Nanoelectronic biosensing of dynamic cellular activities

Detecting dynamic cellular activities such as exocytosis and bioelectricity is important in the field of molecular biology and medicine. Comparing to conventional biochemical assay, biophysical measurements, and optical methods, electronic biosensing based on nanomaterials have shown promising platform in resolving rapid biological events with ultra sensitivity, high spatial and temporal resolution. Here, we use silicon nanowire (SiNW) and single walled carbon nanotube (SWNT) configured as field effect transistor to detect dynamic cellular activities, in particular the time course of cytokines secreted from immune cells or adipose cells and bioelectrical activities of ion channels from electrogenic cells. In this thesis, perfectly aligned arrays of long SiNWs were fabricated using top-down CMOS (complementary metal oxide semiconductor) compatible fabrication techniques and standardized in large-scale production of microelectronics. We demonstrate that these nanowire devices are able to detect cytokines secreted from cells with femtomolar sensitivity, high specificity, wide detection range, and ability for parallel multiplexed monitoring. The detection platform provide a novel tool to reveal the poorly understood signaling mechanisms of the molecules as well as their relevance in secretion related disease.DOCTOR OF PHILOSOPHY (SCBE

Cytokine and Cancer Biomarkers Detection: The Dawn of Electrochemical Paper-Based Biosensor

Although the established ELISA-based sensing platforms have many benefits, the importance of cytokine and cancer biomarkers detection for point-of-care diagnostics has propelled the search for more specific, sensitive, simple, accessible, yet economical sensor. Paper-based biosensor holds promise for future in-situ applications and can provide rapid analysis and data without the need to conduct in a laboratory. Electrochemical detection plays a vital role in interpreting results obtained from qualitative assessment to quantitative determination. In this review, various factors affecting the design of an electrochemical paper-based biosensor are highlighted and discussed in depth. Different detection methods, along with the latest development in utilizing them in cytokine and cancer biomarkers detection, are reviewed. Lastly, the fabrication of portable electrochemical paper-based biosensor is ideal in deliberating positive societal implications in developing countries with limited resources and accessibility to healthcare services

Cytokine and cancer biomarkers detection : the dawn of electrochemical paper-based biosensor

Although the established ELISA-based sensing platforms have many benefits, the importance of cytokine and cancer biomarkers detection for point-of-care diagnostics has propelled the search for more specific, sensitive, simple, accessible, yet economical sensor. Paper-based biosensor holds promise for future in-situ applications and can provide rapid analysis and data without the need to conduct in a laboratory. Electrochemical detection plays a vital role in interpreting results obtained from qualitative assessment to quantitative determination. In this review, various factors affecting the design of an electrochemical paper-based biosensor are highlighted and discussed in depth. Different detection methods, along with the latest development in utilizing them in cytokine and cancer biomarkers detection, are reviewed. Lastly, the fabrication of portable electrochemical paper-based biosensor is ideal in deliberating positive societal implications in developing countries with limited resources and accessibility to healthcare services.Ministry of Education (MOE)Published versionThe authors would like to acknowledge the financial support for this work funded by Singapore Ministry of Education Academic Research Fund Tier 1 (MOE-2018-T1-001-004)

Measuring membrane capacitance during a depolarizing stimulus

Regulated by the combined actions of various proteins and lipids, exocytosis in neurons or neuroendocrine cells is a highly dynamic process. It involves the transition of secretory vesicles through distinct molecular states in a time scale of seconds and final rapid Ca dependent vesicle fusion in a time scale of milliseconds. It is critical to resolve the highly dynamic kinetic steps along the molecular cascade of exocytosis in order to pin down the specific actions of regulatory molecules and eventually decipher this complex and fundamental process.RG 41/0

3D numerical simulation of a Coulter counter array with analysis of electrokinetic forces

Coulter counters have played an important role in biological cell assays since their introduction decades ago. Several types of high throughput micro-Coulter counters based on lab-on-chip devices have been commercialized recently. In this paper, we propose a highly integrated micro-Coulter counter array working under low DC voltage. The real-time electrical current change, including the pulse amplitude and width, of the micro-Coulter counter with novel structure is systematically investigated numerically. The major types of forces exerted on the particle in the micro-Coulter counter, including hydrodynamic force and electrokinetic force are quantitatively analyzed. The simulation in this study shows the pulse profile, such as width and amplitude, is affected by both particle size and the flow condition. The special cases of multiple particle aggregation and cross-talk between neighboring channels are also considered for their effects on the electric current pulses. This simulation provides critical insight and guidance for developing next new generations of micro-Coulter counter

Nanoelectronic detection of triggered secretion of pro-inflammatory cytokines using CMOS compatible silicon nanowires

Nanotechnology, such as nanoelectronic biosensors, is bringing new opportunities and tools to the studies of cell biology, clinical applications, and drug discovery. In this study, cyrstalline silicon nanowire based field-effect transistors fabricated using top-down approach were employed to parallelly detect pro-inflammatory cytokines in the complex biological fluids (cell culture medium and blood samples) with high specificity and femtomolar sensitivity. Using this technique, the dynamic secretion of TNFalpha and IL6 was revealed during the immune response of macrophages and rats to the stimulation of bacteria endotoxin. This technique could provide a unique platform to examine the profile of complex immune responses for fundamental studies and diagnosis.Accepted versio

Fabrication of poly (diallyldimethylammonium chloride) (PDDA) functionalized multi-walled carbon nanotubes paper electrode for simultaneous detection of dopamine and ascorbic acid

A paper-based electrode based on nanocomposite, comprising of carboxylated multi-walled carbon nanotubes (MWNTs) and poly (diallyldimethylammonium chloride) (PDDA), has been successfully developed for simultaneous detection of dopamine (DA) and ascorbic acid (AA) in 0.1 M phosphate buffer solution (PBS). The fabrication of PDDA/MWNTs electrodes involves two steps: PDDA absorbed onto the surface of carboxylated MWNTs and drop-casting the aqueous mixture of PDDA/MWNTs onto the paper. The electrode size was defined by a window cut into a laminating film. Differential pulse voltammetry was performed with DA concentration ranging from 2 μM to 500 μM in the presence of 1mM AA. On the surface of PDDA/MWNTs electrode, DA and AA were oxidized respectively at distinguishable potential of 0.156 and -0.068 V (vs. Ag/AgCl). The detection limit of DA was estimated to be 0.8 μM. This nanocomposite electrode has potential application in bioanalysis and biomedicine.MOE (Min. of Education, S’pore)Published versio

Non-invasive detection of cellular bioelectricity based on carbon nanotube devices for high-throughput drug screening

Nanoelectronic biosensors based on readily fabricated networks of single-walled carbon nanotubes (SWNT-net) were used to non-invasively detect cellular bioelectrical signals. This nanotube approach promises applications in both fundamental research and high-throughput drug screening targeting on ion channels