Development of Optical Biosensor Using Protein A-Conjugated Chitosan-Gold Nanoparticles for Diagnosis of Cystic Echinococcosis.

Human echinococcosis is a serious parasitic diseasethat still affects millions of people in many parts of the world. Since it can offer a critical threat to people's health, it is important to discover a rapid, convenient, and economical method for detection. Herein, we propose a novel point of care assay, namely, an enhanced immuno-dot-blot assay for diagnosis of cystic echinococcosis (hydatidosis). This method is based on the formation of a sandwich complex between a goldnanoprobe (chitosan-gold nanoparticleprotein A) and hydatid cyst antigen (Ag B), which holds anti-Ag B antibodies. Briefly, protein A was conjugated to chitosan-gold nanoparticles via glutaraldehyde chemistry. Then, Ag B was immobilized on the surface of a nitrocellulose membrane, which was followed by the addition of the sera sample and gold nanoprobes. The positive signals were easily detectable by naked eye. The signal intensity of this biosensor was proportional to the concentration of active anti- antibodies on the surface of the nanoparticles, titer of antibodies in the sera samples, and concentration of Ag B coated on the nitrocellulose membrane. The minimum concentration to use the protein A for conjugation to detect titer of anti- IgGand the concentration of Ag B coated in nitrocellulose membrane were 0.5 and 0.3 mg/mL, respectively. This enhanced immuno-dot-blot assay offers a simple diagnostic technique withoutthe need for expensive equipment for diagnosis of echinococcosis.