Denise Williams

Participant: PROMISE AGEP Research Symposium


Denise N. Williams

Department: Chemistry and Biochemistry

Institution: University of Maryland Baltimore County (UMBC)



Future Antibiotics? Interactions between Quantum Dots and Bacterial Cells

Quantum dots are luminescent semiconductor nanoparticles with unique optical and chemical properties. These properties have found purpose in technologies of several different fields of science, including energy harvesting, computing, chemistry, and biology. Specifically considering biological implications, QDs can be found in luminescent probes, cancer sensors, and constructs for antibiotic purposes. Essential to the use of QDs in biology is the understanding of how QDs interact with their environment. Research to this end has focused on unintended interactions between QDs and bacteria as their size and metal components have known harmful impacts on bacteria viability, but scientists are beginning to research how to turn unintended and harmful interactions into targeted ones. This talk will review the concept of turning cell-penetrating interactions between QDs and bacteria into targeted treatments specifically against pathogenic bacteria.



Synthesis and Environmental Studies of CdSe/ZnS and ZnSe/ZnS Quantum Dots

Denise Williams1, Sunipa Pramanik2, Christy Haynes2, and Zeev Rosenzweig1

  1. University of Maryland Baltimore County, Department of Chemistry and Biochemistry, Baltimore, MD 21250
  2. University of Minnesota, Department of Chemistry, Minneapolis, MN 55455

This presentation describes the synthesis, characterization, and environmental impact of luminescent CdSe/ZnS and ZnSe/ZnS quantum dots (QD). Cadmium-containing QD, such as CdSe/ZnS, are commonly used because of their superior optical properties in comparison to other material QD. More recently though, cadmium-free alternatives, such as ZnSe/ZnS QD, are becoming more attractive because they lack this known toxic element which should inevitable reduce the environmental impact of QD. The synthesis of the CdSe/ZnS and ZnSe/ZnS systems are similar colloidal processes, differing only in the use of dopants for the ZnSe/ZnS QD to cause the emission profile to mirror that of the CdSe/ZnS QD. The material characterization of these QD involves analysis of brightness, polydispersity, lifetime, chemical stability, and photostability using absorbance, fluorescence, and mass spectrometry techniques. With the anticipation that cadmium-free QD may replace cadmium-containing QDs in a wide range of applications, the environmental impact of the two systems is modeled in this study with the organism Shewanella oneidensis MR-1. These studies have validated the hypothesis that the ZnSe/ZnS QD can be significantly less toxic than their cadmium alternative, while allowing for an optically comparable technology.



Denise N. Williams is a third year graduate student at the University of Maryland, Baltimore County (UMBC) as a member of Dr. Zeev Rosenzweig’s research group. With this group, she studies the synthesis, characterization and environmental impact of optically active quantum dots. Denise is currently a National Science Foundation AGEP Fellow, a Meyerhoff Graduate Fellow, and a research member of the Center for Sustainable Nanotechnology. Prior to her time at UMBC, Denise earned a Bachelor of Science in Chemistry and a Bachelor of Science in Forensic Science from the University of New Haven in West Haven, Connecticut in May 2015.



Denise Williams’ current research focuses on the synthesis and characterization of luminescent CdSe, CdTe, ZnSe, and InP quantum dots (QDs) in an effort to replace toxic cadmium-containing nanomaterials with sustainable materials of similar optical capabilities. She has begun synthesizing and comparing the chemical properties, optical properties and toxic impacts of ZnSe QDs and CdSe QDs against model liposomes, bacteria, and nematodes. Thus far, a clear difference in the interactions these QDs have with their environment is evident and being investigated on a molecular level.

Beyond comparing the material implications on QD interactions, the affect various surface coatings have on interactions between QDs and bacteria is under investigation. Molecular, polymer, and peptide coatings have been investigated in the field to deter and to cause specific interactions between nanoparticles and bacteria. Denise’s research will aim to add unique polymer and peptide coatings to the surface of cadmium-free QDs in order to specifically target pathogenic bacteria over bacteria essential for human and environmental health.



  1. Williams, D.; Pramanik, S.; Haynes, C.; Rosenzweig, Z. (2017, August). Shewanella oneidensis MR-1 Toxicity Studies with CdSe and ZnSe Quantum Dots. Oral presentation at the 254th American Chemical Society National Meeting & Exposition in the Colloids division.
  2. Williams, D. (2017, March). Bacterial impact studies of CdSe quantum dots versus ZnSe quantum dots. Three Minute Thesis competition presentation at UMBC Graduate Research Conference. First place presentation.
  3. Tull, R. G.; Reed. A. M.; Felder, P. P.; Hester, S.; Williams, D. N.; Medina, Y.; Lo, A.; Aparaka, E. T.; Ordonez, P. Hashtag #ThinkBigDiversity: Social Media Hacking Activities as Hybridized Mentoring Mechanisms for Underrepresented Minorities in STEM. 2017 ASEE Annual Conference & Exposition, Columbus, Ohio. 2017
  4. Pham, S.; Kuether, J.; Gallagher, M.; Hernandez, R.; Williams, D.; Zhi, B.; Mensch, A.; Hamers, R.; Rosenzweig, Z.; Fairbrother, D. Howard; Krause, M.; Feng, V. Z, ; Haynes, C. Carbon Dots: A modular activity to teach fluorescence and nanotechnology at multiple levels. Chem. Edu. 2017, 94 (8), 1143–1149.
  5. Lyons, T. Y.; Williams, D. N.; Rosenzweig, Z. Addition of Fluorescence Lifetime Spectroscopy to the Tool Kit Used to Study the Formation and Degradation of Luminescent Quantum Dots in Solution. Langmuir. 2017, 33 (12), 3018-3027.


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