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Localized surface-tension-driven forces (microscale Marangoni effect) caused by a temperature inhomogeneity from the decay of optically excited surface plasmons into phonons have been engaged in the actuation of adsorbed and applied liquid on a thin metal film. Microfluidic operations of transport, separation, mixing, and sorting have been experimentally and theoretically demonstrated using this all-optical modulation scheme.

The study of the spatially resolved physical and compositional properties of materials at the nanoscale is increasingly challenging due to the level of complexity of biological specimens such as those of interest in bioenergy production. Mode synthesizing atomic force microscopy (MSAFM) has emerged as a promising metrology tool for such studies. It is shown that, by tuning the mechanical excitation of the probe–sample system, MSAFM can be used to dynamically investigate the multifaceted complexity of plant cells. The results are argued to be of importance both for the characteristics of the invoked synthesized modes and for accessing new features of the samples. As a specific system to investigate, we present images of Populus, before and after a holopulping treatment, a crucial step in the biomass delignification process. [ABSTRACT FROM AUTHOR]

The study of the spatially resolved physical and compositional properties of materials at the nanoscale is increasingly challenging due to the level of complexity of biological specimens such as those of interest in bioenergy production. Mode synthesizing atomic force microscopy (MSAFM) has emerged as a promising metrology tool for such studies. It is shown that, by tuning the mechanical excitation of the probe-sample system, MSAFM can be used to dynamically investigate the multifaceted complexity of plant cells. The results are argued to be of importance both for the characteristics of the invoked synthesized modes and for accessing new features of the samples. As a specific system to investigate, we present images of Populus, before and after a holopulping treatment, a crucial step in the biomass delignification process.

Scanning probe microscopy has emerged as a powerful approach to a broader understanding of the molecular architecture of cell walls, which may shed light on the challenge of efficient cellulosic ethanol production. We have obtained preliminary images of both Populus and switchgrass samples using atomic force microscopy (AFM). The results show distinctive features that are shared by switchgrass and Populus. These features may be attributable to the lignocellulosic cell wall composition, as the collected images exhibit the characteristic macromolecular globule structures attributable to the lignocellulosic systems. Using both AFM and a single case of mode synthesizing atomic force microscopy (MSAFM) to characterize Populus, we obtained images that clearly show the cell wall structure. The results are of importance in providing a better understanding of the characteristic features of both mature cells as well as developing plant cells. In addition, we present spectroscopic investigation of the same samples.

The emerging interest in understanding the interactions of nanomaterial with biological systems necessitates imaging tools that capture the spatial and temporal distributions and attributes of the resulting nano-bio amalgam. Studies targeting organ specific response and/or nanoparticle-specific system toxicity would be profoundly benefited from tools that would allow imaging and tracking of in-vivo or in-vitro processes and particle-fate studies. Recently we demonstrated that mode synthesizing atomic force microscopy (MSAFM) can provide subsurface nanoscale information on the mechanical properties of materials at the nanoscale. However, the underlying mechanism of this imaging methodology is currently subject to theoretical and experimental investigation. In this paper we present further analysis by investigating tip-sample excitation forces associated with nanomechanical image formation. Images and force curves acquired under various operational frequencies and amplitudes are presented. We examine samples of mouse cells, where buried distributions of single-walled carbon nanohorns and silica nanoparticles are visualized.

When a liquid droplet experiences a temperature inhomogeneity along its bounding surface, a surface energy gradient is engendered, which when, in a continuous sense, exceeding a threshold, results in a convective flow dissipating the energy. If the associated temperature gradients are sustained by the interface between the liquid and a supporting substrate, the induced flow can result in the lateral motion of the droplet overcoming the viscosity and inertia. Recently, pico-liter adsorbed and applied droplets were shown experimentally to be transported, and divided by the decay of optically excited surface plasmons into phonons in a thin gold foil. The decaying events locally modify the temperature of the liquid-solid interface, establishing microscale thermal gradients of sufficient magnitude for the droplet to undergo thermocapillary flow. We present experimental evidence of such gradients resulting in local surface modification associated with the excitation of surface plasmons. We show theoretically that the observed effect is due to Marangoni forces, and computationally visualize the flow characteristics for the experimental parameters. As an application based on our results, we propose a method for an all-optical modulation of light by light mediated by the droplet oscillations. Furthermore, the results have important consequences for microfluidics, droplet actuation, and simultaneous surface plasmon resonance sensing and spectroscopy.

We present experimental results from an all-optical microfluidic platform that may be complimented by a thin film all-electrical network. Using these configurations we have studied the microfluidic convective flow systems of silicone oil, glycerol, and 1,3,5-trinitrotoluene on open surfaces through the production of surface tension gradients derived from thermal gradients. We show that sufficient localized thermal variation can be created utilizing surface plasmons and/or engaging individually addressable resistive thermal elements. Both studies manipulate fluids via Marangoni forces, each having their unique exploitable advantages. Surface plasmon excitation in metal foils are the driving engine of many physical-, chemical-, and bio-sensing applications. Incorporating, for the first time, the plasmon concept in microfluidics, our results thus demonstrate great potential for simultaneous fluid actuation and sensing.

The Knudsen effect is estimated theoretically and observed experimentally using a U-shaped silicon microcantilever. Though Knudsen forces are extremely small in most cases involving microcantilevers, there exist situations where these forces can be significant and may be important in atomic force microscopy and in microelectromechanical systems (MEMS). The criteria for the presence of Knudsen forces are outlined and an analytical expression in the form of a linear function of the pressure is given for the force in the free molecular regime. The experimental results display peaks in the transitional regime while varying linearly in the molecular regime.