Elliot J. Smith

Light-Controlled Propulsion of Catalytic Microengines†

Control over the autonomous motion of artificial nano/ micromachines is essential for real biomedical and nanotechnological applications. Consequently, a complete nanomachine should be able to be turned on and off at will. Developments over the last few years on synthetic catalytic nano/microengines and motors have enabled the harvesting of chemical energy from local molecules and transforming it into an effective autonomous motion. Several impressive applications have recently reported the use of artificial micromachines for the detection of biomolecules with roving nanomotors, transport of animal cells in a fluid, and other microcargo delivery. Recently, the use of a light source has been implemented to propel microparticle-based motors generated by a selfdiffusiophoretic mechanism. Despite this interesting approach, the motion of the particles is limited by the dissolution of the materials and to the ultraviolet (UV) spectrum. Moreover, a reversible method to start and stop the propulsion of micromotors by a visible-light source remains a challenge. Here we report the tuning of the propulsion power of Ti/ Cr/Pt catalytic microengines (m-engines) through illumination of a solution by a white-light source. We show that light suppresses the generation of microbubbles, stopping the engines if they are fixed-to or self-propelled above a platinum-patterned surface. The m-engines are reactivated by dimming the light source that illuminates the fuel solution. The illumination of the solution with visible light in the presence of Pt diminishes the concentration of hydrogen peroxide fuel and degrades the surfactant, consequently reducing the motility of the microjets. Electrochemical measurements and analysis of the surface tension support our findings. We also study the influence of different wavelengths over the visible spectrum (500–750 nm) on the formation of microbubbles. Rolled-up Ti/Cr/Pt catalytic m-engines with diameters of 5–10 mm and a length of 50 mm were prepared as described previously elsewhere and in the Experimental Section. Microengines were immersed into solutions of aqueous H2O2 (2.5% v/v) as fuel and benzalkonium chloride (ADBAC) (0.5% v/v), as the surfactant, to determine the influence of white light on the mobility of the m-engines. At lower concentrations of both chemicals, the generation of microbubbles is significantly reduced. Thus, the motility of the catalytic m-engines is controlled by a small change in the fuel (H2O2 and/or surfactant) concentration. These conditions allow us to investigate a concentration range close to the metastable state, that is, where the probability of stopping the m-engines is high. Figure 1A

Lab-in-a-Tube: Detection of Individual Mouse Cells for Analysis in Flexible Split-Wall Microtube Resonator Sensors

We report a method for the precise capturing of embryonic fibroblast mouse cells into rolled-up microtube resonators. The microtubes contain a nanometer-sized gap in their wall which defines a new type of optofluidic sensor, i.e., a flexible split-wall microtube resonator sensor, employed as a label-free fully integrative detection tool for individual cells. The sensor action works through peak sharpening and spectral shifts of whispering gallery modes within the microresonators under light illumination.

Combined surface plasmon and classical waveguiding through metamaterial fiber design.

A metamaterial integration for fiber optics, leading to a dual effect of surface plasmon and classical waveguiding, is presented along with experimental potentiality. We theoretically propose a metamaterial fiber in which, depending on the wavelength (from ultraviolet to infrared) and the particular metamaterial composition, one can transmit information through surface plasmon mediated or classical waveguidance. The metamaterial can be used as the core or cladding of a fiber which allows waveguidance through a subwavelength geometry.

System investigation of a rolled-up metamaterial optical hyperlens structure

An investigation of the material makeup and surrounding medium of an optical rolled-up hyperlens is presented. A working spectral range of the hyperlens for different material combinations is studied along with an examination of hyperlens immersion, which suppresses the diffraction of waves exiting the lens due to impedance matching, leading to a higher intensity output. This hyperlens immersion technique can be implemented into cell culture and molecular analysis.

Local-illuminated ultrathin silicon nanomembranes with photovoltaic effect and negative transconductance.

and bioanalytic microsystems. [ 10 , 11 ] Schottky barriers at contacts to nanomaterials are often observed and may play a critical role for their electrical properties, [ 12 – 14 ] in particular for nanomembranes. [ 15 ] On the other hand, certain tricks played on Schottky barriers can offer routes to novel devices like ambipolar transistors [ 16 ] and solar cells. [ 17 , 18 ] Recently, local illumination was exploited in scanning photocurrent spectroscopy to probe the effect of contact properties on device characteristics of silicon nanowires, graphene, and carbon nanotubes. [ 14 , 19–21 ] However, there are only few reports to apply such basic Schottky contacts to nanomaterials to realize interesting electronic devices. [ 18 ]

Polymer delamination: towards unique three-dimensional microstructures

A method which eliminates the need for a sacrificial layer in rolled-up systems is put forth. Instead, the self-assembly relies solely on the delamination of a patterned polymer layer. This polymer layer can contain any of a number of inorganic active nanomembranes which exhibit a variety of material properties for numerous system functionalities.

Erratum: “System investigation of a rolled-up metamaterial optical hyperlens structure” [Appl. Phys. Lett. 95, 083104 (2009)]

Typing errors as well as a calculation error were made in the original publication of this letter. Here we correct the equations, resulting calculations, and figures of the original letter. The effective media theory equations for calculating the permittivity were both written incorrectly in the letter, and an incorrect version of the effective radial permittivity was used for our calculations. This makes the hyperbolic range of Fig. 2 a , and the dispersion relation graphs in Figs. 1 d and 2 b , incorrect. The correct equations are as follows: r= cm+cd m d / cd m+cm d and = cm m+cd d / cm +cd . The revised Fig. 1 and 2 calculated with the correct permittivity formulas are shown below. Using rolled-up bilayers for creating the hyperlens and the hyperlens immersion technique presented in the original letter still stand valid despite these errors. Using the correct equation for the radial permittivity results in a lower spectral range where the dispersion relation is hyperbolic for the material systems we chose to look at. However, for a higher ratio of oxide:metal, the dispersion relation becomes elliptical, as shown in the revised Figs. 1 d and 2. This elliptical dispersion, as mentioned in the original letter, allows for the transmission of high order spatial information into the farfield even though light is not mediated through an unbound dispersion relation. Despite the ability to resolve subwavelength objects with an elliptical dispersion relation, the opti-

Optical components for lab-in-a-tube systems

We present a review on recent advancements in rolled-up optical components created using strain engineering. A look at optical and optofluidic resonators as well as the hyperlens and an optical fiber metamaterial device is given. These individual ultra-compact components allow researchers to develop large arrays of a future highly-integrated biological sensing device known as a lab-in-a-tube. These lab-in-a-tube devices would allow for a very large parallel but individual analysis of thousands of cells, molecules and bacteria on a single chip.