Received on April 8, 2006
Accepted on August 16, 2006

Automation and Analytical Techniques

Rapid, Simple, and Sensitive Immunoagglutination Assay with SiO₂ Particles and Quartz Crystal Microbalance for Quantifying Schistosoma japonicum Antibodies

¹ State Key Laboratory for Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Hunan University, Changsha, P.R. China
² Institute of Schistosomiasis, Xiangya School of Medicine, Central South University, Changsha, China

^* To whom correspondence should be addressed. E-mail: huawang{at}hnu.cn.

Background: The resurgence of the parasitic disease schistosomiasis calls for more efficient diagnostic tests. We developed a rapid, simple, portable, and sensitive immunoagglutination assay that uses SiO₂ particles and quartz crystal microbalance (QCM) for quantifying Schistosoma japonicum (Sj) antibodies (SjAb).

Methods: As replacements for traditional latex microspheres, we prepared submicrometer-sized silica particles derivatized with Sj antigens to specifically agglutinate in the presence of SjAb targets, and we used the QCM monitor to measure the resulting frequency shifts. We optimized the assay medium by adding poly(ethylene glycol) (PEG) as a response accelerator of immunoagglutination. To minimize or eliminate any nonspecific agglutination or adsorption interferences, we conducted appropriate sealing procedures separately for silica particles and the QCM probe.

Results: The measured frequency changes were linearly related to the SjAb concentrations in infected rabbit serum. The PEG-assisted immunoagglutination system is quantitatively sensitive to SjAb concentrations ranging from 0.70 to 32.31 mg/L, with a detection limit of 0.46 mg/L. The obtained linear regression equation was: y = 43.61 x + 80.44 (r = 0.9872). Several serum specimens were evaluated by the developed QCM immunoassay in comparison with the ELISA, validating the feasibility of practical applications.

Conclusions: This novel immunoagglutination-based QCM detection format is rapid, simple to use, and more portable than conventional diagnostic immunoassays, thus offering a promising alternative tool that can be used for point-of-care clinical diagnosis of schistosomiasis, particularly in epidemic situations.