SERS-based detection in an optofluidic ring resonator platform.

Ian M White,Xudong Fan,John Gohring

doi:10.1364/oe.15.017433

Abstract

The development of surface enhanced Raman scattering (SERS) detection has made Raman spectroscopy relevant for highly sensitive labon- a-chip bio/chemical sensors. Despite the tremendous benefit in specificity that a Raman-based sensor can deliver, development of a lab-on-a- chip SERS tool has been limited thus far. In this work, we utilize an optofluidic ring resonator (OFRR) platform to develop a SERS-based detection tool with integrated microfluidics. The liquid core optical ring resonator (LCORR) serves both as the microfluidic sample delivery mechanism and as a ring resonator, exciting the metal nanoclusters and target analytes as they pass through the channel. Using this OFRR approach and R6G as the analyte, we have achieved a measured detection limit of 400 pM. The measured Raman signal in this case is likely generated by only a few hundred R6G molecules, which foreshadows the development of a SERS-based lab-on-a-chip bio/chemical sensor capable of detecting a low number of target analyte molecules.

Highlights

A number of bio/chemical sensing techniques have been under development in recent years, including techniques that rely on fluorescent labeling and those that perform detection using label-free mechanisms such as refractive index or electrochemical effects
To develop a highly sensitive surface enhanced Raman scattering (SERS) detection platform with integrated microfluidics, we use a design based on an optofluidic ring resonator platform
Our design uses the liquid core optical ring resonator (LCORR) glass capillary to deliver the sample to the sensor, which is an inherently integrated ring resonator

Summary

Introduction

A number of bio/chemical sensing techniques have been under development in recent years, including techniques that rely on fluorescent labeling and those that perform detection using label-free mechanisms such as refractive index or electrochemical effects. The intensive research on SERS detection has led to several demonstrations of single molecule detection with Raman enhancements as high as 1014 [4,5,6] Translation of these spectacular results to lab-on-a-chip platforms with integrated microfluidics is still in progress. We use the liquid core optical ring resonator (LCORR), which was first demonstrated as a refractometric sensing platform and later a label-free biomolecule detection platform with integrated microfluidics [11,12]. As the sample flows through the LCORR capillary, analytes that pass through the ring resonator evanescent field may produce Raman scattered photons. The ring resonator is a microfluidic channel, and the WGM excitation is separated from the sample, making the detection system more practical and adaptable than the microsphere to a lab-on-a-chip design [17]

Experimental setup

WGM evanescent field is the excitation source

SERS signal depends linearly on WGM input intensity

SERS signal dependence on concentration in LCORR is not linear

Findings

Summary and discussion