Sensitive Mie scattering immunoagglutination assay of porcine reproductive and respiratory syndrome virus (PRRSV) from lung tissue samples in a microfluidic chip.

A microfluidic immunosensor utilizing Mie scattering immunoaggultination assay was developed for rapid and sensitive detection of porcine reproductive and respiratory syndrome virus (PRRSV) from lung tissue samples of domesticated pigs. Antibodies against PRRSV were conjugated to the surface of highly carboxylated polystyrene microparticles (diameter=920nm) and mixed with the diluted PRRSV tissue samples in a Y-shaped microchannel. Antibody-antigen binding induced microparticle immunoagglutination, which was detected by measuring the forward 45° light scattering of 380nm incident beam using microcallipered, proximity fiber optics. For comparison, multi-well experiments were also performed using the same optical detection setup. The detection limit was determined to be 10(-3)TCID(50)ml(-1) for PRRSV dissolved in PBS, while those of previous RT-PCR studies for PRRSV were 10(1)TCID(50)ml(-1) (conventional assays) or <1TCID(50)ml(-1) (quantitative real-time assays). Mie scattering simulations were able to predict the shape of the PRRSV standard curve, indicating that any non-linearity of the standard curve can be interpreted purely as an optical phenomenon. Each assay took less than 5min. A strong correlation could be found between RT-PCR and this method for the lung tissue samples, even though their respective detection mechanisms are different fundamentally (nucleic acids for RT-PCR and virus antigens for light scattering immunoagglutination assay). Several different dilution factors were also tested for tissue samples, and 1/10 and 1/100 were found to be usable. If the microfluidic chips are used only once (i.e. without re-using them), both superior sensitivity and satisfactory specificity can be demonstrated. Specificity studies revealed the presence of Type II PRRSV and non-presence of Type I PRRSV and that the microfluidic chip assay could detect Type II North American strain of PRRSV for the animals tested. This work demonstrates the potential of the Mie scattering immunoassay on a microfluidic chip towards real-time detection system for viral pathogens in domesticated animals.