The fundamental and applied physics of noble-metal nanoparticles is currently attracting much attention. To a great extent this is due to promising new applications of noble-metal colloidal nanoparticles in fields such as materials science, [1] biophysics, [2] molecular electronics, and fluorescence-spectral engineering based on surface-enhancement effects. [3] In particular the nanoparticles have promising applications as bright fluorescent markers with enhanced photostability in fluorescence microscopy, sensor technology, and microarrays. The enhancement of the fluorescence emission of molecules near a metal surface arises from interactions with surface plasmon (SP) resonances in the metal particles. [4][5][6] These interactions may also result in shortening of the excited-state lifetime thus improving the photostability of the dye.[7]The optical properties of a fluorescent molecule located near a metal nanoparticle are affected by the near-field electrodynamical environment. [4][5][6] This can cause an enhancement or quenching of the fluorescence depending on the distance between the molecule and the metal surface. In the case of fluorescent molecules located at very short distances from a metal surface, non-radiative energy transfer to SPs in the metal takes place. [8,9] Electromagnetic-field enhancement due to SPs, however, still occurs at longer distances from the metal core. As a result, there is an optimal fluorescent molecule to metal-core distance for fluorescence enhancement. Important factors affecting the strength of the fluorescence enhancement are the size and shape of the nanoparticle, the orientation of the dye dipole moments relative to the nanoparticle surface normal, the overlap of the absorption and emission bands of the dye with the plasmon band of the metal, and the radiative decay rate and quantum yield (Q) of the fluorescent molecules.

As the nanotechnology field continues to develop, assessing nanoparticle toxicity is very important for advancing nanoparticles for biomedical application. Here we report cytotoxicity of gold nanomaterial of different size and shape using MTT test, absorption spectroscopy and TEM. Spherical gold nanoparticles with different sizes are not inherently toxic to human skin cells, but gold nanorods are highly toxic due to the presence of CTAB as coating material. Due to CTAB toxicity, and aggregation of gold nanomaterials in the presence of cell media, it is a real challenge to study the cytotoxicity of gold nanomaterials individually.

As nanotechnology field continues to develop, assessing nanoparticle toxicity is very important for advancing nanoparticles for daily life application. In this Letter, we report the effect of surface coating on cyto, geno and photo-toxicity of silver nanomaterials of different shapes on human skin HaCaT keratinocytes. We found that the citrate coated colloidal silver nanoparticles at 100 µg/mL level are not geno-, cyto- and phtotoxic. On the other hand, citrate coated powder form of the silver nanoparticles are toxic. We have demonstrated that coating of the silver nanoparticles with a biodegradable polymer prevents the toxicity of the powder. Toxicity mechanism has been discussed.

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The form of the exciton absorption band for 1D molecular chains and their luminescence are investigated in glass matrices of various composition and in Langmuir–Blodgett (LB) films under selective excitation. It is shown that the exciton absorption band for 1D chains is always asymmetric. The shape of the low-frequency edge of their absorption band changes from the Gaussian to the Lorentzian depending on the method of obtaining of 1D chains due to a change in the diagonal and off-diagonal disorder in molecular chains. Under selective excitation of 1D molecular chains, the effect of considerable luminescence band narrowing is not observed. This is associated with statistical properties of the exciton absorption band and with relaxation processes in the materials under investigation in the excited state.