Biopsy with thermally-responsive untethered microtools.

Thermally activated, untethered microgrippers can reach narrow conduits in the body and be used to excise tissue for diagnostic analyses. As depicted in the figure, the feasibility of an in vivo biopsy of the porcine bile duct using untethered microgrippers is demonstrated.

Voltage-gated ion transport through semiconducting conical nanopores formed by metal nanoparticle-assisted plasma etching.

Nanopores with conical geometries have been found to rectify ionic current in electrolytes. While nanopores in semiconducting membranes are known to modulate ionic transport through gated modification of pore surface charge, the fabrication of conical nanopores in silicon (Si) has proven challenging. Here, we report the discovery that gold (Au) nanoparticle (NP)-assisted plasma etching results in the formation of conical etch profiles in Si. These conical profiles result due to enhanced Si etch rates in the vicinity of the Au NPs. We show that this process provides a convenient and versatile means to fabricate conical nanopores in Si membranes and crystals with variable pore-diameters and cone-angles. We investigated ionic transport through these pores and observed that rectification ratios could be enhanced by a factor of over 100 by voltage gating alone, and that these pores could function as ionic switches with high on-off ratios of approximately 260. Further, we demonstrate voltage gated control over protein transport, which is of importance in lab-on-a-chip devices and biomolecular separations.

A one-step etching method to produce gold nanoparticle coated silicon microwells and microchannels.

Gold (Au) nanoparticles (NPs) have large surface areas and novel optical properties and can be readily functionalized using thiol-based chemistry; hence, they are useful in bioanalytical chemistry. Here, we describe a one-step, plasma-etching process that results in the spontaneous formation of Au NP coated recessed microstructures in silicon (Si). Mechanistically, the plasma etch rate of Si was enhanced in the vicinity of 10-100 nm thick Au patterns resulting in the formation of microwells or microchannels uniformly coated with 20-30 nm sized Au NPs. The methodology provides versatility in the types of microstructures that can be formed by varying the shape and dimensions of the Au patterns and the etch time. We also describe selective binding of antibodies to Au NP coated Si microwells using thiol-based surface modification.

Importance of surface patterns for defect mitigation in three-dimensional self-assembly.

This article investigates the three-dimensional self-assembly of submillimeter scale polyhedra using surface forces. Using a combination of energy landscape calculations and experiments, we investigate the influence of patterns of hydrophobic surfaces on generating defect-free, closed-packed aggregates of polyhedra, with a focus on cubic units. Calculations show that surface patterning strongly affects the interaction between individual units as well as that of the unit with the growing assembly. As expected, an increase in the hydrophobic surface area on each face results in larger global minima. However, it is the distribution of hydrophobic surface area on each cubic face that is strongly correlated to the energetic parameters driving low-defect assembly. For patterns with the same overall area, minimizing the radius of gyration and maximizing the angular distribution leads to steep energy curves, with a lower propensity for entrapment in metastable states. Experimentally, 200-500 microm sized metallic polyhedra were fabricated using a self-folding process, and the exposed surfaces were coated with a hydrophobic polymer. Cubes with surface patterns were agitated to cause aggregative self-assembly. Experimental results were consistent with energy calculations and suggest that geometric patterns with large overall areas, low radii of gyration, and high angular distributions result in efficient and low-defect assembly.

Pick-and-place using chemically actuated microgrippers.

In this communication, we demonstrate the concept of single-use, chemically triggered, reversible tools in the form of mobile grippers that can be used to manipulate micro-objects. Both the closing and opening of the mobile grippers are triggered by chemicals, namely acetic acid (CH(3)COOH) and hydrogen peroxide (H(2)O(2)), respectively. The grippers close and open en masse based on chemically triggered, mechanical property changes within trilayer joints patterned within the gripper, and no external power is needed for operation. We describe the actuation of the gripper using a multilayer thin film model and demonstrate the utility of the gripper by picking-and-placing 200 microm diameter tubes and beads. Our pick-and-place microgripper is a first step toward the development of functional Micro Chemo-Mechanical Systems (MCMS), which are actuated by chemistry as opposed to electricity [as in Micro Electro-Mechanical Systems (MEMS)].