Herein, we developed
a natural surface-enhanced Raman scattering
(SERS) substrate based on size-tunable Au@Ag nanoparticle-coated mussel
shell to form large-scale three-dimensional (3D) supercrystals (up
to 10 cm2) that exhibit surface-laminated structures and
crossed nanoplates and nanochannels. The high content of CaCO3 in the mussel shell results in superior hydrophobicity for
analyte enrichment, and the crossed nanoplates and nanochannels provided
rich SERS hot spots, which together lead to high sensitivity. Finite-difference
time-domain simulations showed that nanoparticles in the channels
exhibit apparently a higher electromagnetic field enhancement than
nanoparticles on the platelets. Thus, under optimized conditions (using
Au@AgNPs with 5 nm shell thickness), highly sensitive SERS detection
with a detection limit as low as 10–9 M for rhodamine
6G was obtained. Moreover, the maximum electromagnetic field enhancement
of different types of 3D supercrystals shows no apparent difference,
and Au@AgNPs were uniformly distributed such that reproducible SERS
measurements with a 6.5% variation (613 cm–1 peak)
over 20 spectra were achieved. More importantly, the as-prepared SERS
substrates can be utilized for the fast discrimination of Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa by discriminant
analysis. This novel Au@Ag self-assembled mussel shell template holds
considerable promise as low-cost, durable, sensitive, and reproducible
substrates for future SERS-based biosensors.