Kenneth Castelino

Field-effect control of protein transport in a nanofluidic transistor circuit

Electrostatic interactions play an important role in nanofluidic channels when the channel size is comparable to the Debye screening length. Electrostatic fields have been used to control concentration and transport of ions in nanofluidic transistors. Here, we report a transistor-reservoir-transistor circuit that can be used to turn “on” or “off” protein transport using electrostatic fields with gate voltages of ±1V. Our results suggest that global electrostatic interactions of the protein were dominant over other interactions in the nanofluidic transistor. The fabrication technique also demonstrates the feasibility of nanofluidic integrated circuits for the manipulation of biomolecules in picoliter volumes.

Diffuse mismatch model of thermal boundary conductance using exact phonon dispersion

The acoustic mismatch model (AMM) and the diffuse mismatch model (DMM) have been traditionally used to calculate the thermal boundary conductance of interfaces. In these calculations, the phonon dispersion relationship is usually approximated by a linear relationship (Debye approximation). This is accurate for wave vectors close to the zone center, but deviates significantly for wave vectors near the zone edges. Here, we present DMM calculations of the thermal conductance of Al–Si, Al–Ge, Cu–Si, and Cu–Ge interfaces by taking into account the full phonon dispersion relationship over the entire Brillouin zone obtained using the Born-von Karman model (BKM). The thermal boundary conductance thus calculated deviates significantly from DMM predictions obtained using the Debye model in all cases.

Toolpath optimization for minimizing airtime during machining

Abstract This paper describes an algorithm for minimizing the non-productive time or ‘airtime’ for milling by optimally connecting different toolpath segments. This problem is formulated as a generalized traveling salesman problem with precedence constraints and is solved using a heuristic method. The performance of the heuristic algorithm and the amount of improvement obtained for different problem sizes is also presented. This algorithm has been implemented in an automated process planning system and can be applied easily to other areas of path planning optimization like fused deposition modeling and laser cutting.

Manufacturing of two and three-dimensional micro/nanostructures by integrating optical tweezers with chemical assembly

Optical tweezers have been used as versatile tools for non-contact manipulation of micrometer-sized entities. This paper proposes a hybrid micro/nanoscale manufacturing system using optical tweezers and chemical linkages for fabricating 2D and 3D micro/nanostructures. A holographic multiple trap optical tweezers system is first used to trap particles in a desired pattern. The particles are then connected to form rigid units using suitable chemistry. Connection schemes based on gold seeding, complementary-DNA linkage and streptavidin-biotin chemistry are presented and possible applications of this technique are explored. This method combines the advantages of top-down and bottom-up approaches and is compatible with organic and inorganic materials.

Highly adaptable MEMS-based display with wide projection angle

We demonstrate a MEMS-based display system with a very wide projection angle of up to 120deg. The system utilizes a gimbal-less two-axis micromirror scanner for high-speed laser beam-steering in both axes. The optical scan angle of the micromirrors is up to 16deg on each axis. A custom-designed fisheye lens is utilized to magnify scan angles. The system can display a variety of vector graphics as well as multiframe animations at arbitrary refresh rates, up to the overall bandwidth limit of the MEMS device. It is also possible to operate the scanners in point-to-point scanning, resonant and/or rastering modes. The system is highly adaptable for projection on a variety of surfaces including projection on specially coated transparent surfaces (Fig. 3.) The size of the displayed area, refresh rate, display mode (vector graphic or image raster,) and many other parameters are all adjustable by the user. The small size of the MEMS devices and lens as well as the ultra-low power consumption of the MEMS devices, in the milliwatt range, makes the overall system highly portable and miniaturizable.

Chemical patterning for the highly specific and programmed assembly of nanostructures

We have developed a new chemical patterning technique based on standard lithography-based processes to assemble nanostructures on surfaces with extraordinarily high selectivity. This patterning process is used to create patterns of aminosilane molecular layers surrounded by highly inert poly (ethylene glycol) (PEG) molecules. While the aminosilane regions facilitate nanostructure assembly, the PEG coating prevents adsorption of molecules and nanostructures, thereby priming the semiconductor substrate for the highly localized and programmed assembly of nanostructures. We demonstrate the power and versatility of this manufacturing process by building multilayered structures of gold nanoparticles attached to molecules of DNA onto the aminosilane patterns, with zero nanocrystal adsorption onto the surrounding PEG regions. The highly specific surface chemistry developed here can be used in conjunction with standard microfabrication and emerging nanofabrication technology to seamlessly integrate various nanostructures with semiconductor electronics.

Design of a monolithic piezoelectrically actuated microelectromechanical tunable vertical-cavity surface-emitting laser.

We report the design of a monolithic piezoelectrically actuated microelectromechanical tunable vertical-cavity surface-emitting laser (VCSEL). The main advantages of piezoelectric actuation compared with conventional capacitive techniques are improved wavelength control, reduced external and tilt losses, and lower power supply voltages. The details of the piezoelectric actuation scheme for a 980-nm VCSEL with a variable air gap are described. A tuning range of approximately 35 nm can theoretically be achieved with a 3-V power supply (2 x reduction from that of electrostatic actuation) by use of a 250-microm-long cantilever beam. The proposed actuation mechanism is insensitive to the pull-in phenomenon, therefore improving wavelength control and reducing threshold current. Drastic improvements in power efficiency make it ideal for low-power applications such as all-optical communication, chip-scale atomic clocks, and biological studies.

MEMS-based high-speed low-power vector display

We demonstrate a MEMS-based vector display system utilizing gimbal-less two-axis micromirror scanners for high-speed laser beam-steering. The system is capable of displaying freehand sketches, parametric curves, text, as well as multiframe animations at arbitrary refresh rates. The scanners can be operated in point-to-point vector scanning or resonant and rastering modes. Due to ultra-low power consumption of the MEMS devices, the system is highly portable, miniature and powered and controlled via a PC USB interface

Fully-Functional Tip-Tilt-Piston Micromirror Array

A fully-functional 2times2-element array of tip-tilt-piston micromirrors with large deflection angles and large piston range is presented. The fabrication of micromirrors with different technique is described

Transport of Ions and Molecules in Nanofluidic Devices

Interesting transport phenomena arise when fluids are confined to nanoscale dimensions in the range of 1–100 nm. We examine three distinct effects that influence ionic and molecular transport as the size of fluidic channels is decreased to the nanoscale. First, the length scale of electrostatic interactions in aqueous solutions becomes comparable to nanochannel size and the number of surface charges becomes comparable to the number of ions in the channel. Second, the size of the channel becomes comparable to the size of biomolecules such as proteins and DNA. Third, large surface area-to-volume ratios result in rapid rates of surface reactions and can dramatically affect transport of molecules through the channel. These phenomena enable us to control transport of ions and molecules in unique ways that are not possible in larger channels. Electrostatic interactions enable local control of ionic concentrations and transport inside nanochannels through field effect in a nanofluidic transistor, which is analogous to the metal-oxide-semiconductor field effect transistor. Furthermore, by controlling surface charge in nanochannels, it is possible to create a nanofluidic diode that rectifies ionic transport through the channel. Biological binding events result in partial blockage of the channel, and can thus be sensed by a decrease in nanochannel conductance. At low ionic concentrations, the effect of biomolecular charge is dominant and it can lead to an increase in conductance. Surface reactions can also be used to control transport of molecules though the channel due to the large surface area-to-volume ratios. Rapid surface reactions enable a new technique of diffusion-limited patterning (DLP), which is useful for patterning of biomolecules and surface charge in nanochannels. These examples illustrate how electrostatic interactions, biomolecular size, and surface reactions can be used for controlling ionic and molecular transport through nanochannels. These phenomena may be useful for operations such as analyte focusing, pH and ionic concentration control, and biosensing in micro- and nanofluidic devices.© 2008 ASME