Plasmonic nanoparticles assemblies templated by helical bacteria and resulting optical activity

Abstract

Plasmonic nanoparticles (NPs) adsorbing onto helical bacteria can lead to formation of NP helicoids with micron scale pitch. Associated chiroptical effects can be utilized as bioanalytical tool for bacterial detection and better understanding of the spectral behavior of helical self‐assembled structures with different scales. Here, we report that enantiomerically pure helices with micron scale of chirality can be assembled on Campylobacter jejuni, a helical bacterium known for severe stomach infections. These organisms have right‐handed helical shapes with a pitch of 1–2 microns and can serve as versatile templates for a variety of NPs. The bacteria itself shows no observable rotatory activity in the visible, red, and near‐IR ranges of electromagnetic spectrum. The bacterial dispersion acquires chiroptical activity at 500–750 nm upon plasmonic functionalization with Au NPs. Finite‐difference time‐domain simulations confirmed the attribution of the chiroptical activity to the helical assembly of gold nanoparticles. The position of the circular dichroism peaks observed for these chiral structures overlaps with those obtained before for Au NPs and their constructs with molecular and nanoscale chirality. This work provides an experimental and computational pathway to utilize chiroplasmonic particles assembled on bacteria for bioanalytical purposes.

Nanophotonic Approaches for Chirality Sensing

“…Chiral NP assemblies have great potential for detecting biomolecules and biomarkers. , The underlying principle behind using these structures is registering the enhancement or attenuation of chiroptical signals upon assembly or disassembly of chiral nanostructures. ,,− In chiral NP assemblies, the LSPRs of individual achiral NPs couple together to form collective modes that extend over the entire NP assembly, similar to the previously discussed corner-stacked nanorod dimers of the Born–Kuhn model. Some nanostructures developed for chirality sensing include Au–Au NP dimers, Au nanorod dimers, , Au–Ag NP dimers, Au–quantum dot NP dimers, and twisted superstructures .…”

Nanoarchitectonics on living cells

“…For example, Kotov and co-workers demonstrated chiral plasmon activities through immobilization of plasmonic Au nanoparticles on a helical bacterium, Campylobacter jejuni , which possesses right-handed helical morphologies with a pitch of 1–2 μm. 58 Chiroptical activity at plasmonic regions (500–750 nm) was confirmed in the nanoparticle-coated bacteria cells, although the bacteria themselves did not show any rotatory activities. Simulations have confirmed that the observed chiroptical activity was originated in helical assembly of gold nanoparticles.…”

Template-assisted self-assembly of achiral plasmonic nanoparticles into chiral structures

“…While few-NP chiral systems were rst demonstrated with PCR-based assembly protocols, 5 and great precision can be achieved by using DNA origami templates, 41,42 larger-scale ensembles have also been achieved using other materials for templating chiral self-assembly. Established examples include the use of peptides, 43,44 chiral bers, 45 or even bacteria, 46 while new Luis Liz-Marzán has been an Ikerbasque Professor and Scien-tic Director of CIC biomaGUNE, in San Sebastián (Spain), since 2012. He graduated in chemistry from the University of Santiago de Compostela, was a postdoctoral researcher at Utrecht University and a Professor at the University of Vigo (1995-2012), as well as a visiting professor at various research institutions worldwide.…”

“…While few-NP chiral systems were first demonstrated with PCR-based assembly protocols, 5 and great precision can be achieved by using DNA origami templates, 41,42 larger-scale ensembles have also been achieved using other materials for templating chiral self-assembly. Established examples include the use of peptides, 43,44 chiral fibers, 45 or even bacteria, 46 while new potential candidates like semiconductor helices are being introduced. 47 In such drastically different materials, slightly twisted orientations of assembled NPs – even at single degree angles – are a sufficient source of asymmetry to induce a collective chiroptical response toward impinging circularly polarized light.…”