Limitation of a localized surface plasmon resonance sensor for Salmonella detection

We have designed a localized surface plasmon resonance (LSPR) biosensor to perform whole cell detection of Salmonella using Au nanoparticles fabricated by an oblique angle deposition technique. The LSPR sensor shows a plasmon peak shift due to the Salmonella antigen and anti-Salmonella antibody reaction as verified by scanning electron microscopy and fluorescence microscopy. However, this shift is not sensitive to the concentration of the bacteria. We have modeled this detection system by means of Mie theory and effective medium theory, and find that due to the small contact area between the nanoparticle and the bacteria and the short range interaction of the local electric field, the plasmon peak shift induced by such a system is about 2–4 nm, regardless of the concentration of the bacteria. This is consistent with the experiments, and an alternative method is needed if the LSPR sensor is used for whole cell bacteria detection.