Large area periodic, systematically changing, multishape nanostructures by laser interference lithography and cell response to these topographies

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\u27s 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

Computational Modeling of Pulsed Laser-Induced Heating and Evaporation of Gold Nanoparticles

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 surface-enhanced Raman spectroscopy, where a proper assessment is indispensable when treating photothermal effects of plasmonic nanoparticles under illumination by pulsed and focused continuous lasers

Optical Waveguides Formed by Silver Ion Exchange in Schott SG11 Glass for Waveguide Evanescent Field Fluorescence Microscopy: Evanescent Images of HEK293 Cells

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

Focal Contact Formation of Vascular Smooth Muscle Cells on Langmuir–Blodgett and Solvent-Cast Films of Biodegradable Poly(ester amide)s

The ability of biomaterials to support the adhesion of cells is a necessary condition for their use in scaffold-guided tissue engineering. Waveguide evanescent field fluorescence (WEFF) microscopy is a relatively new microscopic technique that allows the number of cell adhesions to a waveguide surface be measured by imaging the interfacial contact region between the cells and their substratum. In this work, the adhesion of human coronary artery smooth muscle cells (HCASMCs) to ultrathin films (20 nm) of poly­(ester amide)­s (PEAs) prepared by Langmuir–Blodgett (LB) technology on waveguides was investigated and compared with conventional vinculin immunostaining on solvent cast PEA films. Cell culture was conducted both in the presence and absence of serum to evaluate the effect of nonspecific protein adsorption that mediates cell adhesion. WEFF microscopy analyses revealed that the cationic PEA enhanced the number of attachment sites compared with the control waveguides regardless of the culture medium. Although differences in cell adhesions between different PEAs were suggested by the results, no statistically significant differences were found. Similar results were observed with presently and previously reported vinculin immunostaining studies, further validating the use of WEFF microscopy to quantify cell adhesions. Moreover, the focal adhesions of the HCASMCs to the PEA surfaces indicate these PEAs can promote integrin signaling, which is vital in cell survival, migration, and proliferation, and ultimately in scaffold-guided vascular tissue engineering