Taking advantage of the high impermeability property of graphene and the sharp surface plasmon resonance (SPR) curve of silver, we numerically demonstrate that SPR imaging biosensors with a graphene-on-silver substrate can be used to achieve the dramatically high sensitivity as well as to prevent silver oxidation. Results of our numerical study show that a silver substrate with a few graphene layers can significantly increase the imaging sensitivity, compared to the conventional gold-film-based SPR imaging biosensor. In particular, single layered graphene deposited on the 60-nm thick silver film amplifies the SPR imaging signal more than three times. Therefore, the proposed SPR substrate could potentially open a new possibility of SPR imaging detection for sensitive and high-throughput assessment of multiple biomolecular interactions.

An advanced optical activation of neural tissues is demonstrated using pulsed infrared light and plasmonic gold nanorods. Photothermal effect localized in plasma membrane triggers action potentials of in vivo neural tissues. Compared with conventional infrared stimulation, the suggested method can increase a neural responsivity and lower a threshold stimulation level significantly, thereby reducing a requisite radiant exposure and the concern of tissue damage.

Mitochondria are organelles that are readily susceptible to temperature elevation. We selectively delivered a coumarin-based fluorescent iron oxide nanoparticle, Mito-CIO, to the mitochondria. Upon 740 nm laser irradiation, the intracellular temperature of HeLa cells was elevated by 2.1 °C within 5 min when using Mito-CIO, and the treatment resulted in better hyperthermia and a more elevated cytotoxicity than HeLa cells treated with coumarin iron oxide (CIO), which was missing the mitochondrial targeting unit. We further confirmed these results in a tumor xenograft mouse model. To our knowledge, this is the first report of a near-infrared laser irradiation-induced hyperthermic particle targeted to mitochondria, enhancing the cytotoxicity in cancer cells. Our present work therefore may open a new direction in the development of photothermal therapeutics.

In this study, we investigated the sensitivity enhancement in nanowire-based surface plasmon resonance (SPR) biosensors using rigorous coupled wave analysis (RCWA). The enhancement, enabled by the excitation of localized surface plasmons in gold nanowires, offers improved performance in sensitivity as well as in reproducibility and customizability. Calculation results found that a T-profile provides higher sensitivity than an inverse T-profile in general and also determined optimum design parameters. Our study on a nanowire-enhanced SPR biosensor demonstrates the potential for significant improvement in the sensitivity through the nanowire-mediated localized SPR.

We have experimentally confirmed sensitivity enhancement of a nanowire-based surface plasmon resonance (SPR) sensor structure. Gold nanowires with periods of 200 and 500 nm were fabricated, respectively, by electron-beam and interference lithography on a gold/SF10 substrate. Sensitivity enhancement was measured to be 44% compared with a conventional thin-film-based SPR structure for nanowires of 200 nm period and 31% for 500 nm when evaluated using ethanol at a varied concentration. This result is consistent with numerical data. Surface roughness is responsible for sensitivity reduction by more than 10%. More significant sensitivity improvement can be achieved by inducing strong localized plasmon coupling with finer nanowires.