Fluorescence inner filters of Arthrospira platensis: Novel perspective for precise fluorescence-based sensors.

Microalgae have been reputed as novel biological materials due to their unique structure, surface functionality and optical activity, making them worthwhile agents in biosensing and theranostic applications. However, further scrutiny is required for utilizing them in routine optical techniques due to their complex structure and diverse chemical components. Here, laser induced fluorescence (LIF) features of a bio-compatible microalgae i. e. Arthrospira platensis (Spirulina) have been assessed. Typical fluorescence properties as well as the inner filter effects (IFEs) were examined and revealed to be strongly dependent on concentration, excitation wavelength, and detection geometry as well. IFEs and resulting spectral shifts have been analyzed considering various SP chromophores, reabsorption processes, and resonance energy transfer (RET) mainly from "Carotenoids to Phycobilisomes" as well as "Phycobilisomes to Chlorophyll-a". As a result, LIF spectral shift due to the re-absorption events (secondary-IFE) is introduced as a credible parameter for design of precise fluorescence-based sensors, due to being less dependent on ambient noises. We hope that the findings provide novel features regarding the LIF of Spirulina (SP) that could be utilized to design and develop optical sensors in the field of photonics, material diagnosis and biomedical theranostics.

LIF spectroscopy of epithelial tissues: Assay of structural changeover due to the cancer progression.

Most of the human cancers occur in epithelial tissues containing basic cells with different shapes, and not only do the spectral properties of the tissue pigments alter due to cancer, but the cellular architecture also change. However, in optical diagnosis of the cancerous tissues, attention has been paid to the spectral changeover of native chromophores as bio-markers. Here, we have attempted to assay the structural alterations of the epithelial tissues during the cancer progression utilizing Laser induced fluorescence (LIF) spectroscopy as a fast, sensitive and easy-to-use method. In this regard, angular dependence of the LIF spectral features of the healthy and cancerous epithelial tissues (soaked in Rhodamine 6G solution) from three different human organs i. e. uterus, colon and kidney with distinct microstructures have been examined. In general, both wavelength and intensity at the peak of the LIF spectra depend on the tissue orientation and the angle of detection respect to the laser beam direction. Those optical parameters also demonstrate distinctive alterations in different tissues that is explicated based on the morphological alteration of the epithelial cells in each carcinoma type provided by pathology data.

Optical characterization of the liver tissue affected by fibrolamellar hepatocellular carcinoma based on internal filters of laser-induced fluorescence.

Laser-induced fluorescence (LIF) spectroscopy has recently gained regards for diagnosis of the cancer in various tissues of the human body. This method in its conventional form, when used for assay of highly scattering media, encounters a lot of noise due to multiple scattering and inner filter effects which overshadows the sensitivity and specificity of the method. Here, angular dependence of the LIF spectral shift due to the reabsorption events have been investigated for characterization of the bio-tissues. The aim was to determine the tissue morphological changeovers due to the cancer progression. The assessment of a rare type of the liver cancer i. e. fibrolamellar hepatocellular carcinoma revealed the significant difference in optical anisotropy of the parenchyma and liver tumor. As a result, utilizing LIF spectroscopy as a fast, highly sensitive and easy-to-use method one can evaluate the optical anisotropy for diagnosing tissues during the cancer progression.

Anisotropic behavior of random lasing in a highly concentrated dye solution.

Angular dependence of the diffusive random laser (DRL) emission is assessed due to excitation of a highly concentrated solution of Rhodamine 6G (Rd6G) comprising monomers and dimers. Dimerization at extremely high concentrations leads to the random fluctuation of the dielectric constant in gain medium. As a result, aggregated dye molecules provide multiple scattering events for propagating photons which is confirmed by enhanced backscattering (EBS) test. This scattering feedback besides Försters resonance energy transfer (FRET) from monomers to dimers provide RL spikes over low quantum yield dimeric fluorescence spectra. The unique spectral feature of RL emission is strong dependence on the angle of detection that results from anisotropic inner filter effect (IFE) within the gain volume due to local excitation of the medium by a pencil-like beam of laser. The results have a merit of importance in optical characterization of the media in which the fluorophores can aggregate significantly.

Assay of honey freshness by a novel optical technique.

Assay of Maillard reaction products (e.g. furosine) is a reputable method for determination of the honey freshness. In this report, novel optical technique is proposed for real-time measurement of the changes of furosine content in honey. The method is based on the unidirectional energy transfer between two peaks of the doubled-peak fluorescence spectrum as secondary inner filter effect (2nd-IFE) in a specific arrangement of the laser induced fluorescence (LIF) setup. Proper optical parameters are defined accordingly, and affirmed to be dependent on the content of furosine in honey. It is shown that the introduced parameters are not sensitive to the LIF intensity fluctuations induced by the ambient noises and particularly alter due to the 2nd-IFE. Furosine level of 8 honey types with different botanical origin were chemically determined before and after the 1 year storage, and compared with the values of the devised spectral parameters. Proofs conducted that the proposed technique can be utilized for evaluation of the honey freshness.

Optical anisotropy measurement in normal and cancerous tissues: backscattering technique.

Investigating the deformation of tissue architecture is one of the most important clinical methods for cancer diagnosis. Optical methods are now widely developed for rapid, precise, and real-time assessment of these alterations at the microscopic scale. One of the proposed methods is enhanced backscattering (EBS) technique that allows in-vivo measurement of the optical scattering characteristics. Here, EBS technique is employed to evaluate the optical anisotropy of human epithelial tissues as a measure to distinguish between normal and cancerous one. Orientation dependence of the mean scattering length is assessed in healthy and cancerous tissues of five different human organs i. e. uterus, bladder, colon, kidney, and liver. Helicity preserving channel and rotating ground glass diffuser are utilized to eliminate the polarization induced anisotropy and the background speckle noises respectively. Analysis of the backscattering cones recorded by a high-resolution CCD camera reveals the modification of the strength and degree of optical anisotropy in different tissues during cancer progression. Pathology data affirm the correlation between the experimental results and the morphological alteration of the epithelial cells in each carcinoma type. In general, tissues with fibrous constructional cells are subject to a decrease in anisotropy due to cancer, whereas those with cuboidal cells experience an increase in anisotropy. This complementary information enhances the potency of the EBS technique as a fast, non-destructive, and easily accessible tool for real-time tissue diagnosis.

Angular distribution of laser-induced fluorescence emission of active dyes in scattering media.

Angular dependence of the intensity and the emissive wavelength of the laser-induced fluorescence emission in hybrid media (fluorophores+nanoparticles) are investigated using various TiO2 densities as guest nanoscatterers in the ethanolic solutions of the host Rd6G and coumarin 4 (C4) molecules. It is shown that the intensity of the scattered photons varies in terms of the detection angle. When the nanoscatterer density increases at a certain excitation energy, the angular anisotropy enhances. While the emissive wavelength exhibits the spectral shift in terms of the angular variation for Rd6G fluorophores, it remains invariant for C4-based suspension. In the former case, the emissive wavelength undergoes a spectral shift in terms of angular variation. Several factors such as the optical path length in the scattering media, the excitation volume, and the re-absorption events of the fluorescence emissions by the non-excited molecules strongly affect the spectral features. In fact, the density of the scatterers, the dye concentration, and the interplay between Stokes shift rate and the overlapping between absorption/emission spectra of the given fluorophores are taken into account as the major parameters to form the angular distribution.

Fluorescence properties of doxorubicin coupled carbon nanocarriers.

The effect of graphene oxide (GO) and nanodiamond (ND) is investigated on the spectral properties of doxorubicin (DOX) fluorescence emissions in the form of (DOX+GO) and (DOX+ND) biomaterials. It is shown that carbon nanostructure additives lead to sensible blueshifts, due to their optical properties and surface functionality. The quenching coefficient KND is obtained to be KND=0.043 (µg/ml)-1 and KGO=0.342 (µg/ml)-1 in DOX solutions. In general, Stern-Volmer attests that excited (DOX+GO) strongly quenches with respect to that of (DOX+ND) regarding its privileged bonding affinity.