A novel colorimetric aptasensor using cysteamine-stabilized gold nanoparticles as probe for rapid and specific detection of tetracycline in raw milk

- A colorimetric aptasensor for tetracycline is achieved using positively-charged AuNPs as probe.
- The determination of tetracycline is observed by naked eyes and absorption spectra.
- This simple assay is highly selective and rapid, suitable for tetracycline screening in raw milk.
- Excellent selectivity comes from the specific recognition between tetracycline and aptamers.

In this paper, a sensitive and specific colorimetric aptasensor for rapid detection of tetracycline (TET) in raw milk was developed by using cysteamine-stabilized gold nanoparticles (CS-AuNPs) as the probe. The highly specific single-stranded DNA (ssDNA) aptamers which bind to TET with high affinity were employed to discriminate other antibiotics, such as oxytetracycline, doxycycline, ciprofloxacin, kanamycin, lomefloxacin, chloramphenicol, ofloxacin, enoxacin. The sensing approach is based on the strongly specific interactions between the TET-binding aptamers and TET over the electrostatic interactions between the negatively-charged TET-binding aptamers and the positively-charged CS-AuNPs. Thus a simple colorimetric aptasensor for TET determination is developed using CS-AuNPs as the colorimetric probe. Under the optimum conditions, the absorbance change (ΔA527) of CS-AuNPs was linearly proportional with TET concentration in the range of 0.20-2.0 μg/mL with the detection limit of 0.039 μg/mL (3σ), which is lower than the permissible level in the European Union (EU) (225 nM) and China (100 μg/kg). The application of this method for samples of TET-spiked raw milk suggested satisfactory recoveries between 91.28% and 100.87%. Owing to the advantages of simple operation procedure, reduced detection time, and excellent selectivity, practical application of the proposed colorimetric assay could be expected to realize in on-site and real-time detection of TET in raw milk.