Microelectrochemical sensors for in vivo brain analysis: an investigation of procedures for modifying Pt electrodes using Nafion^®

Abstract

Various Nafion ® coating procedures were examined in order to design a simple and reproducible coating method to maximise permselective characteristics, and thus eliminate signals from electroactive interferents, in sensors designed for direct in vivo measurements in the brain. Interferents investigated included ascorbic acid (AA), the principal endogenous electroactive interferent present in the brain, and uric acid. Application of the Nafion ® (5% commercial solution) using a thermally annealing procedure involving 5 pre-coats, and 2 subsequent dip-bake layers resulted in elimination of interferent signals. It also produced complete blocking of the signal for the neurotransmitter dopamine. The optimum time and temperature for annealing was found to be 5 min at 210 °C. An examination of shelf life over two weeks indicated negligible AA interference over this period. Preliminary investigations with respect to the potential use of these Nafion ® -modified Pt electrodes in the design of implantable, first generation, peroxide detecting biosensors indicated that the modified electrode had no effect on O 2 permeability but did produce a significant decrease in H 2 O 2 sensitivity. While this may preclude their use in biosensor development they may be more suitable for detection of gaseous neurochemicals such as nitric oxide.

Brain nitric oxide: Regional characterisation of a real-time microelectrochemical sensor

“…The other end of the wire acted as the active (disk) surface. The electrode was modified as previously described (Brown et al, 2009;Brown and Lowry, 2003;Finnerty et al, 2012).…”

“…500 M (Miele and Fillenz, 1996). It is imperative to confirm that the Nafion ® membrane has not degraded when placed in the in vivo environment and that the sensor exhibits similar selectivity characteristics to those recorded in vitro (Brown et al, 2009;Brown and Lowry, 2003). With its high concentration and ease of oxidation, ascorbate is probably the simplest molecule to detect and monitor in brain ECF using in vivo voltammetry techniques (Lowry and O'Neill, 2006;O'Neill et al, 1998).…”

“…This has also been highlighted recently by Garthwaite, who expressed a great need for a reliable method of directly measuring endogenously generated NO in tissues with the necessary sensitivity or spatial and temporal precision (Garthwaite, 2008). We have previously reported the in vitro (Brown et al, 2009;Brown and Lowry, 2003) and in vivo (Finnerty et al, 2012) characterisation of a Nafion ® -modified Pt sensor designed for real-time monitoring of brain extracellular NO. In vitro findings confirmed that the Nafion ® (5/2) sensor had a response time suitable for in vivo monitoring, linearity over the relevant concentration range for NO, freedom from protein and lipid fouling, and minimal interference from a variety of endogenous species, including ascorbic acid, dopamine and serotonin over physiologically relevant concentration ranges.…”

Nitric Oxide Signaling in the Medial Prefrontal Cortex is Involved in the Biochemical and Behavioral Effects of Phencyclidine

“…Such an activation is suggested to be essential for the behavioral effects of NMDA antagonists as local application of AMPA/kainate antagonists has been shown to block the effects of PCP and ketamine on stereotypy, locomotor activity, and working memory (Moghaddam et al, 1997;Takahata and Moghaddam, 2003). In addition, preliminary studies using in vivo voltammetry and NO-sensitive microsensors (Brown and Lowry, 2003) indicate that NO production is increased in the medial PFC following systemic PCP administration in rats (Lowry JP et al in collaboration, data not published). Tentatively, an NO dysregulation in this region could affect several neurotransmitter systems and thus contribute substantially to the behavioral effects of NMDA antagonists.…”

Calibration of NO sensors for in-vivo voltammetry: laboratory synthesis of NO and the use of UV?visible spectroscopy for determining stock concentrations

“…We have recently become interested in developing a new sensor for monitoring brain extracellular levels of NO. As a first step in this process we have developed a novel permselective membrane coating to eliminate interference signals [12], because in designing an in-vivo sensor one must maximise not only speed and sensitivity but also interference rejection of other endogenous electroactive species. This is particularly important for NO, because it is present at nanomolar concentrations and has a halflife of 2-6 seconds in vivo [13].…”