Detection of very small amounts of a chemical contaminant, virus or bacteria in food systems is an important potential application of nanotechnology. The exciting possibility of combining biology and nanoscale technology into sensors holds the potential of increased sensitivity and therefore a significantly reduced response-time to sense potential problems.
“Graphene oxide has potential applications in a variety of biological fields because of its unique characteristics, In addition, due to large absorption cross-sections and the non-radioactive electronic excitation energy transfer from a fluorophore to GO, GO has been employed to construct fluorescence resonance energy transfer (FRET) biosensors,” Professor Chuanlai Xu from the State Key Lab of Food Science & Technology, and Director, Joint Lab of Biointerface and Biodetection, JiangNan University, tells Nanowerk. Xu and his collaborators have developed a novel, rapid, and sensitive fluorescence sensor to detect BPA. The team reported their findings in ACS Applied Materials & Interfaces (“Building An Aptamer/Graphene Oxide FRET Biosensor for One-Step Detection of Bisphenol A”).
Schematic illustration of the biosensor for BPA based on the target-induced conformational change of the anti-BPA aptamer and the interactions between the FAM-ssDNA probe and GO. (Reprinted with permission by American Chemical Society) (click on image to enlarge)
Bisphenol A (BPA) is a chemical produced in large quantities for use primarily in the production of polycarbonate plastics and epoxy resins. Polycarbonate plastics have many applications including use in some food and drink packaging, e.g., water bottles, food packaging materials, impact-resistant safety equipment, and medical devices. Epoxy resins are used as lacquers to coat metal products such as food cans, bottle tops, and water supply pipes. Some research has shown that BPA can seep into food or beverages from containers that are made with BPA. Exposure to BPA is a concern because of possible health effects of BPA on the brain, behavior and prostate gland of fetuses, infants and children. While the actual toxicity of BPA is still debated, the direct measurement of BPA is difficult because of the weak response given by conventional electrochemical sensors, and current optical analysis methods are susceptible to the influence of interfering substances. The novel BPA biosensor developed by the Chinese team now provides a method for the rapid detection and risk assessment of BPA with high sensitivity and selectivity. Aptamers – single-stranded oligonucleotides that can be generated for a target molecule with high affinity – are highly suitable receptors for the selective and high-proficiency detection of a wide range of molecular targets. For instance, researchers have previously shown that aptamer-functionalized graphene can detect mercury in mussels. “Our sensor is based on water-soluble and well-dispersed graphene oxide, which was used as the fluorescence quenching agent, and a specific anti-BPA aptamer labeled by FAM (FAM-ssDNA),” Xu explains. “In the absence of BPA, FAM-ssDNA can be adsorbed onto the GO surface, leading to FRET between GO and FAM-ssDNA. Subsequently, the fluorescence can be quenched quickly. Conversely, BPA can interact with FAM-ssDNA and switch its conformation to prevent the adsorption of GO, resulting in fluorescence recovery in the sensing system.” Under different concentrations of BPA, based on the target-induced conformational change of anti-BPA aptamer and the interactions between the fluorescently modified anti-BPA aptamer (FAM-ssDNA) and GO, the team’s experimental results show that the intensity of the fluorescence signal was changed. They say that these results are comparable to traditional ELISA as well as other instrument-based methods, suggesting that this novel sensor might find applications in food safety testing and the monitoring of industrial production processes. The researchers suggest that their GO-based assay offers several advantages:
- Fluorescent sensors tend to have higher sensitivity compared to most of the colorimetric sensors;
- The relationship between GO and FAM-ssDNA provide theoretical support for the experiment;
- GO can be easily chemically synthesized with large quantities. Besides, the method avoids the dual label of ssDNA with fluorophore and quencher units, which significantly lowers the detection cost.
By Michael Berger