Aptamer-based assay for the sensitive detection of antibiotics in food and water samples
Antibiotics have been widely used in human medicine, aquaculture and agriculture to treat serious infectious diseases. However, overuse and misuse of antibiotics in some areas have contributed to the residues of antibiotic contaminants in water bodies and food products such as meat and dairy. This misuse has resulted in the generation of super bacteria with tolerance to normal antibiotics thereby reducing the efficiency of treatment. Therefore, there is a huge demand for highly efficient and practical methods for the detection and analysis of antibiotics in food and water samples.
Current methods for the detection of antibiotics typically involve the following methods such as:
- ELISA
- Chromatography
- Mass-spectrometry
- Surface-enhanced Raman scattering (SERS)
- SPR and electrochemical biosensors.
The techniques however are quite expensive, time-consuming and operated by trained personnel. Moreover, the development of biosensors platforms for the detection of antibiotics has been difficult too, due to the lack of suitable antibodies and their relatively small signals.
Aptamer based assays and biosensors, on the other hand, have shown to offer faster, simpler, less expensive methods for detection of antibiotics. Aptamers are known to be:
- More stable than antibodies
- More cost-effective
- Easily modified chemically
- Better stability than antibodies
- Easily produced in bulk
Furthermore, the unique binding properties of aptamers have shown great potential for biosensors using optical, electrochemical, and mass- sensitive approaches.
Taking advantage of aptamers and enhanced sensitivity of colorimetric biosensors, the following researchers developed an easy point-of-care platform for sensitive detection of antibiotics in water and milk samples.
Aptamer based assay for the detection of antibiotics in water samples
Chloramphenicol (CAP) is a potent drug used to treat a variety of bacterial infections. However, due to its toxic effects on human health, the use of CAP is banned in food-producing animals, emphasizing the necessity for its ultrasensitive detection. Li et al., 2019 developed an aptamer-based assay for the detection of CAP in water samples. The team utilized an iron-based metal-organic framework (MOF) that oxidized tetramethylbenzidine (TMB) in the presence of hydrogen peroxide for colorimetric detection. Binding of chloramphenicol to aptamer gold nanoparticles in the presence of MOF reduced oxidation of TMB and decreased absorbance. TEM images suggested that the CAP – aptamer – AuNP conjugates coat the outside of the MOF, restricting electron transfer.
High selectivity and sensitivity were obtained for CAP detection with the limit of detection of 25 nM or 8 ng/ml. The method was also demonstrated using aptamers selective for other interfering species such as oxytetracycline, tetracycline and ampicillin. The detection reliability and easy operation of the aptamer-based platform render it a promising candidate for antibiotic detection in water quality monitoring practices.
Aptamer based assay for the detection of antibiotics in milk samples
Xu et al., 2018 developed an ultrasensitive and selective colorimetric strategy using highly selective DNA aptamers for the determination of the antibiotics oxytetracycline (OTC) and kanamycin (KAN) in spiked milk samples. The team used magnetic beads (SDB) for separation, HRP for colorimetric detection and gold nanoparticles (AuNPs)- for signal amplification. The aptamers were hybridized with cDNA and immobilized on magnetic beads (SDB).
In the presence of one target, the aptamer was released, and therefore, the cDNA was free to hybridize with the HRP-signal probe immobilized on AuNPs, which in turn catalyzed the conversion of substrates. Owing to the enzymatically catalyzed colorimetric signals (from transparent to blue or yellow), OTC and KAN were quantitatively detected in a wide linear range from 10-6 to 105pg/ml. The lower detection limit of 1 ag/ml for OTC and KAN demonstrated the superiority of aptamer-based detection over currently available methods for antibiotic analysis in the applications of food monitoring and clinical diagnosis.
Overall, aptamers can be readily incorporated into existing colorimetric assays and ELISA platforms, showing target specific responses even in crude sample matrices enhancing its practical utility.
At Aptamer Group, we have developed and validated aptamer reagents to numerous antibiotics and other small molecules for use in biosensors and various other assay formats. These aptamers can be used in a rapid, gain-of-signal assay to quantify sample compounds, to reduce the heavy reliance on antibodies and mass spec. To learn more about our small molecule aptamer detection methods and how they can benefit your research, please contact us.
References
Li, J. et al. Novel sensing platform based on gold nanoparticle-aptamer and Fe-metal-organic framework for multiple antibiotic detection and signal amplification. Environment International. 2019. 125: 135-141.
Xu, Y., Lu, C., Sun, Y. et al. A colorimetric aptasensor for the antibiotics oxytetracycline and kanamycin based on the use of magnetic beads and gold nanoparticles. Microchim Acta 185, 548 (2018). https://doi.org/10.1007/s00604-018-3077-y
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