Label-free and culture-free microbe detection by three dimensional hot-junctions of flexible Raman-enhancing nanohybrid platelets.

Abstract

Novel nanohybrid arrays of silver (Ag)-on-silicate platelets with flexibility and three-dimensional (3D) hot-junctions (particularly in z-direction) were discovered for improving the stability of free nanoparticles and the mobility of rigid (glass or silicon-based) substrates in surface-enhanced Raman scattering (SERS) detection technology. Since the Ag nanoparticles are adsorbed on both sides of few nanometer-thick silicate platelets (single-layer exfoliated clay), the geometric arrangement of Ag on both sides of the nanoplatelets (Ag/NSP) may induce strong hot-junctions (z-direction) in reference to the pristine montmorillonite clay (multi-layers) at the thickness of ∼20 nm, measured by small molecules (adenine of DNA) and bacteria (S. aureus). Enormous red-shifts (16 nm wavelength difference) were observed between single layer and multi-layer silicate platelets, showing that huge surface plasmon enhancement comes from hot junctions in the z-direction (∼7 times higher than 2D hot-junctions of traditional SERS biochips). Further, the Ag/NSP SERS substrate displays a free floating mobility and optical transparency (less background interference), which inherently increase the contacted surface-area between the substrate and microorganisms, to enhance the SERS sensitivity. The surface modulation with a surfactant could be complimentary towards a variety of microorganisms including hydrophobic microbes, irregular-shaped microorganisms and larger biological cells due to their mutual specific surface interactions. It was anticipated to apply in the rapid detection for varied microbes with label-free and culture-free characterizations.