Nanoparticles and photosensitisers; their interactions and antibacterial properties

This work reports on the coupling of light activated antimicrobial (LAA) agents with gold nanoparticles to provide new materials that displayed enhanced antimicrobial properties. A versatile and robust approach to the synthesis of gold-thiol-photosensitiser light activated antimicrobials has been developed. In the synthetic approach the thiols attached to the gold nanoparticles were tiopronin and glutathione. The photosensitisers attached to the thiols were toluidine blue and tin chlorin e6 respectively. It was found gold-tiopronin-toluidine blue nanoparticles at 1 µM concentration were efficient as light activated antimicrobials, that had a reduction of colony forming units (cfu) of S. aureus by 4.5 log 10 compared with, 0.5 log 10 for toluidine blue at the same concentration. The attachment of photosensitisers to thiol protected gold nanoparticles enhanced the lethal photosensitisation of bacteria. The second approach was mixing of charge stabilised gold nanoparticles with various photosensitisers. When charge stabilised gold nanoparticles when mixed with toluidine blue (20 µM), showed a reduction in colony forming units (cfu) for S. aureus of 2.5 log 10 compared with 1.5 log 10 for only toluidine blue at the same concentration. This established that covalent attachment of the photosensitiser was not necessary for the enhancement in the lethal photosensitisation of bacteria. Also, it was discovered that certain dyes which have basic, cationic natures have different interactions with charge stabilised gold nanoparticles. A separate study focusing on semi-conductor quantum dots and the photosensitiser toluidine blue was undertaken to investigate any relationship between nanoparticles and photosensitisers. It was found that semi-conductor quantum dots enhance the effect of toluidine blue in the lethal photosensitisation of bacteria. An excess of a 1.7 log 10 enhancement in bacterial kill was observed with quantum dot concentration of 0.0075 µM and toluidine blue concentration of 20 µM. In summary, the efficacy of photosensitisers can be enhanced by the presence of nanoparticles of gold and CdSe

Nanoparticles and photosensitisers; their interactions and antibacterial properties.

This work reports on the coupling of light activated antimicrobial (LAA) agents with gold nanoparticles to provide new materials that displayed enhanced antimicrobial properties. A versatile and robust approach to the synthesis of gold-thiol-photosensitiser light activated antimicrobials has been developed. In the synthetic approach the thiols attached to the gold nanoparticles were tiopronin and glutathione. The photosensitisers attached to the thiols were toluidine blue and tin chlorin e6 respectively. It was found gold-tiopronin-toluidine blue nanoparticles at 1 µM concentration were efficient as light activated antimicrobials, that had a reduction of colony forming units (cfu) of S. aureus by 4.5 log 10 compared with, 0.5 log 10 for toluidine blue at the same concentration. The attachment of photosensitisers to thiol protected gold nanoparticles enhanced the lethal photosensitisation of bacteria. The second approach was mixing of charge stabilised gold nanoparticles with various photosensitisers. When charge stabilised gold nanoparticles when mixed with toluidine blue (20 µM), showed a reduction in colony forming units (cfu) for S. aureus of 2.5 log 10 compared with 1.5 log 10 for only toluidine blue at the same concentration. This established that covalent attachment of the photosensitiser was not necessary for the enhancement in the lethal photosensitisation of bacteria. Also, it was discovered that certain dyes which have basic, cationic natures have different interactions with charge stabilised gold nanoparticles. A separate study focusing on semi-conductor quantum dots and the photosensitiser toluidine blue was undertaken to investigate any relationship between nanoparticles and photosensitisers. It was found that semi-conductor quantum dots enhance the effect of toluidine blue in the lethal photosensitisation of bacteria. An excess of a 1.7 log 10 enhancement in bacterial kill was observed with quantum dot concentration of 0.0075 µM and toluidine blue concentration of 20 µM. In summary, the efficacy of photosensitisers can be enhanced by the presence of nanoparticles of gold and CdSe.

The interaction between gold nanoparticles and cationic and anionic dyes: enhanced UV-visible absorption

The interactions of charge stabilised gold nanoparticles with cationic and anionic dyes are reported. The nanoparticles were synthesised by the Turkevich citrate reduction method. It was found that when a solution of thiazine dye is titrated against gold citrate hydrosol, at a critical concentration of dye there is an enhanced maximum absorption in the dye. The extinction coefficient is increased up to ten-fold. This enhancement was observed for a number of cationic thiazine dyes, of which methylene blue and toluidine blue are established light-activated antimicrobial agents. The same enhancement was not observed for anionic, acidic dyes such as rose bengal which showed no communication with the gold nanoparticles and showed UV-visible titration experiments with well formed isosbestic points. By studying the interaction of the dye and gold nanoparticles under conditions of different ionic strength and by using a zetasizer and TEM to measure the gold nanoparticle size it was demonstrated that the cause of enhancement was not due to nanoparticle aggregation. It is proposed that thiazine cationic dyes coordinate around a gold nanoparticle and give significantly enhanced UV-visible absorption

A mystery solved? Photoelectron spectroscopic and quantum chemical studies of the ion states of CeCp3(+).

The electronic states of CeCp(3)(+) have been studied experimentally by variable photon energy photoelectron spectroscopy, and computationally using multi-configurational ab initio methods. Relative partial photoionisation cross section and branching ratio data are presented to confirm our previous conclusion that bands A and D in the valence photoelectron spectrum, despite their 3.2 eV separation, are produced by ionization of the single 4f electron of CeCp(3) [M. Coreno, M. de Simone, J. C. Green, N. Kaltsoyannis, N. Narband and A. Sella, Chem. Phys. Lett., 432, 2006, 17]. The origin of this effect is probed using the CASSCF/CASPT2 approach. While configurations based on the canonical CASSCF orbitals are found to be an unreliable description of the ground and excited states of CeCp(3)(+), the state-specific natural orbitals and their occupations yield greater insight, allowing us to characterize ion states in terms of the presence or otherwise of a Ce 4f-localised electron. Neither the CeCp(3)(+) ground state (assigned to band A), and two excited states ((1)A' and (1)A'', associated with band D), possess such a metal-based electron, as expected of f ionization. The (1)A' and (1)A'' states differ from the ground state in having a significant Ce 5d population, arising from Cp --> Ce charge transfer, which accompanies f ionization, and which is responsible for the energetic separation of bands A and D in the valence photoelectron spectrum

Variable photon energy photoelectron spectroscopy of tris-cyclopentadienyl lanthanides

The gas phase photoelectron (PE) spectra of LnCp3 (Cp = η-C5H5; Ln = Pr, Nd, Sm), measured with a wide range of photon energy, are reported. Resonances observed in the photon energy regions of 4d to 4f excitation enable identification of ion states resulting from 4f ionization. For all three compounds molecular ion states characteristic of both 4f(n) and 4f(n-1) configurations are observed (Pr, n = 2; Nd, n = 3; Sm, n = 6). The molecular ion ground states have a hole in the uppermost ligand orbital of a' symmetry and are reached by either ligand or f electron ionization. The results are discussed in the context of the previously reported spectra of the Ce, Yb and Lu analogues. For YbCp3 f orbital/ligand interaction is proposed in the molecular ground state and for CeCp3(+) in the molecular ion ground state. For PrCp3 and NdCp3 final state effects are proposed as the origin of the dual configuration structure in their PE spectra. When the contributing orbitals are close in energy the 4f/a' interaction can give rise to significant covalent bonding even in the absence of effective overlap