Single-Molecule Triplet-State Photon Antibunching at Room Temperature

We have probed single-molecule metal-to-ligand charge transfer (MLCT) dynamics of a ruthenium complex at room temperature. Using photon antibunching measurements under continuous wave (CW) laser excitation, nonclassical photon statistics, and excitation power dependent measurements, we were able to selectively measure the single-molecule MLCT state lifetime. This work demonstrated, as the first single-molecule photon antibunching measurement of the triplet excited state, a new application of single-molecule spectroscopy on excited-state dynamics and ground-state recovering dynamics of an important class of chemical species that have often been used and studied in energy conversion and electron transfer

Single-Molecule Triplet-State Photon Antibunching at Room Temperature

We have probed single-molecule metal-to-ligand charge transfer (MLCT) dynamics of a ruthenium complex at room temperature. Using photon antibunching measurements under continuous wave (CW) laser excitation, nonclassical photon statistics, and excitation power dependent measurements, we were able to selectively measure the single-molecule MLCT state lifetime. This work demonstrated, as the first single-molecule photon antibunching measurement of the triplet excited state, a new application of single-molecule spectroscopy on excited-state dynamics and ground-state recovering dynamics of an important class of chemical species that have often been used and studied in energy conversion and electron transfer

Clay Nanoparticle-Supported Single-Molecule Fluorescence Spectroelectrochemistry

Here we report that clay nanoparticles allow formation of a modified transparent electrode, spontaneous adsorption of fluorescent redox molecules on the clay layer, and thus the subsequent observation of single-molecule fluorescence spectroelectrochemistry. We can trace single-molecule fluorescence spectroelectrochemistry by probing the fluorescence intensity change of individually immobilized single redox molecules modulated via cyclic voltammetric potential scanning. This work opens a new approach to explore interfacial electron transfer mechanisms of redox reactions

Single-Molecule Spectroscopy of the Conjugated Polymer MEH-PPV

Single-Molecule Spectroscopy of the Conjugated Polymer MEH-PP

Revealing Two-State Protein−Protein Interactions of Calmodulin by Single-Molecule Spectroscopy

We report a single-molecule fluorescence resonance energy transfer (FRET) and polarization study of conformational dynamics of calmodulin (CaM) interacting with a target peptide, C28W of a 28 amino acid oligomer. The C28W peptide represents the essential binding sequence domain of the Ca-ATPase protein interacting with CaM, which is important in cellular signaling for the regulation of energy in metabolism. However, the mechanism of the CaM/C28W recognition complex formation is still unclear. The amino-terminal (N-terminal) domain of the CaM was labeled with a fluorescein-based arsenical hairpin binder (FlAsH) that enables our unambiguous probing of the CaM N-terminal target-binding domain motions on a millisecond time scale without convolution of the probe-dye random motions. By analyzing the distribution of FRET efficiency between FlAsH labeled CaM and Texas Red labeled C28W and the polarization fluctuation dynamics and distributions of the CaM N-terminal domain, we reveal binding−unbinding motions of the N-terminal domain of the CaM in CaM/C28W complexes, which is strong evidence of a two-state binding interaction of CaM-mediated cell signaling

Lipid-Polymer Bilaminar Oxygen Nanobubbles for Enhanced Photodynamic Therapy of Cancer

Hypoxia in solid tumors may be a hindrance to effective treatments of tumors in achieving their therapeutic potential, especially for photodynamic therapy (PDT) which requires oxygen as the supplement substrate. Oxygen delivery using perfluorocarbon emulsions or lipid oxygen microbubbles has been developed as the agents to supply endogenous oxygen to fuel singlet oxygen generation in PDT. However, such methods suffer from premature oxygen release and storage issues. To address these limitations, we designed lipid-polymer bilaminar oxygen nanobubbles with chlorin e6 (Ce6) conjugated to the polymer shell as a novel oxygen self-supplement agent for PDT. The resultant nanobubbles possessed excellent stability to reduce the risk of premature oxygen release and were stored as freeze-dried powders to avoid shelf storage issues. In vitro and in vivo experimental results demonstrated that the nanobubbles exhibited much higher cellular uptake rates and tumor targeting efficiency compared to free Ce6. Using the oxygen nanobubbles for PDT, a significant enhancement of therapeutic efficacy and survival rates was achieved on a C6 glioma-bearing mice model with no noticeable side effects, owing to the greatly enhanced singlet oxygen generation powered by oxygen encapsulated nanobubbles

Photoswitchable Nanoparticles Enable High-Resolution Cell Imaging: PULSAR Microscopy

Photoswitchable Nanoparticles Enable High-Resolution Cell Imaging: PULSAR Microscop

Photoswitchable Nanoprobes Offer Unlimited Brightness in Frequency-Domain Imaging

A single probe has limited brightness in time-domain imaging and such limitation frequently renders individual molecules undetectable in the presence of interference or complex cellular structures. However, a single photoswitchable probe produces a signal, which can be separated from interference or noise using photoswitching-enabled Fourier transformation (PFT). As a result, the light-modulated probes can be made super bright in the frequency domain simply by acquiring more cycles in the time domain

Magneto-Plasmonic Nanocapsules for Multimodal-Imaging and Magnetically Guided Combination Cancer Therapy

Integrating multiple discrete functionalities into hollow-mesoporous architecture with distinctive electronic/magnetic property is of particular interest for building multifunctional drug carriers with complementary theranostic modalities. In this article, the “non-contact” incorporation of gold nanorod (GNR) into porous magnetic nanoshell is achieved via yolk–shell structure, which was intrinsically different from previous direct chemical or heterogeneous conjugation of the two components. The highly preserved plasmonic feature of GNRs enabled photothermal induced photoacoustic imaging and hyperthermia capabilities. The magnetic shell consisted of stacked primary iron oxide nanocrystals yields strong superparamagnetic response with excellent permeability for magnetically targeted drug delivery. Interestingly, the special coordination between doxorubicin and iron species enabled pH/local heating dual-responsive drug release with minor leakage at neutral pH. Under the guidance of magnetic resonance/photoacoustic dual-modal imaging and magnetically tumor targeting using the nanoagents, the photothermal-chemo synergistic therapy was conducted via near-infrared laser for highly efficient tumor eradication

Ultrafast Imaging of Surface Plasmons Propagating on a Gold Surface

We record time-resolved nonlinear photoemission electron microscopy (tr-PEEM) images of propagating surface plasmons (PSPs) launched from a lithographically patterned rectangular trench on a flat gold surface. Our tr-PEEM scheme involves a pair of identical, spatially separated, and interferometrically locked femtosecond laser pulses. Power-dependent PEEM images provide experimental evidence for a sequential coherent nonlinear photoemission process, in which one laser source launches a PSP through a linear interaction, and the second subsequently probes the PSP via two-photon photoemission. The recorded time-resolved movies of a PSP allow us to directly measure various properties of the surface-bound wave packet, including its carrier wavelength (783 nm) and group velocity (0.95c). In addition, tr-PEEM images reveal that the launched PSP may be detected at least 250 μm away from the coupling trench structure