Raman and scanning tunneling spectroscopic investigations on graphene-silver nanocomposites

Graphene-silver (G-Ag) nanocomposites were prepared using liquid phase exfoliation of graphite flakes followed by a reduction of silver nitrate. The plasmonic characteristics of these nanocomposites are highly sensitive to the Ag concentration in the films. Raman spectroscopic investigations indicated that the effect of the surface-enhanced Raman scattering is present significantly in the Raman spectra of G-Ag nanocomposites. The intensity of the D, G, and 2D Raman bands is found to increase with silver concentration. The interaction between graphene and silver nanoparticles causes the G-band to split depending on the concentration of Ag. Scanning tunneling spectroscopic investigations showed that silver causes the Fermi level of graphene to shift towards the conduction band indicating the n-type doping and interestingly the existence of an offset current in the I-V characteristics of G-Ag nanocomposites differing from the zero value observed for graphene. Keywords: Graphene-silver nanocomposites, Raman spectroscopy, Scanning tunneling spectroscopy, Density of state

Doxorubicin-Polysorbate 80 Conjugates: Targeting Effective and Sustained Delivery to the Brain

Targeting therapeutic agents to the brain to treat the central nervous system (CNS) diseases is a major challenge due to the blood-brain-barrier (BBB). In this study, an attempt was made to deliver a model drug such as doxorubicin (DOX) to the brain in a mice model through DOX-Polysorbate 80 (DOX-PS80) conjugates. DOX was successfully conjugated with the non-ionic surfactant Polysorbate 80 (PS80) by carbamate linkage and the conjugate was characterized by different spectroscopic techniques such as FTIR, UV-Visible and NMR. The DOX conjugation efficacy was found to be 43.69 ± 4.72 %. The in vitro cumulative release of DOX from the conjugates was found to be 4.9 ± 0.8 % in PBS of pH 7.3 and 3.9 ± 0.6 % in simulated cerebrospinal fluid (CSF) of pH 7.3 at the end of 10 days. In vitro BBB permeability assay was carried out using bEnd.3 cells and DOX-PS80 conjugate showed a 3-fold increase in BBB permeability compared to controls. In vitro cytotoxicity assay using U251 human glioblastoma cells showed an IC50 value of 38.10 µg/mL for DOX-PS80. Cell uptake studies revealed that DOX-PS80 was effectively taken up (90%) by the bEnd.3 and U251 cells and localized in cytoplasm at the end of 24 h. Tumor spheroid assay and in vivo experiments in Swiss albino mice demonstrated the possibility of DOX-PS80 conjugate crossing the BBB and delivering the drug molecules to the target site for treating CNS disorders

Molecular-Architectonics of Gold Nanoclusters for enhanced fluorescence and photosensitizing property for Image Guided Photodynamic Therapy of Hypoxic Tumor

Gold nanoclusters (AuNCs) comprising a metal core of few atoms and a shell of thiols have unique photoluminescence unlike its bigger counterparts. Due to the ligand-to-metal charge transfer, long-lived excited state and excited triplet state has been exhibited by some metal clusters attributing to their inherent photosensitizing (PS) property. Hence, AuNCs have significant impact in biomedical domains like image assisted photodynamic therapy (PDT). In this work, the molecular nanoarchitectonics of self assembled cysteine-capped AuNCs has been tailored to improve its photosensitizing and emission properties for PDT and simultaneous imaging applications. The unique molecular nanoarchitectonics contributed to the aggregation induced emission (AIE) property of gold cluster contributing to the enhanced photosensitizing and bio-imaging property. We performed in-silico model to study the interaction of cysteine to gold cluster, its ground and excited-state properties, and the charge transfer mechanism. Cysteine-capped AuNCs yielded efficient generation of cytotoxic radicals which has contributions from the dispersed independent gold cluster as well as the self assembled nanoarchitecture. Thus, the cysteine-capped AuNCs could generate free radicals for cancer therapy by both Type I and Type II photosensitizing pathways, with the Type I reaction relevant for use in the hypoxic tumour environment. The metal cluster also exhibited excellent biocompatibility in cancer cells. The image-guided photodynamic exhibited significant cell death after 60s laser irradiation. Thus, the unique molecular nanoarchitectonics of the synthesised AuNCs has resulted in a promising new theranostic nano-platform with potential clinical applications