Camilo A. Mejia

Light-Assisted, Templated Self-Assembly Using a Photonic-Crystal Slab

We experimentally demonstrate the technique of light-assisted, templated self-assembly (LATS). We excite a guided-resonance mode of a photonic-crystal slab with 1.55 μm laser light to create an array of optical traps. We demonstrate assembly of a square lattice of 520 nm diameter polystyrene particles spaced by 860 nm. Our results demonstrate how LATS can be used to fabricate reconfigurable structures with symmetries different from traditional colloidal self-assembly, which is limited by free energetic constraints.

Optical stretching of giant unilamellar vesicles with an integrated dual-beam optical trap

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.

Light-Assisted, Templated Self-Assembly of Gold Nanoparticle Chains

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.

Optical stretching as a tool to investigate the mechanical properties of lipid bilayers

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.

Correction to Light-Assisted, Templated Self-Assembly Using a Photonic-Crystal Slab

W this erratum, we provide the corrected optical force map and optical potential for Figure 5. The grid resolution used in the original calculation was not sufficient to guarantee convergence. The grid spacing has been reserved to 5 nm, and the forces are now calculated with the bottom edge of the particle 5 nm above the surface of the slab. The forces are obtained from a volumetric integral of the Lorentz force, using the electromagnetic fields obtained from a finite-difference time domain simulation (Lumerical). This method allows smaller particle-slab separations than the Maxwell Stress Tensor method used previously. The corrected forces are shown in Figure 5a. The corrected in-plane potential is shown in Figure 5b,c. The minimum is at the center of the unit cell. The total potential, which includes the effect of sinking, also has a minimum at the center of the unit cell. The total potential is deeper than the in-plane potential. Shao-Hua Wu and Ningfeng Huang contributed to this correction. They were not authors on the original manuscript. N. H. identified the convergence issues in the original calculation. S.-H. W. carried out calculations and verified convergence.

Experimental demonstration of light-assisted, templated self assembly using photonic-crystal slabs

We demonstrate experimentally that the near field of a photonic-crystal slab can be used to trap square arrays of nanoparticles. This process of light-assisted, templated, self assembly exploits the guided-resonance mode of the photonic crystal for force enhancement.

Light-Assisted Assembly of Nanoparticle Arrays Using Resonant Modes of Photonic-Crystal Slabs

We demonstrate for the first time the trapping of arrays of particles using guided resonance modes in photonic-crystal slabs. The resonantly-enhanced evanescent field attracts particles toward the slab, resulting in the formation of periodic nanoparticle arrays.

Stretching of Lipid Membranes Using Optical Forces

A dual-beam optical trap is used to investigate the mechanical properties of Giant Unilamellar Vesicles (GUVs), synthetic lipid-bilayer systems commonly used for studying membrane mechanics. GUV deformation is analyzed to extract the membrane bending modulus.

Optical trapping of metal-dielectric nanoparticle clusters near photonic crystal microcavities

We predict the formation of a stably trapped metal-dielectric nanoparticle cluster near a photonic crystal cavity. The cavity mode traps a gold particle, which provides a secondary trapping site for a pair of dielectric particles.

Guided resonance modes in photovoltaics and light-assisted self assembly

We present our recent work on applications of the guided resonance modes of two-dimensionally periodic photonic crystals.