l-lactate measures in brain tissue with ceramic-based multisite microelectrodes

A newly developed multisite array microelectrode for in vivo measurements of l-lactate is presented. The resulting microelectrode is composed of three functional layers. First, Nafion is used to repel interfering electroactive anions, such as ascorbate. Second, l-lactate oxidase immobilized onto the recording sites is used to convert l-lactate to hydrogen peroxide. The H2O2 produced is proportional to l-lactate concentrations and is quantified at the platinum recording sites. Third, a layer of polyurethane is coated over the l-lactate oxidase to adjust the linear range of the microelectrode to one that is compatible with in vivo measurements. This layer reduces the amount of l-lactate that diffuses to the enzyme while not significantly limiting oxygen diffusion. The resulting l-lactate microelectrodes were linear to 20 mM (R2 = 0.997 ± 0.001) and beyond in some cases with detection limits of 0.078 ± 0.013 mM (n = 12). The selectivity and response time of these electrodes make them suitable for in vivo measurements in brain tissue. Self-referencing recordings may be utilized to further improve the selectivity of the recordings. However this is not necessary for most applications in the brain, because the resting and stimulated levels of dopamine (DA), norepinephrine (NE), and other potentially interfering cations are two to three orders of magnitude lower than that of in vivo l-lactate, which is in the millimolar range. Preliminary in vivo measures of l-lactate in the brain of anesthetized rats support that the microelectrodes are capable of measuring rapid endogenous changes in vivo.