Beena Jain

The Effect of pH and Surfactant on the Aggregation Behavior of Chlorin p6: A Fluorescence Spectroscopic Study¶

Abstract Steady state and time-resolved fluorescence properties of chlorin p6, a potential drug for photodynamic therapy, have been investigated as functions of pH. A decrease in pH of the medium has been shown to cause protonation of the ionizable carboxylic acid side chain, leading to an increase in hydrophobicity and consequent aggregation. The aggregates dissociate on further protonation. The dissociation is explained in terms of formation of cations and their mutual repulsion. A synchronous fluorescence spectroscopic study revealed the presence of two anionic forms in equilibrium at physiological pH, with a shift in the equilibrium on slight decrease in the pH. The anionic nature of chlorin p6 in aqueous solutions at physiological pH has been confirmed by complexation with surfactants. The nature of the charge on the headgroups of the surfactants has been found to govern the formation of chlorin–surfactant complexes.

Photodynamic action of Rose Bengal silica nanoparticle complex on breast and oral cancer cell lines.

Rose Bengal, an anionic photosensitizer was conjugated to organically modified silica nanoparticles having 3‐amino propyl groups by electrostatic or covalent interaction. The drug‐nanoparticle complexes were characterized by FTIR, light scattering and zeta potential measurements. Significant changes were observed in the spectroscopic properties of the drug when it is conjugated with nanoparticles. The toxicity of the free drug and drug‐nanoparticle complex was studied against oral (4451) and breast (MCF‐7) cancer cell lines. Both complexes with nanoparticles were more phototoxic than free Rose Bengal, with the covalent complex being the more effective. Studies carried out on cellular uptake, photostability and singlet oxygen generation suggest that enhanced phototoxicity is primarily due to the enhanced uptake of the drug‐nanoparticle complex.

Depolarization of light in tissue phantoms: effect of collection geometry

Abstract We report measurement of depolarization of light on propagation through matched scattering samples having the same anisotropy parameter (g) and optical thickness (τ=μs×d, d being the physical thickness) but different values for scattering coefficient (μs). Significant differences were observed in the depolarization behavior of the samples so matched. The depolarization of both linear and circularly polarized light was always larger for the sample with higher value of μs. Further, for lower value of g (g∼0.1), the difference in depolarization between matched samples was larger for circularly polarized light than that for linearly polarized light. Exactly the opposite result was obtained for matched samples with larger g values (g∼0.9). We show that these differences in the depolarization behavior of matched samples are dependent on the collection geometry and arise because for a given collection angle, a greater fraction of multiply scattered photons are collected for the sample having higher μs.

Experimental investigation of perturbation Monte-Carlo based derivative estimation for imaging low-scattering tissue

Experimental results for imaging the low-scattering tissue phantoms based on the derivative estimation through perturbation Monte-Carlo (pMC) method are presented. It is proven that pMC-based methods give superior reconstructions compared to diffusion-based reconstruction methods. An easy way to estimate the Jacobian using analytical expression obtained from perturbation Monte-Carlo method is employed. Simulation studies on the same objects, considered in the experiment, are performed and corresponding results are found to be in reasonable agreement with the experimental studies. It is shown that inter-parameter cross talk in diffusion based methods lead to false results for the low-scattering tissue, where as the pMC-based method gives accurate results.

Spectroscopic investigations on the binding of the photosensitizer Chlorin p6 with amine-modified silica nanoparticles in aqueous media.

Absorption and emission properties of the amphiphilic photosensitizer Chlorin p6 were investigated in aqueous medium in the presence of silica nanoparticles (SiNPs) having positively charged amino groups. The results of these studies reveal that the acid–base ionization equilibrium of Chlorin p6 in aqueous medium is significantly affected as a result of strong electrostatic binding between the negatively charged drug and SiNP. The spectroscopic signature of the drug bound to SiNPs suggests that the tri‐anionic form of the drug remains bound to the positively charged SiNPs at pH 8.0. As the pH is progressively decreased the formation of hydrophobic aggregates is disrupted significantly due to the presence of electrostatic binding force, which competes with intermolecular hydrophobic forces. The interplay of hydrophobic and electrostatic forces in the drug–nanoparticle binding process might affect the relative uptake and photodynamic efficacy of the free drug and the drug–nanoparticle complex in cancer cells.

Time-gated optical imaging through turbid media using stimulated Raman scattering: Studies on image contrast

In this paper, we report the development of experimental set-up for time-gated optical imaging through turbid media using stimulated Raman scattering. Our studies on the contrast of time-gated images show that for a given optical thickness, the image contrast is better for sample with lower scattering coefficient and higher physical thickness, and that the contrast improves with decreasing value of anisotropy parameters of the scatterers. These results are consistent with time-resolved Monte Carlo simulations.

Depolarization of light in turbid medium: effect of collection geometry

Larger depolarization of incident polarized light has been reported for tissues compared to tissue phantoms with matched optical thickness (τ=μs×d, μs being the scattering coefficient and d the physical thickness). We show that this arises because for the sample with larger μs more multiply scattered photons are detected in a narrow collection angle typically used in experiments. These results were verified by time resolved studies on transmitted light as well as by Monte Carlo simulation.

Chemical treatment of photoluminescent porous silicon

Porous silicon layers formed by electrochemical anodizing show photoluminescence in the visible region. We report on the effect of chemical treatments such as hydrofluoric acid dip, ammonium fluoride solution treatment and boiling water treatment on the photoluminescence of porous silicon. In view of our results the mechanism of photoluminescence of porous silicon is discussed.