Abdur Rub Abdur Rahman

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.

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.

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.

A Monolithically Integrated Pressure/Oxygen/Temperature Sensing SoC for Multimodality Intracranial Neuromonitoring

A fully integrated SoC for multimodality intracranial neuromonitoring is presented in this paper. Three sensors including a capacitive MEMS pressure sensor, an electrochemical oxygen sensor and a solid-state temperature sensor are integrated together in a single chip with their respective interface circuits. Chopper stabilization and dynamic element matching techniques are applied in sensor interface circuits to reduce circuit noise and offset. On-chip calibration is implemented for each sensor to compensate process variations. Measured sensitivity of the pressure, oxygen, and temperature sensors are 18.6 aF/mmHg, 194 pA/mmHg, and 2 mV/°C, respectively. Implemented in 0.18 m CMOS, the SoC occupies an area of 1.4 mm × 4 mm and consumes 166 μW DC power. A prototype catheter for intracranial pressure (ICP) monitoring has been implemented and the performance has been verified with ex vivo experiment.

Electrokinetic Analysis of Cell Translocation in Low-Cost Microfluidic Cytometry for Tumor Cell Detection and Enumeration

Conventional Coulter counters have been introduced as an important tool in biological cell assays since several decades ago. Recently, the emerging portable Coulter counter has demonstrated its merits in point of care diagnostics, such as on chip detection and enumeration of circulating tumor cells (CTC). The working principle is based on the cell translocation time and amplitude of electrical current change that the cell induces. In this paper, we provide an analysis of a Coulter counter that evaluates the hydrodynamic and electrokinetic properties of polystyrene microparticles in a microfluidic channel. The hydrodynamic force and electrokinetic force are concurrently analyzed to determine the translocation time and the electrical current pulses induced by the particles. Finally, we characterize the chip performance for CTC detection. The experimental results validate the numerical analysis of the microfluidic chip. The presented model can provide critical insight and guidance for developing micro-Coulter counter for point of care prognosis.

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.

A pressure/oxygen/temperature sensing SoC for multimodality intracranial neuromonitoring

A fully integrated SoC for multimodality intracranial neuromonitoring is presented. This SoC includes a capacitive MEMS pressure sensor, an electrochemical oxygen sensor, a solid-state temperature sensor and sensor interface circuits in a single chip. Chopper stabilization and dynamic element matching techniques are applied in sensor interface circuits to reduce circuit noise and offset. On-chip calibration is implemented for each sensor to compensate process variations. Measured accuracies of the pressure, oxygen, and temperature sensors are ±1 mmHg, ±1 mmHg, and ±0.2 oC, respectively. Implemented in 0.18-μm CMOS, the SoC occupies an area of 1.4 mm × 4mm and consumes 188-μW DC power.

Cell surface receptors: rapid quantification of live cell receptors using bioluminescence in a flow-based microfluidic device (small 8/2015).

C. T. Lim and co-workers describe a rapid and sensitive bioluminescence-based microfluidic method for quantifying receptor numbers on live cells. On page 943, this integrated, lens-free optical platform allows the determination of signals from the cell surface with high sensitivity. Compared to conventional approaches, the combined use of bioluminescence and microfluidics makes it safe to use, reduces background noise, improves sensitivity, requires smaller sample volumes, and allows high-throughput sampling over thousands of cells.

Abstract 1451: Microfluidic-based unbiased enrichment (negative selection) of circulating non-hematopoietic tumor cells directly from whole blood without centrifugation.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC The enumeration and analysis of circulating non-hematopoietic tumor cells (CTCs) is of increasing interest for monitoring disease progression or response to treatment, specifically as a companion diagnostic for new anti-cancer drugs, and for research into the mechanisms of disease progression and metastases. Ideally, CTCs would be enriched from very small samples, with minimal handling, high recovery, and no requirement for the expression of specific surface markers. Two technologies have been combined to meet these requirements. Hematopoietic white blood cells (WBCs) in whole blood were first cross-linked to magnetic particles using EasySep™ anti-CD45 TAC. The sample was diluted and placed in a magnet for 30 min.; an outlet in the bottom of the sample tube was then opened and the sample flowed by gravity into a microfluidic chamber containing a high-precision micro-slit membrane. Red blood cells (RBCs) flowed through the microfluidic chamber, while larger cells such as CTCs were retained in the chamber. The cells in the chamber were washed with PBS and then identified by staining with Hoechst [nuclear], anti-cytokeratin antibodies [epithelial cells], and anti-CD45 antibodies [hematopoietic cells]. CTCs were defined as Hoechst+, cytokeratin+ and CD45-. The recovery of MCF-7 breast adenocarcinoma cells spiked into normal whole blood, at 10, 30, 50, or 100 cells / 2 mL blood was 95 ± 23% (7 ± 1, n=3 for 10 cells; 24 ± 3, n=3 for 30 cells; 57 ± 3, n=3 for 50 cells; 113 ± 27, n=3 for 100 cells) and the log depletion of WBCs exceeded 2.3. The recovery of H1975 lung adenocarcinoma cells spiked into normal whole blood, at 10, 30, 50, or 100 cells / 2 mL blood was 93 ± 8% (9 ± 1, n=3 for 10 cells; 28 ± 3, n=3 for 30 cells; 48 ± 6, n=3 for 50 cells; 94 ± 2, n=3 for 100 cells), and the log depletion of WBCs exceeded 2.14. 13 patient samples [10 NSCLC and 3 CRC] were processed with this method and CTCs were detected in every sample. The number of CTC detected from 2 mL of blood ranged from 1 to 51. WBC log depletion ranged from 2.01 to 2.79. No RBCs were observed on the membrane of the microfluidic chamber. The entire process requires ∼ 60 minutes and could easily be automated. RBC depletion is essentially complete without the use of centrifugation or chemicals which may be deleterious to CTCs. The minimal sample handling permits high recovery of desired cells, allowing the detection of CTCs in much smaller samples than are currently used for clinical evaluation. CTCs are enriched without bias as to their surface antigen expression, and are not labeled with antibodies prior to detection. CTCs can be stained and visualized directly on the microfluidic chip. This unbiased enrichment approach could be used to assess the mutation status of CTC in real time. Citation Format: Carrie E. Peters, Hamizah Ahmad, Drew Kellerman, Bhuvanendran Nair Gourikutty Sajay, Chang Chia-Pin, Wong Chee Chung, Abdur Rub Abdur Rahman, Karina L. McQueen, Terry E. Thomas. Microfluidic-based unbiased enrichment (negative selection) of circulating non-hematopoietic tumor cells directly from whole blood without centrifugation. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1451. doi:10.1158/1538-7445.AM2013-1451