Joon S. Shim

An on-chip whole blood/plasma separator with bead-packed microchannel on COC polymer

A disposable on-chip whole blood/plasma separator, which is able to separate plasma from whole human blood by capillary force through a bead-packed microchannel, has been designed, fabricated and characterized in this work. Various sizes of silica beads were slurry-packed through a microchannel using a bump structure which held beads in a defined region. The bead-packed microchannel induces a capillary force which allows plasma to move forward through the bead-packed column more rapidly than red blood cells (RBCs). The blood/plasma separator with bead-packed microchannel has successfully separated plasma from the whole blood without haemolysis of RBCs. The separation method developed in this work can be applied to various on-chip stationary filtrations of RBC for point-of-care clinical diagnostics.

An On-Site Heavy Metal Analyzer With Polymer Lab-on-a-Chips for Continuous Sampling and Monitoring

An on-site analyzer system for monitoring of heavy metals has been presented. This analyzer can automatically perform long-term continuous water sampling and on-site heavy metals measurement using an array of disposable polymer lab-on-a-chips (lab chip) and a continuous flow sensing method. The system consists of a plastic fluidic motherboard with a microchannels network, microvalves and pump, control circuits, a wireless communication module, a potentiostat, LabVIEW control, and seven disposable heavy metal lab chips. Square wave anodic stripping voltammetry was performed using a microfabricated planar bismuth electrode on the chip for detecting heavy metal (e.g., cadmium, Cd) concentrations. Sensing performance sensitivity was improved with by the continuous flow sensing method propelled by the analyzer. On-site measurement of the Cd concentration change of the soil pore and ground water samples from a lab-scale reactor was automatically performed to evaluate the performance of the analyzer with lab chips.

The precise self-assembly of individual carbon nanotubes using magnetic capturing and fluidic alignment

A new method for the self-assembly of a carbon nanotube (CNT) using magnetic capturing and fluidic alignment has been developed and characterized in this work. In this new method, the residual iron (Fe) catalyst positioned at one end of the CNT was utilized as a self-assembly driver to attract and position the CNT, while the assembled CNT was aligned by the shear force induced from the fluid flow through the assembly channel. The self-assembly procedures were successfully developed and the electrical properties of the assembled multi-walled carbon nanotube (MWNT) and single-walled carbon nanotube (SWNT) were fully characterized. The new assembly method developed in this work shows its feasibility for the precise self-assembly of parallel CNTs for electronic devices and nanobiosensors.

Optical immunosensor using carbon nanotubes coated with a photovoltaic polymer

In this work, an on-chip optical immunosensor using an individually assembled carbon nanotube (CNT) coated with a photovoltaic polymer has been proposed, developed, characterized, and applied for the detection of cardiac biomarkers. An individual CNT was self-assembled on a nickel (Ni)-patterned electrode by magnetically attracting the residual iron catalyst at one end of the CNT. After the CNT self-assembled electrode was prepared, it was coated with a photovoltaic polymer to implement a CNT photodetector. Under an incident light, the photovoltaic polymer generated electrons that changed the conductivity of the CNT. The CNT photodetector was finally insulated with parylene to prevent interruptions of charged molecules in a sample solution, such as non-specifically bound proteins and various ions. Chemiluminescent immunoassay was directly performed on the CNT photodetector for an on-chip detection of cardiac troponin T (cTnT) with a detection limit of 12 pg/mL. High sensitivity and reliable selectivity have been achieved through the use of on-chip measurement of chemiluminescent light by the CNT photodetector. As a result, the developed device is envisaged as a new platform for optical immunosensing using the individually self-assembled CNT for point-of-care (POC) clinical diagnostics.

Self-aligned nanogaps on multilayer electrodes for fluidic and magnetic assembly of carbon nanotubes.

A self-aligned nanogap between multiple metal layers has been developed using a new controlled undercut and metallization technique (CUMT), and practically applied for self-assembly of individual carbon nanotubes (CNTs) over the developed nanogap. This new method allows conventional optical lithography to fabricate nanogap electrodes and self-aligned patterns with nanoscale precision. The self-aligned nickel (Ni) pattern on the nanogap electrode works as an assembly spot where the residual iron (Fe) catalyst at the end of the CNT is magnetically captured. The captured CNT is forced to be aligned parallel to the flow direction by fluidic shear force. The combined forces of magnetic attraction and fluidic alignment provide massive self-assembly of CNTs at target positions. Both multiwalled nanotubes (MWNTs) and single walled nanotubes (SWNTs) were successfully assembled over the nanogap electrodes, and their electrical characteristics were fully characterized. The CNTs self-assembled on the developed electrodes with a nanogap and showed a very reliable and reproducible current-voltage (I-V) characteristic. The method developed in this work can envisage the mass fabrication of individual CNT-assembled devices which can be applied to nanoelectronic devices or nanobiosensors.

Comparing polyelectrolyte multilayer-coated PMMA microfluidic devices and glass microchips for electrophoretic separations.

There is a continuing drive in microfluidics to transfer microchip systems from the more expensive glass microchips to cheaper polymer microchips. Here, we investigate using polyelectrolyte multilayers (PEM) as a coating system for PMMA microchips to improve their functionality. The multilayer system was prepared by layer‐to‐layer deposition of poly(diallyldimethylammonium) chloride and polystyrene sulfonate. Practical aspects of coating PMMA microchips were explored. The multilayer buildup process was monitored using EOF measurements, and the stability of the PEM was investigated. The performance of the PEM‐PMMA microchip was compared with those of a standard glass microchip and a PEM‐glass microchip in terms of EOF and separating two fluorescent dyes. Several key findings in the development of the multilayer coating procedure for PMMA chips are also presented. It was found that, with careful preparation, a PEM‐PMMA microchip can be prepared that has properties comparable – and in some cases superior – to those of a standard glass microchip.

Formation of lipid bilayers inside microfluidic channel array for monitoring membrane-embedded nanopores of phi29 DNA packaging nanomotor

An efficient method to form lipid bilayers inside an array of microfluidic channels has been developed and applied to monitor the membrane-embedded phi29 DNA packaging motor with an electrochemical characterization on a lab-on-a-chip (LOC) platform. A push-pull junction capturing approach was applied to confine a small amount of the lipid solution inside a microchannel. The selective permeability between solvents and water in PDMS was utilized to extract the solvent from the lipid solution, resulting in a self-formation of the lipid bilayer in the microchannel array. Each microchannel was independently connected to a silver/silver chloride (Ag/AgCl) electrode array, leading to a high-throughput monitoring of the nanopore insertion in the formed lipid bilayers. The formation of multiple lipid bilayers inside an array of microchannels and the simultaneous electrical and optical monitoring of multiple bilayer provides an efficient LOC platform for the further development of single phi29 motor pore sensing and high throughput single pore dsDNA sequencing.

Simple passive micromixer using recombinant multiple flow streams

A passive microfluidic mixer with high performance is designed and fabricated in this work. Diamond-shaped obstacles were chosen to split the flow into several streams, which are then guided back together after the obstacle. To keep pressure drop low, the channel cross-sectional area was maintained equal to the input cross-sectional area, and this was held constant throughout the device. The proposed design was modeled using computational fluid dynamics (CFD) software. The effects of channel width, channel length, location of obstructions, and Reynolds Number (Re) were investigated. The simulated results were verified experimentally. Simulation data showed that the designed micromixer achieved 90% mixing at a channel length of 4.35 mm with pressure drop of 584 Pa at Re = 1, while experimental data for Re = 0.1 showed 90% mixing at 7 mm. The mixer functions well especially at the low Re (Re = 0.1).

High precision fluidic alignment of carbon nanotubes using magnetic attraction on a metal catalyst

Precise self-assembly of carbon nanotubes (CNTs) by magnetic attraction on a catalyst and alignment by fluidic shear forces is reported in this work. The solution containing dispersed nanotubes was flowed in a microchannel and external magnetic field was applied by a permanent magnet for attracting a metal catalyst located at the end of the CNT. The assembly procedure and electrical characterization of the assembled nanotubes are presented and results are discussed. This work can provide a potential breakthrough for creating massively parallel CNT circuits for high performance nano electronic devices or nano biosensors.

Interdigitated Array Electrodes with Nano Gaps Using Optical Lithography and Controlled Undercut Method

Interdigitated array (IDA) electrodes with nano-gaps were fabricated using a newly developed optical lithography and controlled undercut method. Nano gaps of 250 nm between electrodes were developed while maintaining a large electrode area. The developed electrodes with nano gaps were applied as an electrochemical biosensor for the detection of poly-aminophenol (PAP) with 10-7 M detection limit. This method may enable the mass-production of disposable biosensors based on the nano-gap IDA electrodes.