Article pubs.acs.org/Langmuir
Fast-Scan Controlled-Adsorption Voltammetry for the Quantification of Absolute Concentrations and Adsorption Dynamics Christopher W. Atcherley,† Nicholas D. Laude,† Kate L. Parent, and Michael L. Heien* Department of Chemistry and Biochemistry, University of Arizona, 1306 East University Boulevard, Tucson, Arizona 85721, United States S Supporting Information *
ABSTRACT: Fast-scan cyclic voltammetry has depended on background subtraction to quantify small changes in neurotransmitter concentration. Because of this requirement, measurements of absolute concentrations using fast-scan cyclic voltammetry have been limited. Here we develop and characterize fast-scan controlled-adsorption voltammetry (FSCAV), which enables direct measurements of absolute concentrations in vitro without the use of flow injection to change the concentration. This enables probing the diffusioncontrolled adsorption dynamics of biogenic amines and other adsorbing species. An implicit finite-difference model of masstransport-limited adsorption was developed and is in agreement with experimental results. Optimization of FSCAV yielded a sensitivity of 81 ± 11 nA/μM for dopamine, corresponding to a limit of detection of 3.7 ± 0.5 nM. Through the combination of novel instrumentation and validated computer simulations, we show that FSCAV is an important measurement tool that can be used to determine absolute concentrations and study masstransport-limited adsorption.
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flow-injection analysis to replicate concentration changes.22 Furthermore, flow injection is a convective process which complicates comparisons to studies in diffusion-controlled environments such as nervous tissue. Here we present the development and characterization of a technique that extends the capabilities of FSCV by exploiting adsorption to quantify absolute neurotransmitter concentrations. This technique is termed fast-scan controlled-adsorption voltammetry (FSCAV) due to the precise control of voltammetric waveforms used in conjunction with a delay time to manipulate adsorption. Dopamine in Tris buffer was used as a model system for optimization of parameters affecting FSCAV and to demonstrate the analytical capabilities of the technique. An implicit finite-difference model was developed using COMSOL Multiphysics 4.3a to validate the results obtained from FSCAV experiments taking into account mass transport and adsorption equilibrium at the electrode surface. The analytes investigated exhibit different adsorption and masstransport properties which affect the response time of sensors. FSCAV is shown to be capable of measuring the absolute concentrations of biogenic amines (limit of detection
