Quantifying Quantum Dots through Förster Resonant Energy Transfer

• Published in: Journal of physical chemistry. C 2011-10, Vol.115 (40), p.19578-19582
• Main Authors: Snee, Preston T, Tyrakowski, Christina M, Page, Leah E, Isovic, Adela, Jawaid, Ali M
• Format: Article
• Language: English
• Subjects: C: Nanops and Nanostructures
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp205833q

Semiconductor nanocrystals (NCs or quantum dots) have significant potential for use in a variety of applications from renewable energy generation to biological imaging. Modern methods of colloidal synthesis can be used to create crystalline materials with tight size distributions; this assures high quantum yields and narrow emission profiles in the case of direct-bandgap semiconductors. The optical properties of NCs may also be tuned with size due to quantum confinement effects. Quantum confinement also creates problems when characterizing nanomaterials; specifically, the absorptivity of a sample is a function of the size and structure of the quantum dots. We demonstrate here a simple method for determining the molar absorptivity of aqueous CdSe/CdZnS NCs through Förster resonant energy transfer. Energy transfer from NC donors to dye acceptors was measured and modeled using standard Förster theory incorporating Poissonian statistics to calculate the acceptor/donor ratio leading to a direct determination of the NC concentration. This process is significantly more simple than standard methods for calculating the size-dependent Beer’s law coefficient of nanomaterials and can be applied to heterogeneous quantum confined systems. The results also yield surprising insight into the internal structure of water-soluble polymer-coated core/shell quantum dots.