MOLECULARLY IMPRINTED POLYMER​ BASED ELECTROCHEMICAL SENSOR FOR THE TRACE ANALYSIS OF MACROLIDE ANTIBIOTICS

Antibiotic resistance has a significant impact on health and economy, WHO recommending an urgent improvement in the surveillance of antibiotics use, hence the need for developing new analytical sensors, capable of detecting minute amounts of antibiotics from different matrices.

The purpose of this study was to develop an electrochemical sensor for the detection of azithromycin, a widely used macrolide antibiotic, from environmental and pharmaceutical samples. Molecular imprinting enables the synthesis of robust polymeric sensing layers endowed with a remarkable chemical and thermal stability and tailored selectivity towards the target molecule, being able to distinguish even closely-related structural analogues. Compared with the conventional non-covalent imprinting, covalently imprinted polymers offer an enhanced selectivity based on double recognition mechanism, both through functional and spatial complementarity. Boronic acids are able to form stimuli-responsive reversible covalent cyclic esters with cis-diol-containing molecules such as azithromycin. To the best our knowledge, there is no report in using boronate esters in antibiotics imprinting.

Therefore, a molecularly imprinted polymer (MIP) modified electrochemical sensor was developed, based on a boronic acid functional monomer (3-thienyl boronic acid), capable of forming stable cyclic esters through covalent interactions with the cis-diol moieties of the template molecule (azithromycin). The imprinted polymeric film was electrodeposited potentiodynamically on the electrode’s surface by copolymerizing the functional monomer with the cross-linker (2,2`-bithiophene). The optimized MIP-based sensor was characterized by different spectroscopic and microscopic techniques (micro-Raman, SEM, AFM).

Indirect electrochemical detection of azithromycin was achieved by cyclic voltammetry using a redox probe ([Fe(CN)₆]^3-/[Fe(CN)₆]^4-) in phosphate buffer (pH 7.0). Under the optimized conditions, the MIP-based sensor can be used multiple times without significant loss (< 10%) in the signal intensity, exhibiting a linear response in the range of 0.5 – 50 μg/mL azithromycin. In addition, the sensor demonstrates high binding affinity towards the template molecule over other antibiotics, with good repeatability (RSD < 6%) and stability.

The fabricated sensor was successfully applied for the quantification of azithromycin from different environmental and pharmaceutical samples, offering good prospects for the implementation of portable, fast, sensitive and selective electrochemical sensing devices for field analysis.

Acknowledgement: This work was supported by a grant of the Romanian National Authority for Scientific Research and Innovation, CNCS/CCCDI-UEFISCDI, project number PN-III-P2-2.1-PED-2016-0172, within PNCDI III.