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Recently we have developed LSPR-mediated high resolution live-cell imaging techniques for adhesive cells on plasmonic metasurface composed of self-assembled gold or silver nanoparticles. Compared with other super-resolution microscopy techniques, our LSPR-mediated imaging is extremely simple but quite effective for monitoring the molecular dynamics at a nanointerface. The LSPR of the plasmonic metasurface provides high-contrast interfacial images due to the confined light within a region a few tens of nanometers from the particles and the enhancement of fluorescence. The improved lateral resolution reaches down to the theoretical limit even during cell movement due to the properties of the metasurface with an extremely high refractive index. In the presentation, we will present our latest imaging data concerning molecular dynamics in live cells, which were not visualized by other super-resolution imaging methods with low temporal resolution.

In this study, we investigated the viscoelastic properties of metal nanoparticle monolayers at the air/water interface by dilational rheology under periodic oscillation of surface area. Au nanoparticles capped with oleylamine form a stable, dense monolayer on a Langmuir film balance. The stress response function of a nanoparticle monolayer was first analyzed using the classical Kelvin-Voigt model, yielding the spring constant and viscosity. The obtained results suggest that the monolayer of nanoparticles is predominantly elastic, forming a two-dimensional physical gel. As the global shape of the signal exhibited a clear nonlinearity, we further analyzed the data with the higher modes in the Fourier series expansion. The imaginary part of the higher mode signal was stronger than the real part, suggesting that the dissipative term mainly causes the nonlinearity. Intriguingly, the response function measured at larger strain amplitude became asymmetric, accompanied by the emergence of even modes. The significance of interactions between nanoparticles was quantitatively assessed by calculating the potential of mean force, indicating that the lateral correlation could reach up to the distance much larger than the particle diameter. The influence of surface chemical functions and core metal has also been examined by using Au nanoparticles capped with partially fluorinated alkanethiolate and Ag nanoparticles capped with myristic acid. The combination of dilational rheology and correlation analyses can help us precisely control two-dimensional colloidal assembly of metal nanoparticles with fine-adjustable localized surface plasmon resonance.

This paper proposes a simple, effective, non-scanning method for the visualization of a cell-attached nanointerface. The method uses localized surface plasmon resonance (LSPR) excited homogeneously on a two-dimensional (2D) self-assembled gold-nanoparticle sheet. The LSPR of the gold-nanoparticle sheet provides high-contrast interfacial images due to the confined light within a region a few tens of nanometers from the particles and the enhancement of fluorescence. Test experiments on rat basophilic leukemia (RBL-2H3) cells with fluorescence-labeled actin filaments revealed high axial and lateral resolution even under a regular epifluorescence microscope, which produced higher quality images than those captured under a total internal reflection fluorescence (TIRF) microscope. This non-scanning-type, high-resolution imaging method will be an effective tool for monitoring interfacial phenomena that exhibit relatively rapid reaction kinetics in various cellular and molecular dynamics.

In this short communication, we report a procedure for the fabrication of microscale pores on a rigid self-assembled Ag nanoparticle monolayer with nanothickness. Here, condensed water droplets on a hydrophobic substrate are used as a pore formation template for Langmuir-Schaefer film deposition. The optical properties of the Ag nanoparticle monolayer were influenced by the porous structure, e.g., the localized surface plasmon resonance (LSPR) peak was weakened and broadened for the porous monolayer compared with the homogeneous monolayer, even though the number of particles on the substrate should be the same between them. The pores obtained by this method were robust and could be used as a mask for metal deposition or local fluorescence imaging. This environmentally friendly technique can provide a micropatterned surface with a minimal cytotoxicity, which has high potential for LSPR mediated biosensing and bioimaging applications.