SENSITIVITY ENHANCEMENT OF OPTICAL IMMUNOSENSORS WITH NANOPARTICLES

In recent years, several optical sensor techniques have been developed for the direct monitoring of biomolecular recognition processes at th e surface of a sensor chip. Applications of these immunosensors for th e determination of substances in serum could be demonstrated only for a few analytes due to the lack of sensitivity. Beside nonspecific bind ing of serum components to the sensor surface, the analytical sensitiv ity of these sensors is limited by the molecular weight of the analyte , so that smaller analyte molecules give only a moderate sensor respon se. In order to enhance the sensor signal, the use of mass labels, suc h as latex particles, was proposed in the literature. However, detecti on limits comparable to those of conventional ELISA techniques could n ot be realized so far. We demonstrate the optimization of a ''nanopart icle enhanced immunosensor assay'' for the detection of thyroid stimul ating hormone, with respect to the particle coating, size, and nonspec ific binding. The developed prototype assay requires a sample volume o f 225 mu L and has a measuring range up to 35 mIU/L. For the first tim e, we obtained a detection limit of 0.03 mIU/L (0.1 pM), which is full y competitive to conventional ELISA techniques. The assay allows serum samples to be measured with good precision and dilution linearity. Th e sensor can be reused several times and shows an excellent correlatio n to a commercial enzyme immunoassay. (C) 1997 Academic Press.