Professor of Chemistry
Ph.D., The University of Chicago, 1993
sandra.j.rosenthal@vanderbilt.edu
Rosenthal Research Group

Nanocrystals
In the Rosenthal group we study semiconducting nanocrystals, a novel material whose optical properties and electronic structure can be precisely tuned by controlling the size of the nanocrystal. We are specifically interested in two applications exploiting the properties of nanocrystals: the use of nanocrystals as the light harvesting element in photovolatic devices and the use of fluorescent nanocrystals as biological probes for membrane proteins involved in neuronal signaling. We have also recently begun a program to explore the possible use of nanocrystals as a white light emitter for implementation in solid state lighting.

Solar Cells
Nanocrystals are an ideal light harvester in photovoltaic devices. The band gap can be exquisitely tuned by controlling the size of the nanocrystal,thus the proper choice of size and type of nanocrystal allows one to create a photovoltaic whose absorption spectrum matches the spectral distribution of sunlight. The nanocrystals absorb sunlight more strongly than dye molecules or the bulk semiconductor material, therefore high optical densities can be achieved while maintaining the requirement of thin films. Perfectly crystalline CdSe nanocrystals are also an artificial reaction center, separating the electron hole pair on a femtosecond timescale. Nanocrystals have an intrinsic dipole moment originating from the top and bottom terminating planes of Se and Cd. Carriers are rapidly localized to the surface of the crystal where they remain for 290ns before recombining. The size-tunable band gap, large absorption coefficients, intrinsic electron hole pair separation, long exciton lifetime, and chemical robustness make nanocrystals the ideal material for solar cells. The photovoltaic devices we make in our laboratory could eventually be fabricated inexpensively at low temperatures and can cover large areas.

Biological Labs
Fluorescent nanocrystals have several advantages over organic dye molecules as fluorescent markers in biology. They are incredibly bright and do not photodegrade. They have narrow, guaussian emission spectra enabling the co-localization of several proteins simultaneously. Drug-conjugated nanocrystals attach to the protein in an extracellular fashion, enabling movies of protein trafficking. We are synthesizing drug-conjugated nanocrystals which have high affinities and selectivities for serotonin, dopamine, and norepinephrine receptor and transporter proteins. These are neurotransmitters which control critical behaviors such as mood, sleep, appetite, and aggression. With the drug-conjugated nanocrystals we will be able to map the distribution of these proteins and be able to determine mechanisms which regulate protein expression at the cell surface. These proteins are also drug targets for the serotonin selective reuptake inhibitors, atypical antipsychotics, and drugs of abuse. The drug-conjugated nanocrystals also form the basis of a high-throughput fluorescence assay for drug discovery.

Solid-State Lighting
In response to ever increasing energy demands and subsequent costs, a tremendous emphasis is being placed on energy saving, solid state lighting devices in the form of light emitting diodes, or LED's. Specifically, a need exists for pure white-light LED's as a more efficient replacement for conventional lighting sources. Switching to solid state lighting would reduce global electricity use by 50% and reduce power consumption by 760 GW in the United States alone over a 20 year period. The complications associated with design and fabrication of such devices have generated great interest in developing white-light phosphors that do not depend on complex doping schemes or combinations of materials. One proposed solution is to use a mixture of semiconductor nanocrystals as the intrinsic emitting layer for an LED device. Semiconductor nanocrystals exhibit high fluorescence quantum efficiencies and large molar absorptivities. However, they still suffer from the problem that simply mixing the traditional red, green, and blue colors to achieve white light results in a loss in total device efficiency due to self absorption for a device of more than a few monolayers. We have demonstrated white-light emission from ultra-small cadmium selenide (CdSe) nanocrystals. This raises the intriguing possibility of using these nanocrystals as a white-light phosphor. These ultra-small nanocrystals exhibit broadband emission (420 - 710 nm) throughout most of the visible light spectrum while not suffering from self absorption. This is the direct result of the extremely narrow size distribution and an unusually large (40-50 nm) Stokes shift making them ideal materials for devices currently under development and also an ideal platform to study the molecule-to-nanocrystal transition.

Fundamental Studies
We also perform fundamental studies on semiconducting nanocrystals. We have pioneered the use of Rutherford backscattering spectroscopy and atomic number scanning transmission electron microscopy to determine atomic level constitution and structure of nanocrystals with unprecedented detail. We use ultrafast spectroscopy to map out the ultrafast carrier dynamics of electrons and holes inside the nanocrystals and to follow the charge transfer reactions of the nanocrystals inside the photovoltaics.

Selected Publications

Bowers MJ, McBride JR, Garrett MD, Sammons JA, Dukes AD, Schreuder MA, Watt TL, Lupini AR, Pennycook SJ, Rosenthal SJ. Structure and Ultrafast Dynamics of White-Light-Emitting CdSe Nanocrystals. Journal of the American Chemical Society. 2009, 131 (16): 5730-+.

Schreuder MA, McBride JR, Dukes AD, Sammons JA, Rosenthal SJ. Control of Surface State Emission via Phosphonic Acid Modulation in Ultrasmall CdSe Nanocrystals: The Role of Ligand Electronegativity. Journal of Physical Chemistry C. 2009, 113 (19): 8169-8176.

Wamement MR, Tomlinson ID, Chang JC, Schreuder MA, Luckabaugh CM, Rosenthal SJ. Controlling the reactivity of ampiphilic quantum dots in biological assays through hydrophobic assembly of custom PEG derivatives. Bioconjugate Chemistry. 2008, 19 (7): 1404-1413.

Smith NJ, Emmett KJ, Rosenthal SJ. Photovoltaic cells fabricated by electrophoretic deposition of CdSe nanocrystals. Applied Physics Letters. 2008, 93 (4): 043504.

Garrett MD, Dukes AD, McBride JR, Smith NJ, Pennycook SJ, Rosenthal SJ. Band edge recombination in CdSe, CdS and CdSxSe1-x alloy nanocrystals observed by ultrafast fluorescence upconversion: The effect of surface trap states. Journal of Physical Chemistry C. 2008, 112 (33): 12736-12746.

Dukes AD, Schreuder MA, Sammons JA, McBride JR, Smith NJ, Rosenthal SJ. Pinned emission from ultrasmall cadmium selenide nanocrystals. Journal of Chemical Physics. 2008, 129 (12): 121102.

Koktysh DS, McBride JR, Rosenthal SJ. Synthesis of SnS nanocrystals by the solvothermal decomposition of a single source precursor. Nanoscale Research Letters. 2007, 2 (3): 144-148.

Tomlinson ID, Warnerment MR, Mason JN, Vergne MJ, Hercules DM, Blakely RD, Rosenthal SJ. Synthesis and characterization of a pegylated derivative of 3-(1,2,3,6-tetrahydro-pyridin-4yl)-1H-indole (IDT199): A high affinity SERT ligand for conjugation to quantum dots. Bioorganic & Medicinal Chemistry Letters. 2007, 17 (20): 5656-5660.

Addae-Mensah KA, Kassebaum NJ, Bowers MJ, Reiserer RS, Rosenthal SJ, Moore PE, Wikswo JP. A flexible, quantum dot-labeled cantilever post array for studying cellular microforces. Sensors and Actuators A-Physical. 2007, 136 (1): 385-397.

Rosenthal SJ, McBride J, Pennycook SJ, Feldman LC. Synthesis, surface studies, composition and structural characterization of CdSe, core/shell and biologically active nanocrystals. Surface Science Reports. 2007, 62 (4): 111-157.

Wijtmans M, Rosenthal SJ, Zwanenburg B, Porter NA. Visible light excitation of CdSe nanocrystals triggers the release of coumarin from cinnamate surface ligands. Journal of the American Chemical Society. 2006, 128 (35): 11720-11726.

Tomlinson ID, Mason JN, Blakely RD, Rosenthal SJ. High affinity inhibitors of the dopamine transporter (DAT): Novel biotinylated ligands for conjugation to quantum dots. Bioorganic & Medicinal Chemistry Letters. 2006, 16 (17): 4664-4667.

Swafford LA, Weigand LA, Bowers MJ, McBride JR, Rapaport JL, Watt TL, Dixit SK, Feldman LC, Rosenthal SJ. Homogeneously alloyed CdSxSe1-(x) nanocrystals: Synthesis, characterization, and composition/size-dependent band gap. Journal of the American Chemical Society. 2006, 128 (37): 12299-12306.

Bentzen EL, Tomlinson ID, Mason J, Gresch P, Warnement MR, Wright D, Sanders-Bush E, Blakely R, Rosenthal SJ. Surface modification to reduce nonspecific binding of quantum dots in live cell assays. Bioconjugate Chemistry. 2005, 16: 1488-1494.

Bowers MJ, McBride JR, Rosenthal SJ. White-light emission from magic-sized cadmium selenide nanocrystals. Journal of the American Chemical Society. 2005, 127: 15378-15379.

Mason JN, Farmer H, Tomlinson ID, Schwartz JW, Savchenko V, DeFelice LJ, Rosenthal SJ, Blakely RD. Novel fluorescence-based approaches for the study of biogenic amine transporter localization, activity, and regulation. Journal of Neuroscience Methods. 2005, 143: 3-25.

McBride JR, Kippeny TC, Pennycook SJ, Rosenthal SJ. Aberration-corrected Z-contrast scanning transmission electron microscopy of CdSe nanocrystals. Nano Letters. 2004, 4: 1279-1283.

L Swafford and Rosenthal SJ, in Molecular Nanoelectronics, M Reed and T Lee. Molecular and Nanocrystal Based Photovoltaics. American Scientific Publishers. 2003, Chapter 10: 263-290.

Rosenthal SJ, Tomlinson A, Adkins EM. Targeting Cell Surface Receptors with Ligand-Conjugated Nanocrystals. Journal of the American Chemical Society. 2002, 124: 4586.

Kippeny T, Swafford LA, Rosenthal SJ. Semiconductor Nanocrystals: A Powerful Visual Aid for Introducing the Particle in a Box. Journal of Chemical Education. 2002, 79: 1094.

Underwood DF, Kippeny T, Rosenthal SJ. Ultrafast Carrier Dynamics in CdSe Nanocrystals Determined by Femtosecond Fluorescence Upconversion Spectroscopy. Physical Chemistry B. 2001, 105: 436-443.

Specialties

• VICB
• Physical Chemistry
• Nanomaterials Chemistry