Fluorescent carbon quantum dots have been used to determine when fresh mackerel have spoiled. The low-cost, selective and highly sensitive technique was developed by Tae Jung Park and colleagues at Chung-Ang University in South Korea, who say that their technique is better than existing methods at detecting certain harmful chemicals associated with food spoilage. Their approach could become an important tool for ensuring the safety and freshness of food.
As food spoils, it can produce a wide variety of harmful chemicals that can be difficult to detect. Spoiling mackerel, for example, gives off a colourless, odourless compound called histamine at levels that can trigger harmful allergic reactions including rashes, vomiting and diarrhoea. It can sometimes be difficult to identify spoiled fish based on their look and smell, so a practical way of monitoring histamine levels would be very useful. Unfortunately, current detection methods are either expensive and time-consuming, or are ineffective at targeting histamine over other chemicals.
To develop a more sophisticated approach to detection, Park and colleagues synthesized a batch of carbon quantum dots (CQDs). These are fluorescent nanoparticles that behave like artificial atoms and emit visible light when irradiated with ultraviolet light. The CQDs were then coated with a compound called NAC, which is then coated with a peptide molecule called Hisp3.
Because of an effect called fluorescence quenching, the presence of Hisp3 reduces the amount of light emitted by the CQDs. However, Hisp3 bonds more strongly to histamine than it does to NAC, which means that exposure to histamine will remove Hisp3 from the CQDs – restoring the fluorescence of the CQDs
In their experiments, Park and colleagues showed how the intensity of this fluorescence was highly sensitive to histamine levels; accurately detecting concentrations ranging from 0.1 to 100 parts-per-million. In addition, the technique is highly selective to histamine, meaning CQD fluorescence was not restored when molecules with similar structures as histamine were introduced.
Physics and food: a multidisciplinary melting pot
The team says that its detection method has a greatly improved performance compared with existing techniques. If applied to mackerel on supermarket shelves, the CQD/Hisp3 mixtures could provide a convenient way for consumers to gauge quality and freshness of the fish, they claim.
Park’s team now plans to expand its approach by identifying peptides that bind to other chemicals emitted by spoiling food. The team also points out that its technique could also be used to develop medical diagnostics.
The research is described in Biosensors and Bioelectronics.