In Situ Two-Step Photoreduced SERS Materials for On-Chip Single-Molecule Spectroscopy with High Reproducibility

Wenjie Yan; Longkun Yang; Jianing Chen; Yaqi Wu; Peijie Wang; Zhipeng Li

doi:10.1002/adma.201702893

In Situ Two-Step Photoreduced SERS Materials for On-Chip Single-Molecule Spectroscopy with High Reproducibility

Adv Mater. 2017 Sep;29(36). doi: 10.1002/adma.201702893. Epub 2017 Jul 18.

Authors

Wenjie Yan¹, Longkun Yang¹, Jianing Chen², Yaqi Wu¹, Peijie Wang¹, Zhipeng Li¹

Affiliations

¹ The Beijing Key Laboratory for Nano-Photonics and Nano-Structure (NPNS), Center for Condensed Matter Physics, Department of Physics, Capital Normal University, Beijing, 100048, P. R. China.
² Beijing National Laboratory for Condensed Matter Physics, Institute of Physics Chinese Academy of Sciences, University of Physics Chinese Academy of Sciences, Collaborative Innovation Center of Quantum Matter, Beijing, 100190, P. R. China.

PMID: 28718979
DOI: 10.1002/adma.201702893

Abstract

A method is developed to synthesize surface-enhanced Raman scattering (SERS) materials capable of single-molecule detection, integrated with a microfluidic system. Using a focused laser, silver nanoparticle aggregates as SERS monitors are fabricated in a microfluidic channel through photochemical reduction. After washing out the monitor, the aggregates are irradiated again by the same laser. This key step leads to full reduction of the residual reactants, which generates numerous small silver nanoparticles on the former nanoaggregates. Consequently, the enhancement ability of the SERS monitor is greatly boosted due to the emergence of new "hot spots." At the same time, the influence of the notorious "memory effect" in microfluidics is substantially suppressed due to the depletion of surface residues. Taking these advantages, two-step photoreduced SERS materials are able to detect different types of molecules with the concentration down to 10^-13 m. Based on a well-accepted bianalyte approach, it is proved that the detection limit reaches the single-molecule level. From a practical point of view, the detection reproducibility at different probing concentrations is also investigated. It is found that the effective single-molecule SERS measurements can be raised up to ≈50%. This microfluidic SERS with high reproducibility and ultrasensitivity will find promising applications in on-chip single-molecule spectroscopy.

Keywords: memory effect; microfluidics; single-molecule spectroscopy; surface-enhanced Raman scattering; two-step photoreduction.