The force of light on objects provides tremendous flexibility for nanoscale manipulation. While conventional optical tweezers use the optical gradient force of a focused laser, 1-3 recent work has leveraged the strong field gradients near microphotonic devices for particle trapping. Here we provide the first experimental demonstration of LATS, assembling a square array of over 100 polystyrene particles near a silicon photonic-crystal slab. Our method, ideally suited for on-chip integration, should provide a platform for flowthrough, serial fabrication of 2D or 3D-nanostructured materials, all-optically tunable photonic devices, and lab-ona-chip applications.The LATS process is shown schematically in Figure 1. Light is incident from below on a photonic-crystal slab, which consists of a silicon device layer patterned with a periodic array of air holes. The slab is designed to support guided-resonance modes, electromagnetic modes for which the light intensity near the slab is strongly enhanced. 18Our previous work has theoretically predicted 16 that when the incident laser is tuned to the wavelength of a guidedresonance mode, nanoparticles will be attracted toward the slab. The attractive, optical force arises from a strong electric-field gradient just above the slab surface. In addition, the nanoparticles will experience lateral optical forces due to the electromagnetic field structure of the guided-resonance mode, resulting in the assembly of a nanoparticle array.Unlike traditional colloidal self-assembly, for which free energy minimization results in hexagonal, closepacked structures, our process is not subject to such constraints. In this paper, we experimentally demonstrate the formation of a square lattice as one such example. Indeed, the use of light to drive the system dramatically alters the

We have integrated a dual-beam optical trap into a microfluidic platform and used it to study membrane mechanics in giant unilamellar vesicles (GUVs). We demonstrate the trapping and stretching of GUVs and characterize the membrane response to a step stress. We then measure area strain as a function of applied stress to extract the bending modulus of the lipid bilayer in the low-tension regime.

We experimentally demonstrate the technique of light-assisted, templated self-assembly (LATS) to trap and assemble 200 nm diameter gold nanoparticles. We excite a guided-resonance mode of a photonic-crystal slab with 1.55 μm laser light to create an array of optical traps. Unlike our previous demonstration of LATS with polystyrene particles, we find that the interparticle interactions play a significant role in the resulting particle patterns. Despite a two-dimensionally periodic intensity profile in the slab, the particles form one-dimensional chains whose orientations can be controlled by the incident polarization of the light. The formation of chains can be understood in terms of a competition between the gradient force due to the excitation of the mode in the slab and optical binding between particles.

Measurements of lipid bilayer bending modulus by various techniques produce widely divergent results. We attempt to resolve some of this ambiguity by measuring bending modulus in a system that can rapidly process large numbers of samples, yielding population statistics. This system is based on optical stretching of giant unilamellar vesicles (GUVs) in a microfluidic dual-beam optical trap (DBOT). The microfluidic DBOT system is used here to measure three populations of GUVs with distinct lipid compositions. We find that gel-phase membranes are significantly stiffer than liquid-phase membranes, consistent with previous reports. We also find that the addition of cholesterol does not alter the bending modulus of membranes composed of a monounsaturated phospholipid.

We conclude that placental RAGE is activated during PE and that RAGE-mediated inflammation in the trophoblast involves increased pro-inflammatory cytokine secretion.