3/24/11. Introduction! Electrogenic cell

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Vincent Simon
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March 2011 Introduction! Electrogenic cell Electrode/electrolyte interface! Electrical double layer! Half-cell potential! Polarization! Electrode equivalent circuits Biopotential electrodes!

1 March 2011 Introduction! Electrogenic cell Electrode/electrolyte interface! Electrical double layer! Half-cell potential! Polarization! Electrode equivalent circuits Biopotential electrodes! Body surface electrodes! Internal electrodes! Implantable electrodes! Electrode arrays! Microfabricated electrodes! Microelectrodes. GBM Dispositifs Médicaux Intelligents 2 Metal-plate electrodes Large surface: Ancient, therefore still used, ECG Metal disk with stainless steel; platinum or gold coated EMG, EEG Smaller diameters Motion artifacts Disposable foam-pad: Cheap! (a) Metal-plate electrode used for application to limbs. (b) Metal-disk electrode applied with surgical tape. (c) Disposable foam-pad electrodes, often used with ECG GBM Dispositifs Médicaux Intelligents 3 1

Insulating package Metal disk (a)" (a) Recessed electrode with hot structure; (b) Cross-sectional view of electrode (a) (c) Cross-sectional view of another disposable electrode.

2 Insulating package Metal disk (a)" (a) Recessed electrode with hot structure; (b) Cross-sectional view of electrode (a) (c) Cross-sectional view of another disposable electrode. Double-sided Adhesive-tape ring Snap coated with Ag-AgCl Plastic cup (b)" Electrolyte gel in recess External snap Gel-coated sponge Plastic disk Reusable Disposable Tack Dead cellular material Foam pad Capillary loops Germinating layer (c)" GBM Dispositifs Médicaux Intelligents 4 Body contours are often irregular Regularly shaped rigid electrodes may not always work Special case : infants Used materials - Polymer or nylon with silver - Carbon filled silicon rubber (Mylar film)." (a) Carbon-filled silicone rubber electrode. (b) Flexible thin-film neonatal electrode. (c) Cross-sectional view of the thin-film electrode in (b) GBM Dispositifs Médicaux Intelligents 5 Needle and wire electrodes for percutaneous measurement of biopotentials: Insulated needle electrode Coaxial needle electrode. Bipolar coaxial electrode. Fine-wire electrode connected to hypodermic needle, before being inserted. Cross-sectional view of skin and muscle, showing coiled fine-wire electrode in place. GBM Dispositifs Médicaux Intelligents 6 2

3 Introduction! Electrogenic cell Electrode/electrolyte interface! Electrical double layer! Half-cell potential! Polarization! Electrode equivalent circuits Biopotential electrodes! Body surface electrodes! Internal electrodes! Implantable electrodes! Electrode arrays! Microfabricated electrodes! Microelectrodes. GBM Dispositifs Médicaux Intelligents 7 Electrodes for detecting fetal ECG (Use of intracutaneous needles) Suction electrode Helical electrode Electrodes for Cardiac stimulation. GBM Dispositifs Médicaux Intelligents 8 Electrodes for detecting biopotentials Wire-loop electrode Platinum-sphere cortical surface potential electrode Multielement depth electrode. GBM Dispositifs Médicaux Intelligents 9 3

ENG measurement (three contacts) Stimulation (2 contacts) Cuff electrodes Helical electrodes Pins electrodes Multicontacts electrodes etc GBM8320 - Dispositifs Médicaux Intelligents 10 Introduction!

4 ENG measurement (three contacts) Stimulation (2 contacts) Cuff electrodes Helical electrodes Pins electrodes Multicontacts electrodes etc GBM Dispositifs Médicaux Intelligents 10 Introduction! Electrogenic cell Electrode/electrolyte interface! Electrical double layer! Half-cell potential! Polarization! Electrode equivalent circuits Biopotential electrodes! Body surface electrodes! Internal electrodes! Implantable electrodes! Electrode arrays! Microfabricated electrodes! Microelectrodes. GBM Dispositifs Médicaux Intelligents 11 Contacts Insulated leads Ag/AgCl electrodes Contacts Ag/AgCl electrodes Insulated leads (a)" Base Base Exposed tip Tines (b)" Examples of microfabricated electrode arrays: (a) One-dimensional plunge electrode array (b) Two-dimensional array, and (c) Three-dimensional array. Base (c)" GBM Dispositifs Médicaux Intelligents 12 4

3/24/11 Beam-lead multiple electrodes after Wise, et

Multiple-chamber electrode after Prohaska et al.

vias Exposed electrodes Silicon probe Si substrate

Miniature insulating chamber Channels Hole Silicon

- Dispositifs Médicaux Intelligents 14 An 8-probe

5 3/24/11 Beam-lead multiple electrodes after Wise, et al. Multielectrode silicon probe after Drake et al. Multiple-chamber electrode after Prohaska et al. Peripheral-nerve electrode based on the design of Edell. Bonding pads SiO2 insulated Au probes Insulated lead vias Exposed electrodes Silicon probe Si substrate Exposed tips (b)! (a)! Miniature insulating chamber Channels Hole Silicon chip Lead via Silicon probe Contact metal film Electrode (c)! (d)! GBM Dispositifs Médicaux Intelligents 13 GBM Dispositifs Médicaux Intelligents 14 An 8-probe array of 64 contacts each Wire-EDM cut Surface electropolish Oxalic acid attack Platinum deposition Epoxy base Support Grinding Assembly. Robofil 2030 GBM Dispositifs Médicaux Intelligents 15 5

Surface electropolish Oxalic acid attack Platinum

GBM8320 - Dispositifs Médicaux Intelligents 16

Electrogenic cell Electrode/electrolyte interface!

Body surface electrodes! Internal electrodes!

Microfabricated electrodes! Microelectrodes.

Structure of a metal microelectrode for intracellular

6 Surface electropolish Oxalic acid attack Platinum deposition Epoxy base Support Grinding Assembly. GBM Dispositifs Médicaux Intelligents 16 Introduction! Electrogenic cell Electrode/electrolyte interface! Electrical double layer! Half-cell potential! Polarization! Electrode equivalent circuits Biopotential electrodes! Body surface electrodes! Internal electrodes! Implantable electrodes! Electrode arrays! Microfabricated electrodes! Microelectrodes. GBM Dispositifs Médicaux Intelligents 17 Structure of a metal microelectrode for intracellular recordings. Structures of two supported metal microelectrodes: (a) Metal-filled glass micropipet (b) Glass micropipet or probe, coated with metal film. GBM Dispositifs Médicaux Intelligents 18 6

The electrical activity of cells can be recorded without disrupting the cell membrane using extracellular recording techniques For extracellular recordings, the cells are located directly on top of a

7 The electrical activity of cells can be recorded without disrupting the cell membrane using extracellular recording techniques For extracellular recordings, the cells are located directly on top of a transducing element, which is, in most cases, either a metallic electrode or an open-gate transistor When electrical activity or a so-called action potential in a cell occurs, ions flow across the cell membrane within msec. Ions sensitive transistors can be used to transduce the cells activity. GBM Dispositifs Médicaux Intelligents 19 When a cell is close to a transducer, the moving ions generate an electric field or voltage, which can be recorded by the metallic microelectrode or field-effect transistor Extracellular recordings are non-invasive (no puncturing of the cell membrane) Models: - Metal electrode - Open fieldeffect transistor. GBM Dispositifs Médicaux Intelligents 20 Two main advantages in using integrated-circuit (IC) or CMOS technology: Connectivity: larger numbers of transducers or electrodes can be addressed by on-chip multiplexing architectures Signal quality; the signal is conditioned right at the electrode by means of dedicated circuitry units (filters, amplifiers) The use of CMOS technology allows to realize a large number of electrodes on a small system chip On-chip microelectronics, as provided by the use of IC or CMOS technology, translate into system capability: signal conditioning can be performed on-chip, ensuring that weak neural signals are faithfully recorded; GBM Dispositifs Médicaux Intelligents 21 7

8 A CMOS system also enables a bidirectional communication via the electrodes (stimulation and recording); Smart switching schemes allow for stimulating the cell ensemble via an arbitrarily selectable set of electrodes, all while recording from other electrodes uninterruptedly during stimulation On-chip analog-to-digital conversion means that such chip produces a robust signal that may be easily manipulated and transferred without compromising its information content Moreover, the use of on-chip electronics allows for the monolithic integration of the complete system on a single chip, which leads to small system dimensions and low power consumption, a key requirement for implantable devices GBM Dispositifs Médicaux Intelligents 22 The use of multiplexers enables the integration of a large number of electrodes or transducers so that measurements at high spatiotemporal resolution become feasible Traditional Microelectrodes arrays (MEAs) without multiplexers usually offer 64 electrodes with each electrode needing a connection to external circuitry, which adds parasitic capacitance and attenuates the weak signals CMOS-based MEAs comprise up to 16,384 electrodes and the needed addressing circuitry on the same chip A disadvantage of CMOS ICs is that silicon is not transparent to visible light in contrast to standard cell culture substrates used in biology GBM Dispositifs Médicaux Intelligents 23 The IC or its components can corrode upon operation and long-term exposure to liquids (salt water) A good packaging solution is needed: To protect the IC against metabolism products To prevent the cells from being poisoned or disturbed by toxic materials released by the IC, such as the CMOS metal aluminum that dissolves in saline solution. Notes : Make a better electrode Research different electrode technologies Ion selective, immunosensors, ISFET, electrochemical MEMS microelectrode technologies Polymer based electrodes.. GBM Dispositifs Médicaux Intelligents 24 8

Biopotential Electrodes

Biomedical Instrumentation Prof. Dr. Nizamettin AYDIN naydin@yildiz.edu.tr naydin@ieee.org http://www.yildiz.edu.tr/~naydin Biopotential Electrodes 1 2 Electrode electrolyte interface The current crosses