No abstract

Pulsed-laser-induced size reduction of plasmonic nanoparticles in solution has long been known for a drawback resulting from polydispersed products. Recently, by adjusting external pressure, laser intensity, and excitation wavelength, the nanosecond pulsed-laser excitations of colloidal gold nanoparticles in pressurized aqueous solution were found to enable tuning of the particle size and size distribution. Nevertheless, the mechanism underlying the phenomenon is poorly understood. Here we propose a model based on temperature calculations via the two-temperature model coupled to a surface evaporation mechanism. Incorporating the temperature-induced plasmon band bleaching during the excitation is crucial. Our computational result indicated that the photothermal evaporation of gold nanoparticles of a given size occurred at temperatures below the boiling point of bulk gold, leading to a smaller particle diameter with increasing laser fluence; the result qualitatively explains the experiment. The method developed here to calculate temperature is applicable to various nanoscale experiments including surfaceenhanced Raman spectroscopy, where a proper assessment is indispensable when treating photothermal effects of plasmonic nanoparticles under illumination by pulsed and focused continuous lasers.

We demonstrate an inexpensive alternative to total internal reflection fluorescence microscopy. A method for imaging ultrathin films and living cells located on waveguides—illuminated with their evanescent fields—is introduced. An extensive analysis of ion-exchanged waveguides focusing on their application as microscopy substrates for studying interfacial phenomena is presented. Experimental results are in excellent agreement with the simulations. As an application osteoblasts (bone matrix forming cells) and ultrathin Langmuir–Blodgett films were imaged. The fluorescence intensity has been used to determine the cell attachment.

Planar glass waveguides with a specific number of modes were fabricated by Ag(+)-Na(+) exchange in Schott SG11 glass. The effective refractive indices were determined using m-line spectroscopy in both s- and p-polarization. By using the reversed Wentzel-Kramers-Brillouin approximation, the index profiles were described by a nonlinear diffusion equation. The diffusion coefficients for Ag(+) were established, as well as the penetration depth of the evanescent field in an aqueous environment for the different modes. The integrals of \E\(2) fields for the evanescent-guided fields were investigated. These are important when evanescent fields are used for illumination in interface microscopy, an alternative method to total internal reflection fluorescence (TIRF) microscopy. The photoluminescent behavior of the waveguides was investigated as a function of ion exchange time and excitation wavelengths. Comparable images were obtained of fluorescently labeled HEK293 cells using TIRF microscopy and waveguide evanescent field fluorescence microscopy. Imaging was performed using HEK293 cells, delivering similar images and information.

Hamilton, Douglas W.; and Mittler, Silvia, "Large area periodic, systematically changing, multishape nanostructures by laser interference lithography and cell response to these topographies" (2013 Abstract. The fabrication details to form large area systematically changing multishape nanoscale structures on a chip by laser interference lithography (LIL) are described. The feasibility of fabricating different geometries including dots, ellipses, holes, and elliptical holes in both x-and y-directions on a single substrate is shown by implementing a Lloyd's interferometer. The fabricated structures at different substrate positions with respect to exposure time, exposure angle and associated light intensity profile are analyzed. Experimental details related to the fabrication of symmetric and biaxial periodic nanostructures on photoresist, silicon surfaces, and ion milled glass substrates are presented. Primary rat calvarial osteoblasts were grown on ion-milled glass substrates with nanotopography with a periodicity of 1200 nm. Fluorescent microscopy revealed that cells formed adhesions sites coincident with the nanotopography after 24 h of growth on the substrates. The results suggest that laser LIL is an easy and inexpensive method to fabricate systematically changing nanostructures for cell adhesion studies. The effect of the different periodicities and transition structures can be studied on a single substrate to reduce the number of samples significantly.