NACL Sensors
Glutamate

Legend: Schematic representation of a Pt/PPD/GluOx biosensor for targeting ECF brain glutamate. The enzyme glutamate oxidase (GluOx) is immobilised in a polymer/protein (PPD/BSA) composite film electrosynthesised in situ on Pt microcylinders, which may be coated with other modifiers, e.g., lipid (PEA). The Pt surface, held at a high positive relative potential, oxidises electroactive species reaching it. Target analyte (Glu) reacts at the enzyme site to produce small hydrogen peroxide molecules that easily diffuse through the various coatings to yield the amperometric signal. Interference molecules, such as ascorbic acid (AA), must penetrate with difficulty the permselective membrane to be oxidised on the Pt.

References:

  • Ryan M.R., Lowry J.P. and O'Neill R.D. (1997) Biosensor for neurotransmitter L-glutamic acid designed for efficient use of L-glutamate oxidase and effective rejection of interference. Analyst, 122, 1419-1424.
  • McMahon C.P. and O'Neill R.D. (2005) A polymer-enzyme composite biosensor with high glutamate sensitivity and low oxygen dependence. Anal. Chem., 77, 1196-1199.

Legend: Pilot experiments (1998) showing the effects of a mild stressor (10-s tail pinch, TP) on the amperometric signals recorded in the striatum of a freely moving rat implanted with either a glutamate biosensor (Pt/PPD/GluOx) or a prototype H2O2 sensor (Pt/PPD/Albumin). The Pt/PPD/GluOx biosensor used recently in another pilot study (2001) that failed to detect glutamate changes associated with 10-s tail pinch, showed ca. 3-times lower in-vitro sensitivity to glutamate than the Pt/PPD/GluOx electrode used here. The calibration bar is for glutamate; the scale for the H2O2 sensor is ca. 10-times more sensitive (i.e., ~0.1 mM).

References:

  • Lowry J.P., Ryan M.R. and O'Neill R.D. (1998) Behaviourally induced changes in extracellular levels of brain glutamate monitored at 1-s resolution with an implanted biosensor. Anal. Commun., 35, 87-89.
  • Lowry J.P., Ryan M.R. and O'Neill R.D. (2001) Interference in biosensor detection of brain glutamate in vivo: possible role of endogenous ECF hydrogen peroxide. In Monitoring Molecules in Neuroscience (edited by O'Connor W.T., et al.), National University of Ireland, Dublin , pp. 70-71.