Sycopel Micro Dialysis Biosensor

The Sycopel Microdialysis Biosensor combines the techniques of in vivo microdialysis and voltammetry in one integrated device enabling "real time" measurement of analytes with greater ease and simplicity. One significant advantage of the Biosensor over conventional techniques is the elimination of the need to collect samples at invervals from a microdialysis probe for later analysis.

The Microdialysis Biosensor has demonstrated its potential by measuring small physiological changes in vivo involved with learning and memory ³, and by measuring activity in the freely-moving rat^2,17. Its adaptability has allowed the device to be used in both drug evaluation studies and in vitro 'bedside monitoring' of human glycerol levels^1,5.

The design of the Microdialysis Biosensor centers around a platinum wire contained within a hollow, 230 µm I.D. semi-permeable membrane. Two 140 µm O.D. vitreous silica tubes provide a means for solution exchange within the probe, giving the microdialysis biosensor its most important feature: the ability to control the micro-environment around the working electrode. This allows enzymes or biologically active molecules to be replaced within minutes, either if they become inactive or if the specificity of the biosensor is to be changed by using different enzyme(s).

Two extra electrodes, a silver or platinum counter-electrode and a silver/silver chloride reference electrode, make up the electrochemical cell and these are both situated away from the main sensing area within a glass or steel upper compartment.

For concomitant electrophysiological studies, stainless steel recording electrodes are fixed in parallel with the membrane allowing field potential recording. This can be used both for positioning the microdialysis biosensor and for subsequent activity recording.

Research includes long term potentiation, epilepsy, drug evaluation, behavioral research. (See references for details.)

Advantages over other needle type voltammetric electrodes.

1. A single microdialysis biosensor can be used in the same area of the brain/tissue for performing both control and required measurements. This is readily achieved using the 'internal plumbing system' and gives the user the ability to change solutions around the working electrode.
2. The outer membrane protects the electrode during implantation.
3. A coating of albumin can help to protect the biosensor from excessive protein adsorption which can reduce sensitivity.
4. Cleaning the biosensor with sonication allows the biosensor to be re-used.
5. The addition of different enzymes can change the biosensor specificity allowing a comparison of different analytes. For example, glucose and lactate concentrations can be compared using the same electrode within a short time space (10 minutes or less depending on the time required to change enzymes).
6. The biosensor is tailor-made to meet the user's requirements.

In addition, a dual configuration mode is available and offers the following combinations of experimentation

• "Real time" measurement of 2 analytes.
• "Real time" measurement of 1 analyte plus drug perfusion.
• "Real time" measurement of 1 analyte plus microdialysis.

Dimensional Diagrams of the 3 standard biosensor models:

Custom biosensors can be manufactured by specifying dimensions A, B, C, D. Please inquire for details.

Sample In Vitro Glutamate Measurements

Glutamate release from in vitro hippocampal slices can be achieved by using the dialysis electode in conjunction with a slice chamber (available from Sycopel International Ltd).

When challenged with increasing [K⁺] ions in the aCSF (12mM for 5 minutes) an increase in glutamate current is observed followed by spontaneous epileptiform activity.⁴

Microdialysis Biosensor Specificity

The specificity of the biosensor is governed by the specificity of the enzyme, hence choice of the appropriate oxidase enzyme enables a wide variety of analytes to be studied. As this is a new technique, there is relatively little published work on the use of the Sycopel Microdialysis Biosensor (see references).

It has been used to measure glycerol, ascorbate and glutamate in vitro and in vivo, but has also shown the ability to measure glucose, acetyl choline⁹ and lactate¹⁰ 'on the bench'.

Examples of some of the commercially available enzymes that could be used are given in the table below.

Typical Measuring Values for a Microdialysis Biosensor

The operating characteristics of a microdialysis biosensor depend on a number of factors. The sensitivity will depend upon whether or not the platinum has been coated in the protective poly(o-phenylenediamine) coat. The coat can cause a small decrease in the rate at which hydrogen peroxide reaches the elctrode, with a consequent small fall in sensitivity. The linear range of response of the sensor will depend on the K_ME (apparent K_M) of the enzyme system. Enzymes that saturate at low K_M will have a smaller linear range than enzymes with larger K_M.

The following values are taken from one biosensor with 2 mm of exposed platinum and with 0.05 units/µL of glutamate oxidase.

References.
Specifications subject to change without notice.
Not responsible for typographical errors.

Phymed Scientific, dba Biotech Products, is a Midwest United States' manufacturer's representative and distributor of biomedical instrumentation and devices to the biomedical market. Our mission is to provide high quality apparatus and instruments especially to those researchers working in the areas of neuroscience and cardiovascular research.

We welcome your inquiries and look forward to being of service to you and your laboratory needs.