Self-assembly of monodisperse composite microgels with bimetallic nanorods as core and PNIPAM as shell into close-packed monolayers and SERS efficiency

• The monolayer film of Au@AgNR@PNIPAM composite microgels was formed by a dip coating method.
• The monolayer film on the silicon surface have high surface coverage, low surface roughness and high stability.
• The plasmonic property of monolayer film on the silicon surface still maintained the LSPR optical performance of Au@AgNRs.
• The monolayer film used as surface enhanced Raman scattering substrate is convenient for analysis and detection.

In this study, monolayer film of composite microgels with bimetallic nanorods as core and PNIPAM as shell (Au@AgNR@PNIPAM) assembly on a modified surface of silicon wafer was formed by a dip coating method. The effects of temperature, pH and concentration of KCl on the surface morphology of monolayer were discussed. And when the temperature was 50 °C; pH value was 4.0; concentration of KCl was 10 mM, a monolayer film would be formed much better. By the characterization of atomic force microscopy (AFM) and field emission scanning electron microscopy (FE-SEM), the monolayer structure of Au@AgNR@PNIPAM composite microgels assembled products was confirmed. The analysis of attenuated total reflection Fourier transform infrared absorption spectrum (ATR-FTIR) confirmed that the chemical composition of monolayer film on the silicon wafer surface was PNIPAM. And the UV–visible spectroscopy showed Au@AgNR in the monolayer film still maintained their LSPR optical performance. Assembled product has high stability, the surface morphology and coverage of the monolayer film did not change significantly when testing in a swing speed of 100 rpm Rocking Shaker within 30 min. The assembled monolayer was used as SERS substrates to trace the 10− 1 M to 10− 4 M 1-naphthol in aqueous solution, and the analysis results was with good reproducibility.

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