Multi-spot, label-free detection of viral infection in complex media by a non-reflecting surface

The measurement of the intensity of light reflected by interfaces with extremely low reflectivity in water enables the label-free, multiplex detection of bio-molecular interactions. The binding of targets in solution to surface-immobilized probes (e.g. antibodies) can be quantified using a simple instrumental set-up, comprising a LED source and a camera. The condition of low reflectivity can be achieved by using a perfluorinated plastic substrate with refractive index very close to that of water. Here we show that, despite its simplicity, the method enables label-free detection in complex samples with high absorbance and turbidity. Diagnostic markers of Tomato spotted wilt virus are revealed in crude plant extracts of Datura stramonium leaves at early stage of infection. The measuring procedure requires only the addition of the sample into a cuvette and the acquisition of a series of images for a few minutes. The light reflectivity of the spots of specific antibodies increases more rapidly if the sample is prepared with infected plants.