Highly sensitive pork meat detection using copper(ii) tetraaza complex by electrochemical biosensor

Abstract

Three copper(ii) tetraaza complexes [Cu(ii)LBr]Br (1a), [Cu(ii)L(CIO₄)](CIO₄) (2a) and [Cu(ii)L](CIO₄)₂ (2b), where L = 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-7,14-diene were prepared and confirmed by FTIR, ¹HNMR and ¹³CNMR. The binding interaction of complex (1a, 2a, 2b) with calf thymus DNA (CT-DNA) was investigated using UV-vis absorption, luminescence titrations, viscosity measurements and molecular docking. The findings suggested that complex 1a, 2a and 2b bind to DNA by electrostatic interaction, and the strengths of the interaction were arranged according to 2b > 1a > 2a. The differences in binding strengths were certainly caused by the complexes' dissimilar charges and counter anions. Complex 2b, with the biggest binding strength towards the DNA, was further applied in developing the porcine sensor. The developed sensor exhibits a broad linear dynamic range, low detection limit, good selectivity, and reproducibility. Analysis of real samples showed that the biosensor had excellent selectivity towards the pork meat compared to chicken and beef meat.

Scheme 1. Synthesis of tetraaza ligand 1 and 2 and copper(ii) tetraaza complexes 1a, 2b and 2b.

Fig. 1. The conceptual scheme of the developed biosensor.

Fig. 2. The binding study evaluations using viscosity and computational study (a) effects of the increasing amount of 1a, 2a, and 2b complexes on the relative viscosity of CT-DNA (b–d) molecular docked structures of the complex with DNA dodecamer duplex of sequence d(CGCGAATTCGCG)₂ (PDB 1D: 1BNA). (b) Complex 1a, (c) complex 2a, (d) complex 2b.

Fig. 3. Layers analysis of the modified SPCE (a) the differential pulse voltammogram response of each self-assembled monolayer (b) the impedance spectroscopy of before and after DNA hybridization in potassium ferricyanide solution (Fe(CN)₆^3−/4−) 0.5 mM at 5 mV s⁻¹ scan rate (c) the infrared spectrum of the modified biosensor (d) the reaction scheme of MPA/EDC/NHS/Probe.

Fig. 4. Performance of the biosensor and real sample analysis (a) the linear response range between 1 × 10⁻¹³ M–1 × 10⁻⁸ M and the dynamic range of the porcine DNA biosensor. (b) Reproducibility of the porcine DNA biosensor at concentrations of 1 × 10⁻² μM and 1 × 10⁻⁷ μM. (c) Selectivity of the porcine DNA biosensor based on complex 2b as redox indicator toward the determination of probe DNA only, complementary DNA, beef DNA and chicken DNA at 1 × 10⁻² μM. (d) Shelf life of the porcine DNA biosensor at the concentration of 1 × 10⁻² μM store at 4 °C (e) A comparative analysis of the response of the constructed porcine DNA biosensor with extracted DNA from pork, chicken and beef meat.