Reduced Graphene Oxide Fabricated Molecular Imprinted Polymeric Layers for Improved Recognition of Ciprofloxacin

Abstract

Introduction Ciprofloxacin is a broad spectrum synthetic antibiotic that is frequently used against gram negative and gram positive bacteria. The increasing use of ciprofloxacin by humans has also results its release in environment as it is detected in different water bodies [1]. The presence of antibiotics in aquatic environment could result the development of antibiotic resistant strains [2], which is a serious concern. The current analytical tools for its sensitive detection are mainly based on spectrometric or chromatographic techniques. Nevertheless these methods are time consuming and require extensive sample preparation steps. It is imperative to design sensitive and robust sensor setups for its rapid detection in water bodies. In this study, we designed molecular imprinted polymeric layers incorporated with graphene derivatives for electrochemical sensing of ciprofloxacin using interdigitated capacitors as transducer. These devices offer rapid response and have low fabrication costs. The combination of reduced graphene oxide (rGO) with molecular imprinted polymer (MIP) has shown enhanced sensitivity and selectivity thus, developing smart sensor devices for straightforward detection of ciprofloxacin. Experimental Graphene oxide (GO) was synthesized by oxidation of graphite powder following modified Hummer’s method. For preparing reduced graphene oxide (rGO), the as-prepared GO was dispersed in distilled water and treated with sodium borohydride as reducing agent at 70°C for about 12 hours. The resultant product was subjected to several washings and dried overnight at 65°C. Molecular imprinted polymer (MIP) was prepared using methacrylic acid (MAA) and ethyleneglycol dimethacrylate (EGDMA) along with ciprofloxacin as template structure in dimethylformamide (DMF). The as-prepared GO/rGO powder was added to above pre-polymer mixture to prepare respective composite coatings. Azoisobutyrnitrile (AIBN) was used to carry out thermally initiated free radical polymerization at 60 °C for 30 minutes. The resultant polymer mixtures were integrated with IDCs by spin coating. The non-imprinted polymer was prepared under same manner without adding template. Moreover, its composite layers with GO/rGO were prepared under similar conditions and integrated with IDCs. Results and Conclusion The sensor response as capacitance shift for rGO-MIP, GO-MIP, MIP and their corresponding non-imprinted layers i.e., rGO-NIP, GO-NIP and NIP was measured for varying concentrations of ciprofloxacin as shown in figure 1. Comparing the response of imprinted layers, it can be noticed that rGO-MIP coated IDCs showed highest sensor shift i.e. 43 µF, while GO-MIP is second best (34 µF) and finally, the pristine MIP is at third place (25 µF). This suggests that incorporation of rGO in MIP [3] enhances the sensor shifts and thus, is a suitable strategy for improving the sensitivity. On other hand, all the non-imprinted layers i.e., rGO-NIP, GO-NIP and pristine NIP showed much lower sensor shifts. Moreover, these layers showed similar sensor shifts indicating that these layers does not possess any specific recognition sites and thus, can be taken as control surface.The selectivity of rGO-MIP sensor is tested by exposing the device against structurally analogous antibiotic drugs. The sensor shifts of rGO-MIP for ciprofloxacin, levofloxacin and moxifloxacin in the concentration range 10-50 ppm is shown in figure 2. It is evident that sensor response for ciprofloxacin is at least 3 times higher than levofloxacin and moxifloxacin. The significantly higher sensor shifts for ciprofloxacin is due to the presence of complementary interaction sites in MIP layer. While levofloxacin and moxifloxacin despite of their similar structures to ciprofloxacin showed much lower sensor shifts. The results suggested that the incorporation of rGO to MIP not only improves sensitivity but also contribute in enhanced selectivity as well.