The concept of aptamers has been around since the early 1990s and has since attracted a lot of attention of research groups globally. Ioana Lock of KK Fine Foods Plc discusses their future impact on food analysis.
Safe food is a legal prerequisite and expected by consumers buying any type of product in a supermarket or at a restaurant. Consequently, manufacturers make the safety of their products a priority. This includes the effective control of microorganisms, allergens, adulterants and other contaminates such as pharmaceutical and veterinary residues, natural and chemical toxins, heavy metals and pesticides. This becomes an increasing challenge as population growth and climate change have a significant impact on the global food chain. There are many control systems in place for the safe production and manufacturing of food. Particularly for manufacturers, one part of these controls are the strict checks of raw materials used and GMP practices. The second part are the analytical results obtained through laboratories to check for contamination, providing confidence in the finished products. Depending on the type of contaminate in question, this requires analysis in the fields of microbiology, chemistry and molecular biology.
Food manufacturers demand from these analyses reliability and fast results to be cost effective. Many of the current routine and standard methods used by laboratories require a variety of equipment and consumables and can be time consuming and therefore expensive. For example, a full analysis of a product for microbiological contamination can take a week, as microorganism colonies need time to grow on specific agars. Speciation testing via PCR analysis requires expensive equipment and the analysis for allergens through ELISA methods requires expensive test kits although they can be performed in a day giving fast results. Consequently, for a method to be viable commercially it must be fast and cost effective so that the laboratories can keep the custom of food manufacturers.
Scientific research in the food sector develops constantly and one of the areas of food analysis is the use of aptamers as biosensors, also known as aptasensors. Aptamers are molecules consisting of single stranded oligonucleotides (DNA or RNA) which have been specifically developed to bind exclusively with a chosen target molecule and can be used in a variety of methods.
The concept of aptamers has been around since the early 1990s and has since attracted a lot of attention of research groups globally [1]. Their function is almost identical to antibodies but with major advantages, such as defined affinity, low cost and the removal of the need for animal testing, making aptamers a very attractive analytical tool. Aptamers have a high affinity to their target and bind specifically once selected. They can be labelled with various molecules, having a range of reporting possibilities, for example, in fluorescence detection. The cost of manufacturing an aptamer is relatively low as they can be chemically synthesised and their sequence easily copied, having a low batch-to-batch variability and being pH stable. This eliminates the need for animal hosts in the production of antibodies and any ethical considerations. Once selected, aptamers can be quickly reproduced for further use in analysis [2].
Aptamers are selected through a method called SELEX (Systematic Evolution of Ligands by Exponential Enrichment). The methodology involves the controlled combination of a random library of oligonucleotides with the desired target. The binding process involves several rounds of selection promoting the selective binding and eliminating non-specific sequences, with final purification of the aptamer and copying through cloning. Since the development of the basic SELEX method, multiple variations of the methodology have emerged. These SELEX methods have been designed dependant on the target molecule or the desired application of the aptamer [3]. The use of aptamers as biosensors has been recognised as a diagnostic tool and finds more and more use for applications within food safety.
Aptamers targeting microorganisms, particularly pathogens, could provide a rapid detection method, avoiding time consuming cell culturing. They could provide a more rapid reporting, allowing manufacturers to take appropriate actions and prevent potential expensive product re-calls. Similar principles apply to the detection of toxins in products. Mycotoxins (fungal toxins) are of growing concern in the food chain, with the European Union having set limits to their presence in products. Due to their capability of high specificity binding to very small molecules, aptamers hold a clear advantage over current immunoassays and chemical detection methods. Allergen control forms an important part of product manufacturing and many current analytical methods can have difficulties due to cross-reactivity, aptamer specificity counters this [4].
Overall, aptamers have the potential to replace antibodies in already existing technologies such as ELISAs’, creating platforms which have multiple capabilities whilst being highly specific and cheap, having the ability to be targeted to any food contaminant or adulterant is clearly an advantage. Aptasensors are highly staple and therefore have the potential to become an ideal tool for direct analysis at production and manufacturing sites, a challenge will be to reduce the amount of sample preparation as complex food matrixes can be notoriously difficult to analyse. With all these advantages, there is still a lack of aptasensors that are commercially available. Currently, aptamers are still used within research rather than commercial applications. This is possibly linked to the resistance of the food sector to adopt new technologies which would replace functioning analytical systems. However, with the increasing challenge of a growing population demanding safe food, aptamers will fill the niche left by current analytical systems. The future of aptamers in food analysis is guaranteed, with focus now laying on building a database with the aim to incorporate them into commercially viable test kits.
Ioana Lock, KK Fine Foods Plc
References
1. Tuerk, C. and L. Gold, Systemic evolution of ligands by exponential enrichment: RNA ligands to bacteriophage T4 DNA polymerase. Science, 1990. 249(4968): p. 505-510.
2. Famulok, M. and G. Mayer, Aptamers and SELEX in Chemistry & Biology. Chemistry & Biology, 2014. 21(9): p. 1055-1058.
3. Aquino-Jarquin, G. and J. D. Toscano-Garibay, RNA Aptamer Evolution: Two decades of SELEction. International Journal of Molecular Sciences, 2011. 12: p. 9155-9171.
4. Amaya-Gonzalez, S., et al., Aptamer-based analysis: A promising alternative for food safety control. Sensors, 2013. 13: p. 16292-16311.
