Fabrication of in situ magnetic capturing and Raman enhancing nanoplatelets for detection of bacteria and biomolecules

In situ magnetic capturing and surface-enhanced Raman scattering (SERS) detection techniques can be used for detecting microbial contamination and uremic toxins. Magnetic SERS substrates were fabricated using immobilized gold nanoparticles (AuNPs) and iron-oxide (Fe3O4) nanoparticles on exfoliated nanoscale silicate platelets (NSPs). The prepared magnetic SERS nanosheets (Fe3O4@AuNPs@NSP nanosheets) were able to not only magnetically capture bacteria and biomolecules but also effectively induce the hot-spot effect and enhance the Raman signal by the surface plasmon resonance of the AuNP arrays. The results showed that both the ratio of AuNPs to Fe3O4 nanoparticles and the order of immobilization on the NSP nanosheets are important factors for inducing magnetic capturing behavior and SERS sensitivity. A method that yielded magnetic capturing behavior was to graft AuNPs on NSP nanosheets first, followed by the immobilization of Fe3O4 nanoparticles. Fe3O4@AuNPs@NSP nanosheets prepared using 0.9 mM HAuCl4 displayed the highest magnetic capturing behavior and SERS enhancement effect, showing an optimal interparticle gap. The bacteria (Escherichia coli) were captured and separated by the magnetic SERS substrates using an applied magnetic field, and then the magnetically captured samples were monitored by Raman spectroscopy for rapid SERS detection. Furthermore, the SERS sensitivity increased by -2 times after magnetic capturing, and the limit of detection for sensing

Automated summary

In this study, magnetic SERS substrates were prepared by immobilizing gold nanoparticles and iron-oxide nanoparticles on exfoliated nanoscale silicate platelets. The substrates showed both magnetic capturing behavior and enhanced Raman signal. The ratio of gold nanoparticles to iron-oxide nanoparticles and the order of immobilization on the nanoscale silicate platelets were found to be important factors for inducing magnetic capturing behavior and enhancing SERS sensitivity.