From Enzymatic Dopamine Biosensors to OECT Biosensors of Dopamine

Abstract

Neurotransmitters are an important category of substances used inside the nervous system, whose detection with biosensors has been seriously addressed in the last decades. Dopamine, a neurotransmitter from the catecholamine family, was recently discovered to have implications for cardiac arrest or muscle contractions. In addition to having many other neuro-psychiatric implications, dopamine can be detected in blood, urine, and sweat. This review highlights the importance of biosensors as influential tools for dopamine recognition. The first part of this article is related to an introduction to biosensors for neurotransmitters, with a focus on dopamine. The regular methods in their detection are expensive and require high expertise personnel. A major direction of evolution of these biosensors has expanded with the integration of active biological materials suitable for molecular recognition near electronic devices. Secondly, for dopamine in particular, the miniaturized biosensors offer excellent sensitivity and specificity and offer cheaper detection than conventional spectrometry, while their linear detection ranges from the last years fall exactly on the clinical intervals. Thirdly, the applications of novel nanomaterials and biomaterials to these biosensors are discussed. Older generations, metabolism-based or enzymatic biosensors, could not detect concentrations below the micro-molar range. But new generations of biosensors combine aptamer receptors and organic electrochemical transistors, OECTs, as transducers. They have pushed the detection limit to the pico-molar and even femto-molar ranges, which fully correspond to the usual ranges of clinical detection of human dopamine in body humors that cover 0.1 ÷ 10 nM. In addition, if ten years ago the use of natural dopamine receptors on cell membranes seemed impossible for biosensors, the actual technology allows co-integrate transistors and vesicles with natural receptors of dopamine, like G protein-coupled receptors. The technology is still complicated, but the uni-molecular detection selectivity is promising.

Keywords: FET; OECT; aptamers; biosensors; dopamine.

Figure 1

Different sensitive nanomaterial-modified electrodes for dopamine detection by oxidation (reprinted from [32] with permission from MDPI).

Figure 2

The configuration of (a) OFET, (b) OFET with extended gate, (c) EGOFET, (d) OECT.

Figure 3

The initial receptor structure with anchored Aptamer1 strand on gold electrode (left side), and the assembling in the Aptamer1/Dopamine/Aptamer2 sandwich, after DA binding by a second split blue-labeled Aptamer2 (Reproduced from [117] with MDPI permission).

Figure 4

(a) The functional OECT structure; (b) the output static characteristics measured in the “on” state at different gate voltages; (c) the transfer static characteristics measured at V_DS = −50 mV in absence of DA in the tested solution and at a minimum concentration defining LOD of 0.5 fM; (d) deviations of the transfer characteristics with different shift voltage, proportional to the DA concentration ranging from 10 pM to 10 nM (Reproduced from [117] with MDPI permission).

Figure 5

The OECT symbol and a biasing network with a sole V_DD source for an OECT transistor.