Tip-enhanced Raman scattering (TERS) can be observed highly sensitive spectral image with high spatial resolution.
However, it shows low reproducibility due to difference and change in optical properties of the metallic tips. For surfaceenhanced
Raman scattering (SERS), the spectra can be reproduced by the scattering spectra due to localized surface
plasmon resonance (LSPR) of the individual metallic nanostructures, which observed with a dark field illumination, and
the calculated electromagnetic field around the nanostructures. In the present study, we tried to relate TERS spectra with
the LSPR spectra and the calculation, in a similar way of SERS. By conventional dark field illumination, LSPR
scattering spectra at the apex of the tip were measured and were compared with the corresponding TERS spectra. By
excitation using polarization parallel to the tip, the polarized LSPR peak was stronger than that by perpendicular
polarization. Also in the case of TERS, the similar trend was observed. It was confirmed whether the vertical
polarization to the sample plane (Z-polarization) is effective or not by the polarized LSPR and TERS spectra. By
excitation at different wavelengths, moreover, TERS enhancement factors were compared. In the calculation for TERS,
the nanostructure like a monopole antenna was adopted, because the EM field is enhanced not at both sides, but at only
apex. The dependence on taper and curvature of the tip were compared with the calculated results for the nanostructure
like a conventional dipole antenna.
One of suspect environmental endocrine disruptors that affect mouse male reproduction by altering the morphology of Sertoli cells and spermatogenic cells is phthalate. The effects of mono(2-ethylhexyl)phthalate (MEHP), one of metabolites of di(2-ethylhexyl)phthalate , on immature mouse testes in vivo were examined. We have recently shown
that MEHP induced Sertoli cells necrosis and spermatogenic cells apoptosis in mice by TUNEL method, F-actin staining,
and ultrastructural study, but there is no data for biochemical changing of testes due to those methods could not explore.
To verify in detail of it, we conducted Raman spectroscopy study with 785 nm wavelength laser line, 50mW of laser power and 3 minutes of exposure time to analysis the MEHP-treated testicular tissue, which has been fixatived by 4% paraformaldehyde (PFA). Five weeks old (5 w.o) male mice were used in this experiment. As the results, the alterations were observed by Raman spectroscopy that there are significantly differences of DNA, actin filament, type IV collagen and amide I between control group (0 μM MEHP) and treatment group (100 μM MEHP). These results significantly support histology staining observation (such as the apoptotic spermatogenic cells which is associated with DNA fragmentation and F-actin disruption) and ultrastructural observation (such as mitochondria rupture and disintegration of nucleus membrane). Raman spectroscopy can be used for 4% PFA-fixatived tissue observation. However, we recommend that Raman spectroscopy may be able to be expanded as an armamentarium not just for the clarification of histology staining and ultrastructural study, but furthermore, it may be as a non-invasion assessment for screening animal tissue toxicity of chemical in future.
The optical property of the ball lens mounted hollow optical fiber Raman probe (BHRP) is studied in the present study.
Since the ball lens has rather large aberration, the focus of the BHRP is dispersed and the spatial resolution in depth
direction goes low. The spatial dispersion of the focal point was evaluated using model samples. The BHRP equipped a
sapphire ball lens of 500 μm diameter was employed. Layered samples consisting of a polymethyl methacrylate
(PMMA) substrate and various thicknesses of polyethylene (PE) films were measured with the BHRP. The relative band
intensities of the upper and the lower layers appear at different rates in the obtained spectra, reflecting the optical
properties of the probe. According to the spectra, the optical dispersion of the focal point is estimated. The result
suggests that the spatial dispersion of the focus point fitted to Gaussian distribution. The working distance (WD) is 53
μm and the FWHM of the fitted Gauss distribution is 64 μm.