Polymer inclusion membrane for the extraction of oxytetracycline from milk prior to aptamer-based biosensing

Abstract

Aptamer-based sensing may suffer from severe limitations when applied to complex biological and food samples. To alleviate the interference of matrix elements, we propose the use of a polymer inclusion membrane (PIM) as a simple, yet effective sample clean-up tool prior to aptamer-based sensing. As a proof-of-concept, Aliquat 336 anion exchanger was incorporated into a plasticized cellulose acetate membrane to transport oxytetracycline (OTC) from raw milk into an aqueous NaCl acceptor solution. Efficient transport has been ensured by adding a chelating agent to the raw milk and adjusting the pH to alkaline. The amount of extracted OTC was determined as a function of time and acceptor phase NaCl concentration. The extracted amount was proportional to the raw milk OTC concentration in the investigated 0.22–2.2 µM range. Circular dichroism spectroscopy was used to examine the conformation of an OTC-binding aptamer to evaluate if PIM extracts are compatible with aptamer-based biosensors. Solid phase extraction (SPE) was used as a reference sample pre-treatment technique. The aptamer retained its native conformation in the PIM extract, contrary to the SPE extract, and responded to the presence of OTC. Consequently, the PIM-based extraction is adaptable to aptasensor constructs. Besides its simplicity, it offers a cheaper and greener alternative to other sample preparation procedures.