51 research outputs found
Multifocus confocal Raman microspectroscopy for fast multimode vibrational imaging of living cells
Chirality Discriminated by Heterodyne-Detected Vibrational Sum Frequency Generation
We first demonstrated chiral vibrational
sum frequency generation
(VSFG) in the heterodyne detection, which enables us to uniquely determine
chiral second-order nonlinear susceptibility consisting of phase and
amplitude and distinguish molecular chirality with high sensitivity.
Liquid limonene was measured to evaluate the heterodyne-detected chiral
VSFG developed in this study. <i>R</i>-(+)- and <i>S</i>-(−)-limonene showed clearly opposite signs in the
complex spectra of the second-order nonlinear susceptibility in the
CH stretching region. This is the first report of the chiral distinction
by VSFG without any a priori knowledge about chiral and achiral spectral
response. Furthermore, from the phase of the chiral VSFG field measured
in the heterodyne detection, the origin of the chiral signal was ascribed
to the bulk limonene. The heterodyne detection also improves detection
limits significantly, allowing us to observe weak chiral signals in
reflection. The heterodyne-detected chiral VSFG can provide information
on absolute molecular configuration
Heterodyne-Detected Achiral and Chiral Vibrational Sum Frequency Generation of Proteins at Air/Water Interface
We present complex achiral and chiral
vibrational sum frequency generation (VSFG) spectra at the air/water
interface of protein solutions by using heterodyne-detected VSFG.
Bovine serum albumin, pepsin, concanavalin A, and α-chymotrypsin
were measured as model proteins. The obtained achiral Im[χ<sup>(2)</sup>] spectra gave us insights into the molecular orientation
of protein molecules and water at the interface. From the chiral Im[χ<sup>(2)</sup>] spectra in the NH stretching and amide I regions, the
secondary structures of the interfacial proteins were deduced. We
attributed the chiral signals in the amide I and NH stretching regions
to the interface on the basis of the phase of the signals. All the
achiral and chiral spectra in each region showed the same sign despite
different secondary-structure contents of the examined proteins. Real-time
observation of the spectral change of α-chymotrypsin was also
performed by heterodyne-detected chiral VSFG. The signal intensity
of the chiral Im[χ<sup>(2)</sup>] spectra in the NH stretching
and amide I regions decreased on the scale of 10 min, originating
from the decrease of the portion of antiparallel β-sheet conformation
in the molecule. The conformational change occurred not in the bulk
but at the interface. Heterodyne-detected achiral and chiral VSFG
are capable of addressing the molecular orientation and conformation
of proteins at air/water interfaces
Sensitive and Quantitative Probe of Molecular Chirality with Heterodyne-Detected Doubly Resonant Sum Frequency Generation Spectroscopy
Heterodyne-detected vibrationally
electronically doubly resonant
chiral sum frequency generation (HD-DR chiral SFG) spectroscopy has
been developed for the study of chiral molecules with chromophores.
The method enables us to detect and distinguish chiral molecules with
high sensitivity and to obtain information on molecular vibrations.
Strong enhancement due to the electronic resonance improves the sensitivity,
and heterodyne detection ensures that the signal intensity is linear
to the sample concentration. Detection of HD-DR chiral SFG signal
from a dilute solution of binaphthol with 20 mM concentration and
tens of nanometers thickness was demonstrated. Taking advantage of
the enantiomer-dependent sign and linearity of the signal to the concentration,
molecular concentrations and enantiomeric excesses were accurately
evaluated. HD-DR chiral SFG is expected to have widespread application
in the study of molecular chirality of thin films or samples of a
very small quantity
Hyperspectral coherent Raman imaging – principle, theory, instrumentation, and applications to life sciences
International audienceCoherent Raman scattering microscopy such as coherent anti-Stokes Raman scattering and stimulated Raman scattering microscopy boosts the weak Raman signal and enables us to perform label-free visualization of the molecular distribution and its dynamical behavior in living cells and tissues with high speed. In comparison with fluorescence imaging, cells and tissues can be visualized without specifying the target molecule. In this review, we describe the characteristics of a hyperspectral coherent Raman imaging method, which is capable of acquiring both spectra and images simultaneously, and review applications to life sciences. Copyright © 2015 John Wiley & Sons, Ltd
- …