Exciton-polaritons created from coupling electronic states of the molecule with quantized radiation field inside a Fabry-Pérot (FP) optical cavity can lead to altered cavity-mediated chemical reactions and provide a platform for studying quantum electrodynamics in chemical physics. We discuss the photophysical properties of polaritons formed with two-dimensional cadmium selenide nanoplatelets inside an optical cavity operating in the strong coupling regime at room temperature with upper and lower polariton Rabi splitting energy of 80 meV.
Quantum dots were encapsulated in polymeric phospholipid micelles conjugated to multiple ligands of SARS-CoV-2 spike protein to form fluorescent biomimetic nanoparticles for SARS-CoV-2 (COVID-QDs). Phosphatidylethanolaminepolyethylene glycol (PE:PEG) was appended with bis(4-methylphenyl)sulfone to form PE:PEG:bis-sulfone and selfassembled into micelles around CdSe/CdS core/shell quantum dots via thin-film rehydration. The introduction of the bissulfone group the surface of the micelle-encapsulated quantum dots provides multiple sites for conjugation to his-tagged SARS-CoV-2 spike protein via a bisalkylation mechanism. Based on the eluted unconjugated fraction, we estimate that an average of seven spike proteins are conjugated per COVID-QD. We treated an in-vitro model system for the neurovascular unit (NVU) with these COVID-QD constructs to investigate the COVID-QDs, and by proxy SARS-CoV-2, may modulate the NVU leading to the COVID-19 associated neuropathophysiology.
Artificial conversion of sunlight to chemical fuels has attracted attention for several decades as a potential source of clean, renewable energy. For example, in light-driven proton reduction to molecular hydrogen, a light-absorbing molecule (the photosensitizer) rapidly transfers a photoexcited electron to a catalyst for reducing protons. We recently found that CdSe quantum dots (QDs) and simple aqueous Ni2+ salts in the presence of a sacrificial electron donor form a highly efficient, active, and robust system for photochemical reduction of protons to molecular hydrogen. To understand why this system has such extraordinary catalytic behavior, ultrafast transient absorption (TA) spectroscopy studies of electron transfer (ET) processes from the QDs to the Ni catalysts were performed. CdSe QDs transfer photoexcited electrons to a Ni-dihydrolipoic acid (Ni-DHLA) catalyst complex extremely fast and with high efficiency: the amplitude-weighted average ET lifetime is 69 ± 2 ps, and ~90% of ultrafast TA signal is assigned to ET processes. Interestingly, under high fluence, sufficient to create on average almost 2 excitons per QD, the relative fraction of TA signal due to ET remains well over 80%, and depopulation from exciton-exciton annihilation is minimal (6%). We also found that increasing QD size and/or shelling the core CdSe QDs with a shell of CdS slowed the ET rate, in agreement with the relative efficiency of photochemical H2 generation. The extremely fast ET provides a fundamental explanation for the exceptional photocatalytic H2 activity of the CdSe QD/Ni-DHLA system and guides new directions for further improvements.
Artificial conversion of sunlight to chemical fuels has attracted attention for several decades as a potential source of clean, renewable energy. We recently found that CdSe quantum dots (QDs) and simple aqueous Ni2+ salts in the presence of a sacrificial electron donor form a highly efficient, active, and robust system for photochemical reduction of protons to molecular hydrogen. Ultrafast transient absorption spectroscopy studies of electron transfer (ET) processes from the QDs to the Ni catalysts reveal extremely fast ET, and provide a fundamental explanation for the exceptional photocatalytic H2 activity. Additionally, by studying H2 production of the Ni catalyst with CdSe/CdS nanoparticles of various structures, it was determined that surface charge density plays an important role in charge transfer and ultimately H2 production activity.
Experimental results of two room-temperature, robust and efficient single-photon sources with definite circular and linear polarization using single-emitter fluorescence in cholesteric and nematic liquid crystal hosts are discussed. For single emitters, we used nanocrystal quantum dots, single color centers in nanodiamonds, and single dye molecules. Single-photon sources based on single emitters in liquid crystals are the room temperature alternatives to cryogenic single-photon sources base on semiconductor heterostructured quantum dots in microcavities prepared by molecular beam epitaxy.
Various single colloidal quantum dots were investigated in chiral liquid crystal 1-D photonic bandgap microcavities
for visible and telecom wavelengths. The microcavity environment provides circular polarization of definite
handedness. Narrow, circularly-polarized microcavity resonances of 3-5 nm width were observed on the band
edges of the stopbands.
Staphylococcus aureus is a leading cause of human illness, and has developed the remarkable ability to resist the
bactericidal capabilities of many of the world's leading antibiotics (i.e. MRSA). In an effort to enable rapid detection
and treatment of MRSA infections, we have developed a DNA detection technology termed the NanoLantern(TM). The
NanoLantern(TM) biosensor technology is based on the simple immobilization of a fluorophore-terminated DNA hairpin
onto a gold chip. This produces a label-free sensor that allows for a positive response to be obtained without extensive
processing of the sample, saving cost and increasing accuracy. We will also discuss a newly developed method of
partial gene analysis, used to develop a DNA hairpin probe that is capable of detecting the presence of the mecR gene, a
gene necessary for methicillin resistance to be present in S. aureus, with 100% sequence specificity. The successful
incorporation of this probe into the NanoLantern(TM) platform, along with the concomitant development of the paired PCR
assay has allowed for the successful detection of methicillin-resistance directly from a culture of S. aureus. These
results represent an important step forward in terms of developing the ability to rapidly and effectively detect the
presence of antibiotic resistance in bacterial infections.
Many-body effects in single-walled carbon nanotubes (SWNTs) were investigated using multi-color transient absorption
spectroscopy. A population of excitons in isolated SWNTs was created by resonantly exciting the lowest allowed
excitonic transition. With low pump fluence, photo-induced bleaching was observed regardless of the probe energy, as
expected. However, at high pump fluence, photo-induced absorption was observed when probing at a higher energy than
the pump. These observations are consistent with a blue-shifted exciton absorption due to phase-space filling effects at
high exciton densities. As a result of the rapid loss of excited state population through Auger recombination, the blue
shift recovered with a time constant of less than 1 ps.
The electronic structure of SWNTs was investigated using the complementary techniques of single molecule photoluminescence spectroscopy and ultrafast optical spectroscopy. We found that photoexcited electrons in SWNTs isolated in surfactant micelles decay through many channels, exhibiting a range of decay times (~200 fs to ~ 120 ps). The magnitude of the longest-lived component in the ultrafast signal specifically depends on resonant excitation, thus suggesting that this lifetime corresponds to the band-edge relaxation time. Fluorescence spectra from single SWNTs are well described by a single, Lorentzian lineshape. However, nanotubes with identical structure fluoresce over a distribution of peak positions and line widths not observed in ensemble studies, caused by localized defects and electrostatic perturbations. Unlike for most other single molecules, for SWNTs the photoluminescence unexpectedly does not show any intensity or spectral fluctuations at 300K. This lack of photoluminescence intensity blinking or bleaching demonstrates that SWNTs have the potential to provide a stable, single molecule infrared photon source, allowing for the exciting possibility of single nanotube integrated photonic devices and biophotonic sensors.
The electronic structure of SWNTs was investigated using the complementary techniques of single molecule photoluminescence spectroscopy and ultrafast optical spectroscopy. We found that photoexcited electrons in SWNTs isolated in surfactant micelles decay through many channels exhibiting a range of decay times (~200 fs to ~ 120 ps). The magnitude of the longest-lived component in the ultrafast signal specifically depends on resonant excitation, thus suggesting that this lifetime corresponds to the band-edge relaxation time. Fluorescence spectra from single SWNTs are well described by a single, Lorentzian lineshape. However, nanotubes with identical structure fluoresce over a distribution of peak positions and line widths not observed in ensemble studies, caused by localized defects and electrostatic perturbations. Unlike for most other single molecules, for SWNTs the photoluminescence unexpectedly does not show any intensity or spectral fluctuations at 300K. This lack of photoluminescence intensity blinking or bleaching demonstrates that SWNTs have the potential to provide a stable, single molecule infrared photon source, allowing for the exciting possibility of single nanotube integrated photonic devices and biophotonic sensors.
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