Development of a new method based on unmodified gold nanoparticles and peptide nucleic acids for detecting bovine...

A simple colorimetric assay is presented for detecting bovine viral diarrhea virus (BVDV)-RNA based on aggregation of gold nanoparticles (AuNPs) in the presence of charge-neutral peptide nucleic acids (PNA). Free charge-neutral PNA oligomers tended to be adsorbed onto AuNPs and act as a coagulant, whereas hybridizing complementary RNA with PNA disrupted PNA-induced AuNP aggregation, and the NPs remained stable. However, non-complementary RNA did not have this effect, and PNA induced aggregation of the AuNPs that resulted in a color change of the reaction from red to blue. The label-free colorimetric assay developed was estimated to have a 10.48 ng/reaction BVDV-RNA detection limit for the visual assay and 1.05 ng/reaction BVDV-RNA using a spectrophotometer. Diagnostic sensitivity and specificity for the assay was in accordance with real-time reverse transcriptase-polymerase chain reaction (RT-PCR) and nested RT-PCR results were 98 and 100%, respectively. Absorption of the 520/620 nm ratio was linear, along with an increase in the target RNA concentration of 1.64-52.4 ng/reaction (R² = 0.992), which showed a linear correlation for the quantitative assay. This study established a rapid visual label and enzyme-free diagnostic assay for detecting BVDV that is applicable in any clinical laboratory.