Refractive index sensing with hybrid surfaces of photonic crystals and dielectric microsphere monolayers

TL;DR

This paper presents a hybrid refractive index sensor combining colorimetric and optical detection methods using photonic crystals and dielectric microspheres, enabling sensitive RI measurements in small areas.

Contribution

The work introduces a novel integrated RI sensor with microsphere monolayers on photonic crystal substrates, enhancing detection capabilities and compatibility with standard microscopes.

Findings

Successfully assembled microsphere monolayers on photonic crystal substrates.

Achieved RI sensing in various liquids with high compatibility.

Demonstrated sensing in areas as small as tens of microns.

Abstract

In this work, a refractive index (RI) sensor with an effective integration of colorimetric detection and optical sensing capabilities has been developed. Colorimetric detection relies on the sensitivity of the structural color of photonic crystal (PC) substrates to the changes in background RI, while the optical sensing is performed by measuring the magnification abilities of the dielectric microspheres, which depends on the position of the photonic nanojet. Based on this concept, we have successfully assembled 35 {\mu}m-diameter barium titanate glass microspheres, 4.9 {\mu}m-diameter polystyrene and silica microsphere monolayers on 1D or 2D PC substrates to perform RI sensing in various liquids. In addition, the developed RI sensor is highly compatible with commercial optical microscopes and applicable for RI sensing in areas as small as tens of square microns.