Differentiating surface and bulk interactions in nanoplasmonic interferometric sensor arrays

TL;DR

This paper introduces a simple nanoplasmonic interferometric sensor that can distinguish between surface-bound protein layers and bulk refractive index changes in complex solutions, using different plasmon penetration depths.

Contribution

The authors develop a nanoplasmonic sensor platform capable of differentiating surface adsorption from bulk effects at a single sensing spot, simplifying detection in complex environments.

Findings

Successfully detected and differentiated a monolayer of BSA from bulk refractive index changes.

Achieved noise levels comparable to traditional SPR sensors with a simpler setup.

Demonstrated potential for miniaturized, real-time sensing applications.

Abstract

Detecting specific target analytes and differentiating them from interfering background effects is a crucial but challenging task in complex multi-component solutions commonly encountered in environmental, chemical, biological, and medical sensing applications. Here we present a simple nanoplasmonic interferometric sensor platform that can differentiate the adsorption of a thin protein layer on the sensor surface (surface effects) from bulk refractive index changes (interfering background effects) at a single sensing spot, exploiting the different penetration depths of multiple propagating surface plasmon polaritons excited in the ring-hole nanostructures. A monolayer of bovine serum albumin (BSA) molecules with an effective thickness of 1.91nm is detected and differentiated from a 10-3 change in the bulk refractive index unit of the solution. The noise level of the retrieved real-time sensor output compares favorably with traditional prism-based surface plasmon resonance sensors, but is achieved using a significantly simpler collinear transmission geometry and a miniaturized sensor footprint.