Ultra-Sensitive, Rapid and On-Site Sensing Harmful Ingredients Used in Aquaculture with Magnetic Fluid SERS.

The integration of surface-enhanced Raman scattering (SERS) spectroscopy with magnetic fluid provides significant utility in point-of-care (POC) testing applications. Bifunctional magnetic-plasmonic composites have been widely employed as SERS substrates. In this study, a simple and cost-effective approach was developed to synthesize magnetic-plasmonic SERS substrates by decorating silver nanoparticles onto magnetic Fe3O4 nanoparticles (AgMNPs), which function both as SERS-active substrates and magnetic fluid particles. The strong magnetic responsivity from AgMNPs can isolate, concentrate, and detect target analytes from the irregular surface of fish skin rapidly. We fabricate a microfluid chip with three sample reservoirs that confine AgMNPs into ever smaller volumes under an applied magnetic field, which enhances the SERS signal and improves the detection limit by two orders of magnitude. The magnetic fluid POC sensor successfully detected malachite green from fish with excellent selectivity and high sensitivity down to the picomolar level. This work achieves a label-free, non-destructive optical sensing approach with promising potential for the detection of various harmful ingredients in food or the environment.

Magnetic field-aligned Fe3O4-coated silver magnetoplasmonic nanochain with enhanced sensitivity for detection of Siglec-15.

Noble metal nanoparticles could provide a significant gain in sensitivity of surface plasmon resonance (SPR) sensor by electromagnetic field coupling between the localized plasmon resonance of nanoparticles and gold film. A facile and cost-effective SPR sensor based on magnetic field-aligned Fe3O4-coated silver magnetoplasmonic nanoparticles (Ag@MNPs) nanochain (M-Ag@MNPs) was proposed to improve the sensitivity of the sensor, which gave access to detect clinical targets at low concentration. Optimization experiments proved that 80 ng mL-1 M-Ag@MNPs-based SPR sensor showed high refractive index sensitivity and increased detection accuracy and quality factor when comparing with those of bare gold. Sialic acid binding Ig like lectins-15 (Siglec-15) was used as proof of concept to verify the sensitivity enhancement performance of M-Ag@MNPs in the actual detection process. SPR angle shifts of M-Ag@MNPs/gold sensor were significantly higher than those of traditional gold sensor under the same concentration of Siglec-15, which was consistent with previous performance analysis. Also, the detection limit of M-Ag@MNPs/gold sensor was calculated to be 1.36 pg mL-1. All these results had proved that aligning M-Ag@MNPs onto the gold chip could improve the performance of the SPR sensor and achieve sensitive detection of small amounts of clinical biomarkers.