Frequently Asked Questions
Q.1. What are the differences between M, CD and FD designs of IMEs?
The M or monolithic design is a single pair of electrodes that are interdigitated. The CD or combined differential is a dual design, or two pairs of interdigitated electrodes. However, in the CD design, the two pairs share a common central electrode that has fingers in two directions; towards the other electrodes and thus serves as an exposed gate electrode. The FD or full differential design comprises two completely separate pairs of electrodes and thus has four leads and may be thought of as two discrete M designs on a single chip.
Q.2. Why does ABTECH offer these different designs?
The M, CD and FD designs afford you flexibility in the way the IMEs are used. M for simple materials characterizations, CD for field-gated phenomena and FD for ratiometric analytical measurements.
Q.3. How is the M device design used?
The M design may be used as a simple, two-electrode (anode and cathode) electrochemical cell (electrolysis) or in the measurement of resistance (DC resistivity or conductivity) or electrical impedance (AC impedance) of films placed on or between the digits of the device.
Q.4. How is the CD device design used?
The CD design allows a polymer film to be cast, grown or deposited over all three electrodes and then have the outer two electrodes be used much like an M device (DC or AC). However, an additional potential may be applied to the central electrode to potentiate the properties, and hence response, of the polymer film. The electrical behavior of the polymer film could thus be altered by the electric field applied to the central gating electrode. This arrangement requires a bi-potentiostat or other measurement configuration. The gated electrode may also be “buried” by an insulating layer.
Q.5. How is the FD device design used?
The FD device can be thought of as two separate M designs on a single chip. This allows the possibility of a ratiometric measurement, that is, the response of one region of interdigitation relative to the other. The FD device may also be prepared with two entirely different polymer films or biological molecules (enzymes, DNA, etc) on each of the two regions of interdigitation. In this way the FD might be used to measure two distinct analytes in the same test medium.
Q.6. Why does ABTECH offer these devices with different conductors?
ABTECH’s IME, IAME and IAIME are available in three different conductors gold (Au), platinum (Pt) and ITO. These conductors, while generally inert, each have different work functions, different surface energies, different surface chemistries, and different bio-contact properties. This gives then unique properties. Au for example is readily modified with alkane thiols, ITO is readily modified with organosilanes, and Pt is easily platinized to be rendered catalytic.
Q.7. What is the difference between packaged (P) and unpackaged (U) devices?
ABTECH’s IMEs are available as packaged and unpackaged devices. Unpackaged (U) devices are microlithographically fabricated chips possessing patterns of conductors on an insulating substrate. The unpackaged device is supplied as a die without lead wires and without any form of encapsulation. The packaged (P) device is provided with a suitable chip carrier / leadwire construct and the points of attachment of the bonding pads of the chip to the chip carrier is encapsulated in suitable (usually epoxy) resin. http://www.abtechsci.com/imep-animated.html
Q.8. Why do packaged IMEs require a two–week lead-time?
Packaged items require a two-week lead time as chips are taken out of inventory in response to a customer's order and are then packaged accordingly. Because packaging (encapsulation with a suitable epoxy resin) limits user flexibility with regard to coating methods, ABTECH prepares packaged chips only in response to confirmed purchase orders or receipt of credit cards. Packaged items are thus not kept in inventory and must thus be prepared in response to a confirmed purchase.
Q.9. What is a STC Test Clip and how is it used?
The STC test clip is the correct connector for all IME chips. The STC is a spring-loaded pinch clip that allows easy and convenient make/break electrical connection to the bonding pads of the various IME dies. The STC possess four leads that terminate in four spring-loaded gold contacts within the jaw of the STC Test Clip. The electrical contacts of the test clip match and mate to the bonding pads of the die. To use the test clip, its jaws are opened and the die is inserted such that the conductive bonding pads of the die mate with the conductors of the test clip upon its closure. Check for connectivity using a multimeter.
Q.10. We are interested in buying IAME chips and adapters. We wish to use these chips for measuring the electrical activities of cells. We wonder if it is at all possible to do this using your IAME chips and, if so, whether someone has done it before. Also, what instrumentation does one need to perform measurements?
The IAME and the IAIME chips may both be used for measuring the electrical impedance characteristics of living cells. The cells must first be cultured to full confluence on the chip, they must also adhere to the chip and an impedance analyzer or lock-in amplifier could be used to obtain the real and imaginary components of the impedance of the cells as a function of time. To achieve cell growth on the chip a culture chamber must be installed over the electrode fingers of the chip. Moreover, chemistries appropriate for the immobilization of the cells (ECM proteins of amino acid sequences) must first be immobilized to the chip.
Q.11. Is the IAME wand adapter a one-time use adapter or can it be reused for connection to multiple IAMEs?
While it is possible to use one wand with multiple IAME chips or IME Chips, they were designed to be used as one wand per chip. The chip is typically glued (Crazy Glue® - cyanoacrylate) to the wand and then the electrical contacts established using a conductive epoxy or low temperature solder. To use a single wand and multiple chips will require that you invent a method of attachment and detachment (other than gluing) and a method for making and breaking (other than conductive epoxy) the electrical contacts from wand to chip. It is therefore advised that you purchase as many wands as you purchase chips. Please take a look at this animation of IAME chip packaging. http://www.abtechsci.com/imep-animated.html
Q.12. To what temperature can I heat my IME/IAME/IAIME/MDEA Chip?
Our chips are fabricated from Schott D263 borosilicate glass and possess an appropriately patterned conductor. These devices are manufactured for RT use and are suitable for modest variations above and below RT. However, it is possible to use these devices at elevated temperatures as well as at cryogenic temperatures. The glass transition temperature, Tg, or softening point for Schott D263 is given by Schott as 557oC. Above this temperature the substrate looses its dimensional stability.
Q.13. I have purchased an IAME / IME Chip and IAME / IME Wand Adapter. How do I make connection of the wand to the chip?
We recommend, without guarantee, the use of a conductive two-part epoxy such as that from Circuit Works CW2400 Part A and CW2400 Part B www.Chemtronics.com. Also, you may solder the connection if you have access to a temperature controlled solder station.
Q.14. I have purchased IMEs and wish to measure conductivity of a well-studied material so that I may obtain cell constants and calibrate the electrode. What is a suitable material to use?
We recommend, without guarantee, the use of standard conductance solutions of potassium chloride (KCl) at constant temperature (25C) according to ISO 7888:1985. Such solutions are commercially available from VWR, Fischer Scientific, Sigma Aldrich, etc. and vary in conductance values from 0.147 to 12.90 mS/cm. See Y. C. Wu and P. A. Berezansky, "Low Electrolytic Conductivity Standards" J. Res. Natl. Inst. Stand. Technol. (1995) 100, 521 and Liju Yang, Adilah Guiseppi-Wilson and Anthony Guiseppi-Elie "Design considerations in the use of interdigitated microsensor electrode arrays (IMEs) for impedimetric characterization of biomimetic hydrogels" Biomedical Microdevices (2010) DOI: 10.1007/s10544-010-9492-4.
Q.15. I have purchased IAME / IME / PME / MDEA or other chip and wish to know, for my thesis or publication, know exactly how these devices are manufactured?
The exact process details of manufacture (pressures, times, temperatures, etc.) are proprietary. However, the general technical description of the manufacture of these chips have been published and may be found in such peer-reviewed journal articles as
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