Abstract
Dopamine (DA) is an important neurotransmitter responsible for the functions and activities of multiple systems in human. Electrochemical detection of DA has the advantages of fast analysis and cost-effectiveness, while a regular electrode probe is restricted to laboratory use because the probe size is too large to be suitable for an in vivo or in vitro analysis. In this study, we have developed porphyrin-based metal organic framework (MOF525) and poly(3,4-ethylenedioxythiophene) (PEDOT)-based composites to modify microelectrode for DA detection. Two types of PEDOT monomers with different functional groups were investigated in this study. By varying the monomer ratios, electrolyte concentrations, and electropolymerization temperature, it was found that the PEDOT monomer containing carboxylic group facilitated the formation of regular morphology during the electropolymerization process. The uniform morphology of the PEDOT promoted the electron transmission efficiency in the same direction, while the MOF525 provided a large reactive surface area for electrocatalysis of DA. Thus, the MOF525/PEDOT composite improved the sensitivity-to-noise ratio of DA signaling, where the sensitivity reached 11 nA/μM in a good linear range of 4–100 µM. In addition, porphyrin-based MOF could also increase the selectivity to DA against other common clinical interferences, such as ascorbic acid and uric acid. The as-synthesized microelectrode modified with MOF525/PEDOT in this study exhibited great potential in real time analysis.
Highlights
Dopamine (DA) is a crucial neurotransmitter of catecholamine family that is produced in adrenal glands, substantia nigra, ventral tegmental area, and hypothalamus [1]
After hydrolysis of EDOT-Ph-COOEt, it was found that the peak at 1.42 ppm disappeared in the 1 H-NMR spectrum, and the peak intensities between 4.36 and 4.43 ppm were greatly reduced (Figure 1b). These results indicated that EDOT-Ph-COOEt was successfully hydrolyzed to EDOT-Ph-COOH, which would be used as one of the monomers in this study
The PEM modified microelectrode did not show a significant oxidation peak, while the MOF525/PEM modified microelectrode showed a moderate oxidation peak at 0.32 V. These results proved that redox active MOF525 can provide the reactive area for electrocatalysis of DA
Summary
Dopamine (DA) is a crucial neurotransmitter of catecholamine family that is produced in adrenal glands, substantia nigra, ventral tegmental area, and hypothalamus [1]. Conventional detection methods of dopamine include chromatography, fluorimetry, chemiluminescence, mass spectrometry, and capillary electrophoresis [7,8,9,10,11] These methods are mature and known for high sensitivity and selectivity, long analysis time and complex equipment setup limit their in vivo or in vitro measurements of the DA concentration due to the transient nature of release and uptake by living cells [12]. Biosensors modified with tyrosinase immobilization have been successfully used in dopamine determination in a biological environment in the presence of ascorbic acid and uric acid [14]. Practical applications of such biosensors are limited by their short lifetime and poor reproducibility [15,16,17]. Chemical sensors modified with a wide range of materials such as carbon-based materials [18,19,20], ionic liquid composites [21,22], metal/semiconductors [23,24,25], and organometallic polymers [26,27] are able to provide similar detection limits in comparison with biosensors, and enable the detection of DA in the presence of interfering compounds mimicking biological systems
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