A Novel Electrochemical Sensor Based on Pd Confined Mesoporous Carbon Hollow Nanospheres for the Sensitive Detection of Ascorbic Acid, Dopamine, and Uric Acid

Abstract

In this study, we designed a novel electrochemical sensor by modifying a glass carbon electrode (GCE) with Pd confined mesoporous carbon hollow nanospheres (Pd/MCHS) for the simultaneous detection of ascorbic acid (AA), dopamine (DA), and uric acid (UA). The structure and morphological characteristics of the Pd/MCHS nanocomposite and the Pd/MCHS/GCE sensor are comprehensively examined using SEM, TEM, XRD and EDX. The electrochemical properties of the prepared sensor are investigated through CV and DPV, which reveal three resolved oxidation peaks for AA, DA, and UA, thereby verifying the simultaneous detection of the three analytes. Benefiting from its tailorable properties, the Pd/MCHS nanocomposite provides a large surface area, rapid electron transfer ability, good catalytic activity, and high conductivity with good electrochemical behavior for the determination of AA, DA, and UA. Under optimized conditions, the Pd/MCHS/GCE sensor exhibited a linear response in the concentration ranges of 300-9000, 2-50, and 20-500 µM for AA, DA, and UA, respectively. The corresponding limit of detection (LOD) values were determined to be 51.03, 0.14, and 4.96 µM, respectively. Moreover, the Pd/MCHS/GCE sensor demonstrated outstanding selectivity, reproducibility, and stability. The recovery percentages of AA, DA, and UA in real samples, including a vitamin C tablet, DA injection, and human urine, range from 99.8-110.9%, 99.04-100.45%, and 98.80-100.49%, respectively. Overall, the proposed sensor can serve as a useful reference for the construction of a high-performance electrochemical sensing platform.

Keywords: Pd/MCHS; and uric acid; ascorbic acid; dopamine; electrochemical sensor.

Figure 1

(a) SEM (inset: size distribution), (b) TEM, (c) HRTEM, and (d–g) elemental mapping images of Pd/MCHS nanocomposite.

Figure 2

XRD pattern of Pd/MCHS nanocomposite.

Figure 3

(a) XPS survey spectra of Pd/MCHS nanocomposite and high-resolution spectra of (b) C 1s, (c) N 1s, and (d) Pd 2p.

Figure 4

CV (a) and EIS (b) curves of GCE and Pd/MCHS GCE sensor in 0.1 M of KCl solution containing 5 mM [Fe(CN)₆]^3−/4−: (i) bare GCE; (ii) Pd/MCHS/GCE sensor. (c) CV curves of 1000 µM AA (ii), 40 µM DA (iii), 80 µM UA (iv), and mixed solution of 1000 µM AA, 40 µM DA, 80 µM UA in 0.1 M PBS (pH 3.0) at GCE (i) and Pd/MCHS/GCE sensor (v).

Figure 5

Electrochemical response of AA, DA, and UA on the Pd/MCHS/GCE sensor.

Figure 6

CV curves of GCE (a) and Pd/MCHS/GCE sensor (c) in 0.1 M of KCl solution containing 1 mM [Fe(CN)₆]^3−/4−. Linear relationship between the peak current (Ip) and the square root of the scan rate of GCE (b) and Pd/MCHS/GCE sensor (d).

Figure 7

Effect of supporting electrolyte type on the sensor response: (i) PBS, (ii) citric acid-sodium citrate buffer solution, (iii) Britton–Robinson (B–R) solution, (iv) ABS, and (v) glycine-hydrochloric acid buffer solution.

Figure 8

(a) CV curves for the oxidation of AA (1000 μM), DA (40 μM), and UA (80 μM) on the Pd/MCHS/GCE sensor under various pH values ranging from 2.5 to 5 (a–f); (b) influence of pH on the oxidation peak potentials; (c) influence of pH on the oxidation peak current: (i) AA; (ii) DA, and (iii) UA.

Figure 9

(a) CV curves for the oxidation of AA (1000 μM), DA (40 μM), and UA (80 μM) on the Pd/MCHS/GCE sensor under different amounts of modifier ranging from 2 µL to 14 µL (a–g). (b) Effect of the amount of Pd/MCHS dispersion on the oxidation peak current: (i) AA, (ii) DA, and (iii) UA.

Figure 10

(a) CV curves of Pd/MCHS/GCE sensor in PBS (pH = 3.0, 0.1 M) containing 1000 μM AA, 40 μM DA, and 80 μM UA under scan rates from 10 to 250 mV·s⁻¹ (a–f). A linear relationship is observed between the oxidation peak current and scan rates: (b) AA, (c) DA, and (d) UA.

Figure 11

Selection of an analytical method for the detection of AA, DA, and UA.

Figure 12

DPV curves of Pd/MCHS/GCE sensor in PBS (pH = 3.0, 0.1 M) solution containing (a) 10 µM DA, 200 µM UA, and different con-centrations of AA from 500 to 9000 µM; (c) 1000 µM AA, 200 µM UA, and different concentrations of DA from 0.5–10 µM to 10–50 µM; (e) 1000 µM AA, 10 µM DA, and different concentrations of UA from 8 to 450 µM. A linear relationship is observed between Ip and the corresponding concentration (C) of (b) AA, (d) DA, and (f) UA.

Figure 13

(a) DPV curves of Pd/MCHS/GCE sensor in PBS (pH = 3.0, 0.1 M) solution containing 300–9000 µM AA, 2–50 µM DA, and 20–500 µM UA. A linear relationship is observed between the peak current (Ip) and concentration (C) of (b) AA, (c) DA, and (d) UA.

Figure 14

Stability of Pd/MCHS/GCE sensor toward 1000 μM AA (i), 40 μM DA (ii), and 80 μM UA (iii) for 10 days.

Figure 15

Selectivity of the Pd/MCHS/GCE sensor toward AA (a), DA (b), and UA (c) in the presence of different interfering species including KNO₃, Na₂SO₄, Ca(NO₃)₂, sucrose, citric acid, and glucose.

Figure 16

(a,c,e) Amperometric response of the sensor under sequential addition of vitamin C tablet, DA injection, and human urine samples, with the AA, DA and UA standard solutions being added three times. (b,d,f) A linear relationship is observed between ΔI and ΔC for vitamin C tablet, DA injection, and human urine samples on the Pd/MCHS/GCE sensor in PBS solution.

Scheme 1

Schematic diagram of the preparation of Pd/MCHS/GCE sensor for the detection of AA, DA, and UA.