The suitability of silicon nanoparticles of 1 nm in diameter for fluorescent sensing was investigated. Silicon nanoparticles were produced in a cluster beam and co-deposited with a beam of vapourised liquids (water, ethanol, isopropanol) onto a cold substrate. Melting of the frozen cluster-ice mixture yielded an aqueous suspension which emitted strong fluorescence in the deep blue spectral range when exposed to UV light. The fluorescence wavelength of the strongest peak was found to correlate with the dipole moment of the solvent molecules which allowed us to derive the transition energy for an isolated nanoparticle. The strong solvent sensitivity showed that the fluorescence originated from a surface state. A second fluorescence peak showed almost no sensitivity to different solvents, hence the peak was attributed to a transition within the bulk-volume of the nanoparticles. Our findings establish that silicon nanoparticles may serve as highly specific bio-sensors in living organism.

The use of nanoparticle photothermal effect as adjuvants in neuromodulation has recently received much attention, with many open questions about new nanostructures’ effect on the action potential. The photothermal properties of hexagonal gold nanoparticles are investigated in this work, including the absorption peak wavelength and light-heat conversion rate, using both experimental and simulation methods. Furthermore, the ability to use these nanostructures in axonal neural stimulation and cardiac stimulation by measuring temperature changes of gold nano-hexagons under 532 nm laser irradiation is studied. In addition, their thermal effect on neural responses is investigated by modeling small-diameter unmyelinated axons and heart pacemaker cells. The results show that the increase in temperature caused by these nano-hexagons can successfully stimulate the small diameter axon and produce an action potential. Experiments have also demonstrated that the heat created by gold nano-hexagons affects toad cardiac rhythm and increases T wave amplitude. An increase in T wave amplitude on toad heart rhythm shows the thermal effect of nano hexagons heat on heart pacemaker cells and intracellular ion flows. This work demonstrates the feasibility of utilizing these nanostructures to create portable and compact medical devices, such as optical pacemakers or cardiac stimulation.

In our attempt to reduce the threshold for dye-based random lasers, a new kind of random lasing media is demonstrated based on silver nano-hexagonal as scattering centers. For this purpose, we use a chemical method to synthesize nano hexagonal silver scatterer points and dissolve them in polymer and Rhodamine B dye media in different concentrations and different sizes. Our results from these samples under different pumping power, confirm the strong dependence on the sizes and concentration on the transition from incoherent to the coherent random laser, which is starts from 0.061 MW cm −2 as threshold power. This threshold power and linewidths of emission peaks decrease by an increase in the size and concentrations of nano-hexagonal points to 0.04 MW cm −2 and 0.2 nm, respectively.

The nonlinear refractive index n2 of hybrid structure composed of metal nanoparticle, Au, and a silicon quantum dot is measured and calculated by means of experimental and theoretical methods, respectively. Experimentally, gold nanoparticles are prepared by laser ablation in liquid method and Si quantum dot by liquid jet method. By using Z-scan technique, the mixture of them is exposed by 532 nm pump light, in close aperture configuration, to obtain the nonlinear refractive index. Moreover, hybrid structure is modeled, and the third-order nonlinear susceptibility χ^3 is calculated by the local field theory. Our results show enhanced third-order nonlinear susceptibility χ^3 and as a result nonlinear refractive index of the sample in the presence of the gold nanoparticles theoretically by the extracted nonlinearity experimentally.