Maria Dimaki

Dielectrophoresis of carbon nanotubes using microelectrodes: a numerical study

Single-walled carbon nanotubes are candidates for a number of electronics and sensing applications, provided nanotubes with semiconducting and metallic band structure can be separated. Dielectrophoresis has recently been demonstrated as a route towards the separation of metallic nanotubes from semiconducting nanotubes, and is moreover a method for controlled assembly of the nanotubes on microstructures that has the possibility to be scaled to wafer-level manufacturing. In this paper we will present numerical calculations of carbon nanotubes subjected to dielectrophoresis, drag force and Brownian motion induced by application of an ac voltage to a set of microelectrodes in a microliquid channel. We calculate the probability of capturing various types of carbon nanotubes, the time frame for the assembly and the efficiency of separation, for different experimental parameters. Our results suggest that relatively low frequencies, where both semiconducting and metallic nanotubes are subject to positive dielectrophoresis, may be optimal for separation, due to large differences in the magnitude of the dielectrophoretic force.

Manipulation of self-assembly amyloid peptide nanotubes by dielectrophoresis

Self‐assembled amyloid peptide nanotubes (SAPNT) were manipulated and immobilized using dielectrophoresis. Micro‐patterned electrodes of Au were fabricated by photolithography and lifted off on a silicon dioxide layer. SAPNT were manipulated by adjusting the amplitude and frequency of the applied voltage. The immobilized SAPNT were evaluated by SEM and atomic force microscopy. The conductivity of the immobilized SAPNT was studied by I–V characterization, for both single SAPNT and bundles. This work illustrates a way to manipulate and integrate biological nanostructures into novel bio‐nanoassemblies with concrete applications, such as field‐effect transistors, microprobes, microarrays, and biosensing devices.

Frequency dependence of the structure and electrical behaviour of carbon nanotube networks assembled by dielectrophoresis

The statistical variations in the properties of carbon nanotubes and their contacts to metallic electrodes can be averaged by using networks of single-walled carbon nanotubes as sensing devices. Carbon nanotube networks have been assembled on microstructures with dielectrophoresis, using an inhomogeneous alternating electric field to attract carbon nanotubes onto the microelectrodes. The networks were assembled on identical microstructures using four different frequencies in the range 10 kHz–10 MHz. From structural and electrical characterization of the assembled structures, we found that at higher frequencies the assembled nanotubes align better with the electric field and are more free of impurities. We also found consistently lower resistances for networks assembled at higher frequencies, suggesting that a high assembly frequency may lead to better quality networks with low contact resistances.

Multichannel Bipotentiostat Integrated With a Microfluidic Platform for Electrochemical Real-Time Monitoring of Cell Cultures

An electrochemical detection system specifically designed for multi-parameter real-time monitoring of stem cell culturing/differentiation in a microfluidic system is presented. It is composed of a very compact 24-channel electronic board, compatible with arrays of microelectrodes and coupled to a microfluidic cell culture system. A versatile data acquisition software enables performing amperometry, cyclic voltammetry and impedance spectroscopy in each of the 12 independent chambers over a 100 kHz bandwidth with current resolution down to 5 pA for 100 ms measuring time. The design of the platform, its realization and experimental characterization are reported, with emphasis on the analysis of impact of input capacitance (i.e., microelectrode size) and microfluidic pump operation on current noise. Programmable sequences of successive injections of analytes (ferricyanide and dopamine) and rinsing buffer solution as well as the impedimetric continuous tracking for seven days of the proliferation of a colony of PC12 cells are successfully demonstrated.

Qualitative mapping of structurally different dipeptide nanotubes.

Biological self-assembled structures are receiving increasing focus within micro- and nanotechnology, for example, as sensing devices, due to the fact that they are cheap to produce and easy to functionalize. Therefore, methods for the characterization of these structures are much needed. In this paper, electrostatic force microscopy (EFM) was used to distinguish between hollow nanotubes formed by self-assembly by a simple aromatic dipeptide, L-phenylalanine, silver-filled peptide-based nanotubes, and silver wires placed on prefabricated SiO2 surfaces with a backgate. The investigation shows that it is possible to distinguish between these three types of structures using this method. Further, an agreement between the detected signal and the structure of the hollow peptide was demonstrated; however only qualitative agreement with the mathematical expressing of the tubes is shown.

Metaphase FISH on a Chip: Miniaturized Microfluidic Device for Fluorescence in situ Hybridization

Fluorescence in situ Hybridization (FISH) is a major cytogenetic technique for clinical genetic diagnosis of both inherited and acquired chromosomal abnormalities. Although FISH techniques have evolved and are often used together with other cytogenetic methods like CGH, PRINS and PNA-FISH, the process continues to be a manual, labour intensive, expensive and time consuming technique, often taking over 3 5 days, even in dedicated labs. We have developed a novel microFISH device to perform metaphase FISH on a chip which overcomes many shortcomings of the current laboratory protocols. This work also introduces a novel splashing device for preparing metaphase spreads on a microscope glass slide, followed by a rapid adhesive tape-based bonding protocol leading to rapid fabrication of the microFISH device. The microFISH device allows for an optimized metaphase FISH protocol on a chip with over a 20-fold reduction in the reagent volume. This is the first demonstration of metaphase FISH on a microfluidic device and offers a possibility of automation and significant cost reduction of many routine diagnostic tests of genetic anomalies.

A Compact Microelectrode Array Chip with Multiple Measuring Sites for Electrochemical Applications

In this paper we demonstrate the fabrication and electrochemical characterization of a microchip with 12 identical but individually addressable electrochemical measuring sites, each consisting of a set of interdigitated electrodes acting as a working electrode as well as two circular electrodes functioning as a counter and reference electrode in close proximity. The electrodes are made of gold on a silicon oxide substrate and are passivated by a silicon nitride membrane. A method for avoiding the creation of high edges at the electrodes (known as lift-off ears) is presented. The microchip design is highly symmetric to accommodate easy electronic integration and provides space for microfluidic inlets and outlets for integrated custom-made microfluidic systems on top.

Electrostatic force microscopy of self-assembled peptide structures

In this report electrostatic force microscopy (EFM) is used to study different peptide self-assembled structures such as tubes and particles. It is shown that not only geometrical information can be obtained using EFM, but also information about the composition of different structures. In particular we use EFM to investigate the structures of diphenylalanine peptide tubes, particles, and CSGAITIG peptide particles placed on pre-fabricated SiO(2) surfaces with a backgate. We show that the cavity in the peptide tubes could be due to the presence of water residues. Additionally we show that self-assembled amyloid peptides form spherical solid structures containing the same self-assembled peptide in its interior. In both cases transmission electron microscopy is used to verify these structures. Further, the limitations of the EFM technique are discussed, especially when the observed structures become small compared with the radius of the AFM tip used. Finally, an agreement between the detected signal and the structure of the hollow peptide tubes is demonstrated.

Fabrication and Characterization of 3D Micro- and Nanoelectrodes for Neuron Recordings

In this paper we discuss the fabrication and characterization of three dimensional (3D) micro- and nanoelectrodes with the goal of using them for extra- and intracellular studies. Two different types of electrodes will be described: high aspect ratio microelectrodes for studying the communication between cells and ultimately for brain slice recordings and small nanoelectrodes for highly localized measurements and ultimately for intracellular studies. Electrical and electrochemical characterization of these electrodes as well as the results of PC12 cell differentiation on chip will be presented and discussed.

Combined Cell Culture-Biosensing Platform Using Vertically Aligned Patterned Peptide Nanofibers for Cellular Studies

This Article presents the development of a combined cell culture-biosensing platform using vertically aligned self-assembled peptide nanofibers. Peptide nanofibers were patterned on a microchip containing gold microelectrodes to provide the cells with a 3D environment enabling them to grow and proliferate. Gold microelectrodes were functionalized with conductive polymers for the electrochemical detection of dopamine released from PC12 cells. The combined cell culture-biosensing platform assured a close proximity of the release site, the cells and the active surface of the sensor, thereby rendering it possible to avoid a loss of sensitivity because of the diffusion of the sample. The obtained results showed that the peptide nanofibers were suitable as a cell culturing substrate for PC12 cells. The peptide nanofibers could be employed as an alternative biological material to increase the adherence properties of PC12 cells. Dopamine was amperometrically detected at a value of 168 fmole.