Aptamer-based assay of ractopamine in human biofluids using thiolated GQDs-chitosan biocompatible nanocomposite modified gold nanostructures: The effect of size and morphology of nanoparticles on the efficient of apta-assay

A representative biosensor contains three components: a biological sensing element, a transducing element, and a display. The sensing element primarily defines the selectivity and sensitivity of the biosensor. To date, many different types of biological components (enzymes, antibodies, or DNA/RNA) have been employed for highly selective responses to specific analytes. A typical electrochemical biosensor makes use of an electrode surface as the platform to immobilize biological sensing components (e.g., antibodies or aptamers), for which the analyte-binding event is monitored based on electrical current variations[1]. Aptamers are single stranded DNA or RNA molecules with high specificity to various ligands. Biosensors based on DNA or RNA aptamers (aptasensors) represent new type of the sensor that utilize unique properties of artificial receptor-aptamers. Aptasensors are of considerable interest due to their application in detection practically unlimited kind of compounds[2]. β-agonists are phenylethanolamines with different substituent groups on the aromatic ring and the terminal amino group, including Ractopamine (RAC), Clenbuterol (CLB), Salbutamol (SAL), Phenylethanolamine (PHL), Procaterol (PRO) and so on[3]. In general, β-agonists are applied as bronchodilators for the treatment of human pulmonary disease and asthma[4]. Now β-agonists and their analogous are illegally used in animals as growth promoters to increase the daily gain. However, β-agonists can be accumulated in animal and be easily stored in human tissues after meat consumption, and result in many serious health problems with symptoms such as palpitations, tremors and tachypnoea[5]. Therefore, establishing a sensitive, rapid and convenient analysis method for detection of β-agonists is great significance for food safety and human health control. In this study, an electrochemical aptasensor based on thiolated graphene quantum dot (GQD), chitosan (Cs), and gold nanoparticles (Au NPs) has been developed for sensitive detection of ractopamine human biofluids. A layer-by-layer strategy were used for the preparation of nanocomposite (GQDs-CS-Au NPs). The prepared interface were utilized for immobilization of specific aptamer. The RAC aptamer was attached on Au NPs of the composite membrane via Au–S bond. Surface morphology of the sensor was studied using field emission scanning electrode microscopy (SEM) and energy dispersive spectroscopy (EDS). The signal for the determination of ractopamine was recorded using differential pulse voltammetry (DPV) at the optimized conditions.