Gold nanoparticles have shown potential applications for cancer detection and localized photothermal therapy (PTT). [1][2][3][4][5] Among the gold nanoparticles that have been studied, gold nanorods are of particular interest because of their tuneable near-infrared (NIR) absorption and the recent success in their size-controlled, large-scale synthesis. [6,7] The strong two-photon photoluminescence (TPL) of gold nanorods render them good contrast agents for cancer cell imaging under two-photon excitation, [8,9] which makes it more suitable to three-dimensional nonlinear optical imaging of biological samples. [10,11] Despite the successful application of gold nanorods in PTT and in vitro cancer imaging, this technique still has a long way to go before it can be implemented clinically. For clinical applications, the energy input should be as low as possible to avoid damage to healthy tissues, which is always a concern for laser-based applications. The energy threshold can be reduced by optimizing tumor targeting of the particles, choosing a suitable laser mode, and improving the light absorption efficiency of the nanorods. It has been observed that a pulsed femtosecond laser beam in PTT was more effective than a continuous wave (CW) laser beam. [12,13] However, most of the gold nanorods are randomly oriented in cells, making it impossible to achieve the maximum energy efficiency due to the limited fraction of excitation of the total nanorods under linearly polarized light. To increase the light absorption efficiency and hence the photothermal effect of the nanorods, a circularly polarized laser beam, which can emit a light beam of all polarization angles within one optical period, can be used to activate as many nanorods as possible, as illustrated by Figure 1a. To demonstrate the circular polarization effect on nanorod excitation, nanorods from a dilute solution were deposited on a cover slide and the same population of nanorods was subject to a linearly and circularly polarized light illumination in sequence. The corresponding images of the nanorods are given in Figure 1b and 1c, respectively. Both single gold nanorods and aggregated nanorods (larger and brighter spots as circled in Fig. 1b) can be identified. It shows that under illumination of circularly polarized light at the same incident power, more nanorods can be excited and be imaged clearly. To demonstrate the circular polarization effect for cancer therapy, we have developed biofunctional nanorods for the specific targeting of cancer cells. Transferrin has been shown to be effective as a ligand for actively targeting malignant cells for the delivery of drugs, proteins and genes. [14,15] Although it has been used to enhance the cellular uptake of gold nanoparticles [16] and quantum dots/rods, [17] conjugating transferrin to gold nanrods for combined imaging and therapy of cancer cells has not been reported. Our work shows the successful development of transferrin-conjugated gold nanorods that can be used for efficient targeting and imaging of cancer cells...

Photorefractive polymer composite trapping properties and a link with chromophore structure

We report what is believed to be the first use of a photorefractive polymer in erasable-rewritable three-dimensional bit optical data storage under two-photon excitation. We successfully demonstrate writing, erasing, and rewriting of multilayered information in a photorefractive polymer consisting of 2,5-dimethyl-4-(p-nitrophenylazo)anisole, 2,4,7-trinitro-9-fluorenone, 9-ethylcarbazole, and poly(N-vinylcarbazole). A three-dimensional bit density of 5 Gbits/cm(3) is achieved by two-photon absorption under pulsed beam illumination at an infrared wavelength of 800 nm in the recording process. Complete erasing of the recording information is achieved by use of ultraviolet illumination.

Reported is an investigation into the effect of spherical aberration caused by the mismatch of the refractive indices between the recording material and its immersion medium on the three-dimensional optical data-storage density in a two-photon bleaching polymer. It is found both theoretically and experimentally that spherical aberration can be compensated for by a change in the tube length at which a microscope objective is operated in recording and reading processes. After compensation for the spherical aberration it is possible to achieve a three-dimensional recording density of 3.5 Tbits/cm(3) for a commercial objective with a numerical aperture of 1.4.

3D bit optical data storage has the ability to reach Tbytes on a recording medium no larger than a compact disc using two‐photon excitation and multi‐layer recording. The introduction of a poly‐vinyl carbazole (PVK) based photorefractive polymer as the recording material allows the system to rewrite the recorded information via the photorefractive effect.[1,2] In this paper, we demonstrate the use of continuous wave illumination for three‐dimensional (3D) bit optical data storage under two‐photon excitation in a new poly(methylmethacrylate)‐based (PMMA) photorefractive polymer. This achievement makes it possible to develop a cheap, compact, sub Tbyte rewritable optical data storage system to further extend the capabilities of compact disc and digital versatile disc technology.