Developing a sensitive method for the electrochemical determination of tetracycline using MB tagged aptamers on gold electrode substrates

In this work, we report the development of electrochemical biosensors for the detection of Tetracycline (TET) using DNA aptamer conjugated with the redox probe Methylene blue (MB) with the following sequence: 5’-MB-CCC CCG GCA GGC CAC GGC TTG GGTTGG TCC CAC TGC GCG-thiol-3’ [1]. The aptamer was immobilized on a gold surface working electrode via chemisorption, utilizing the Au-S bond and the detection of TET was performed by differential pulse voltammetry (DPV) [2]. The binding of TET resulted in conformational changes of the aptamer and as a result, MB became closer to the sensor surface, increasing the current peak. Experiments were performed with different buffers with and without NaCl, at pH=7.6 and 5. The binding buffer, leading to best results was the one with NaCl at pH=7.6, which is also in agreement with Alawad et al. [3]. The limit of detection (LOD) was determined to be 60 nM, which is below the maximum residue limit (MRL) in milk samples. Comparisons between current immunosensor technologies and our aptasensor were also performed.