Patthara Kongsuphol

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.

Aptamer-based array electrodes for quantitative interferon-γ detection

Present work describes the methylene blue tagged thiolated aptamer-modified gold micro-array based biosensor for specific detection of IFN-γ. The microchips with the microelectrode array were fabricated using standard silicon microfabrication technologies, and modified with methylene blue tagged aptamer using standard gold thiol chemistry. Electrodes were characterized and tested using Cyclic Voltammetric (CV) and Square Wave Voltammetry (SQW) measurements in a standard three-electrode format at room temperature. On an aptamer modified electrode, aptamer density was estimated to be about 4.4 × 10(12)molecules/cm(2). In IFN-γ studies, oxidation peak currents were found to decrease and more than 50% signal suppression was achieved at 500 ng/ml. Further, the magnitude of signal suppression was found to be logarithmically proportional to the IFN-γ in the concentration range of 1-500 ng/ml, with a detection limit of 1.3 ng/ml (i.e. 0.8 fmol in used sample volume of 10 µl). Biosensor showed negligible signal changes (5%) in a very high non-specific protein background, while still able to differentiate target protein IFN-γ at 5 ng/ml. The results indicated that our sensor binds selectively to target molecules, and the non-specific binding where adsorption of BSA protein molecules may be effectively omitted from consideration.

On-chip electrochemical immunoassay platform for specific protein biomarker estimation in undiluted serum using off-surface membrane matrix

The manuscript presents a new biosensor platform using bioreceptors modified porous 2-dimensional (2D) membrane based off-surface matrix for on-chip electrochemical immunoassay. Antibody based bioreceptors modified 2D matrix of porous polycarbonate (PC) membrane with densely packed 20µm holes as off-surface matrix was incorporated in very close proximity of the sensor surface and integrated with fluidic system for reagent flow and incubation chamber. Covalent attachment of antibodies on 2D PC membrane based off-matrix was achieved using 4-fluoro-3-nitro-azidobenzene (FNAB) cross-linker. Anti-TNF-α/FNAB/PC membrane was integrated over array of micro fingers of gold based sensor chip using double side tape spacer and StartingBlock phosphate buffer saline- Tween-20; (PBS-T20) blocking buffer was utilized to minimize nonspecific binding. Differential pulse voltammetric studies of Anti-Tnf-α/FNAB/PC-Au for protein biomarker (TNF-α) detection and estimation in undiluted serum indicated that the immunosensor system can detect TNF-α linearly in 100pg/ml to 100ng/ml range with insignificant interference from other cytokines and serum proteins. Further, immunosensor exhibited high sensitivity of 194nA/(ng/ml) and 240nA/(ng/ml), respectively for single and double membrane based system. Thus, use of 2D membrane based off surface matrix may present the new platform to sensitively measure biomarkers electrochemically to pg/ml range with insignificant nonspecific binding and false signal in undiluted serum.

Off surface matrix based on-chip electrochemical biosensor platform for protein biomarker detection in undiluted serum

The manuscript describes a concept of using off surface matrix modified with capturing biomolecule for on-chip electrochemical biosensing. 3D matrix made by laser engraving of polymethyl methacrylate (PMMA) sheet as off surface matrix was integrated in very close vicinity of the electrode surface. Laser engraving and holes in PMMA along with spacing from surface provide fluidic channel and incubation chamber. Covalent binding of capturing biomolecule (anti-TNF-α antibody) on off-surface matrix was achieved via azide group activity of 4-fluoro-3-nitro-azidobenzene (FNAB), which act as cross-linker and further covalently binds to anti-TNF-α antibody via thermal reaction. Anti-TNF-α/FNAB/PMMA matrix was then integrated over comb structured gold electrode array based sensor chip. Separate surface modification followed by integration of sensor helped to prevent the sensor chip surface from fouling during functionalization. Nonspecific binding was prevented using starting block T20 (PBS). Results for estimating protein biomarker (TNF-α) in undiluted serum using Anti-TNF-α/FNAB/PMMA/Au reveal that system can detect TNF-α in 100pg/ml to 100ng/ml range with high sensitivity of 119nA/(ng/ml), with negligible interference from serum proteins and other cytokines. Thus, use of off surface matrix may provide the opportunity to electrochemically sense biomarkers sensitively to ng/ml range with negligible nonspecific binding and false signal in undiluted serum.

Human adipocyte differentiation and characterization in a perfusion-based cell culture device

Adipocytes have gained significant attention recently, because they are not only functioning as energy storage but also as endocrine cells. Adipocytes secret various signaling molecules, including adiponectin, MCP-1, and IL-6, termed collectively as “adipokines”. Adipokines regulate glucose metabolism, thereby play an important role in obesity, diabetes type 2, and other metabolic disorders. Conventionally, to study the secretory function, adipocytes are cultured in vitro in static conditions. However, static culturing condition falls short of mimicking the interstitial fluid flows in living systems. Here, we developed a perfusion device which allows dynamic culture of adipocytes under constant and mild flow using a double-layered fluidic structure. Adipocytes were cultured in the bottom layer while the culture media were constantly flown in the upper layer and perfused through a porous membrane that separate the two chambers. The porous membrane between the two chambers physically separates the cells from the flow stream while maintain a fluidic connection by diffusion. This setting not only provides continuous nutrient supply to adipocytes but also maintains a steady and mild shear stress on the cell membrane. It was found the perfusion-based culture conditions promoted faster growth of primary preadipocytes and stimulated greater adipogenesis compared to static culture condition. Adipocytes cultured under perfusion systems produced more MCP-1 and IL-6, but less adiponectin. When stimulated with TNF-α, adipocytes expressed higher level of MCP-1 and IL-6, but lower level of adiponectin. No significant glucose uptake regulation was observed after treating the adipocytes with insulin in both static and perfusion-based culture. Our results demonstrate that perfusion-base culture has played a role in the adipocyte function particularly the secretion of adipokines. More future studies are required to unveil the mechanisms behind perfusion’s impact on adipocytes.

On-chip immune cell activation and subsequent time-resolved magnetic bead-based cytokine detection

Cytokine profiling and immunophenotyping offer great potential for understanding many disease mechanisms, personalized diagnosis, and immunotherapy. Here, we demonstrate a time-resolved detection of cytokine from a single cell cluster using an in situ magnetic immune assay. An array of triple-layered microfluidic chambers was fabricated to enable simultaneous cell culture under perfusion flow and detection of the induced cytokines at multiple time-points. Each culture chamber comprises three fluidic compartments which are dedicated to, cell culture, perfusion and immunoassay. The three compartments are separated by porous membranes, which allow the diffusion of fresh nutrient from the perfusion compartment into the cell culture compartment and cytokines secretion from the cell culture compartment into the immune assay compartment. This structure hence enables capturing the released cytokines without disturbing the cell culture and without minimizing benefit gain from perfusion. Functionalized magnetic beads were used as a solid phase carrier for cytokine capturing and quantification. The cytokines released from differential stimuli were quantified in situ in non-differentiated U937 monocytes and differentiated macrophages.

Lateral micro fluidic channels array chip fabrication for automated patch clamp application

Traditionally, patch-clamp recording is accomplished with a micromanipulator-positioned glass pipette under a microscope. A cell membrane patch is sucked into the glass pipette and forms a high electrical resistance seal. The high cost and labor-intensive methods of conventional patch clamp have prevented the full potential of ion channels as a drug target class being fully realized. Automated patch clamp systems have recently been developed, in order to inexpensively collect large amounts of data in a shorter period of time. More common automation patch-clamp systems use microchips with tiny (1-2μm) holes in a plate instead of pipettes to create the gigaseals and record from single cells. In our previously reported works, a lateral aperture of a buried micro channel was demonstrated, which differs from the common planar patch aperture and is easier fluidic integration and packaging, higher-density array comparing with planar patch aperture. In this paper, we present the optimized fabrication process and integrated the optimized fabrication process to a new designed lateral patch-clamp array chip with 12 independent lateral patch-clamping sites for patch clamp application. At last, the new designed lateral patch clamp devices are utilized to conduct whole cell patch clamp measurements in rat insulinoma (INS-1) cells. High gigaseals (>1 GΩ) were formed between the glass capillary apertures and INS-1 cells. Steady state I-V plots elicited characteristic ion channel properties and longevity of the whole cell mode could be maintained for 1 h without any breakage of the gigaseals, which long enough to apply various compounds and ion channel drugs.

Recording I–V signals from INS-1 Cells using silicon based patch clamp device

Here we utilize a silicon based lateral patch clamp chip to study insulin secreting rat insulinoma (INS-1) cells. Electrical properties of various potassium and calcium ion channels were characterized. High gigaohm (GO) seals were achieved between the microfabricated glass capillary apertures and INS-1 cells. Longevity of the whole cell mode could be maintained for 1 hr. Steady state I-V plots elicited characteristic ion channel properties, and pave the way for future drug discovery experiments and developing a cheap platform using the silicon based approach.