Transmitive Spectral SPR Droplet Biosensing: Principle,Sensor Design,and Experimental Demonstration

Surface plasmons resonance (SPR) architectures based on grating coupler/disperser combination is an attractive alternative for spectral-based biochemical sensing. In this paper, we investigate theoretically and experimentally a new concept where the plasmon coupling occurs through a thin film grating and sensing occurs via the first evanescent diffraction order in transmitive mode. The surface plasmon wave excitation induces a peak in the wavelength as well as in the angular spectra of the detected first transmitted diffraction order. Accordingly, a change in SPR spectrum of the detected diffraction order can be used to quantify the amount of the target molecules immobilized on the sensor surface, and therefore, the concentration of these molecules in the analyte solution. The developed sensor architecture is dedicated to droplet biochemical sensing and appears to be especially suitable for biosensor integration and miniaturization. The presented sensor concept is perfectly suited for mass production of low-cost and reproducible SPR sensor chip for biochemical analysis. The implemented setup gives access to multichannel biosensing with the potential for efficient internal referencing essential to achieve sufficiently high reproducibility and accuracy of the measurements.