Surface enhanced Raman scattering (SERS)-active bacterial detection by Layer-by-Layer (LbL) assembly all-nanoparticle microcapsules

Polymeric microcapsules composed by the Layer-by-Layer (LbL) approach have been used for various applications including drug delivery into cells and in vivo, conducting enzyme catalyzed reactions, performing sensoric functions. Typically, LbL-assembled microcapsules have been formulated via alternating deposition of positively and negatively charged polyelectrolytes onto sacrificial templates or so-called cores. In this work, we extend the LbL assembly to produce microcapsules solely based on nanoparticles instead of polymers. We have identified that 5 layers of nanoparticles is the minimum number of layers for a stable assembly of capsules on calcium carbonate templates. Subsequently, these capsules comprised of nanoparticles were applied as Surface Enhanced Raman Scattering (SERS) platform, where the nanoparticle-based shell of capsules is shown to enable SERS of both solutes and macromolecular structures such as bacterial cells.