On the quenching of semiconductor quantum dot photoluminescence by proximal gold nanoparticles

Luminescent quantum dots (QDs) were proven to be very effective fluorescence resonance energy transfer donors with an array of organic dye acceptors, and several fluorescence resonance energy transfer based biosensing assemblies utilizing QDs have been demonstrated in the past few years. Conversely, gold nanoparticles (Au-NPs) are known for their capacity to induce strong fluorescence quenching of conventional dye donors. Using a rigid variable-length polypeptide as a bifunctional biological linker, we monitor the photoluminescence quenching of CdSe-ZnS QDs by Au-NP acceptors arrayed around the QD surface, where the center-to-center separation distance was varied over a broad range of values (approximately 50-200 Angstrom). We measure the Au-NP-induced quenching rates for such QD conjugates using steady-state and time-resolved fluorescence measurements and examine the results within the context of theoretical treatments based on the Förster dipole-dipole resonance energy transfer, dipole-metal particle energy transfer, and nanosurface energy transfer. Our results indicate that nonradiative quenching of the QD emission by proximal Au-NPs is due to long-distance dipole-metal interactions that extend significantly beyond the classical Förster range, in agreement with previous studies using organic dye-Au-NP donor-acceptor pairs.