Electrostatic self-assembly of 2D Janus PS@Au nanoraspberry photonic-crystal array with enhanced near-infrared SERS activity

We developed a simple electrostatic self-assembly strategy to fabricate a kind of 2D Janus PS@Au nanoraspberry photonic-crystal array with a compelling near-infrared (NIR) SERS performance. Due to the opposite charges, the small positively-charged Au nanoparticles could effectively self-assemble on the 2D larger negatively-charged polystyrene (PS) latex photonic crystal. The number of Au nanoparticles deposited on the PS latex was highly controllable after tuning the ionic strength of the Au nanoparticle solution. These Janus PS@Au nanoraspberry arrays demonstrate a strong NIR-SERS activity with the enhanced factor up to 1.44 x 10(9) and an ultra-low molecular detection limit of 10(-11) M. The strongly-enhanced NIR-SERS performance is ascribed to the high density of hotspots formed in the unique Janus nanoraspberry structure and the photonic-crystal structure. With the simplicity of the electrostatic self-assembly strategy, the uniformity and tunability of the NIR-SERS activity, we envision that this work not only provides a new way for the fabrication of NIR-SERS substrates but also paves the way for bridging the light coupling with the matter, particularly in the NIR wavelength region.