Effect of the chiral blocks of functionalized fullerene on levofloxacin enantioselective voltammetric sensing

Antibiotics are one of the most important bioactive and chemotherapeutic groups of compounds. However, as a result of their excessive consumption for human treatment, veterinary and food industries, it can lead to direct toxic effects, pathogen resistance and allergic hypersensitivity in humans. The situation calls for developing sensitive and selective techniques for antibiotics analysis to monitor their appropriate use, public health, and new drugs design. In this study the glassy carbon voltammetric sensors (GCE) based on layer-by-layer deposited graphene oxide (rGO) and functionalized fullerene (C60) were proposed for the levofloxacin (Lev: S-(–)-Ofloxacin) sensing. Since Lev is an optically active substance, it can be assumed that the sensitive layer of sensor with chiral selector will selectively interact with the antibiotic through various intermolecular interactions. Therefore, a number of selectors with different optical center configurations were obtained and studied, such as S/R-2-chloro-N-(1-phenylethyl)acetamide fullerene (S/R-C60AA), and S/R-N,N'-bis(1-phenylethyl)malonamide fullerene (S/R-C60MA). The structure of obtained selectors was confirmed by NMR and IR spectroscopy, polarimetric studies were carried out. The proposed sensors were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) using standard redox probe. Morphological studies were carried out by scanning electron microscopy (SEM). Possible binding sites between Lev and selectors were revealed by computational studies. Some patterns of changes in the electrochemical behavior of Lev depending on the composition of the sensitive layer of the sensor were obtained by differential pulse voltammetry (DPV). Quantitative determination of Lev was carried out using sensor GCE/rGO/S-C60AA. Calibration plot was found to be linear in two ranges, such as 1.0·10−6–3.0·10−5 M and 3.0·10−5–5.0·10−4 M with sensitivity values of 82.14 and 58.71 μA/mM, respectively. The limits of detection and quantitation were calculated to be 3.7·10−8 M and 1.2·10−7 M, respectively (according to 3Sb/m and 10Sb/m). The developed sensor has a simple design, good analytical and operational characteristics compared to some previous reports in the literature. In addition, the sensor was successfully tested for Lev quantification in real samples of biological fluids and pharmaceutical formulations with a good recovery percentage ranged in 91.5–104.4 %.