Enhancement of Electrochemical Detection of Gluten with Surface Modification Based on Molecularly Imprinted Polymers Combined with Superparamagnetic Iron Oxide Nanoparticles

Abstract

Novel molecularly imprinted polymers (MIPs) represent a selectively recognized technique for electrochemical detection design. This rapid and simple method prepared via chemical synthesis consists of a monomer crosslinked with an initiator, whereas low sensitivity remains a drawback. Nanomaterials can improve charge transfer for MIP surface modification in order to overcome this problem. SPIONs have semiconductor and superparamagnetic properties that can enhance carrier mobility, causing high sensitivity of electrochemical detection. In this work, surface modification was achieved with a combination of MIP and SPIONs for gluten detection. The SPIONs were synthesized via the chemical co-precipitation method and mixed with MIPs by polymerizing gluten and methyl methacrylate (MMA), presented as a template and a monomer. Magnetic MIP (MMIP) was modified on a carbon-plate electrode. The morphology of modified electrode surfaces was determined by scanning electron microscopy-energy-dispersive X-ray spectrometry. The performance of the MMIP electrode was confirmed by cyclic voltammetry, amperometry, and electrochemical impedance spectroscopy. The MMIP electrode for gluten detection shows a dynamic linear range of 5-50 ppm, with a correlation coefficient of 0.994 and a low detection limit of 1.50 ppm, which is less than the U.S. Food and Drug Administration requirements (20 ppm); moreover, it exhibits excellent selectivity, sensitivity, stability, and reproducibility.

Keywords: electrochemical analysis; gluten; magnetic molecularly imprinted polymers.

Figure 1

Schematic diagram of the MMIP–gluten electrode preparation and modeled electrode surface modification.

Figure 2

FE-SEM image of the MMIP–gluten electrode (a) and EDS images of iron(II) (b) and oxygen (c).

Figure 3

Electrochemical behaviors of MMIP-, MIP-, and NIP-modified electrodes analyzed via amperometry (a) and impedance spectroscopy (b). EIS circuit of the MMIP electrode (c).

Figure 4

Effect of the applied external magnetic field’s force on current (a) and resistance (b).

Figure 5

Amperometry responses of the MMIP-modified electrode in the detection of different gluten concentrations (a). The calibration curves of gluten, as detected by the MMIP-modified electrode (b).

Figure 6

Stability (a) and reproducibility (b) of the MMIP–gluten-modified electrode.

Figure 7

Current (a) and resistance response (b) of the gluten, as measured by the MMIP-modified electrode.

Figure 8

Current (a) and resistivity response (b) of the gluten in crackers.