Increased sensitivity of lateral flow immunoassay for ochratoxin A through silver enhancement

Silver nucleation on gold has been exploited for signal amplification and has found application in several qualitative and quantitative bio-sensing techniques, thanks to the simplicity of the method and the high sensitivity achieved. Very recently, this technique has been tentatively applied to improve the performance of gold-based immunoassays. In this work, the exploitation of the signal amplification due to silver deposition on gold nanoparticles has been first applied to a competitive lateral flow immunoassay (LFIA). The signal enhancement due to silver allowed us to strongly reduce the amount of the competitor and of specific antibodies employed to build an LF device for measuring ochratoxin A (OTA), thus permitting the attainment of a highly sensitive assessment of OTA contamination, with a sensitivity gain of more than 10-fold compared to the gold-based LFIA that used the same immunoreagents and to all previously reported LFIA for measuring OTA. In addition, a less sensitive "quantitative" LFIA could be established, by suitably tuning competitor and antibody amounts, which was characterized by reproducible and accurate OTA determinations (RSD% 6-12%, recovery% 82-117%). The quantitative system allowed a reliable OTA quantification in wines and grape musts at the microgram per liter level requested by the European legislation, as demonstrated by a highly results obtained through the quantitative silver-enhanced LFIA and a reference HPLC-FLD on 30 samples.