Resonance Raman and surface-enhanced Raman spectroscopy were employed to study the interaction of hypericin with human serum albumin. The identification of the binding place for hypericin as well as the model for albumin−hypericin complex are presented. In this model hypericin interacts with tryptophan placed in II A subdomain of albumin. This interaction reflects (i) a change of the hydrophobicity of the tryptophan environment, (ii) the formation of an H-bond between the carbonyl group of hypericin and N1−H group of tryptophan, leading to a protonated-like carbonyl in the drug, (iii) a decrease of the strength of H bonding at the N1−H site of tryptophan, and (iv) a change of the tryptophan side-chain conformation.

By means of UV-VIS absorption and fluorescence spectroscopy, we demonstrate that the photosensitizer hypericin (Hyp) interacts nonspecifically with low-density lipoproteins (LDL), most probably with the lipid fraction of LDL. The molar ratio of monomeric Hyp binding to nonoxidized LDL and mildly oxidized LDL is 30:1. Increasing the Hyp concentration further leads to the formation of Hyp aggregates inside the LDL molecule. We also demonstrate that photoactivated Hyp oxidizes LDL in a light dose and excitation wavelength dependent manner. The level of oxidation of LDL depends on the amount of Hyp inside the LDL molecule. The maximum of the photosensitized oxidation of the LDL by Hyp is achieved for a 30:1 molar ratio, which corresponds to the maximum concentration of monomeric form of Hyp in LDL.

In this work, we report the detection of the organochlorine pesticides aldrin, dieldrin, lindane, and α-endosulfan by using surface-enhanced Raman spectroscopy (SERS) and optimization of the SERS-sensing substrate. In order to overcome the inherent problem of the low affinity of the above pesticides, we have developed a strategy consisting of functionalization of the metal surface with alkyl dithiols in order to achieve two different goals: (i) to induce the nanoparticle linkage and create interparticle junctions where sensitive hot spots needed for SERS enhancement are present, and (ii) to create a specific environment in the nanogaps between silver and gold nanoparticles, making them suitable for the assembly and SERS detection of the analyzed pesticides. Afterward, an optimization of the sensing substrate was performed by varying the experimental conditions: type of metal nanoparticles, molecular linker (aromatic versus aliphatic dithiols and the length of the intermediate chain), surface coverage, laser excitation wavelength. From the adsorption isotherms, it was possible to deduce the corresponding adsorption constant and the limit of detection. The present results confirm the high sensitivity of SERS for the detection of the organochlorine pesticides with a limit of detection reaching 10(-8) M, thus providing a solid basis for the construction of suitable nanosensors for the identification and quantitative analysis of this type of chemical.