Nanophotonic waveguide enhanced Raman spectroscopy of biological submonolayers

TL;DR

This paper introduces NWERS, a nanophotonic waveguide-based Raman spectroscopy technique that significantly enhances signal detection for biological monolayers, enabling real-time, label-free analysis on a chip-scale device.

Contribution

The authors develop and demonstrate NWERS, a novel method that enhances Raman signals from biological monolayers using nanophotonic waveguides, allowing rapid, real-time surface characterization.

Findings

Signal enhancement over 10,000 times compared to confocal Raman.

Real-time monitoring of DNA hybridization and protein density.

Potential for integrated, chip-scale lab-on-a-chip devices.

Abstract

Characterizing a monolayer of biological molecules has been a major challenge. We demonstrate nanophotonic wave-guide enhanced Raman spectroscopy (NWERS) of monolayers in the near-infrared region, enabling real-time measurements of the hybridization of DNA strands and the density of sub-monolayers of biotin-streptavidin complex immobilized on top of a photonics chip. NWERS is based on enhanced evanescent excitation and collection of spontaneous Raman scattering near nanophotonic waveguides, which for a one centimeter silicon nitride waveguide delivers a signal that is more than four orders of magnitude higher in comparison to a confocal Raman microscope. The reduced acquisition time and specificity of the signal allows for a quantitative and real-time characterization of surface species, hitherto not possible using Raman spectroscopy. NWERS provides a direct analytic tool for monolayer research and also opens a route to compact microscope-less lab-on-a-chip devices with integrated sources, spectrometers and detectors fabricated using a mass-producible CMOS technology platform.