The development of new and improved photothermal contrast agents for the successful treatment of cancer (or other diseases) via plasmonic photothermal therapy (PPTT) is a crucial part of the application of nanotechnology in medicine. Gold nanorods (AuNRs) have been found to be the most effective photothermal contrast agents, both in vitro and in vivo. Therefore, determining the optimum AuNR size needed for applications in PPTT is of great interest. In the present work, we utilized theoretical calculations as well as experimental techniques in vitro to determine this optimum AuNR size by comparing plasmonic properties and the efficacy as photothermal contrast agents of three different sizes of AuNRs. Our theoretical calculations showed that the contribution of absorbance to the total extinction, the electric field, and the distance at which this field extends away from the nanoparticle surface all govern the effectiveness of the amount of heat these particles generate upon NIR laser irradiation. Comparing between three different AuNRs (38 × 11, 28 × 8, and 17 × 5 nm), we determined that the 28 × 8 nm AuNR is the most effective in plasmonic photothermal heat generation. These results encouraged us to carry out in vitro experiments to compare the PPTT efficacy of the different sized AuNRs. The 28 × 8 nm AuNR was found to be the most effective photothermal contrast agent for PPTT of human oral squamous cell carcinoma. This size AuNR has the best compromise between the total amount of light absorbed and the fraction of which is converted to heat. In addition, the distance at which the electric field extends from the particle surface is most ideal for this size AuNR, as it is sufficient to allow for coupling between the fields of adjacent particles in solution (i.e., particle aggregates), resulting in effective heating in solution.

Gold nanoring dimers were fabricated via EBL with dimensions of 127.6 ± 2.5 and 57.8 ± 2.3 nm for the outer and inner diameters, respectively, with interparticle separations ranging from 17.8 ± 3.4 to 239.2 ± 3.7 nm. The coupling between the inner and outer surfaces of a single nanoring renders it very sensitive to any anisotropy. We found that anisotropy in the particle geometry and anisotropy introduced by the substrate combine to create very unique spectral features in this system.

In recent years, considerable efforts have been made to improve the performance of photoactive nanostructured materials for water splitting applications. Herein, we report on the assembly and use of a bacteriorhodopsin (bR)/TiO 2 nanotube array hybrid electrode system. Photoanode materials composed of $ 7mm long self-ordered and vertically oriented nanotube array of titanium dioxide films were fabricated via the anodization of Ti foil in formamide electrolytes containing NH 4 F at room temperature followed by sensitization of the electrodes with bR. The stability of bR on the TiO 2 surface was found to depend on the pretreatment process of the TiO 2 films. Our results demonstrate the opportunity to fabricate fairly stable bR/TiO 2 hybrid electrodes that can be used as photoanodes for photoelectrochemical water splitting. Under AM 1.5 illumination (100 mW/cm 2 ), the hybrid electrodes achieved a photocurrent density of 0.65 mA/cm 2 which is a $ 50% increase over that measured for pure TiO 2 nanotubes (0.43 mA/cm 2 ) fabricated and tested under the same conditions. In the presence of a redox electrolyte, the photocurrent increased to 0.87 mA/cm 2 . To the best of our knowledge, this is the first report on the use of bR/TiO 2 hybrid electrodes in photoelectrochemical water oxidation cells. We believe the proton pumping property of bR can be used in a variety of applications, especially those related to third generation photovoltaic cells.

Optical determination of the exact concentration of any given colloidal suspension of nanoparticles (NP) is complicated by the relative scarcity of NP-specific extinction coefficients and the rigor and expense of determining these constants experimentally. The discrete dipole approximation (DDA) theoretical technique allows for facile determination of NP energetic properties, therefore relating the extinction intensity provided by DDA to the extinction coefficient needed to determine the concentration of NP solutions would be extremely beneficial. We experimentally determine the extinction coefficients for a range of gold nanosphere and gold nanorod sizes, supplement these values with available literature values, and then use the Discrete Dipole Approximation theoretical technique to model the optical properties of each of these nanoparticles. We then develop a relationship between the theoretical extinction intensity provided by DDA and the extinction coefficients obtained experimentally. These relationships will allow future users to accurately predict extinction coefficients that are specific to the exact dimensions of the gold nanosphere or gold nanorod in question. Use of these relationships will greatly reduce both the time-scale and the cost of determining nanoparticle extinction coefficients by circumventing the need for costly, time-consuming analytical experiments.

This investigation demonstrates the contributions of absorption and scattering to the extinction spectrum of silver nanocubes with multipole resonances and the complexity of the resulting plasmon field strengths for these varying modes. The three-dimensional plasmonic field distribution and orientation around a silver nanosphere (AgNS; 40 nm) and a silver nanocube (AgNC; 40, 60, 86 nm) were calculated in the visible via the discrete dipole approximation. The three-dimensional nature of these particles allows for significant contribution from the quadrupole mode in some cases. The AgNS displays one plasmon band, its dipole mode, and has little contribution from scattering. The maximum plasmon field occurs at the extinction maximum, as expected. The 40 nm AgNC exhibits multiple plasmon bands, and the highest maximum field strength is attained from excitation of the quadrupole mode, not the dipole mode. As the size of the AgNC increases, the contribution from scattering increases. When the contribution from scattering is greater than the contribution from absorption in a AgNC, the field strength within a plasmon mode trends with the absorption and not with the extinction or scattering. This should be considered in applications of AgNCs, as excitation of the largest peak in the experimental extinction spectrum will not always result in the strongest plasmon field strength.