Jeong Bong Lee

Disposable smart lab on a chip for point-of-care clinical diagnostics

This paper presents the development of a disposable plastic biochip incorporating smart passive microfluidics with embedded on-chip power sources and integrated biosensor array for applications in clinical diagnostics and point-of-care testing. The fully integrated disposable biochip is capable of precise volume control with smart microfluidic manipulation without costly on-chip microfluidic components. The biochip has a unique power source using on-chip pressurized air reservoirs, for microfluidic manipulation, avoiding the need for complex microfluidic pumps. In addition, the disposable plastic biochip has successfully been tested for the measurements of partial oxygen concentration, glucose, and lactate level in human blood using an integrated biosensor array. This paper presents details of the smart passive microfluidic system, the on-chip power source, and the biosensor array together with a detailed discussion of the plastic micromachining techniques used for chip fabrication. A handheld analyzer capable of multiparameter detection of clinically relevant parameters has also been developed to detect the signals from the cartridge type disposable biochip. The handheld analyzer developed in this work is currently the smallest analyzer capable of multiparameter detection for point-of-care testing.

A tapered hollow metallic microneedle array using backside exposure of SU-8

This paper presents a novel fabrication process for a tapered hollow metallic microneedle array using backside exposure of SU-8, and analytic solutions of critical buckling of a tapered hollow microneedle. An SU-8 mesa was formed on a Pyrex glass substrate and another SU-8 layer, which was spun on top of the SU-8 mesa, was exposed through the backside of the glass substrate. An array of SU-8 tapered pillar structures, with angles in the range of 3.1 ◦ –5 ◦ , was formed on top of the SU-8 mesa. Conformal electrodeposition of metal was carried out followed by a mechanical polishing using a planarizing polymeric layer. All organic layers were then removed to create a metallic hollow microneedle array with a fluidic reservoir on the backside. Both 200 µm and 400 µm tall, 10 by 10 arrays of metallic microneedles with inner diameters of the tip in the range of 33.6–101 µm and wall thickness of 10–20 µm were fabricated. Analytic solutions of the critical buckling of arbitrary-angled truncated cone-shaped columns are also presented. It was found that a single 400 µm tall hollow cylindrical microneedle made of electroplated nickel with a wall thickness of 20 µm, a tapered angle of 3.08 ◦ and a tip inner diameter of 33.6 µ mh as a critical buckling force of 1.8 N. This analytic solution can be used for square or rectangular cross-sectioned column structures with proper modifications.

Microjet cooling devices for thermal management of electronics

This research is an effort to demonstrate the applicability of miniaturized synthetic jet (microjet) technology to the area of thermal management of microelectronic devices. Synthetic jets are jets which are formed from entrainment and expulsion of the fluid in which they are embedded. Design issues of microjet cooling devices are discussed along with characterization of excitation elements and the turbulent synthetic jets produced thereby. Geometrical parameters of the microjet cooling devices were empirically optimized with regards to cooling performance. The cooling performance of the optimized microjets was compared with previous theoretical and empirical studies of conventional jet impingement. The cooling performance of the microjet devices has been investigated in an open environment as well as in a vented and closed case environment. In such experiments, the synthetic jet impinges normal to the surface of a packaged thermal test die, comprising a heater and a diode-based temperature sensor. This test assembly allows simultaneous heat generation and temperature sensing of the package, thereby enabling assessment of the performance of the synthetic jet. Using microjet cooling devices, a thermal resistance of 30.1/spl deg/C/W has been achieved (when unforced cooling is used, thermal resistance is 59.6/spl deg/C/W) when the test chip is located at 15mm spacing from the jet exit plane. In order to more directly compare and scale the cooling results, a preliminary study on heat transfer correlations of the microjet cooling device has been performed. Finally, a comparison of the performance of the microjet cooler with standard cooling fans is given.

Mechanically tunable photonic crystal structure

We report a tunable nanophotonic device concept based on flexible photonic crystal, which is comprised of a periodic array of high-index dielectric material and a low-index flexible polymer. Tunability is achieved by applying mechanical force with nano-/microelectromechanical system actuators. The mechanical stress induces changes in the periodicity of the photonic crystal and consequently modifies the photonic band structure. To demonstrate the concept, we theoretically investigated the effect of mechanical stress on the anomalous refraction behavior and observed a very wide tunability in the beam propagation direction. This concept provides a means to achieve real-time, dynamic control of photonic band structure and will thus expand the utility of photonic crystal structures in advanced nanophotonic systems.

Recovery of nonwetting characteristics by surface modification of gallium-based liquid metal droplets using hydrochloric acid vapor

The applicability of gallium-based liquid metal alloy has been limited by the oxidation problem. In this paper, we report a simple method to remove the oxide layer on the surface of such alloy to recover its nonwetting characteristics, using hydrochloric acid (HCl) vapor. Through the HCl vapor treatment, we successfully restored the nonwetting characteristics of the alloy and suppressed its viscoelasticity. We analyzed the change of surface chemistry before and after the HCl vapor treatment using X-ray photoelectron spectroscopy (XPS) and low-energy ion-scattering spectroscopy (LEIS). Results showed that the oxidized surface of the commercial gallium-based alloy Galinstan (Ga(2)O(3) and Ga(2)O) was replaced with InCl(3) and GaCl(3) after the treatment. Surface tension and static contact angle on a Teflon-coated glass of the HCl-vapor-treated Galinstan were measured to be 523.8 mN/m and 152.5°. A droplet bouncing test was successfully carried out to demonstrate the nonwetting characteristics of the HCl-vapor-treated Galinstan. Finally, the stability of the transformed surface of the HCl-vapor-treated Galinstan was investigated by measuring the contact angle and LEIS spectra after reoxidation in an ambient environment.

Biocompatible SU-8-Based Microprobes for Recording Neural Spike Signals From Regenerated Peripheral Nerve Fibers

A biocompatible neural microprobe constructed using well-established SU-8 microfabrication techniques is described that was designed to record fiber spike signals from regenerated axons within peripheral nerves. These microprobes features bipolar longitudinal gold electrodes recessed below the surface within ldquogroovesrdquo designed to guide the growth of regenerating axons along the length of the grooves and limit the number of fibers that come in contact with the longitudinal electrodes. In addition, screening microprobe toxicity using cultures of human skin fibroblasts, the biocompatibility of these SU-8 microprobes for neural interface applications, in particular, was specifically verified using primary cultures of two sensitive cell types found in peripheral nerves: purified Schwann cells and explanted dorsal root ganglion (DRG) neurons and their fibers. The SU-8 microprobes were surgically implanted into transected rat Sciatic nerves within a unique peripheral nerve regeneration tube. Long-term fiber spike signals were recorded with these SU-8 microprobes in 13 chronically implanted rats for periods from 4 to 51 weeks without any signs of tissue damage or inflammatory reaction.

Negative refraction in a Si-polymer photonic Crystal membrane

We have observed negative refraction in a photonic crystal (PC) membrane structure at near-infrared wavelengths. The device is fabricated on a silicon-on-insulator substrate and consists of a silicon rod matrix suspended in a polymer where optical energy is delivered by ridge waveguides with various incident angles. The propagation direction inside the PC shows extraordinary refraction with an angle consistent with our two-dimensional numerical simulations. To our knowledge, this is the first experimental observation of isotropic negative refraction in a Si-based planar PC structure at optical frequencies. The realization of negative refraction in a planar Si-based system enables applications in negative index imaging to be integrated into compact optical circuits.

A SU-8-Based Microfabricated Implantable Inductively Coupled Passive RF Wireless Intraocular Pressure Sensor

With the growing demand in noncontact detection of human diseases, this paper presents an implantable passive wireless pressure sensor using an inductively coupled wireless sensing technique, particularly designed to monitor the intraocular pressure (IOP) of glaucoma patients. The microfabricated IOP sensor consists of a planar spiral gold coil inductor, a two-parallel-gold-plate (metal-insulator-metal) capacitor, and a SU-8 pressure-sensitive diaphragm. The IOP sensor is fully encapsulated inside biocompatible SU-8 stacking layers to isolate the IOP sensor from the biological tissue medium environment. By measuring the impedance phase dip frequency shift from the external coil, the IOP signal can be obtained through the implanted IOP sensor. The optimized size of the manually wound external coil was investigated. The readout distance is up to 6 mm from the implanted sensor. Characterization results show that the microfabricated IOP sensor has relatively high sensitivities-7035 ppm/mmHg in air and 3770 ppm/mmHg in saline medium-with pressure resolution lower than 1 mmHg, which is adequate for IOP monitoring application.

MEMS-Based Inductively Coupled RFID Transponder for Implantable Wireless Sensor Applications

In this paper, we present the development of an inductively coupled mini RFID transponder using MEMS technology for implantable wireless sensor applications. The transponder (approximately 25 mm3 in volume) consists of a small solenoid inductor with a high-permeability magnetic core (dia.=750 mum), a chip capacitor and a RFID chip. They are integrated onto a micromachined SU8 polymer substrate and it is operated in the frequency range of 13.56-27 MHz. Voltages up to 4 V were obtained at a small 0.5 muH transponder coil from a 2.2-muH reader coil at 5 mm distance based on a resonant magnetic coupling mechanism. The assembled transponder was tested using a commercial RFID reader at 13.56 MHz and successful communication was established at a distance of 10 mm.

Thermo-optic photonic crystal light modulator

A device concept is proposed for modulating light in silicon-based photonic crystal devices by using highly localized high-temperature modulation of a compact device to vary the position of the cutoff frequency in a photonic crystal waveguide and modulate light. The position of the cutoff frequency can be varied by up to 60nm at the telecommunication wavelength of 1550nm by locally increasing the temperature of the device. Modulators of a few to several micrometers in width can be designed that can modulate light with extinction ratios up to 50dB and low insertion loss.