares for interdisciplinary research, and gaining a real-world perspective of the need for their research to progress "beyond the bench". This REU will provide precisely this opportunity by combining Vanderbilt's unique interdisciplinary research opportunities at the nanoscale, with participation in research in a discipline-based experimental laboratory or computational setting. Consequently, students trained through this interdisciplinary summer program will leave with an appreciation of the skills needed to successfully contribute to the emerging disciplines of nanoscience and nanotechnology. The REU students will also be offered the opportunity for training in the integration of research with education and outreach through participation in the Vanderbilt Summer Academy for gifted high school students who have expressed an interest in nanoscience and nanotechnology.

This REU site is co-funded by the NSF Divisions of Materials Science (DMR) and Engineering Education and Centers (ENG/EEC).

0957701
Rosenthal
Vanderbilt U.

Technical Summary:
This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).

This proposal is for the acquisition of a deposition tool that has the capability to sequentially evaporate high quality, defect-free organic, metal, and oxide films without cross-contamination or exposure to air. An attached spin-coating coating unit (also in inert environment) allows the integration of nanocrystals and polymers, extending the fabricating capabilities of the tool. The instrumentation will be used for a broad range of research projects spanning the disciplines of physics, chemistry, engineering and the life sciences, all within the central theme of nanoscience. The capabilities of this deposition cluster tool will enable transformative research initiatives addressing a large range of forefront nanoscience and nanotechnology challenges, from nanoscale plasmonics to biological sensing on single cells, and from efficient solid-state lighting to graphene devices. The deposition tool will also enhance student learning, as students who grow their own materials and design/build their own materials structures are forced to engage the science at a much deeper level than they would if relying on outside sources for samples made elsewhere. The instrument will be housed and operated by the Vanderbilt Institute for Nanoscale Science and Engineering and will improve the research and training of many young scientists including under-represented students (supported by a NSF IGERT for Fisk (an HBCU) and Vanderbilt) and a diverse group of professors near the beginning of their careers. In addition to incorporating the instrumentation into graduate and undergraduate course work, the deposition system will be a part of three outreach efforts involving summer programs for high school students.


Layman Summary:
This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).

Intrinsic to building any device is the capability to deposit material. A single deposition might be the evaporation of aluminum onto graphene to make electrical contact, whereas more complicated structures might involve evaporating multiple layers of different organic materials and metals to make a desired device structure, such as a solar cell or a solid state lighting device. This proposal is for the acquisition of a versatile materials deposition system that has the capabilities to deposit organic films, metal films, and metal oxide films. The deposition system is in an air free environment such that the films do not react with air, and the different materials are in different chambers in such a fashion that depositing one film layer does not contaminate another, and such that the films can be deposited sequentially. The instrumentation will be used for a broad range of research projects spanning the disciplines of physics, chemistry, engineering and the life sciences, all within the central theme of nanoscience.
The capabilities of this instrument will enable transformative research initiatives addressing a large range of forefront nanoscience and nanotechnology challenges, from nanoscale plasmonics to biological sensing on single cells, and from efficient solid-state lighting to graphene devices. The instrument will be housed and operated by the Vanderbilt Institute for Nanoscale Science and Engineering and will improve the research and training of many young scientists including under-represented students (supported by a NSF IGERT for Fisk (an HBCU) and Vanderbilt) and a diverse group of professors near the beginning of their careers. In addition to incorporating the instrumentation into graduate and undergraduate course work, the deposition system will be a part of three outreach efforts involving summer programs for high school students. Many of the proposed research efforts utilizing the deposition system pertain to energy, including the creation of new types of solar cells, bio-fuel cells, and energy conserving solid state lighting. Progress in these areas would benefit society by creating renewable energy, reducing demand on current power sources, and subsequently reducing greenhouse gas emissions.

This research aims to elucidate how the atomic structure of core/shell nanocrystals (quantum dots) impacts their photophysics. In this work, Prof. Sandra Rosenthal and Prof. James McBride of Vanderbilt University leverage modern chemical techniques to synthesize quantum dots of varying composition and shell coverage, which will then be imaged with atomic resolution via aberration-corrected scanning transmission electron microscopy (STEM). Further, these structures will be characterized utilizing single nanocrystal spectroscopy as well as ultrafast fluorescence upconversion spectroscopy to obtain blinking statistics in addition to exciton dynamics. Ultimately, methodologies to perform correlated single nanocrystal spectroscopy and aberration-corrected STEM will be developed in order to precisely determine which specific nanostructures provide the highest fluorescence yield, photostability and reduced blinking; information that is lost in ensemble measurements.

The utilization of state-of-the-art electron microscopy in conjunction with single molecule fluorescence techniques will clarify the true effect of shell coverage and composition. This will have immediate impact on commercial applications utilizing quantum dot fluorescence as biological probes and current efforts to incorporate highly fluorescent and stable quantum dots for solid-state lighting. Improvement in fluorescent probes will lead to higher sensitivity for drug discovery applications as well as allowing for direct measurements of biological dynamics at the single molecule level. Additionally, perfecting quantum dot design will greatly enhance the efficiency and extend the lifetime of quantum dot-based solid state lighting devices. Undergraduate research will play an integral role in the synthesis and characterization of the nanocrystals, while fostering an understanding of how to devise, implement an experiment, and how to interpret and present data. A kit demonstrating the size-dependent quantum dot fluorescence as an introduction to 'nano' will be developed for the Vanderbilt Students Volunteers for Science organization (VSVS), which arranged more than four hundred classroom visits last year and will be extended to rural TN via an NSF EPSCoR award.

With this award, the Macromolecular, Supramolecular and Nanochemistry Program of the Chemistry Division is funding Professors Sandra Rosenthal and James McBride at Vanderbilt University to accelerate the development of sub-microscopic crystals of semiconductors, or quantum dots. These structures emit light and are used in diverse applications such as solid state lighting and displays and labeling of biological structures for analysis using microscopy. The PIs have developed a new characterization method to determine how the efficiency of light emission from a quantum dot is correlated to its atomic structure. The ultimate goal is to optimize the light emission of quantum dot systems that do not utilize toxic lead and cadmium. As a part of this effort, the growing field of nanotechnology is being introduced to the next generation of scientists through undergraduate research opportunities and outreach activities for rural middle-school students.

The proposed work is to synthesize cadmium free, colloidal core/shell nanocrystals and to characterize their ensemble charge carrier dynamics using femtosecond fluorescence upconversion spectroscopy. In parallel, the best performing structures will be identified by correlating fluorescence dynamics at the single nanocrystal level with the same particle's atomic structure and chemical composition determined using high resolution high angle annular darkfield scanning transmission electron microscopy (HAADF-STEM) in conjunction with energy dispersive spectroscopy mapping (STEM-EDS) utilizing Vanderbilt's Tecnai Osiris. The information gained through the ensemble carrier dynamics and the correlation study provides a target to improve the current synthesis methodology.

The Macromolecular, Supramolecular, and Nanochemistry Program in the Chemistry Division supports Professor Sandra Rosenthal and her group at Vanderbilt University to study new quantum dots that are free of toxic heavy metals. Quantum dots which are nanometer-sized versions of semiconductors represent a success stories arising out of the nanotechnology revolution. Quantum dots are notable for their size-dependent light interactions. Quantum dots are tools for neuroscience as they can be used to track individual proteins on a living cell?s surface. Quantum dots occupy a growing portion of the electronic display market due to the vivid colors they produce. While the use and importance of quantum dots are growing, the best performing quantum dots are composed of cadmium, a toxic heavy metal. Indium-based quantum dots are made from non-toxic materials and show comparable color purity and brightness, but struggle in challenging environments such as those found in biological systems. To accelerate the development of new quantum dots, Professor Rosenthal and her research team are using a method to directly correlate the structure of individual quantum dots with their optical performance. In systems where every atom in each quantum dot matters, this methodology can reveal new insights into how complex quantum dot structures yield specific optical behavior. This research enables scientists and engineers to precisely design and synthesize customized quantum dot light emitters as part of advanced manufacturing efforts. As a part of this project, the next generation of scientists are introduced to the growing field of nanotechnology through undergraduate research opportunities and outreach activities for the middle-school students in rural Tennessee.

With this award from the Macromolecular, Supramolecular, and Nanochemistry Program, Professor Rosenthal?s research group develops and studies heavy metal-free colloidal quantum dots, including transition metal-based systems. The heavy metal-free quantum dots are being synthesized with complex architectures with the goal of tuning their brightness and photostability. Ultrafast fluorescence upconversion and nanosecond fluorescence spectroscopy are employed to probe both the short and long-time scale carrier dynamics of the photogenerated electrons and holes revealing the effectiveness of the surface passivation. Advanced analytical electron microscopy in conjunction with aberration-corrected scanning transmission electron microscopy (STEM) are used to reveal the chemical and atomic arrangement of the synthesized quantum dots. Further, correlated single particle nanocrystal spectroscopy with STEM imaging is being used to identify structure-function relationships that provide guidance for subsequent synthesis.

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.