Synthesis of MOF525/PEDOT Composites as Microelectrodes for Electrochemical Sensing of Dopamine

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.

Keywords: biosensor; dopamine detection; electrocatalysis; electropolymerization; microelectrode; poly(3,4-ethylenedioxythiophene) (PEDOT).

Figure 1

¹H-NMR spectra of (a) EDOT-Ph-COOEt and (b) EDOT-Ph-COOH.

Figure 2

MOF525 characterizations by (a) nitrogen adsorption-desorption isotherms, (b) XRD, and (c) SEM.

Figure 3

Cyclic voltammetry (CV) traces of (a) unmodified microelectrode and (b) modified microelectrodes in the presence of 0- or 0.5-mM DA (scan rate: 30 mV/s).

Figure 4

(a) CV traces of bare and modified flat microelectrodes; SEM images of MOF525/PEM on the (b) Pt/Ir microelectrode and (c) flat electrode (inset: EDX of elemental distribution. Red: S (representing PEM), and green: Zr (representing MOF525)).

Figure 5

The SEM images of MOF525/PEM composites synthesized with various EDOT-MeOH/EDOT ratios: (a) 3:1; (b) 2:1; (c) 1:1; (d) 0.33:1; (e) 0.2:1; and (f) the CV traces of MOF525/PEM composites modified microelectrode synthesized under various EDOT-MeOH/EDOT ratios.

Figure 6

The SEM images of MOF525/PEM composites synthesized under: (a) 0.01 M; (b) 0.1 M; and (c) 0.2 M TBAP solution; and (d) the CV traces of MOF525/PEM composites modified microelectrode synthesized under various TBAP concentrations.

Figure 7

The SEM images of MOF525/PEM composites synthesized under: (a) 0.005 M; (b) 0.01 M; (c) 0.02 M TBAP solution at −42.5 °C; and (d) the CV traces of MOF525/PEM composites modified microelectrode synthesized under various TBAP concentrations at −42.5 °C.

Figure 8

The SEM images of (a) MOF525/PEpC; (b) high-resolution MOF525/PEpC; and (c) the CV traces of unmodified and PEpC-based microelectrodes.

Figure 9

Differential pulse voltammetry (DPV) curves of (a) MOF525/PEpC modified microelectrode in ABS (pH = 5) with DA concentrations from 4 to 100 µM (Inset: linear dependence of the peak current against DA concentration), (b) detection of AA, UA and DA, respectively, and (c) stability of MOF525/PEpC modified microelectrodes in 10 cycles.

Figure 9

Differential pulse voltammetry (DPV) curves of (a) MOF525/PEpC modified microelectrode in ABS (pH = 5) with DA concentrations from 4 to 100 µM (Inset: linear dependence of the peak current against DA concentration), (b) detection of AA, UA and DA, respectively, and (c) stability of MOF525/PEpC modified microelectrodes in 10 cycles.