RESUMEN
Precise measurement of the potential of mean force is necessary for a fundamental understanding of the dynamics and chemical reactivity of a biological macromolecule. The unique advantage provided by the recently developed constant-information approach to analyzing time-dependent single-molecule fluorescence measurements was used with maximum entropy deconvolution to create a procedure for the accurate determination of molecular conformational distributions, and analytical expressions for the errors in these distributions were derived. This new method was applied to a derivatized poly(L-proline) series, P(n)CG3K(biotin) (n = 8, 12, 15, 18, and 24), using a modular, server-based single-molecule spectrometer that is capable of registering photon arrival times with a continuous-wave excitation source. To account for potential influence from the microscopic environment, factors that were calibrated and corrected molecule by molecule include background, cross-talk, and detection efficiency. For each single poly(L-proline) molecule, sharply peaked Förster type resonance energy transfer (FRET) efficiency and distance distributions were recovered, indicating a static end-to-end distance on the time scale of measurement. The experimental distances were compared with models of varying rigidity. The results suggest that the 23 angstroms persistence length wormlike chain model derived from experiments with high molecular weight poly(L-proline) is applicable to short chains as well.
Asunto(s)
Transferencia Resonante de Energía de Fluorescencia/métodos , Péptidos/química , Algoritmos , Biotina/análogos & derivados , Biotina/química , Polarización de Fluorescencia , Transferencia Resonante de Energía de Fluorescencia/instrumentación , Colorantes Fluorescentes/química , Conformación Molecular , Peso MolecularRESUMEN
The photoluminescence dynamics of colloidal CdSe/ZnS/streptavidin quantum dots were studied using time-resolved single-molecule spectroscopy. Statistical tests of the photon-counting data suggested that the simple "on/off" discrete state model is inconsistent with experimental results. Instead, a continuous emission state distribution model was found to be more appropriate. Autocorrelation analysis of lifetime and intensity fluctuations showed a nonlinear correlation between them. These results were consistent with the model that charged quantum dots were also emissive, and that time-dependent charge migration gave rise to the observed photoluminescence dynamics.
Asunto(s)
Compuestos de Cadmio/química , Mediciones Luminiscentes , Modelos Químicos , Puntos Cuánticos , Compuestos de Selenio/química , Sulfuros/química , Compuestos de Zinc/química , Compuestos de Cadmio/efectos de la radiación , Simulación por Computador , Luz , Ensayo de Materiales , Compuestos de Selenio/efectos de la radiación , Sulfuros/efectos de la radiación , Compuestos de Zinc/efectos de la radiaciónRESUMEN
Nanostructures of colloidal CdSe/ZnS core/shell quantum dots (QDs) surrounded by a discrete number of Au nanoparticles were generated via DNA hybridization and purified by gel electrophoresis. Statistics from TEM analysis showed a high yield of designed structures. The distance between Au particles and QD, the number of Au around the central QD, and the size of Au and QD can be adjusted. Rationally designed structures such as these hold great promise for researching the physical interactions between semiconductor and Au nanoparticles and for developing more efficient nanoprobes.
