From the famous 1918 H1N1 influenza to the present COVID-19 pandemic, the need for improved viral detection techniques is all too apparent. The aim of the present paper is to show that identification of individual virus particles in clinical sample materials quickly and reliably is near at hand. First of all, our team has developed techniques for identification of virions based on a modular atomic force microscopy (AFM). Furthermore, femtosecond adaptive spectroscopic techniques with enhanced resolution via coherent anti-Stokes Raman scattering (FASTER CARS) using tip-enhanced techniques markedly improves the sensitivity [M. O. Scully, et al., Proc. Natl. Acad. Sci. U.S.A. 99, 10994–11001 (2002)].
Lateral flow assay (LFA) has long been used as a biomarker detection technique. It has advantages such as low cost, rapid readout, portability, and ease of use. However, its qualitative readout process and lack of sensitivity are limiting factors. We report a photon-counting approach to accurately quantify LFAs while enhancing sensitivity. In particular, we demonstrate that the density of SARS-CoV-2 antibodies can be quantified and measured with an enhanced sensitivity using this simple laser optical analysis.
Raman spectroscopy
is a powerful tool for molecular chemical analysis
and bioimaging, which shows an astonishing sensitivity when combined
with a huge enhancement by the coherence and surface effects. Noble
metal nanoparticles have been commonly used for the spontaneous surface-enhanced
Raman scattering (SERS) and for the surface-enhanced coherent anti-Stokes
Raman scattering (SECARS) spectroscopies, as they provide large enhancement
factors via the electromagnetic and chemical mechanisms. Recently,
two-dimensional (2D) semiconductors, such as monolayer molybdenum
disulfide (MoS2), were used for potential SERS applications
as cheaper substrates compared to noble metal nanoparticles. However,
the coherent enhancement of SECARS on 2D materials has not been previously
explored. Here we present the experimental SECARS measurements of
pyridine–ethanol solutions containing 2D MoS2 nanocrystals
with the giant chemical enhancement factor of 109 over
coherent anti-Stokes Raman scattering (CARS), which is attributed
to the charge transfer states and resonant MoS2 excitation.
As a comparison, the SERS signals on MoS2 using incoherent
nonresonant excitation show at least 2 orders of magnitude smaller
enhancement. Time-resolved SECARS measurements directly reveal the
increased vibrational dephasing rates, which provide strong evidence
for the charge transfer in the pyridine–ethanol–MoS2 system.
Molecular
polaritons created by the strong coupling between matter
and field in microcavities enable the control of molecular dynamical
processes and optical response. Multidimensional infrared spectroscopy
is proposed for monitoring the polariton-assisted cooperative properties.
The response of molecules to local fluctuations is incorporated and
the full dynamics is monitored through the time- and frequency-resolved
multidimensional signal. The cooperativity against solvent-induced
disorder and its connection to the localization of the vibrational
excitations are predicted. New insights are provided for recent 2DIR
experiments on vibrational polaritons.
We study backward cooperative emissions from a dense sodium atomic vapor. Ultrashort pulses produced from a conventional amplified femtosecond laser system with an optical parametric amplifier are used to excite sodium atoms resonantly on the two-photon 3S 1 2 -4S 1 2 transition. Backward superfluorescent emissions (BSFEs), both on the 4S 1 2 -3P 3 2 and 4S 1 2 -3P 1 2 transitions, are observed. The picosecond temporal characteristics of the BSFE are observed using an ultrafast streak camera. The power laws for the dependencies of the average time delay and the intensity of the BSFEs on input power are analyzed in the sense of cooperative emission from nonidentical atomic species. As a result, an absolute (rather than relative) time delay and its fluctuations (free of any possible external noise) are determined experimentally. The possibility of a backward swept-gain superfluorescence as an artificial laser guide star in the sodium layer in the mesosphere is also discussed.
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