We report the layer-by-layer coating of living fungi cells (Saccharomyces cerevisiae and Trichoderma asperellum) with polyelectrolytes poly(allylamine hydrochloride)/sodium poly(styrene sulfonate) and bovine serum albumin/DNA and citrate-stabilized gold and silver nanoparticles. It was found that the nanoparticles were effectively incorporated between oppositely charged polyelectrolyte layers, modifying the topography and the roughness of cell walls. The formation of large aggregates of nanoparticles on the cell walls of encapsulated cells was shown. It was found that the encapsulated cells preserved their viability and the shells were soft enough to allow the growth of mycelium. The surface-enhanced Raman scattering (SERS) was used to investigate the biochemical environments of the gold and silver nanoparticles immobilized on the surface of T. asperellum conidia. The SERS spectra from encapsulated conidia and polyelectrolytes indicate that both gold and silver nanoparticles interact with cell walls from different locations, and nanoparticle-polyelectrolyte interaction is limited. The approach described in this paper might have potential applications in modification of living cells.
Multi-walled carbon nanotube modified graphite electrodes (MWNT-GEs) have been created for the voltammetric determination of α-tocopherol and retinol. The electrode surface was characterized by atomic force microscopy. The MWNT-GEs presented structured surfaces and a significant (26-fold) increase in roughness over unmodified graphite electrodes (8.2 vs. 0.32 nm for MWNT-GEs and GEs, respectively). Their surfaces consisted of aggregates with a highly regular "thorn-like" structure. α-Tocopherol and retinol were oxidized on the bare GEs and the MWNT-GEs in 0.1 M HClO 4 in acetonitrile. Decreases in the overpotential of 0.2 and 0.04 V for α-tocopherol and retinol, respectively, and increased oxidation currents were observed on the MWNT-GEs in comparison with the unmodified electrodes. The calibration graphs were linear in the range 0.065-2.00 mM for α-tocopherol and 0.05-1.50 mM for retinol. The detection limits were found to be 0.05 and 0.04 mM for α-tocopherol and retinol, respectively. The developed electrodes were applied to determine α-tocopherol and retinol in pharmaceuticals. The results obtained agreed well with coulometric titration data.
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