Kang Kug Lee

Surface modification of silicon and polydimethylsiloxane surfaces with vapor-phase-deposited ultrathin fluorosilane films for biomedical nanodevices

Ultrathin coatings of fluorosilane films for silicon and polydimethylsiloxane (PDMS) nanochannels are desirable to control the hydrophobicity of the surface and reduce or prevent undesired protein adsorption or cell interactions critical for the performance of most biomedical micro/nanodevices. Surface modifications using vapor-phase deposition become increasingly important for some biomedical nanodevices and have advantages over liquid-phase deposition since the vapor phase can permeate more efficiently into silicon nanochannels. In this study, vapor-phase deposition was used to deposit ultrathin films of four fluorosilanes on silicon and PDMS and identify deposition conditions for an optimal process. The films were characterized by means of a contact angle analyzer for hydrophobicity, an ellipsometer for film thickness, and an atomic force microscope for surface roughness of these films. Results of this study and relevant mechanisms are the subject of this article.

State-of-the-art lab chip sensors for environmental water monitoring

As a result of increased water demand and water pollution, both surface water and groundwater quantity and quality are of major concern worldwide. In particular, the presence of nutrients and heavy metals in water is a serious threat to human health. The initial step for the effective management of surface waters and groundwater requires regular, continuous monitoring of water quality in terms of contaminant distribution and source identification. Because of this, there is a need for screening and monitoring measurements of these compounds at contaminated areas. However, traditional monitoring techniques are typically still based on laboratory analyses of representative field-collected samples; this necessitates considerable effort and expense, and the sample may change before analysis. Furthermore, currently available equipment is so large that it cannot usually be made portable. Alternatively, lab chip and electrochemical sensing-based portable monitoring systems appear well suited to complement standard analytical methods for a number of environmental monitoring applications. In addition, this type of portable system could save tremendous amounts of time, reagent, and sample if it is installed at contaminated sites such as Superfund sites (the USAs worst toxic waste sites) and Resource Conservation and Recovery Act (RCRA) facilities or in rivers and lakes. Accordingly, state-of-the-art monitoring equipment is necessary for accurate assessments of water quality. This article reviews details on our development of these lab-on-a-chip (LOC) sensors.

Nanotribological characterization of fluoropolymer thin films for biomedical micro/nanoelectromechanical system applications

A vapor phase deposition system was designed to coat uniform, conformal and ultrathin coatings of fluoropolymer and fluorosilane thin films inside silicon nanochannels. Surface modifications using vapor phase deposition become increasingly important for biomedical micro/nanoelectromechanical system (BioMEMS/NEMS) applications and have advantages over liquid phase deposition since the vapor can permeate more efficiently into silicon nanochannels. In this article, we explore the use of vapor phase deposition to deposit ultrathin films of two fluoropolymers and a fluorosilane, identifying deposition parameters to optimize the process. The films are desirable to control the hydrophobicity of the surface and reduce or prevent undesired protein adsorption or cell interactions, which may cause detrimental effects to the performance of most BioMEMS/NEMS devices. The films were characterized by means of a contact angle analyzer for hydrophobicity and an ellipsometer for film thickness. Atomic force microscopy was ...

Potentiometric and voltammetric polymer lab chip sensors for determination of nitrate, pH and Cd(II) in water

Due to their toxicity to humans and animals, heavy metals and nitrate in groundwater are of particular concern. The combination of high toxicity and widespread occurrence has created a pressing need for effective monitoring and measurement of nitrate and heavy metals in soil pore water and groundwater at shallow depths. In this work, a new electrochemical sensing platform with the self-assembly nanobeads-packed (nBP) hetero columns has been developed for the pH and nitrate measurements. In addition, for on-site determination of cadmium (Cd(II)), a bismuth (Bi(III)) based polymer lab chip sensor using the square-wave anodic stripping voltammetry (SWASV) sensing principle has been designed, fabricated and successfully characterized. Factors affecting sensitivity and precision of the sensor, including deposition potential and deposition time, were studied. Miniaturized electrochemical lab chip sensors could be very valuable in environmental monitoring area due to their many benefits, such as greatly reduced sensing cost, sensing system portability, and ease of use.

Superhydrophilic multilayer silica nanoparticle networks on a polymer microchannel using a spray layer-by-layer nanoassembly method.

Nanoporous and superhydrophilic multilayer silica nanoparticle networks have been developed on a hydrophobic cyclic olefin copolymer (COC) microchannel using a spray layer-by-layer (LbL) electrostatic nanoassembly method. This powerful and promising LbL method provides a simple, cost-effective, and high-throughput nanoporous silica multilayer selectively onto the hydrophobic polymer surfaces. These newly developed multilayer networks have also been successfully characterized by contact angle measurement, environmental scanning electron microscopy (ESEM), energy-dispersive X-ray spectroscopy (EDS), and atomic force microscopy (AFM). The superhydrophilic effect, which was confirmed by the contact angle measurements, of the silica networks ensured the hydrophilic nature of the selectively constructed nanoporous silica nanoparticles onto the patterned hydrophobic COC microchannel. The capillary effect of the developed surface was characterized by measuring the length of a test liquid driven by the induced capillary forces in an on-chip capillary pumping platform with horizontal microchannels. The pumping capability achieved from the sprayed nanoporous surface for the on-chip micropump was mainly due to the strong capillary imbibition driven by the multicoated bilayers of hydrophilic silica nanoparticles. The developed networks with spray-assembled nanoparticles were also applied for an on-chip blood plasma separation platform with closed microchannels. The spray LbL method developed in this work can be a highly practical approach for the modification of various polymer microchannels because of several advantages such as an extremely simple process for the multilayer formation and flexibly controlled surface functionality at room temperature.

Spiral-based microfluidic device for long-term time course imaging of Neurospora crassa with single nucleus resolution

Real-time imaging of fluorescent reporters plays a critical role in elucidating fundamental molecular mechanisms including circadian rhythms in the model filamentous fungus, Neurospora crassa. However, monitoring N. crassa for an extended period of time with single nucleus resolution is a technically challenging task due to hyphal growth that rapidly moves beyond a region of interest during microscopy experiments. In this report, we have proposed a two-dimensional spiral-based microfluidic platform and applied for monitoring the single-nucleus dynamics in N. crassa for long-term time course experiments.

Circadian rhythms in Neurospora crassa on a polydimethylsiloxane microfluidic device for real-time gas perturbations

Racetubes, a conventional system employing hollow glass tubes, are typically used for monitoring circadian rhythms from the model filamentous fungus, Neurospora crassa. However, a major technical limitation in using a conventional system is that racetubes are not amenable for real-time gas perturbations. In this work, we demonstrate a simple microfluidic device combined with real-time gas perturbations for monitoring circadian rhythms in Neurospora crassa using bioluminescence assays. The developed platform is a useful toolbox for investigating molecular responses under various gas conditions for Neurospora and can also be applied to other microorganisms.