Fluoride-assisted detection of glutathione by surface Ce3+/Ce4+ engineered nanoceria.

Nanoceria has evolved as a promising nanomaterial due to its unique enzyme-like properties, including excellent oxidase mimetic activity, which significantly increases in the presence of fluoride ions. However, this significant increase in oxidase activity has never been utilised as a signal enhancer for the detection of biological analytes partly because of the lack of understanding of the mechanism involved in this process. In this study, we show that the surface oxidation state of cerium ions plays a very crucial role in different enzymatic activities, especially the oxidase mimetic activity by engineering nanoceria with three different surface Ce4+/Ce3+ compositions. Using DFT calculations combined with Bader charge analysis, it is demonstrated that stoichiometric ceria registers a higher oxidase mimetic activity than oxygen-deficient ceria with a low Ce4+/Ce3+ ratio due to a higher charge transfer from a substrate, 3,3',5,5' tetramethylbenzidine (TMB), to the ceria surface. We also show that the fluoride ions can significantly increase the charge transfer from the TMB surface to ceria irrespective of the surface Ce4+/Ce3+ ratio. Using this knowledge, we first compare the fluoride sensing properties of nanoceria with high Ce4+ and mixed Ce4+/Ce3+ oxidation states and further demonstrate that the linear detection range of fluoride ions can be extended to 1-10 ppm for nanoceria with mixed oxidation states. Then, we also demonstrate an assay for fluoride assisted detection of glutathione, an antioxidant with elevated levels during cancer, using nanoceria with a high surface Ce4+/Ce3+ ratio. The addition of fluoride ions in this assay allows the detection of glutathione in the linear range of 2.5-50 ppm with a limit of detection (LOD) of 3.8 ppm. These studies not only underpin the role of the surface Ce4+/Ce3+ ratio in tuning the fluoride assisted boost in the oxidase mimetic activity of nanoceria but also its strategic application in designing better colourimetric assays.

Egg-yolk core-shell mesoporous silica nanoparticles for high doxorubicin loading and delivery to prostate cancer cells.

Mesoporous silica-based nanoparticles (MSNs) have gained rapid interest as a drug delivery system (DDS) and demonstrated their versatility in delivering drugs for the treatment of various cancers. However, the drug loading efficiency of MSNs is low and is usually improved by improving textural properties through complicated synthesis methods or by post synthesis modification of the surface that can result in the loss of surface area and modify its drug release properties. In this study, we report a direct single-step synthesis of MSNs with a unique egg-yolk core-shell morphology, large pore volume and a hydrophilic surface, decorated with nitrogen rich surface functionalities for increasing its drug loading capacity. This combination of excellent textural properties and surface functionalisation was achieved by a simple soft templating method using dual surfactants and the silica sources assisted by employing either triethylamine (TEA) or triethanolamine (TEO) as the hydrolysis agent. The morphology and well-ordered mesoporous structure can simply be tuned by changing the pH of the synthesis medium that affects the self-assembly mechanism of the micelles. HRTEM image of samples clearly revealed an egg-yolk core-shell morphology with a thin mesoporous silica shell. The optimised MSN samples synthesized at a pH of 11 using either TEA or TEO depicted a higher doxorubicin (Dox) loading capacity of 425 µg mg-1 and 481 µg mg-1 respectively, as compared to only 347 µg mg-1 for MSN samples due to the uniform distribution of nitrogen functionalities. The anticancer activity of Dox loaded MSNs evaluated in two different prostate cancer cell lines (PC-3 and LNCaP) showed a higher cytotoxicity of the drug loaded on optimised MSN samples as compared to pristine MSNs without affecting the cellular uptake of the particles. These results suggest that the unique single-step synthesis and functionalisation method resulted in successfully achieving higher drug loading in egg-yolk core-shell nitrogen functionalised MSNs and could be implemented as an effective carrier of chemotherapeutic drugs.

Development of photoresponsive zinc oxide nanoparticle - encapsulated lignin functionalized with 2-[(E)-(2-hydroxy naphthalen-1-yl) diazenyl] benzoic acid: A promising photoactive agent for antimicrobial photodynamic therapy.

BACKGROUND: By coalescing nanotechnology with photochemistry and microbiology, a new type of photoactive antimicrobial agent based on zinc oxide nanoparticles incorporated into biomacromolecular lignin was formulated, which possesses a wide-spectrum antimicrobial activity, providing effects in the field of antimicrobial photodynamic therapy. METHODS: The biomacromolecule lignin was functionally modified with 2-[(E)-(2-hydroxy naphthalen-1-yl) diazenyl] benzoic acid by Steglich esterification, and loaded with zinc oxide nanoparticles. The products were characterized by UV-Visible, FTIR, and NMR spectroscopic techniques, and by SEM, TEM, and X-ray diffraction analysis (XRD). The photoresponsive behavior of the dye, functionally modified lignin-dye ester and its nanoparticle dispersed product was investigated. The photoinduced antibacterial and antifungal effects of zinc oxide nanoparticle encapsulated functionally modified lignin were explicated in detail. RESULTS: The photostabilization property of the chromophoric system was found to be enhanced when attached to lignin, and was further improved by the encapsulation of photoactive zinc oxide nanoparticles. The detailed studies on the photoinduced antibacterial and antifungal property revealed that upon light irradiation the antibacterial and antifungal efficacies of the test system got magnified. CONCLUSIONS: Incorporation of photoactive zinc oxide nanoparticles into the functionalized macromolecular system could make important changes in their photoresponsive abilities such as enhanced light absorption behavior and photostabilization properties enriched with photoinduced antimicrobial efficacy, which rendered the functionally modified system a potential photoinduced antimicrobial agent. They may find use in various biomedical applications especially in antimicrobial photodynamic therapy.

Molecular and vibrational structure of tetroxo d0 metal complexes in their excited states. a study based on time-dependent density functional calculations and Franck-Condon theory.

We have applied time dependent density functional theory to study excited state structures of the tetroxo d(0) transition metal complexes MnO(4)(-), TcO(4)(-), RuO(4), and OsO(4). The excited state geometry optimization was based on a newly implemented scheme [Seth et al. Theor. Chem. Acc. 2011, 129, 331]. The first excited state has a C(3v) geometry for all investigated complexes and is due to a "charge transfer" transition from the oxygen based HOMO to the metal based LUMO. The second excited state can uniformly be characterized by "charge transfer" from the oxygen HOMO-1 to the metal LUMO with a D(2d) geometry for TcO(4)(-), RuO(4), and OsO(4) and two C(2v) geometries for MnO(4)(-). It is finally found that the third excited state of MnO(4)(-) representing the HOMO to metal based LUMO+1 orbital transition has a D(2d) geometry. On the basis of the calculated excited state structures and vibrational modes, the Franck-Condon method was used to simulate the vibronic structure of the absorption spectra for the tetroxo d(0) transition metal complexes. The Franck-Condon scheme seems to reproduce the salient features of the experimental spectra as well as the simulated vibronic structure for MnO(4)(-) generated from an alternative scheme [Neugebauer J. J. Phys. Chem. A 2005, 109, 1168] that does not apply the Franck-Condon approximation.