Enhanced Plasmonic Particle Trapping Using a Hybrid Structure of Nanoparticles and Nanorods

So Yun Lee, Hyung Min Kim, Jinho Park, Seong Keun Kim , Jae Ryoun Youn, and Young Seok Song

Plasmon-enhanced particle trapping was demonstrated using a hybrid structure of nanoparticles and nanorods. In order to intensify localized surface plasmon resonance (LSPR), gold nanoparticles (AuNPs) were deposited on zinc oxide nanorods (ZnONRs). The synergistic effect caused by the hybrid structure was identified experimentally. Numerical analysis revealed that the LSPR-induced photophysical processes such as plasmonic heating and near-field enhancement were improved by the existence of ZnONRs. The role of the ZnONR in enhancing the particle-trapping velocity was explored by examining the scattered electric field, Poynting vector, and temperature gradient over the nanostructures calculated from the simulation. It was found that polystyrene microparticles and Escherichia coli cells were successfully trapped by using the ZnONR/AuNP plasmonic structure. A relatively high dielectric constant and nanorod geometry of ZnO enabled the hybrid substrate to enhance trapping performance, compared with a control case fabricated using only gold nanoislands.

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Spatiotemporally Resolved Tracking of Bacterial Responses to ROS-Mediated Damage at the Single-Cell Level with Quantitative Functional Microscopy

Alvaro Barroso, Malte Christian Grüner, Taylor Forbes, Cornelia Denz, and Cristian Alejandro Strassert

Herein we report on the implementation of photofunctional microparticles in combination with optical tweezers for the investigation of bacterial responses to oxidative stress by means of quantitative functional microscopy. A combination of a strongly hydrophobic axially substituted Si(IV) phthalocyanine adsorbed onto silica microparticles was developed, and the structural and photophysical characterization was carried out. The microparticles are able to produce reactive oxygen species under the fluorescence microscope upon irradiation with red light, and the behaviour of individual bacteria can be consequently investigated in situ and in real time at single cell level. For this purpose, a methodology was introduced to monitor phototriggered changes with spatiotemporal resolution. The defined distance between the photoactive particles and individual bacteria can be fixed under the microscope before the photosensitization process is started, and the photoinduced damage can be monitored by tracing the time-dependent fluorescence turn-on of a suitable marker. The results showed a distance-dependent photoinduced death time, defined as the onset of the incorporation of propidium iodide. Our methodology constitutes a new tool for the in vitro design and evaluation of photosensitizers for the treatment of cancer and infectious diseases with the aid of functional optical microscopy, as it enables a quantitative response evaluation of living systems towards oxidative stress. More generally, it provides a way to understand the response of an ensemble of living entities to reactive oxygen species by analyzing the behavior of a set of individual organisms.

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Femtosecond Nanostructuring of Glass with Optically Trapped Microspheres and Chemical Etching

Aleksander Shakhov, Artyom Astafiev, Alexander Gulin, and Victor A. Nadtochenko

Laser processing with optically trapped microspheres is a promising tool for nanopatterning at sub-diffraction limited resolution in a wide range of technological and biomedical applications. In this paper, we investigate sub-diffraction limited structuring of borosilicate glass with femtosecond pulses in the near-field of optically trapped microspheres combined with chemical post-processing. Glass surface was processed by single laser pulses at 780 nm focused by silica microspheres and then subjected to selective etching in KOH, which produced pits in the laser affected zones (LAZs). Chemical post-processing allowed obtaining structures with better resolution and reproducibility. We demonstrate production of reproducible pits with diameter as small as 70 nm (λ/11). Complex 2-Dimensional structures with 100 nm (λ/8) resolution were written on the glass surface point by point with microspheres manipulated by optical tweezers. Furthermore, the mechanism of laser modification underlying selective etching was investigated with mass-spectrum analysis. We propose that increased etching rate of laser-treated glass result from change in its chemical composition and oxygen deficiency.

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