Ren-Guei Wu

Microfluidic Systems for Biosensing

In the past two decades, Micro Fluidic Systems (MFS) have emerged as a powerful tool for biosensing, particularly in enriching and purifying molecules and cells in biological samples. Compared with conventional sensing techniques, distinctive advantages of using MFS for biomedicine include ultra-high sensitivity, higher throughput, in-situ monitoring and lower cost. This review aims to summarize the recent advancements in two major types of micro fluidic systems, continuous and discrete MFS, as well as their biomedical applications. The state-of-the-art of active and passive mechanisms of fluid manipulation for mixing, separation, purification and concentration will also be elaborated. Future trends of using MFS in detection at molecular or cellular level, especially in stem cell therapy, tissue engineering and regenerative medicine, are also prospected.

Nanocapillary electrophoretic electrochemical chip: towards analysis of biochemicals released by single cells

A novel nanocapillary electrophoretic electrochemical (Nano-CEEC) chip has been developed to demonstrate the possibility of zeptomole-level detection of neurotransmitters released from single living cells. The chip integrates three subunits to collect and concentrate scarce neurotransmitters released from single PC-12 cells, including a pair of targeting electrodes for single cells captured by controlling the surface charge density; a dual-asymmetry electrokinetic flow device for sample collection, pre-concentration and separation in a nanochannel; and an online electrochemical detector for zeptomole-level sample detection. This Nano-CEEC chip integrates a polydimethylsiloxane microchannel for cell sampling and biomolecule separation and a silicon dioxide nanochannel for sample pre-concentration and amperometric detection. The cell-capture voltage ranges from 0.1 to 1.5 V with a frequency of 1–10 kHz for PC-12 cells, and the single cell-capture efficiency is optimized by varying the duration of the applied field. All of the processes, from cell sampling to neurotransmitter detection, can be completed within 15 min. Catecholamines, including dopamine and norepinephrine (noradrenaline) released from coupled single cells, have been successfully detected using the Nano-CEEC chip. A detection limit of 30–75 zeptomoles was achieved, which is close to the levels released by a single neuron in vitro.

Dual-asymmetry electrokinetic flow focusing for pre-concentration and analysis of catecholamines in CE electrochemical nanochannels.

In this research, a technique incorporating dual‐asymmetry electrokinetic flow (DAEKF) was applied to a nanoCE electrochemical device for the pre‐concentration and detection of catecholamines. The DAEKF was constructed by first generating a ζ‐potential difference between the top and bottom walls, which had been pre‐treated with O2 and H2O surface plasma, respectively, yielding a 2‐D gradient shear flow across the channel depth. The shear flow was then exposed to a varying ζ‐potential along the downstream direction by control of the field‐effect in order to cause downward rotational flow in the channel. By this mechanism, almost all of the samples were effectively brought down to the electrode surface for analysis. Simulations were carried out to reveal the mechanism of concentration caused by the DAEKF, and the results reasonably describe our experiment findings. This DAEKF technique was applied to a glass/glass CE electrochemical nanochip for the analysis of catecholamines. The optimum detection limit was determined to be 1.25 and 3.3 nM of dopamine and catechol, respectively. A detection limit at the zeptomole level for dopamine can be obtained in this device, which is close to the level released by a single neuron cell in vitro.

A UV-sensitive hydrogel based combinatory drug delivery chip (UV gel-Drug Chip) for cancer cocktail drug screening

The effective and efficient treatment of diseases, such as HIV, cancer or hereditary diseases, requires accurate and precise control of the combinatorial drug-dosage and their release. Herein, we introduce a simple photosensitive poly(ethylene glycol) diacrylate (PEGDA) hydrogel based platform for high dynamic range testing of combinatorial cocktail drug screening using three chemical and two protein drug treatments for colon cancer. UV cross linked PEGDA hydrogel droplet arrays on a Teflon patterned glass substrate enable a rapid yet accurate selection and dosage assignment of the drugs. Precisely loaded cocktails of the anticancer drugs were simultaneously released in-parallel with the PEGDA hydrogel chips into 2D or 3D cultured HCT-8 colon cancer cells for combinatorial drug screening. We demonstrate the functionality of our UV gel-Drug Chips 1000 fold range of concentrations for each of the five drugs in 30 seconds to find the optimized drug cocktail using a fractional factorial control system. Our device has low drug consumption, requiring only 12 nL per screening run per droplet. In addition, our UV gel-Drug Chips were employed for find the optimized drug cocktail using a fractional search algorithm. Our cocktail drug response results for both 2D (cell viability is 7.3%) and 3D (cell viability is 10.8%) colon cancer cells were analogous to those found by conventional method (6.8 and 9.3 respectively). In contrast to conventional method, our approach is faster, more effective, less time consuming and requires a lower amounts of drug volume.

High-throughput white blood cells (leukocytes) separation and enrichment from whole blood by hydrodynamic and inertial force

To solve clogging in microchannel and low separation rate in microfluidic devices that containing high concentration whole blood cells (4.3×106 cells/μl) with the remaining <;1% consisting peripheral blood leukocytes and platelets [1-2]. In this work we introduce a like-biomimetic structure to separate red blood cells from whole blood and to enrich leukocytes (white blood cells) through the elastic properties of blood cell by the interaction of inertial force, shear lift, and wall crowding effect in a continuous flow system. A high separation efficiency (~84%) and high throughput flow rate (200μl/s or 10ml/min) was obtained in this microfluidic chip.

Cocktail drug delivery chip for cancer drug screening

This study introduces a combinatory assay platform that allows high-throughput but low-drug-dosage screening of five anti-cancer drugs as a cocktail for personalized cancer treatment. Photosensitive PEGDA hydrogel was employed for drug dosage definition through drop array formation and selective UV crosslinking process. The finally defined cocktail drugs in hydrogel will be directly released in parallel when combined with cell chips. This device is capable to combine 5 drugs with 1000 folds dynamic range in 30 second with low drug consumption for in-parallel cocktail screening process.

Uniform Nafion ® coated HRA anode for high performance micro DMFC

This paper proposes a high reaction area (HRA) electrode with finely dispersed electrocatalysts supported on carbon nanotubes (CNTs) for high performance micro direct methanol fuel cell (μDMFC). Ionomer Nafion^® loading by spin-coating on the catalysts was in-detail investigated for performance enhancement in anodic half-cell. In terms of electrochemical surface area (ESA) and charge transfer resistance (R<inf>CT</inf>), the ionomer-coated Pt/CNTs/Si-based plate electrode at 4000rpm (ESA: 32.37m²/g<inf>Pt</inf>, R<inf>CT</inf>: 19Ωcm²) is demonstrated superior than the best performed electrocatalysts in previous studies (ESA: 25∼35m²/g<inf>Pt</inf>, R<inf>CT</inf>: 35∼60Ωcm²), providing enhanced catalytic activity and much faster charge transfer rate during the methanol electro-oxidation.

Toward the detection of single cell releasing through high efficient chip-based nano fluidic systems

By enhancing the speed, accuracy, and sensitivity, it opens up a new possibility for direct analysis of biologically relevant entities such as nucleic acids and proteins in single cell level. Nanofluidic systems with critical dimensions which were comparable to the molecular scales can provide the aforementioned performance, offering a novel basis for ultrasensitive and high-resolution bio-detections and medical diagnostics. Inspired by this concept, a nanofluidic system, integrated with a novel multi-nanocahnnel filter, an electrokinetic nano-preconcentrator, and a nanofluidic DAEKF detector for the detection of single cell releasing, is developed. A diluted solution of culture medium from PC-12 cells excited with excess nicotine concentration was detected with near single cell level amounts (c.a. 3000–10000 molecules) in this system after all processing in 20 min. Results showed that this multi-depth micro/nanofluidic chip exhibits superior sensitivity, efficiency, reliability, and reproducibility than those of conventional microchip electrophoresis /electrochromatography systems.

Micro-CEC chip with gradient hydrophobic stationary phase (GHSP) provided by mwcnts nanocolumns-applied to protein analysis in MALDI-TOF-MS

In this research, we present a chip based capillary electrochromatography (CEC) carrying out a highly efficient separation of biomolecules through gradient hydrophobic stationary phase (GHSP) provided by multiwalled carbon nanotubes (MWCNTs) nanocolumns. 4-azidoaniline was employed for the surface modification of the MWCNTs to form a gradient stationary phase by a photochemical reaction through a gradient light filter. This device was used for separating proteins (20 µM FITC-BSA and FITC-Cytochrome C) with different hydrophobic characteristics, and MALDI-TOF-MS detection was employed to verify the separation efficiency in this MWCNTs nanocolumn. The best separation resolution of the FITC-BSA column efficiency was 2.5 × 104 (plats/m).

MWCNTS array incorporated nanochannel with charge-selectivity for high efficient biomolecule preconcentration

This paper presents a study of electrokinetic transport in a nano-fluidic chip that allows for the selection and pre-concentration of molecular mixtures by a high density multi-wall carbon nanotubes array (MCNTs) in nano-channels. Parylene (poly(p-xylylene) was deposited on MWCNTs walls as a dielectric material, the surface charge characters and density could adjusted when an induced polarizes filed was applied. The MCNTs array was used as an induced-surface charge filter to attract the charged molecules on the wall surface by van der Waals and electrostatic force. The surface charge of MCNTs is inversely proportional to the channel wall thickness and proportional to the dielectric constant of Parylene thin layer as well as the applied external electric-field. The competition between electroosmotic dragging force and nonlinear electrophoretic forces induced by polarization effect is suggested responsible for the setup of two preconcentration regimes at both cathodic and anodic sides of the nanochannel. A 105–6 folds high concentration capability of FITC-labelied IgG has been achieved in 15 min in this device which is not easily carried out by standard MEMS process. The fabrication of this device with direct growth of MWCNTs inside nanochannel is first reported to apply to electro-preconcentration.