36 research outputs found
Electrically addressable vesicles: Tools for dielectrophoresis metrology
Dielectrophoresis (DEP) has emerged as an important tool for the manipulation of bioparticles ranging from the submicron to the tens of microns in size. Here we show the use of phospholipid vesicle electroformation techniques to develop a new class of test particles with specifically engineered electrical propserties to enable identifiable dielectrophoretic responses in microfabricated systems. These electrically addressable vesicles (EAVs) enable the creation of electrically distinct populations of test particles for DEP. EAVs offer control of both their inner aqueous core and outer membrane properties; by encapsulating solutions of different electrolyte strength inside the vesicle and by incorporating functionalized phospholipids containing poly(ethylene glycol) (PEG) brushes attached to their hydrophilic headgroup in the vesicle membrane, we demonstrate control of the vesicles’ electrical polarizabilities. This combined with the ability to encode information about the properties of the vesicle in its fluorescence signature forms the first steps toward the development of EAV populations as metrology tools for any DEP-based microsystem.National Institutes of Health (U.S.) (Grant RR199652)National Institutes of Health (U.S.) (Grant EB005753)Merck/CSBi (Fellowship)Solomon Buchsbaum AT&T Research Fun
Control of Length and Spatial Functionality of Single-Wall Carbon Nanotube AFM Nanoprobes
Single-wall carbon nanotube (SWNT) nanofibrils were assembled onto conductive
atomic force microscopy (AFM) probes with the help of dielectrophoresis (DEP).
This process involved the application of a 10 V, 2 MHz, AC bias between a
metal-coated AFM probe and a dilute suspension of SWNTs. This exerted a
positive dielectrophoretic force onto the nanotubes that caused them to align
while precipitating out onto the probe. The gradual removal of the AFM probe
away from the SWNT suspension consolidated these nanotubes into nanofibrils
with a high degree of alignment as demonstrated with polarization Raman
experiments. By varying the pulling speed, immersion time, and concentration of
the SWNT suspension, one can tailor the diameter and thus the stiffness of
these probes. Precise length trimming of these nanofibrils was also performed
by their gradual immersion and dissolution into a liquid that strongly
interacted with nanotubes, (i.e., sodium dodecyl sulfate (SDS) solution).
Vacuum annealing these nanoprobes at temperature up to 450 degree C further
increased their stiffness and rendered them insoluble to SDS and all other
aqueous media. Regrowth of a new SWNT nanofibril from the side or at the end of
a previously grown SWNT nanofibril was also demonstrated by a repeated
dielectrophoretic assembly at the desired immersion depth. These SWNT
nanofibril-equipped AFM probes are electrically conductive and mechanically
robust for use as high-aspect-ratio electrochemical nanoprobes
Dielectrophoretic concentration and separation of live and dead bacteria in an array of insulators
An insulator-based (electrodeless) dielectrophoretic concentrator for microbes in water
Dielectrophoresis (DEP), the motion of a particle caused by an applied electric field gradient, can concentrate microorganisms non-destructively. In insulator-based dielectrophoresis (iDEP) insulating microstructures produce non-uniform electric fields to drive DEP in microsystems. This article describes the performance of an iDEP device in removing and concentrating bacterial cells, spores and viruses while operated with a DC applied electric field and pressure gradient. Such a device can selectively trap particles when dielectrophoresis overcomes electrokinesis or advection. The dielectrophoretic trapping behavior of labeled microorganisms in a glass-etched iDEP device was observed over a wide range of DC applied electric fields. When fields higher than a particle-specific threshold are applied, particles are reversibly trapped in the device. Experiments with Bacillus subtilis spores and the Tobacco Mosaic Virus (TMV) exhibited higher trapping thresholds than those of bacterial cells. The iDEP device was characterized in terms of concentration factor and removal efficiency. Under the experimental conditions used in this study with an initial dilution of 1 × 105 cells/ml, concentration factors of the order of 3000× and removal efficiencies approaching 100% were observed with Escherichia coli cells. These results are the first characterization of an iDEP device for the concentration and removal of microbes in water