We demonstrated the plasmonic metallic nanostructure fabricated by direct nanoimprinting of gold nanoparticles (AuNPs). This approach combines the patterning and lift-off processes into a simple one-step process without the need for expensive patterning lithographies and the stringent requirement of the lift-off process for nanostructures. Good imprinting integrity was accomplished with a negligible residual layer. The dynamic optical responses of the imprinted gold pillars from AuNPs to the bulk material during the annealing process were investigated. The localized surface plasmon resonance (LSPR) properties of AuNPs or gold pillar arrays can be controlled and tuned during the annealing process. The sensitivity of the gold pillar array in terms of the wavelength shift per refractive index unit (RIU) reached 259 nm/RIU. The size of the imprinted gold pillars is highly scalable in our process. The corresponding resonance wavelengths can be widely tuned from the visible to infrared region by changing the size of the gold pillars, thus providing a wide range of sensing capability.

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The determination of cell confluency and subculture timing for cell culture consistency is crucial in the field of cell-based research, but there is no universal standard concerning optimal confluence. In this study, gold nanodot arrays on glass substrates were used as culture substrates, and their spectral shifts of localized surface plasmon resonance (LSPR) were employed to monitor cell growth and quantify cell confluency. Experiments including cell counting, metabolic activity, focal adhesion, and cell cycle were also performed to confirm the cell growth monitoring accuracy of the LSPR signals. The LSPR signal exhibited the same trends like the increase of cell numbers and cell metabolic activity and reached the maximum as the cell growth achieved confluency, suggesting its great capability as an effective indicator to predict suitable subculture timing. The proposed sensing approach is a noninterventional, nondestructive, real-time, and useful tool to help biologists quantify the optimal subculture timing, achieve cell culture consistency, and obtain reproducible experimental results efficiently.

This paper presents a simple approach for the selective growth of patterned monolayer gold nanoparticles (AuNPs) and bulk gold nanostructures through photoreduction. Photoreduction can occur on the surface of SU-8 but not on the surface of poly(methyl methacrylate) (PMMA). Therefore, a PMMA mask was introduced to the SU-8 surface to confine the area for AuNP production. We developed a residual layer-free nanotransfer printing process to transfer the PMMA mask from a perfluoropolyether mold onto the SU-8 surface. After the exposure of a drop of HAuCl 4 over the SU-8 surface masked by PMMA to UV light, AuNPs formed on the uncovered SU-8 surface. Gold nanostructures with various shapes, including nanodisks, nanorings, nanorod dimers, and asymmetric U-shaped split-ring resonators, were produced through the proposed approach. The optical properties of the fabricated nanostructures were investigated and found to be consistent with the simulation. Overall, this study provides a reliable and predictable process for fabricating gold nanostructures with various shapes, which can be beneficial for plasmonic applications.

Ultra-reduced nanocavities in plasmonic nano-pleat arrays achieved by gold sputtering on perfluoropolyether molds and one-step nanotransfer printing.