Green Synthesis of Ni@PEDOT and Ni@PEDOT/Au (Core@Shell) Inverse Opals for Simultaneous Detection of Ascorbic Acid, Dopamine, and Uric Acid

Abstract

We demonstrate a water-based synthetic route to fabricate composite inverse opals for simultaneous detection of ascorbic acid (AA), dopamine (DA), and uric acid (UA). Our process involves the conformal deposition of poly(3,4-ethylenedioxythiophene) (PEDOT) and PEDOT/Au on the skeletons of Ni inverse opals via cyclic voltammetric scans (CV) to initiate the electropolymerization of 3,4-ethylenedioxythiophene (EDOT) monomers. The resulting samples, Ni@PEDOT, and Ni@PEDOT/Au inverse opals, exhibit a three-dimensional ordered macroporous platform with a large surface area and interconnected pore channels, desirable attributes for facile mass transfer and strong reaction for analytes. Structural characterization and material/chemical analysis including scanning electron microscope, X-ray photoelectron spectroscopy, and Raman spectroscopy are carried out. The sensing performances of Ni@PEDOT and Ni@PEDOT/Au inverse opals are explored by conducting CV scans with various concentrations of AA, DA, and UA. By leveraging the structural advantages of inverse opals and the selection of PEDOT/Au composite, the Ni@PEDOT/Au inverse opals reveal improved sensing performances over those of conventional PEDOT-based nanostructured sensors.

Keywords: Au nanoparticles; PEDOT; ascorbic acid; colloidal crystals; dopamine; electrochemical sensing; inverse opals; uric acid.

Figure 1

The SEM images for polystyrene (PS) colloidal crystals in cross-sectional view; (a) low magnification and (b) high magnification, as well as in top view; (c) low magnification and (d) high magnification.

Figure 2

The SEM images for Ni inverse opals in cross-sectional view; (a) low magnification and (b) high magnification, as well as in top view; (c) low magnification and (d) high magnification.

Figure 3

The cyclic voltammetry (CV) profiles for 3 cycles for the conformal deposition of (a) PEDOT and (b) PEDOT/Au on the skeletons of Ni inverse opals.

Figure 4

The cross-sectional SEM images for planar Ni@PEDOT films; (a) low magnification and (b) high magnification, Ni@PEDOT inverse opals; (c) low magnification and (d) high magnification, and Ni@PEDOT/Au inverse opals; (e) low magnification and (f) high magnification. The insets are their corresponding top-view images.

Figure 5

The Raman spectra for Ni@PEDOT and Ni@PEDOT/Au inverse opals, respectively.

Figure 6

The XPS spectra of (a) C(1s), (b) O(1s), (c) S(2p), (d) Ni(2p), and (e) Au(4f) for Ni@PEDOT and Ni@PEDOT/Au inverse opals, respectively.

Figure 7

The complex impedance spectra for planar Ni@PEDOT film, as well as Ni@PEDOT and Ni@PEDOT/Au inverse opals in 0.1 M phosphate-buffered saline (PBS).

Figure 8

The CV profiles for pristine Ni inverse opals in a) 0.1 M PBS and b) 0.1 M PBS containing 194 μM ascorbic acid (AA), 194 μM dopamine (DA), and 134.4 μM uric acid (UA).

Figure 9

The CV profiles for (a) planar Ni@PEDOT film, as well as (c) Ni@PEDOT and (e) Ni@PEDOT/Au inverse opals, respectively. The electrolyte is 0.1 M PBS containing various concentrations of AA (0–194 μM), DA (0–194 μM), and UA (0–134.4 μM). The exact compositions of individual electrolytes are listed in Table 3. The corresponding background-subtracted CV profiles are displayed in (b), (d), and (f), respectively.

Figure 10

The linear relations of anodic current (after the subtraction of capacitive current) as a function of the concentration of AA, DA, and UA for (a) planar Ni@PEDOT film, as well as (b) Ni@PEDOT and (c) Ni@PEDOT/Au inverse opals, respectively.