Development of lanthanum oxide nanoparticles-based biosensor for highly selective and sensitive detection of ciprofloxacin in milk

Abstract

Antibiotics are being used widely in veterinary practices for the therapeutic management of livestock and the inhibition of microbial infections. Over-use and possibly fraudulent misuse of these antibiotics as dietary growth promoters necessitate the development of surveillance and monitoring technologies [1]. The over-usage of drugs has led to antibiotic resistance in bacteria, creating challenges for many societies, hospitals, and health centers due to an increase in overall patient numbers and costly treatment [2]. Ciprofloxacin (CPX) [1-cyclopropyl-6-fluoro-1,4-dihydro-4-oxo-7-(1-piperazinyl) 3-quinolone carboxylic acid], is a very stable antibiotic that does not go through complete metabolism in the body, and 30-90 % of CPX remains constantly [3]. The growing public concern of accumulation of drug residues in the food supply chain and livestock has led to the general administration of this antibiotic [4-6]. There is a strong probability that it reaches the environment through patients’ urine samples and wastewater due to inadequate metabolization of CPX in the body, which induces antibiotic resistance. In the coming future, the phenomenon of antibiotic resistance will be more complex.[7] As a result, there is an urgent requirement to closely track the use and discharge of these medications in the atmosphere via the human body. Several techniques for the detection of CPX have been used so far, including spectrophotometry [8], liquid chromatography-mass spectrophotometry [9], immunoassay, chemiluminescence, capillary electrophoresis [10], and electrochemical techniques [11]. The disadvantage of these approaches is that they are all time-consuming, costly, complex methods, and they all necessitate advanced automation and the assistance of skilled users. To resolve this problem, various efforts have been made to develop simple, rapid, inexpensive, and sensitive bio/sensors for CPX detection electrochemically. In this study, nanostructured lanthanum oxide nanoparticles (nLa₂O₃ NPs) were synthesized by the co-precipitation method, which is considered the facile and quickest nanoparticles synthesis process [12]. As-synthesized nLa₂O₃ NPs have been characterized with various analytical and spectroscopic and morphological techniques such as X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, contact angle, transmission electron microscopy, and electrochemical methods. These nLa₂O₃ NPs were used for enhancing the conductivity of the immunosensor. In brief, nLa₂O₃ NPs were functionalized by APTES and were deposited electrophoretically on the surface of ITO glass substrate followed by immobilizing anti-CPX antibodies covalently via EDC-NHS chemistry. Blocking of the non-specific area was done with the help of BSA. Further, the nLa₂O₃ NPs have significant physio-electrochemical properties that have resulted in developing a highly efficient electrochemical biosensor for the detection of CPX having excellent sensitivity, repeatability, stability, and selectivity. The change in electrochemical response studies of the developed immunosensor (BSA/anti-CPX/APTES/nLa₂O₃/ITO) was monitored by differential pulse voltammetry (DPV) to detect CPX. Under optimized conditions, studies showed that the developed biosensor had a wide linear detection range of 0.001-0.5 ng mL⁻¹ and 1-1000 ng mL⁻¹, a lower detection limit of 1 pM mL^-1 with two sensitivities of 11.44 mA ng^-1 mL cm^-2 (R² of 0.968), and 7.88 mA ng^-1 mL cm^-2 (R²=0.972). The developed immunosensor showed good reproducibility, repeatability, sensitivity, and stability that was effectively explored to detect CPX in milk samples. To the best of our knowledge, this is the first work on the development of an electrochemical-based immunosensor for the detection of CPX using nLa₂O₃ NPs.