Biochemical Sensors

A biosensor is an analytical device that can convert a biological reaction into an electrical (voltage) signal. Biosensors consist of a biological element (e.g. enzyme, whole cell, etc) that is immobilized on a membrane and connected to a transducer (probe). The reaction occurs at the membrane where the substrate of interest is converted to a product that causes an electrical response. This response is measured by the transducer and then amplified, processed and displayed using a meter and PowerLab data acquisition system.

Potentiometric Biosensors
Potentiometric biosensors use ion selective electrodes to measure a biological reaction. A simple example is the glass pH electrode. As a biosensor it consists of an immobilized enzyme membrane surrounding the thin glass membrane of the pH probe. The biological reaction occurs at the enzymatic membrane and generates hydrogen ions (H⁺). The H⁺ ions diffuse and bind to a glass membrane, thereby generating an electrical potential that is proportional to the substrate concentration. A separate reference electrode (e.g. Ag/AgCl) is also required. Most pH meters with an analog output are suitable for use with a PowerLab data acquisition system.

Note: More information is available from the pH and Ionic Concentrations application page.

Amperometric Biosensors & Mass Sensors
Amperometric biosensors, mass sensors and associated amplifiers/meters can be used with a PowerLab data acquisition system provided that they have a suitable analog output (± 10V).

LabChart
LabChart software (for Windows and Macintosh) combines the familiar simplicity of a traditional strip chart recorder with the powerful analysis features of a digital acquisition system. LabChart software and a PowerLab data acquisition unit provide data integrity, easy selection of hardware settings, powerful online and offline analysis, procedure automation, seamless extraction of experimental data and flexible display options. Acquisition and analysis capabilities can be further increased with LabChart Extensions and LabChart Modules. LabChart Modules are available as part of LabChart Pro and LabChart Extensions are free for download from the website for existing LabChart users.


GLP and 21 CFR Part 11
For those researchers working within a laboratory requiring GLP and 21 CFR Part 11 compliance the GLP Client and GLP Server are available for use with LabChart (Windows only) and PowerLab data acquisition systems. For more information, visit the Good Laboratory Practice application page or contact your nearest ADInstruments representative.

Signal Conditioners
ML165 pH Amp
This amplifier is a dual front-end suitable for pH, ion selective, and temperature measurements in solution recordings. It is supplied with a RTD Temperature Probe. It can be used with:

• MLA060 Redox Electrode
• MLA042 pH Electrode
• MI-405 Miniature Glass Electrode for pH
• MI-409 Miniature Reference Electrode

Biosensors

• MLA060 Redox Electrode - The combination Redox Electrode is suitable for operation from 0 to 60°C. The double junction is easily cleaned, making it suitable for biological samples.
• MLA042 pH Electrode - The combination pH Electrode operates from 0 to 60°C and for a pH of 0 to 14. The double junction is easily cleaned and therefore the electrode is suitable for biological samples, in particular those of low ionic strength.
• MI-405 Miniature Glass Electrode for pH - This miniature electrode has many applications in general purpose analyses and in microchemical studies. It requires the use of an external reference electrode such as the MI-409 Miniature Reference Electrode.
• MI-409 Miniature Reference Electrode - This electrode is designed for use with any pH or ion selective electrodes and used with the ML165 pH Amp. It has an internal Ag-AgCl internal reference electrode with KCl filling solution.

Quantitative on-line monitoring of hippocampus glucose and lactate metabolism in organotypic cultures using biosensor technology

J B Gramsbergen, G Leegsma-Vogt, K Venema, J Noraberg and J Korf, Journal of Neurochemistry, 399-408, 2003

Organotypic hippocampal slice cultures were prepared from Wistar rats at post-natal day 7 and grown by the static interface culture method………….. In this study we cultured the slices individually on 12-mm semiporous membrane inserts in a 24-well culture tray (Corning Costar, Corning, NY, USA). After 3–4 days in vitro, culture medium, composed of 50% Opti-MEM, 25% horse serum and 25% Hanks balanced salt solution (all from Gibco Brl, Life Technologies Ltd, Paisley, Scotland) supplemented by D-glucose (25 mM final concentration; Merck, Darmstadt, Germany), was replaced by chemically defined, serum-free Neurobasal medium (Gibco Brl) with a glucose concentration of 25 mM and supplemented with glutamine (1 mM; Sigma, Vallensbaek Strand, Denmark) and 2% B27 supplement (Gibco Brl)…….After 3–4 weeks growth and maturation in this medium, the slice culture was transferred to the perfusion device for monitoring of glucose and lactate. Tissue chamber for slice cultures A syringe pump (PHD 2000 Infusion/Withdraw; Harvard Apparatus, Inc., Holliston, MA, USA) maintained a pre-set flow of medium (0.5–1 µL/min) through a microperfusion chamber which, via a membrane, was in direct contact with the slice culture. This chamber consisted of a plastic holder (forming the floor), a 50-µm thick spacer with a diamond-shaped hole, an inlet and an outlet at the outer corners of the diamond-shaped space and the semiporous membrane of a culture plate insert (Millicell CM; hydrophilic polytetrafluoroethylene (PTFE), pore size 0.4 µm, insert size 12 mm; Millipore Corporation, Bedford, MA, USA) placed on top of it. The dead volume of this microperfusion chamber was approximately 5 µL. The membrane of the insert served as tissue support of the slice culture and allowed exchange of substrates and metabolites with the perfusion medium, whereas the top of the slice culture remained in direct contact with ambient air (or any other gas mixture). In this way each slice culture could be easily transferred from the tissue incubator to the perfusion/monitoring device on its own membrane insert. Air and medium temperature was controlled (36ºC) by the oven of the electrochemical detector. On-line monitoring technique On-line monitoring of glucose and lactate in the perfusate of single hippocampal slice cultures was done using enzyme-based FIA…………..A carrier solution of ferrocene phosphate-buffered saline [137 mM NaCl, 2.7 mM KCl, 8 mM Na2HPO4, 2.5 mM KH2PO4 (all from Merck), 0.5 mM ferrocenemonocarboxylic acid (Lancaster Synthesis, Morecambe, UK), 0.1% vol. Kathon CG (Rhom and Haas, Croydon, UK) in milliQ water, adjusted to pH 7.4 with NaOH, filtered (OE66 membrane filter, 0.2 µm; Schleicher and Schuell, Dassel, Germany) and degassed with helium] was pumped (0.5 mL/min) through the glucose and lactate sensors using an HPLC pump (LC-10AD; Shimadzu Corporation, Kyoto, Japan). Medium samples were injected into the FIA system at pre-set time intervals (e.g. 1 min) using an automatic injection Vici Cheminert C4 valve with a 20-nL internal loop (Vici-Valco Instruments, Houston, TX, USA) and split (1 : 1) to allow simultaneous flow of sample through the glucose and lactate sensors, which were kept at 36ºC. The sensors consisted of sandwich-type enzyme reactors, containing an oxidase (glucose oxidase, approximately 200 U, EC1.1.3.4 or lactate oxidase, approximately 10 U) and horseradish peroxidase (approximately 200 U, EC1.11.1.7) (all enzymes from Roche, Mannheim, Germany) and an electrochemical flow cell (VT03; Antec Leyden, Zoetermeer, the Netherlands; glassy carbon working electrode kept at 0.00 mV vs. Ag/AgCl reference electrode) connected to a potentiostate (Decade; Antec Leyden). The currents (nA) were simultaneously recorded on a double-pen recorder (BD 112; Kipp en Zonen, Zoetermeer, the Netherlands) and on a MacIntosh computer using a PowerLab/4 SP data-recording unit (ADInstruments Pty Ltd, Castle Hill, NSW, Australia) with Chart/Peaks software (ADInstruments).