The coupling of a gold nanoparticle to peptides and/or nucleic acids can allow imaging of intracellular events when optically labelled by molecular dyes. The use of a gold bio-optical transponder (BOT) capable of simultaneously reporting the timing of intracellular cargo delivery, cargo release from a gold nanoparticle, and subsequent cellular processing provides direct insight into the endo-lysosomal processing of nano-based delivery probes. The paper will explore use of BOT sensors to monitor peptide dependent uptake of AuNPs into native vs drug resistant melanoma cells; monitor the effect off surface coupling of gene knock-in, and explore the ability to evaluate the evolving intracellular pH (pHi) during endosomal maturation. The BOT is designed around use of multicolor surface energy transfer (SET) to simultaneously track processes and provide an internal reference for ratiometric analysis of events. The use of a BOT based sensor to explore intracellular processing may enable greater insight into our understanding of the fundamental processes of biology.
Energy transfer from organic fluorophores to small metal nanoparticles is being used as a molecular beacon tool to monitor the kinetic processes of the hammerhead ribozyme. This marks the first time that nanomaterials have been used to monitor ribozyme kinetics. The quantum efficiency of energy transfer from the fluorophore to the gold nanoparticle follows a distance dependence behavior, which allows the real-time characterization of ribozyme complex structure and cleavage kinetics. The rate of cleavage for our ribozyme at pH=6.5 and 37°C is measured to be on the order of 10<sup>-2</sup> min<sup>-1</sup>, which is the correct order of magnitude for similar ribozymes at this pH in the literature.
In this submission, we report on the results of spectroscopic studies of charge carrier dynamics in colloidal In<sub>1-x</sub>Ga<sub>x</sub>P quantum dots (QDs) with low levels of Ga doping (<i>x</i>~1%). These QDs exhibit large global Stokes shift of fluorescence (up to 300 meV) along with high emission yield (up to 30% in solution and 25% in films under blue excitation at 300 K) after post-synthesis photo-chemical treatment. In order to reveal the nature of large fluorescence Stokes shift and study the band-edge carriers dynamics, we performed time-resolved measurements of emission and photo-induced absorption changes in QDs with different sizes and surface passivation. The work was focused on the studies of differences between QDs subjected to photochemical surface passivation and bare nanoparticles. Time-resolved absorption spectroscopy indicates that holes' trapping strongly depends on passivation of surface trap states and can even suppress Auger multiparticle recombination in poorly passivated nanoparticles. Transient fluorescence measurements in well-passivated nanoparticles demonstrate that at short delays (<2 ns), emission Stokes shift is almost twice smaller than in steady-state measurements and matches the emission band in unpassivated QDs. At longer delays, time-resolved emission matches the spectra obtained with continuous wave (CW) excitation. We propose that initially photoluminescence occurs from quantum-confined state and subsequent hole relaxation onto surface/interface sites gives rise to emission with large global Stokes shift. In poorly passivated QDs, holes escape quickly to deep-trap states that leads to formation of low-efficiency broad emission band red-shifted with respect to the excitonic PL band.
Conference Committee Involvement (2)
Colloidal Nanoparticles for Biomedical Applications VIII
2 February 2013 | San Francisco, California, United States
Colloidal Nanocrystals for Biomedical Applications VII
21 January 2012 | San Francisco, California, United States