Effect of colliding partners on the performance of SF6 and SO2 trace measurements in photoacoustic spectroscopy.

A photoacoustic (PA) cell was designed based on the numerical simulation and then was fabricated in order to investigate the effect of various buffer gases on the acoustic signals and the resonant frequencies. The sizes of resonator and buffer chambers were suitably selected to improve signal-to-noise ratio. Atmospheric SF6 impact is high due to its significant green house effect. A series of experiments were performed to detect SF6 trace in the air and various types of rare gases. Similar experiments were carried out for the urban and industrial pollutant SO2 in the same environments. The resonant frequencies were measured at various pressures for several rare gases, namely He, Ne, Ar, Kr, and Xe. The PA spectroscopy of molecular traces in various gases gives rise to sensible spectral shift. It was shown that the use of heavier buffer gases at atmospheric pressure lead to detection of the lower concentrations. In general, the relatively intense acoustic signal is recorded for the heaviest species Xe due to its large vibrational-transitional excitation cross section. Conversely, the light elements dissipate laser energy much larger than the heavy species during the successive collisional excitations. Therefore the trace molecules in helium exhibit a notable rise in the resonant frequency accompanying a small PA signal.

Red/blue spectral shifts of laser-induced fluorescence emission due to different nanoparticle suspensions in various dye solutions.

Red/blue shifts of laser-induced fluorescence (LIF) are investigated using several guest dielectric nanoscatterers, such as TiO2, ZnO, Al2O3, and SiO2, in the host Rd6G, RdB, Coumarin 4, and Coumarin 7 ethanolic solutions. A couple of inflection points are identified varying nanoparticle (NP) density into dye solutions based on LIF spectroscopy. The inflection of the spectral shift exhibits that the suspension of NPs in dye solutions significantly involves a couple of competitive chemical and optical mechanisms during photon traveling in scattering media regarding ballistic and diffusive transport. It is shown that the low, medium, and high NP additives in fluorescent suspension induce blue, red, and blue spectral shifts, respectively.

Discrimination of normal and cancerous human skin tissues based on laser-induced spectral shift fluorescence microscopy.

A homemade spectral shift fluorescence microscope (SSFM) is coupled with a spectrometer to record the spectral images of specimens based on the emission wavelength. Here a reliable diagnosis of neoplasia is achieved according to the spectral fluorescence properties of ex-vivo skin tissues after rhodamine6G (Rd6G) staining. It is shown that certain spectral shifts occur for nonmelanoma/melanoma lesions against normal/benign nevus, leading to spectral micrographs. In fact, there is a strong correlation between the emission wavelength and the sort of skin lesions, mainly due to the Rd6G interaction with the mitochondria of cancerous cells. The normal tissues generally enjoy a significant red shift regarding the laser line (37 nm). Conversely, plenty of fluorophores are conjugated to unhealthy cells giving rise to a relative blue shift i.e., typically SCC (6 nm), BCC (14 nm), and melanoma (19 nm) against healthy tissues. In other words, the redshift takes place with respect to the excitation wavelength i.e., melanoma (18 nm), BCC (23 nm), and SCC (31 nm) with respect to the laser line. Consequently, three data sets are available in the form of micrographs, addressing pixel-by-pixel signal intensity, emission wavelength, and fluorophore concentration of specimens for prompt diagnosis.

Fluorescence quenching effects of carbon nano-structures (Graphene Oxide and Nano Diamond) coupled with Methylene Blue.

Here, the effect of Graphene Oxide (GO) and Nano Diamond (ND) carriers on the spectral properties of the fluorescence emissions of MB suspensions in the form of (MB + GO) and (MB + ND) biomaterials are investigated. The strong affinity of MB fluorophores with GO/ND nanostructures lead to the chemical bonding formation that affects the quenching coefficient and spectral shift. According to Stern-Volmer linearity despite, the excited (MB + GO) is strongly quenched due to its privileged bonding affinity, however the (MB + ND) does not. Furthermore, the corresponding quenching coefficients are measured. In fact, GO additives in the MB suspension gives rise to a sensible blue shift due to its surface functionality while no spectral shift takes place in the case of (MB + ND). We have shown that the complex formation such as (MB + GO) is strongly correlated to the GO quenching coefficient due to the hydrogen bonding and π - π staking, whereas there is a loose dependence with the blue shift phenomena. Furthermore, we have compared the quenching coefficients of Rd6G and DOX with MB fluorophore to attest the quenching coefficient is strongly correlated to the molecular structure and its active sites. The findings could be helpful in the course of simultaneous PDT and fluorescence imaging.

Laser induced fluorescence spectroscopy of various carbon nanostructures (GO, G and nanodiamond) in Rd6G solution.

The effect of carbon nanostructures such as graphene (G), graphene oxide (GO) and nanodiamond (ND) on the spectral properties of Rhodamine 6G (Rd6G) emission due to the laser induced fluorescence (LIF) was investigated. It is shown that the addition of carbon nano- structures lead to sensible Red/Blue shifts which depend on the optical properties and surface functionality of nanoparticles. The current theories such as resonance energy transfer (RET), fluorescence quenching and photon propagation in scattering media support the experimental findings. Stern-Volmer curves for dynamic and static quenching of Rd6G molecules embedded with G, GO and nanodiamond are correlated with spectral shifts. Furthermore, time evolution of the spectral shift contributes to determine loading/release rates of fluorescent species with large S-parameter on the given nano-carriers.