Abstract
A simple technique is presented to fabricate stable and reproducible plasmonic substrates using chicken eggshell as bio-templates, an otherwise everyday waste material. The 3-dimensional (3D) submicron features on the outer shell (OS), inner shell (IS), and shell membrane (SM) regions are sputter coated with gold and characterized for surface-enhanced Raman scattering (SERS) performance with respect to coating thickness, enhancement factor (EF), hot-spots distribution, and reproducibility. The OS and IS substrates have similar EF (2.6 × 106 and 1.8 × 106, respectively), while the SM provides smaller EF (1.5 × 105) due to its larger characteristic feature size. The variability from them (calculated as relative standard deviation, %RSD) are less than 7, 15, and 9 for the OS, IS, and SM substrates, respectively. Due to the larger EF and better signal reproducibility, the OS region is used for label-free sensing and identification of Escherichia coli and Bacillus subtilis bacteria as an example of the potential SERS applications. It is demonstrated that the detection limit could reach the level of single bacterial cells. The OS and IS regions are also used as templates to fabricate 3D flexible SERS substrates using polydimethylsiloxane and characterized. The simple, low-cost, and green route of fabricating plasmonic substrates represents an innovative alternative approach without the needs for nanofabrication facilities. Coupled with hyperspectral Raman imaging, high-throughput bio-sensing can be carried out at the single pathogen level.
Highlights
Surface-enhanced Raman scattering (SERS) has gained significant attention as an emerging analytical tool since its discovery [1,2,3,4,5]
Tanahashi et al deposited Ag nanoparticles (100–250 nm) on TiO2-coated cicada wings to obtain a SERS substrate and reported 25 times signal enhancement when compared to thin Ag film [25]. These results suggest that plasmonic substrates, based on bio-templates, can potentially be employed in bio-sensing
We systematically investigate the SERS performance of three different eggshell regions, outer shell (OS), inner shell (IS), and shell membrane (SM), after a thin Au coating
Summary
Surface-enhanced Raman scattering (SERS) has gained significant attention as an emerging analytical tool since its discovery [1,2,3,4,5]. Recent progress in nanoscience has led to highly reproducible techniques for fabricating complex nanostructures for SERS. These techniques include electron-beam lithography, chemical etching, colloid immobilization, annealing of metal-ion-implanted silicon, and nanosphere lithography [15,16,17]. Most of these patterning techniques still require significant laboratory infrastructures and sophisticated preparation procedures, limiting further adoption of SERS by researchers without nanofabrication expertise [18]. Obtaining a clean, non-toxic, and environment friendly fabrication technique is very appealing
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