Electrochemical Biosensors for Genetically Modified Crops Detection: Comparison
Please note this is a comparison between Version 4 by Beatrix Zheng and Version 3 by Beatrix Zheng.

Food safety issues are directly related to people's quality of life, so there is a need to develop efficient and reliable food contaminants’ detection devices to ensure the safety and quality of food. Electrochemical biosensors have the significant advantages of miniaturization, low cost, high sensitivity, high selectivity, rapid detection, and low detection limits using small amounts of samples, which are expected to enable on-site analysis of food products.

  • electrochemistry
  • biosensor
  • food safety
  • high sensitivity
  • high selectivity

1. Introduction

Safe food is a fundamental need for human health. Food safety can be affected by harmful substances such as allergens, pathogens (e.g., parasites, bacteria, viruses, prions, etc.), toxic agents or radioactive substances [1]. To safeguard human health, regulatory agencies such as the United States Food and Drug Administration (USFDA), the European Food Safety Authority (EFSA), and the Chinese Food and Drug Administration (CFDA) have imposed limits on the maximum levels of various contaminants in food. Nevertheless, in 2015, the World Health Organization (WHO) estimated that more than 600 million cases of foodborne diseases and 420,000 deaths are likely to occur each year, due to foodborne diseases caused by 31 foodborne pathogens at the global and subregional levels [2]. In agriculture, pesticides control pests and diseases in crops and ensure crop yield and quality. However, the overuse of pesticides can leave residues on crops that threaten human health through the food chain [3]. In addition, many food additive safety incidents had occurred around the world, such as aquatic products containing malachite green, red-hearted duck eggs dyed with Sudan red, melamine milk powder, industrial gelatin yogurt, etc., causing distrust and fear among people [4]. In order to screen and monitor the safety of food and prevent harm from food contaminants, a sensitive and reliable on-site analysis technology for food contaminants is highly desired. At present, there are many mature technologies for food safety detection, such as gas chromatography (GC), high-performance liquid chromatography (HPLC), gas chromatography-mass spectrometry (GC-MS), liquid chromatography-mass spectrometry (LCMS), and enzyme-linked immunosorbent assay (ELISA) [5]. However, most of these methods have disadvantages, such as complicated operation, high detection costs, long detection time, and high requirements for the samples tested, which are prone to false positives. To improve this situation, simple, rapid, economical, and portable electrochemical biosensors have attracted much attention. They could not only achieve high specificity and sensitivity, but also enable real-time monitoring in the field. The basic components and principles of an electrochemical biosensor for food contaminants detection are shown in Figure 1. It can convert the biological signal generated by the specific combination of the target analytes and the sensitive elements into an electrical signal, which is detected by the electrochemical methods. Finally, signal processing is performed by a computer to achieve quantitative or qualitative detection of food contaminants.
Figure 1. Schematic diagram of an electrochemical biosensor for food contaminants detection.
Common electrochemical methods include potentiometry, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), square wave voltammetry (SWV), and differential pulse voltammetry (DPV). Potentiometry is one of the simplest electrochemical techniques, characterized by a short response time, high selectivity, and extremely low detection limit [6]. Cyclic voltammetry is performed with the applied electrical potential oscillating over a range, while electrochemical impedance spectroscopy is usually performed at a fixed potential over a frequency range [7]. Square wave voltammetry is one of the most advanced and versatile members of the pulse voltammetry technology family, which has high analytical sensitivity and measurement speed [8]. Differential pulse voltammetry is more sensitive than conventional pulse, derivative conventional pulse, and cyclic voltammetry, and is suitable for studying the electrochemical process at the interface of metal-electrolyte solution [9]. Although electrochemical biosensors have not been widely used in food safety detection, their significant advantages deserve further investigation.

2. Genetically Modified Crops

Genetically Modified Crops (GMC) are plants in which genes with target traits are modified by genetic engineering techniques and then introduced into the genome of the recipient plant [10]. These exogenous genes are not only stably inherited in the offspring, but can also lead to beneficial traits such as insect resistance, herbicide resistance, and disease resistance in the crop. However, the biosafety of GMC has been controversial. Currently, the detection of GMC components mainly includes gene nucleic acid detection, protein detection, and metabolite detection [10]. although traditional detection methods such as PCR, ELISA, and HPLC are mature and reliable, they cannot meet the practical needs of high speed and low cost. Therefore, a fast, accurate, and low-cost field detection platform for transgenic crops is needed. The following is a discussion of electrochemical biosensors for GM soybean and maize detection (Table 1).
Marcos et al. [11] developed an electrochemical immunosensor for the detection of the transgenic soy protein CP4 EPSPS in soybean seeds, which does not require a labeling and signal amplification system. The sensor schematic is shown in Figure 2. The CP4 EPSPS antibodies were first modified on the gold electrodes, and the modified gold electrode was incubated in soy protein solutions of different concentrations at 37 °C for 30 min. After washing with ultrapure water, the electrodes were immersed in an electrochemical cell containing K4[Fe(CN)6] (1 mM) and LiCl (0.1 M) solutions. Electrochemical measurements were performed using SWV, and the peak current was linearly related to the concentration of soy protein in the range of 0.005–0.3 mg/mL, with a detection limit of 38 ng/mL CP4 EPSPS (below 0.00038% CP4 EPSPS). Since many countries recommend labeling foods containing higher than 0.9% CP4 EPSPS, the detection limit of this sensor meets the detection needs.
Figure 2. Schematic diagram of the electrochemical immunosensor for the detection of CP4 EPSPS (Adapted with permission from Ref. [11]. 2022, Marcos et al.).
Gao et al. [12] also established a label-free electrochemical sensing platform for the detection of transgenic soybean SHZD32-1. Soybean SHZD32-1 seeds were ground into powder and then genomic DNA samples were extracted by a CTAB-based method. GCDs modified on the SPCE surface can be attached to single-stranded DNA probes via Au-S bonds while improving the conductivity of the DNA sensor. After binding of the DNA probes to transgenic soybean DNA, the electron transfer resistance (Ret) on the sensor surface was quantified by the Ret response increased with logarithmic increase in target DNA concentration over a linear range of 1.0 × 10−7–1.0 × 10−13 M, with a detection limit of 3.1 × 10−14 M. This label-free sensor is made by inserting the SPCE into a handheld EI analyzer is conveniently fabricated, demonstrating simplicity of construction and operation, requiring no additional indicators or cumbersome procedures, and can be used in a friendly manner by non-specialists.
Cui et al. [13] developed a label-free electrochemical impedance gene sensor using gold carbon dots (GCDs) and an easy-to-use portable device. It consists of a handheld electrochemical impedance (EI) analyzer equipped with a coin-sized SPCE. Figure 3 shows the preparation process of this sensor, GCDs were used to modify a screen-printed carbon electrode and capture probes were immobilized by Au-S bonding. Transgenic maize sample DNA was extracted using a one-step extraction method with direct plant lysis buffer and amplified by recombinase polymerase amplification (RPA). The capture probes immobilized on the sensor were identical to the forward RPA primer. After the amplification products bound to the capture probes, the EI signal increased due to the formation of a biocomplex that hindered the interfacial electron transfer. The proposed genetic sensor combined with RPA can detect maize Ruifeng12-5 in a linear range of 0.10–5.0% with a detection limit of 0.10%, roughly calculated as 36 copies/µL based on the size of the maize haploid genome. The sensor device is simple to prepare and does not require expensive instruments or specialized personnel and has wide application prospects.
Figure 3.
Fabrication process of EI gene sensor based on GCD (Reprinted with permission from Ref.
. 2022, Cui et al.).


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