Multiplexed biosensors based on interference of surface plasmons in multimode nanoslits

Multiplexed biosensors enable the simultaneous detection of multiple analytes within a single sample-a capability that holds significant importance in various fields, including environmental monitoring, food safety, and medical diagnostics. In medical diagnostics, detecting multiple biomarkers simultaneously is crucial for enhancing the diagnostic accuracy of conditions such as infectious diseases, cancer, and metabolic disorders. Biosensors based on surface plasmon resonance (SPR) are remarkable due to their high sensitivity compared to other technologies. However, current multiplexed SPR-based biosensors are bulky, expensive, and difficult to integrate in lab-on-a-chip configurations. Here, we propose a multiplexed biosensor as a periodic array of plasmonic biosensor unit cells, consisting of a plasmonic interferometer located on the top of the substrate, excited by a pair of grating couplers such that the surface plasmons converge to a multimode nanoslit that produces the output signal emerging through the substrate. Microfluidic channels are integrated into the structure, thereby defining the sensing regions of each interferometer. The biosensor unit cells can be monitored individually and simultaneously by imaging their output onto a camera. Absorbing shadow elements are integrated into the structure to minimize crosstalk and background light, thereby enabling excitation of the entire array by a single large monochromatic Gaussian beam. The array can be scaled lithographically, and its interrogation is scaled by increasing the size and power of the Gaussian beam and the size of the monitoring camera. We demonstrate the concept via electromagnetic simulations and predict resolutions of R _b=6.3×10^-6 R I U and R _s=10p m for bulk and surface sensing.