Surface Plasmon Resonance Imaging
Detection of single nano particles by surface plasmon resonance imaging
Recently, a new approach in SPR imaging was suggested, allowing the detection of single nanoparticles. The developed approach can be applied for characterization of nano particles of different sorts in liquid, gaseous or vacuum environments. Any particle bound on the sensor surface gives rise to a characteristic pattern with a light spot of few micrometers in diameter on the image.
Polystyrene nanoparticles (refractive index n=1.58) of different size in water solution (refractive index n=1.33) were studied to calibrate the detected SPR signal and estimate the minimal detectable size of the method. The brightness of the observed spot is nearly proportional to the particle size. As a result, the light intensity caused by small particles surpasses the intensity of Mie scatteringby by several orders of magnitude, which is decreasing as the sixth power of the particle diameter. This allows detecting of polystyrene particles down to few tens nanometers in diameter.
This effect can be used to develop of a powerful analytical method. The particles bound on the sensor surface can be directly counted and the counting rate can serve as the measure of particle concentration. The sensor area of several square millimeters can be monitored simultaneously. This provides a very high concentration sensitivity which can be used for medical diagnostic of virus diseases and/or for continuous monitoring of virus contamination of public areas. The counting rate for the binding of polystyrene particles depends linearly on the concentration. Observed counting rate was in a good agreement with the value calculated based on a two-compartment model of mass transfer in a fluidic cell. This gives us a chance for etalon-free measurements of particle concentration. Concentrations of HI virus-like particles in buffer solution were measured, and the results were in good agreement with the results of ELISA analysis.