Microfiber-directed reversible assembly of Au nanoparticles for SERS detection of pollutants.

Surface-enhanced Raman scattering (SERS) spectroscopy has attracted tremendous interest as a highly sensitive label-free tool to detect pollutants in aqueous environments. However, the high cost and poor reusability of conventional SERS substrates restrict their further applications in rapid and reproducible pollutant detection. Here, we report a reliable optical manipulation method to achieve rapid photothermal self-assembly of Au nanoparticles (AuNPs) in water within 30 s by a tapered optical fiber, which is utilized for highly sensitive SERS substrate preparation. The results show that the SERS substrate achieves low detection limits of 10-9 mol/L with an enhancement factor (EF) of 106 for chemical pollutants solutions, including thiram, pyrene, and rhodamine 6G. The SERS enhancement effect based on assembled AuNPs was more than 20 times that based on a gold colloid solution. As a result, the smart reversible assembly of AuNPs exhibits switchable plasmonic coupling for tuning SERS activity, which is promising for the application of SERS-based sensors and environmental pollutant detection.

Photothermal microfluidic-assisted self-cleaning effect for a highly reusable SERS sensor.

The synergistic integration of optofluidic and surface enhanced Raman scattering (SERS) sensing is a new analytical technique that provides a number of unique characteristics for enhancing the sensing performance and simplifying the design of microsystems. Here, we propose a reusable optofluidic SERS sensor by integrating Au nanoisland substrate (AuNIS)-coated fiber into a microfluidic chip. Through both systematic experimental and theoretical analysis, the sensor enables efficient self-cleaning based on its optical-to-heat-hydrodynamic energy conversion property. Besides, the sensor exhibits the instrument detection limit down to 10-13mol/L and enhancement factor of 106 for Rhodamine 6G. Our optofluidic SERS sensor with such a photothermal microfluidic-assisted self-cleaning method has the advantages of portability, simple operation, and high cleaning efficiency, which will provide a new, to the best of our knowledge, concept and approach for cost-effective and reusable sensors.