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Nanomaterial-modified detection systems represent a chief driver towards the adoption of electrochemical methods, since nanomaterials enable functional tunability, ability to self-assemble, and novel electrical, optical and catalytic properties that emerge at this scale. This results in tremendous gains in terms of sensitivity, selectivity and versatility. We review the electrochemical methods and mechanisms that may be applied to the detection of neurological drugs. We focus on understanding how specific nano-sized modifiers may be applied to influence the electron transfer event to result in gains in sensitivity, selectivity and versatility of the detection system. This critical review is structured on the basis of the Anatomical Therapeutic Chemical (ATC) Classification System, specifically ATC Code N (neurotransmitters). Specific sections are dedicated to the widely used electrodes based on the carbon materials, supporting electrolytes, and on electrochemical detection paradigms for neurological drugs and neurotransmitters within the groups referred to as ATC codes N01 to N07. We finally discuss emerging trends and future challenges such as the development of strategies for simultaneous detection of multiple targets with high spatial and temporal resolutions, the integration of microfluidic strategies for selective and localized analyte pre-concentration, the real-time monitoring of neurotransmitter secretions from active cell cultures under electro- and chemotactic cues, aptamer-based biosensors, and the miniaturization of the sensing system for detection in small sample volumes and for enabling cost savings due to manufacturing scale-up. The Electronic Supporting Material (ESM) includes review articles dealing with the review topic in last 40 years, as well as key properties of the analytes, viz., pKa values, half-life of drugs and their electrochemical mechanisms. The ESM also defines analytical figures of merit of the drugs and neurotransmitters. The article contains 198 references in the main manuscript and 207 references in the Electronic Supporting Material.FigureᅟElectronic supplementary materialThe online version of this article (doi:10.1007/s00604-014-1308-4) contains supplementary material, which is available to authorized users.

Neuropeptides are vital to the transmission and modulation of neurological signals, with Neuropeptide Y (NPY) and Orexin A (OXA) offering diagnostic information on stress, depression, and neurotrauma. NPY is an especially significant biomarker, since it can be noninvasively collected from sweat, but its detection has been limited by poor sensitivity, long assay times, and the inability to scale-down sample volumes. Herein, we apply electrokinetic preconcentration of the neuropeptide onto patterned graphene-modified electrodes in a nanochannel by frequency-selective dielectrophoresis for 10 s or by electrochemical adsorptive accumulation for 300 s, to enable the electrochemical detection of NPY and OXA at picomolar levels from subnanoliter samples, with sufficient signal sensitivity to avoid interferences from high levels of dopamine and ascorbic acid within biological matrices. Given the high sensitivity of the methodology within small volume samples, we envision its utility toward off-line detection from droplets collected by microdialysis for the eventual measurement of neuropeptides at high spatial and temporal resolutions.

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We report on a competitive electrochemical detection system that is free of wash-steps and enables the real-time monitoring of adenosine triphosphate (ATP) in a quantitative manner over a five-log concentration range. The system utilizes a recognition surface based on ATP aptamer (ATPA) capture probes pre-bound to electro-active Flavin adenine dinucleotide (FAD) molecules, and a signaling surface utilizing graphene (Gr) and gold nanoparticle (AuNP) modified carbon paste electrode (Gr-AuNP-CPE) that is optimized to enhance electron transfer kinetics and signal sensitivity. Binding of ATP to ATPA at the recognition surface causes the release of an equivalent concentration of FAD that can be quantitatively monitored in real-time at the signaling surface, thereby enabling a wide linear working range (1.14 ×10−10–3.0×10−5M), a low detection limit (2.01×10−11M using graphene and AuNP modified glassy carbon), and fast target binding kinetics (steady-state signal within 12 minutes at detection limit). Unlike assays based on capture probe-immobilized electrodes, this double-surface competitive assay offers the ability to speed-up target binding kinetics by increasing the capture probe concentration, with no limitations due to intermolecular coulombic interactions and non-specific binding. We utilize the real-time monitoring capability to compute kinetic parameters for target binding and to make quantitative distinctions on degree of base-pair mismatch through monitoring target binding kinetics over a wide concentration range. Based on simplicity of the assay chemistry and the quantitative detection of ATP within fruit and serum media, as demonstrated by comparison of ATP levels against those determined using a standard HPLC-UV absorbance method, we envision a versatile detection platform for applications requiring real-time monitoring over a wide target concentration range.