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.