A Sensitive and Accurate Electrochemical Sensor Based on Biomass-Derived Porous Carbon for the Detection of Ascorbic Acid

Abstract

Ascorbic acid (AA) is a vital biomarker for human metabolic processes, and many diseases are strongly linked to aberrant variations in its content. It is crucial to detect the levels of AA with sensitivity, speed, and accuracy. In this work, three-dimensional honeycomb-like porous carbons derived from discarded walnut (green) husks (DWGH-HCPCs) were synthesized using a process involving hydrothermal treatment, freeze-drying, and carbonization. The DWGH-HCPCs, with a high specific surface area of 419.72 m² g^-1, large pore volume of 0.35 cm³ g^-1 and high density of defective sites, are used to fabricate the electrochemical sensor for the detection of AA. The electrochemical performance of the DWGH-HCPC-modified glassy carbon electrode (GCE) (DWGH-HCPC/GCE) was investigated through chronoamperometry, differential pulse voltammetry, and cyclic voltammetry. Compared with the GCE, the DWGH-HCPC/GCE exhibits higher sensitivities (34.7 μA mM^-1 and 22.7 μA mM^-1), a wider linear range (10-1040 μM and 1040-3380 μM), and a lower detection limit (0.26 μM) for AA detection. Specifically, the real sample concentrations of AA in beverages and artificial urine were successfully identified by DWGH-HCPC/GCE. Additionally, the DWGH-HCPC/GCE demonstrated great feasibility in the simultaneous detection of AA, dopamine (DA), and uric acid (UA). Therefore, as a green, eco-friendly, and low-cost electrode modifier, DWGH-HCPCs have broad prospects in the development of electrochemical sensing platforms for food and medical applications.

Keywords: ascorbic acid; biomass; electrochemical sensor; porous carbon.

Scheme 1

Synthesis of DWGS-HCPCs for the amperometric determination of AA.

Figure 1

(A,B) SEM images of DWGS-HCPCs. (C) N₂ adsorption–desorption isotherm of DWGS-HCPCs. Inset: the pore size distribution of DWGS-HCPCs. (D) Raman spectrum of DWGS-HCPCs. (E) XRD pattern of DWGS-HCPCs. (F) FT-IR spectrum of DWGS-HCPCs.

Figure 2

CVs at the GCE (a) and DWGS-HCPC/GCE (b) in 5 mM K₃[Fe(CN)₆] containing 0.1 M KCl. Scan rate: 10 mV s⁻¹.

Figure 3

(A) CVs at the GCE (a) and DWGS-HCPC/GCE (b) for 3 mM AA. Dotted lines: background responses. Scan rate: 10 mV s⁻¹. Electrolyte: N₂-saturated 0.1 M pH 7.0 PBS. (B) Current vs. time curves at the GCE (c) and DWGS-HCPC/GCE (d) with continuous increase of the amount of AA. Inset: corresponding calibration curves of AA at the GCE (e) and DWGS-HCPC/GCE (f). (C) Current vs. time curve at the DWGS-HCPC/GCE with the addition of 100 μM AA, 150 μM DA, 100 μM UA, 100 μM CA and 1 mM GLU. (D) CVs for 6 mM AA (g), 3 mM DA (h) and 6 mM UA (i). Electrolyte: N₂-saturated 0.1 M pH 7.0 PBS. Scan rate: 10 mV s⁻¹. (E) The current vs. time curves with 300 μM AA at the GCE (j) and DWGS-HCPC/GCE (k). (F) The current vs. time curves with the real sample and three equal amounts of standard AA solutions (100 μM, 100 μM, 100 μM) at DWGS-HCPC/GCE. Applied potential in (B,C,E,F): 0.015 V. Electrolyte in (B,C,E,F): vigorously magnetically stirred N₂-saturated 0.1 M pH 7.0 PBS.

Figure 4

(A) CVs at the GCE (a) and DWGS-HCPC/GCE (b) for 6 mM AA, 3 mM DA and 6 mM UA. Scan rate: 10 mV s⁻¹. (B) DPVs at the GCE (c) and DWGS-HCPC/GCE (d) for 6 mM AA, 3 mM DA and 6 mM UA. Electrolyte in A and B: N₂-saturated 0.1 M pH 7.0 PBS.