Chee Chung Wong

EIS-based biosensor for ultra-sensitive detection of TNF-α from non-diluted human serum

Serum background is a critical issue for biosensor development as it interferes with the detection of target molecules and may give rise to false positive signal. We present here highly sensitive and selective TNF-α biosensor which is able to detect TNF-α from non-diluted human serum using magnetic bead coupled antibody and electrochemical impedance spectroscopy (EIS) techniques. The process is designed to detect TNF-α from human serum in three stages; (1) abundant protein backgrounds are depleted from the serum using magnetic bead coupled albumin and IgG antibodies, (2) after background depletion TNF-α is captured using magnetic bead coupled TNF-α antibody, and (3) the captured TNF-α is eluted from the magnetic beads and measured using EIS technique in which comb structured gold microelectrodes array (CSGM) is utilized to enhance the detection sensitivity. The system is able to achieve the limit of detection (LOD) at 1 pg/ml (57 fM) and a linear relationship between increasing TNF-α concentrations and charge-transfer resistance in a dynamic range of 1-1000 pg/ml.

Anti-EpCAM modified LC-SPDP monolayer on gold microelectrode based electrochemical biosensor for MCF-7 cells detection

A succinimidyl 6-(3-[2-pyridyldithio]-propionamido) hexanoate (LC-SPDP) self-assembled monolayer (SAM) prepared onto a 500 μm (diameter) gold microelectrode (Au) surface has been utilized for covalent immobilization of anti-EpCAM antibody. Amino group on anti-EpCAM antibody was covalently bound with succinimidyl group on SAM via amide bond and unreacted active groups of LC-SPDP were blocked using 1% ethanol amine (EA). These anti-EpCAM/LC-SPDP/Au electrodes were characterized using cyclic voltammetric (CV) and fluorescence techniques, respectively. The anti-EpCAM/LC-SPDP/Au electrodes were exposed to solutions with different MCF-7 cell concentrations and CV technique was used to determine the cell concentration. Further, CV studies on blank 500 and 50 μm (diameter) gold microelectrodes were used to identify cell via molecular profiling using ferrocene amidopentyl carboxylic acid based redox tagging and magnetic beads based enhancement. CV results confirm that the anti-EpCAM/LC-SPDP/Au based biosensor could detect MCF-7 cells in the range of 1×10(5)-1×10(8) with correlation coefficient of 0.999 and detection limit of 1×10(5) cells ml(-1) i.e. 100 cells in solution used for incubation (1 μl). Molecular profiling studies suggest that smaller size microelectrode (50 μm; diameter) with magnetic beads based enhancement can be employed to identify cell type. This work establishes the feasibility of using microelectrode based platform for breast cancer specific MCF-7 cell concentration estimation and their molecular profiling.

Effects of the Electrode Size and Modification Protocol on a Label-Free Electrochemical Biosensor

In the present work, the effect of a surface modification protocol along with the electrode size has been investigated for developing an efficient, label-free electrochemical biosensing method for diagnosis of traumatic brain injury (TBI) biomarkers. A microdisk electrode array (MDEA) and a macroelectrode with a comb structure (MECS) were modified with an anti-GFAP (GFAP = glial fibrillary acidic protein) antibody using two protocols for optimum and label-free detection of GFAP, a promising acute-phase TBI biomarker. For the MDEA, an array of six microdisks with a 100 μm diameter and, for the MECS, a 3.2 mm × 5.5 mm electrode 5 μm wide with 10 μm spaced comb fingers were modified using an optimized protocol for dithiobis(succinimidyl propionate) (DSP) self-assembled monolayer formation. Anti-GFAP was covalently bound, and the remaining free DSP groups were blocked using ethanolamine (Ea). Sensors were exposed to solutions with different GFAP concentrations, and a label-free electrochemical impedance spectroscopy (EIS) technique was used to determine the concentration. EIS results confirmed that both types of Ea/anti-GFAP/DSP/Au electrodes modified with an optimized DSP-based protocol can accurately detect GFAP in the range of 1 pg mL(-1) to 100 ng mL(-1) with a detection limit of 1 pg mL(-1). However, the cross-use of the MDEA protocol on the MECS and vice versa resulted in very low sensitivity or poor signal resolution, underscoring the importance of proper matching of the electrode size and type and the surface modification protocol.

Size based sorting and patterning of microbeads by evaporation driven flow in a 3D micro-traps array

We present a three-dimensional (3D) micro-traps array for size selective sorting and patterning of microbeads via evaporation-driven capillary flow. The interconnected micro-traps array was manufactured by silicon micromachining. Microliters of aqueous solution containing particle mixtures of different sized (0.2 to 20 μm diameter) beads were dispensed onto the micro-traps substrate. The smaller particles spontaneously wicked towards the periphery of the chip, while the larger beads were orderly docked within the micro-traps array.

CMOS based high density micro array platform for electrochemical detection and enumeration of cells

A highly sensitive label-free complementary-metal-oxide-semiconductor (CMOS) based high density micro-array for electrochemical detection and enumeration of breast tumor cell (MCF-7) is presented. The electrochemical impedance spectroscopy (EIS) based detection platform exhibited detection at single cell resolution (22 μm) and enumeration with mapping accuracy of ~80%. Maximum tumor-cell impedance increase of 28% was recorded.

Integrated electronic and microfluidic packaging for CMOS biosensor chip

In recent years, advanced incorporation of complementary metal oxide semiconductor (CMOS) biosensor chips with sensory microarrays has gained tremendous attention. In this paper, we investigated a maskless approach to microfluidic channel fabrication that integrates seamlessly with CMOS biosensor chip packaging. The microfluidic channels were formed via precisely controlled dispensing of adhesive to define microfluidic dam structures. This was followed by encapsulation of the microfluidic dam with a lid, thereby producing an impervious seal. Four types of commercial adhesives used in medical/implantable devices were evaluated in this study; a silicone-based adhesive, an ultraviolet curable epoxy, an ultraviolet curing acrylate adhesive, and a thermal curing epoxy. The adhesives were evaluated based on the performance criteria such as: (i) critical dimension (CD) of microfluidic channels, (ii) minimum microfluidic dam height, (iii) biocompatibility, and (iv) bond strength of the adhesive between CMOS substrate film to the lid material. The test vehicles comprising of ITO glass lid material, SiN substrate material and various evaluated adhesives, were subjected to burst pressure leak test. From the results obtained, Dow Corning® 3140 silicone-based adhesive has the best performance as a suitable adhesive for microfluidic dam structure formation. Lastly, a seamless approach to integrating electronic and microfluidic packaging through the use of controlled adhesive dispensing and a pick and place assembly tool was demonstrated with the use of Dow Corning® 3140 adhesive for microfluidic biological applications.