Effect of Electrode Shape on Impedance of Single HeLa Cell: A COMSOL Simulation

In disease prophylaxis, single cell inspection provides more detailed data compared to conventional examinations. At the individual cell level, the electrical properties of the cell are helpful for understanding the effects of cellular behavior. The electric field distribution affects the results of single cell impedance measurements whereas the electrode geometry affects the electric field distributions. Therefore, this study obtained numerical solutions by using the COMSOL multiphysics package to perform FEM simulations of the effects of electrode geometry on microfluidic devices. An equivalent circuit model incorporating the PBS solution, a pair of electrodes, and a cell is used to obtain the impedance of a single HeLa cell. Simulations indicated that the circle and parallel electrodes provide higher electric field strength compared to cross and standard electrodes at the same operating voltage. Additionally, increasing the operating voltage reduces the impedance magnitude of a single HeLa cell in all electrode shapes. Decreasing impedance magnitude of the single HeLa cell increases measurement sensitivity, but higher operational voltage will damage single HeLa cell

A simulation study of single cell inside an integrated dual nanoneedle-microfludic system

Electrical properties of living cells have been proven to play significant roles in understanding of various biological activities including disease progression both at the cellular and molecular levels. Analyzing the cell’s electrical states especially in single cell analysis (SCA) lead to differentiate between normal cell and cancer cell. This paper presents a simulation study of micro-channel and nanoneedle structure, fluid manipulation and current flow through HeLa cell inside a microfluidic channel. To perform electrical measurement, gold dual nanoneedle has been utilized. The simulation result revealed, the cell penetration occurs at microchannel dimension and solution flow rate is 22 µm x 70 µm x 25 µm (width x length x height) and 0.396 pL/min, respectively. The purposed device has capability to characterize the electrical property of single cells can be used as a novel method for cell viability detection in instantaneous manner

Investigation of ac-magnetic field stimulated nanoelectroporation of magneto-electric nano-drug-carrier inside CNS cells

In this research, we demonstrate cell uptake of magneto-electric nanoparticles (MENPs) through nanoelectroporation (NEP) using alternating current (ac)-magnetic field stimulation. Uptake of MENPs was confirmed using focused-ion-beam assisted transmission electron microscopy (FIB-TEM) and validated by a numerical simulation model. The NEP was performed in microglial (MG) brain cells, which are highly sensitive for neuro-viral infection and were selected as target for nano-neuro-therapeutics. When the ac-magnetic field optimized (60 Oe at 1?kHz), MENPs were taken up by MG cells without affecting cell health (viability?\u3e?92%). FIB-TEM analysis of porated MG cells confirmed the non-agglomerated distribution of MENPs inside the cell and no loss of their elemental and crystalline characteristics. The presented NEP method can be adopted as a part of future nanotherapeutics and nanoneurosurgery strategies where a high uptake of a nanomedicine is required for effective and timely treatment of brain diseases

Dielectrophoretic characterization of particles and erythrocytes

Medical lab work, such as blood testing, will one day be near instantaneous and inexpensive via capabilities enabled by the fast growing world of microtechnology. In this research study, sorting and separation of different ABO blood types have been investigated by applying alternating and direct electric fields using class=SpellE\u3edielectrophoresis in microdevices. Poly(dimethylsiloxane) (PDMS) microdevices, fabricated by standard photolithography techniques have been used. Embedded perpendicular platinum (Pt) electrodes to generate forces in AC dielectrophoresis were used to successfully distinguish positive ABO blood types, with O+ distinguishable from other blood types at \u3e95% confidence. This is an important foundation for exploring DC dielectrophoretic sorting of blood types. The expansion of red blood cell sorting employing direct current insulative class=SpellE\u3edielectrophoresis (DC-iDEP) is novel. Here Pt electrodes were remotely situated in the inlet and outlet ports of the microdevice and an insulating obstacle generates the required dielectrophoretic force. The presence of ABO antigens on the red blood cell were found to affect the class=SpellE\u3edielectrophoretic deflection around the insulating obstacle thus sorting cells by type. To optimize the placement of insulating obstacle in the microchannel, COMSOL Multiphysics® simulations were performed. Microdevice dimensions were optimized by evaluating the behaviors of fluorescent polystyrene particles of three different sizes roughly corresponding to the three main components of blood: platelets (2-4 µm), erythrocytes (6-8 µm) and leukocytes (10-15 µm). This work provided the operating conditions for successfully performing size dependent blood cell insulator based DC dielectrophoresis in PDMS microdevices. In subsequent studies, the optimized microdevice geometry was then used for continuous separation of erythrocytes. The class=SpellE\u3emicrodevice design enabled erythrocyte collection into specific channels based on the cell’s deflection from the high field density region of the obstacle. The channel with the highest concentration of cells is indicative of the ABO blood type of the sample. DC resistance measurement system for quantification of erythrocytes was developed with single PDMS class=SpellE\u3emicrochannel system to be integrated with the DC- class=SpellE\u3eiDEP device developed in this research. This lab-on-a-chip technology application could be applied to emergency situations and naturalcalamities for accurate, fast, and portable blood typing with minimal error

Manipulating and assembling metallic beads with Optoelectronic Tweezers

Optoelectronic tweezers (OET) or light-patterned dielectrophoresis (DEP) has been developed as a micromanipulation technology for controlling micro- and nano-particles with applications such as cell sorting and studying cell communications. Additionally, the capability of moving small objects accurately and assembling them into arbitrary 2D patterns also makes OET an attractive technology for microfabrication applications. In this work, we demonstrated the use of OET to manipulate conductive silver-coated Poly(methyl methacrylate) (PMMA) microspheres (50μm diameter) into tailored patterns. It was found that the microspheres could be moved at a max velocity of 3200μm/s, corresponding to 4.2 nano-newton (10−9N) DEP force, and also could be positioned with high accuracy via this DEP force. The underlying mechanism for this strong DEP force is shown by our simulations to be caused by a significant increase of the electric field close to the particles, due to the interaction between the field and the silver shells coating the microspheres. The associated increase in electrical gradient causes DEP forces that are much stronger than any previously reported for an OET device, which facilitates manipulation of the metallic microspheres efficiently without compromise in positioning accuracy and is important for applications on electronic component assembling and circuit construction

Manipulating and assembling metallic beads with optoelectronic tweezers

Optoelectronic tweezers (OET) or light-patterned dielectrophoresis (DEP) has been developed as a micromanipulation technology for controlling micro- and nano-particles with applications such as cell sorting and studying cell communications. Additionally, the capability of moving small objects accurately and assembling them into arbitrary 2D patterns also makes OET an attractive technology for microfabrication applications. In this work, we demonstrated the use of OET to manipulate conductive silver-coated Poly(methyl methacrylate) (PMMA) microspheres (50 μm diameter) into tailored patterns. It was found that the microspheres could be moved at a max velocity of 3200 μm/s, corresponding to 4.2 nano-newton (10−9 N) DEP force, and also could be positioned with high accuracy via this DEP force. The underlying mechanism for this strong DEP force is shown by our simulations to be caused by a significant increase of the electric field close to the particles, due to the interaction between the field and the silver shells coating the microspheres. The associated increase in electrical gradient causes DEP forces that are much stronger than any previously reported for an OET device, which facilitates manipulation of the metallic microspheres efficiently without compromise in positioning accuracy and is important for applications on electronic component assembling and circuit construction

Dielectrophoretic characterization of particles and erythrocytes

Medical lab work, such as blood testing, will one day be near instantaneous and inexpensive via capabilities enabled by the fast growing world of microtechnology. In this research study, sorting and separation of different ABO blood types have been investigated by applying alternating and direct electric fields using class=SpellE\u3edielectrophoresis in microdevices. Poly(dimethylsiloxane) (PDMS) microdevices, fabricated by standard photolithography techniques have been used. Embedded perpendicular platinum (Pt) electrodes to generate forces in AC dielectrophoresis were used to successfully distinguish positive ABO blood types, with O+ distinguishable from other blood types at \u3e95% confidence. This is an important foundation for exploring DC dielectrophoretic sorting of blood types. The expansion of red blood cell sorting employing direct current insulative class=SpellE\u3edielectrophoresis (DC-iDEP) is novel. Here Pt electrodes were remotely situated in the inlet and outlet ports of the microdevice and an insulating obstacle generates the required dielectrophoretic force. The presence of ABO antigens on the red blood cell were found to affect the class=SpellE\u3edielectrophoretic deflection around the insulating obstacle thus sorting cells by type. To optimize the placement of insulating obstacle in the microchannel, COMSOL Multiphysics® simulations were performed. Microdevice dimensions were optimized by evaluating the behaviors of fluorescent polystyrene particles of three different sizes roughly corresponding to the three main components of blood: platelets (2-4 µm), erythrocytes (6-8 µm) and leukocytes (10-15 µm). This work provided the operating conditions for successfully performing size dependent blood cell insulator based DC dielectrophoresis in PDMS microdevices. In subsequent studies, the optimized microdevice geometry was then used for continuous separation of erythrocytes. The class=SpellE\u3emicrodevice design enabled erythrocyte collection into specific channels based on the cell’s deflection from the high field density region of the obstacle. The channel with the highest concentration of cells is indicative of the ABO blood type of the sample. DC resistance measurement system for quantification of erythrocytes was developed with single PDMS class=SpellE\u3emicrochannel system to be integrated with the DC- class=SpellE\u3eiDEP device developed in this research. This lab-on-a-chip technology application could be applied to emergency situations and naturalcalamities for accurate, fast, and portable blood typing with minimal error

Scanning Ion Conductance Microscopy for Single Cell Imaging and Analysis

Most biological experiments are performed on an ensemble of cells under the assumption that all cells are identical. However, recent evidence from single cells studies reveals that this assumption is incorrect. Individual cells within the same generation may differ dramatically, and these differences have important consequences for the health and function of the entire living body. I have used Scanning Ion Conductance Microscopy (SICM) for imaging and analysis of topographical change of single cell membrane, which is difficult to be revealed by optical microscopes. Morphological change in the fixed and live HeLa cell membrane during endocytosis of conjugated polymer nanoparticles was studied. Results demonstrated SICM is a powerful tool to study the interaction between nanoparticle and cell membrane during internalization of nanoparticles through the membrane. This research can improve our fundamental understanding of cellular behavior and will be helpful for drug delivery applications. Based on conventional SICM, we have developed a novel method to simultaneous map the topography and potential distributions of the single living cells membranes. At the first step, multifunctional nanopipettes (nanopore/nanoelectrode) have been fabricated and characterized. To demonstrate the potential sensing capability and understand the mechanism, I measured the ionic current and local electric potential change during translocation of 40 nm charged gold nanoparticles. Our results reveal the capability of the multifunctional probe for the highly sensitive detection of the ionic current and local electrical potential changes during the translocation of the charged entity through the nanopore. From the potential change, we revealed the dynamic assembly of GNPs before entering the nanopore. The experimental results are also nicely explained by the finite element method based numerical simulation results. At the second step, I have measured the surface potential of living cell membrane at selected locations. Very recently, I have obtained results to show that we can map the extracellular membrane potential distribution of the complicated living cell membrane with sub-micron spatial resolution.This new imaging technique can help biologist to explore the extracellular potential distribution of varieties of cells quantitatively.These studies will have impacts on several biomedical applications such as regenerative repair and cancer treatment

Coupling Scanning Electrochemical Microscopy and 3D Modelling to Probe Membrane Permeability of Human Bladder Cancer (T24) Cells

Scanning electrochemical microscopy (SECM) scans a biased ultramicroelectrode (≤ 25 µm) probe over a sample to characterize topography, physical properties and chemical reactivity. In this dissertation, SECM was used to investigate the metal-induced changes in membrane response of single live human bladder cancer cells (T24). SECM imaging was coupled to 3D finite element method (FEM) simulations which were the first of their kind, providing advanced quantification of sample traits under conditions not previously usable. The effects of Cd2+ on T24 cell membrane permeability were examined. Experimental depth-scan imaging was coupled with full 3D FEM simulations, eliminating many limitations of previous 2D-axially symmetric models. Hundreds of probe approach curves (PACs) can now be extracted from depth-images and theoretically fit to quantify membrane permeability at any location across the cell surface (Chapter 2). SECM was utilized to examine the membrane response of T24 cells following exposure to toxic dichromate (Cr(VI)). Two electrochemical mediators were examined, the membrane permeable ferrocenemethanol (FcCH2OH) and impermeable ferrocenecarboxylate (FcCOO‑). Cr(VI) induced permeability change was observed with both mediators and compared (Chapter 3). Chronic Cr(VI) induced cell stress, was then examined. Similar permeability curve shape was observed, with shifts in response time based on concentration of Cr(VI) stressor (Chapter 4). Trace essential metals such as Cr(III) are essential in low concentrations but toxic in high concentration. Membrane-response was investigated by SECM, using both FcCH2OH and FcCOO- redox mediators. Theoretical SECM depth-scans were produced using 3D FEM simulations, and used to quantify cell membrane permeability (Chapter 5). Complex close-proximity cell clusters were experimentally imaged by SECM 3D scanning mode. Tailored 3D model geometries were created, generating complimentary theoretical maps of the experimental cell clusters. The simulations were capable of providing a strong theoretical fit to the experimental results. Limits of cell proximity for SECM characterization were determined based on the probe size (Chapter 6). Nanoscale SECM imaging of single live cells were performed using a laser-pulled 130 nm radius Pt disk electrode. A tailored 3D model was created, from which cell topography was accurately characterized using membrane-impermeable Ru(NH3)63+, and cell membrane permeability was quantified with FcCH2OH (Chapter 7)