Polyethyleneimine-assisted formation of Ag-SiO 2 hybrid microspheres for H 2 O 2 sensing and SERS applications.

Herein, we report a simple, cost-effective, and eco-friendly approach for producing polyethyleneimine (PEI)-assisted silver nanoparticle-supported silica microspheres through evaporation-induced assembly (EIA). The silica-PEI microspheres obtained through EIA consisted of highly trapped PEI molecules owing to their electrosorption onto oppositely charged silica colloids. The trapped PEI molecules in the microspheres played a crucial role in linking silver ions to form silver ion-PEI complexes, which were then reduced to form silver nanoparticles. Further, the complex interactions between PEI and silica colloids led to enhanced porosity in the microspheres, enabling the efficient adsorption of Ag ions. The characterization of the Ag-SiO 2 microspheres was carried out using various techniques, including field-emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD), small-angle X-ray scattering (SAXS), and Fourier transform infrared (FTIR) spectroscopy, which confirmed the successful formation of Ag nanoparticles on microspheres, and a plausible formation mechanism is elucidated. The Ag-SiO 2 microspheres exhibited good sensing properties for hydrogen peroxide (H 2 O 2 ), with an estimated limit of detection of 1.08 mM and a sensitivity of 0.033 μA mM -1 mm -2 . The microspheres were also used as a surface-enhanced Raman scattering (SERS) substrate, which demonstrated high sensitivity in detecting rhodamine 6G down to a concentration of 2 × 10 -6 M. The present approach elucidates a promising alternative to conventional methods that face challenges, such as scalability issues, complex and cumbersome synthesis procedures, and the use of strong reducing agents. With the potential for industrial-level scalability, this method offers a viable strategy for producing Ag-SiO 2 microspheres with possible applications in biomedical and sensing technologies.