Sheath-Flow Microfluidic Approach for Combined Surface Enhanced Raman Scattering and Electrochemical Detection

Abstract

The combination of hydrodynamic focusing with embedded capillaries in a microfluidic device is shown to enable both surface enhanced Raman scattering (SERS) and electrochemical characterization of analytes at nanomolar concentrations in flow. The approach utilizes a versatile polystyrene device that contains an encapsulated microelectrode and fluidic tubing, which is shown to enable straightforward hydrodynamic focusing onto the electrode surface to improve detection. A polydimethyslsiloxane (PDMS) microchannel positioned over both the embedded tubing and SERS active electrode (aligned ∼200 μm from each other) generates a sheath flow that confines the analyte molecules eluting from the embedded tubing over the SERS electrode, increasing the interaction between the Riboflavin (vitamin B2) and the SERS active electrode. The microfluidic device was characterized using finite element simulations, amperometry, and Raman experiments. This device shows a SERS and amperometric detection limit near 1 and 100 nM, respectively. This combination of SERS and amperometry in a single device provides an improved method to identify and quantify electroactive analytes over either technique independently.

Role of Surface Adsorption in the Surface-Enhanced Raman Scattering and Electrochemical Detection of Neurotransmitters

“…The ratio of the sheath and capillary flow rates optimizes the focusing effect, as previously reported. 25 …”

“…25 The fast moving sheath-flow confines the analyte within a region above the surface and promotes analyte-substrate interactions. The fluid dynamics enable the control of the flux to the SERS electrode, improving both electrochemical and SERS sensitivity when compared to other detection methods.…”

Bioanalytical applications of surface-enhanced Raman spectroscopy: de novo molecular identification

“…Bailey et al used the combination of microfluidics, sheath-flow SERS, and amperometry to quantify vitamin B 2 , also known as riboflavin. 114 Silver was electrodeposited onto a gold electrode to act as a SERS active electrode. The SERS detection limit was observed at 1 nM while the electrochemical detection limit was 89 nM.…”

“…They reported the orientation of the analyte relative to the SERS electrode contributes to the enhancement of certain vibrational bands. 114 Stokes et al quantified folic acid (pterin based-vitamin B 9 ) in water and detected it in human serum. 115 The LOD was calculated to be 0.018 μM.…”

Increased SERS Detection Efficiency for Characterizing Rare Events in Flow

“…SERS has been used for detection of analytes in aqueous solutions in a variety of detection platforms, which has enabled improved detection of bacteria, drugs of abuse, and other chemicals. 2–8 Innovative approaches have been reported for detection in flow. Plasmonic nanodome arrays have been developed and implemented into a flow cell for monitoring drugs in IV tubing.…”