A Novel Mıcrocantılever Sensor System For The Selectıve Determınatıon Of Antıbıotıcs

Abstract

This thesis focuses on the detection of ciprofloxacin and erythromycin antibiotics in water resources, which cause adverse effects on wildlife in aquatic environments and human life by polluting the drinking waters. Detection of these antibiotics down to picogram mass resolution is crucial, since even the presence in trace amounts refer to pollution of the water resources. The main objective of this thesis study was to detect ciprofloxacin and erythromycin antibiotics with a novel approach by merging the molecular imprinting technology and microcantilever mass sensors. The developed nanosensor relies on the detection via adsorption of these molecules to the template specific cavities of molecularly imprinted polymeric (MIP) nanoparticles. The ciprofloxacin and erythromycin imprinted polymers were synthesized with miniemulsion polymerization technique. Their size, shape and dispersity characterization was carried out with Scanning Electron Microscope (SEM) and their layer structure was characterized by Atomic Force Microscopy (AFM). SEM images yielded that ciprofloxacin and erythromycin imprinted polymeric nanoparticles were both spherical in shape had sizes of around 160 nm and 30 nm, respectively. Three different methods were tried during the immobilization of prepared polymeric nanoparticles on the surface of the cantilever. AFM images revealed the particle morphology that were absorbed on the cantilever. It was found that a monolayer surface coverage was accomplished with a covalent immobilization technique. The validation of prepared nanosensor was accomplished for both of the imprinted polymeric nanoparticles specific to chosen antibiotics by employing the dynamic sensing mode. During validation studies, binding kinetics both in liquid and in air were checked. As the polymeric nanoparticles were immobilized on the surface of the cantilever, any molecule adsorption resulted in a frequency shift to lower values. From the shifts recorded, masses of the total adsorbed molecules were calculated. The sensitivity of the sensor systems in air for the detection of ciprofloxacin and erythromycin were determined as 2.2 Hz/pg and 1.6 Hz/pg, respectively. The limit of detection values were calculated as 2.2 µM for ciprofloxacin sensor and 1 µM for erythromycin sensor in air. The selectivity studies were performed by checking the affinities of physically and chemically similar antibiotics on ciprofloxacin and erythromycin imprinted polymers, which were found to show 7 and 8 fold lower affinities, respectively. Similarly, sensitivity of the nanosensor was checked by using non-imprinted polymeric nanoparticles, which were prepared with the same method except the template molecule inclusion. In that case, the binding affinities of ciprofloxacin and erythromycin towards non-imprinted polymers were found to be 5 and 3 folds lower compared to imprinted polymers. The obtained results were compared with data from the earlier studies done in this field and interpretations were made. Being one of the first studies in MIP based microcantilever sensor, the developed system has the potential to be pioneer in mass sensing applications.