Nanoparticles from colloidal solutionwith controlled composition, size, and shapeserve as excellent building blocks for plasmonic devices and metasurfaces. However, understanding hierarchical driving forces affecting the geometry of oligomers and interparticle gap spacings is still needed to fabricate high-density architectures over large areas. Here, electrohydrodynamic (EHD) flow is used as a long-range driving force to enable carbodiimide cross-linking between nanospheres and produces oligomers exhibiting sub-nanometer gap spacing over mm 2 areas. Anhydride linkers between nanospheres are observed via surface-enhanced Raman scattering (SERS) spectroscopy. The anhydride linkers are cleavable via nucleophilic substitution and enable placement of nucleophilic molecules in electromagnetic hotspots. Atomistic simulations elucidate that the transient attractive force provided by EHD flow is needed to provide a sufficient residence time for anhydride cross-linking to overcome slow reaction kinetics. This synergistic analysis shows assembly involves an interplay between long-range driving forces increasing nanoparticle− nanoparticle interactions and probability that ligands are in proximity to overcome activation energy barriers associated with short-range chemical reactions. Absorption spectroscopy and electromagnetic full-wave simulations show that variations in nanogap spacing have a greater influence on optical response than variations in close-packed oligomer geometry. The EHD flow−anhydride cross-linking assembly method enables close-packed oligomers with uniform gap spacings that produce uniform SERS enhancement factors. These results demonstrate the efficacy of colloidal driving forces to selectively enable chemical reactions leading to future assembly platforms for large-area nanodevices.

Detection of bacterial metabolites at low concentrations in fluids with complex background allows for applications ranging from detecting biomarkers of respiratory infections to identifying contaminated medical instruments. Surface-enhanced Raman scattering (SERS) spectroscopy, when utilizing plasmonic nanogaps, has the relatively unique capacity to reach trace molecular detection limits in a label-free format, yet large-area device fabrication incorporating nanogaps with this level of performance has proven difficult. Here, we demonstrate the advantages of using chemical assembly to fabricate SERS surfaces with controlled nanometer gap spacings between plasmonic nanospheres. Control of nanogap spacings via the length of the chemical crosslinker provides uniform SERS signals, exhibiting detection of pyocyanin, a secondary metabolite of Pseudomonas aeruginosa, in aqueous media at concentration of 100 pg·mL. When using machine learning algorithms to analyze the SERS data of the conditioned medium from a bacterial culture, having a more complex background, we achieve 1 ng·mL limit of detection of pyocyanin and robust quantification of concentration spanning 5 orders of magnitude. Nanogaps are also incorporated in an in-line microfluidic device, enabling longitudinal monitoring of P. aeruginosa biofilm formation via rapid pyocyanin detection in a medium effluent as early as 3 h after inoculation and quantification in under 9 h. Surface-attached bacteria exposed to a bactericidal antibiotic were differentially less susceptible after 10 h of growth, indicating that these devices may be useful for early intervention of bacterial infections.

Unilamellar vesicles composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) with varying 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-poly(ethylene glycol)-2000-N-[3-(2-pyridyldithio) propionate] (DSPE-PEG-PDP) concentration between 0 mol % and 24 mol % were assembled on atomically flat template-stripped gold (TS Au) surfaces. Force spectroscopy, using an atomic force microscope (AFM), of the resulting tethered lipid bilayer membranes (tLBMs) in buffer provided information regarding mechanical response as a function of tethering molecule, DSPE-PEG-PDP, concentration. Young’s modulus was determined by fitting the force–indentation curve with a recently modified Sneddon model that corrects for contributions from the substrate underneath. At low concentrations, Young’s modulus is lower than that of a supported POPC LBM, i.e., directly sitting on a solid substrate. The decrease in modulus is attributed to increased membrane fluidity as coupling between the tLBM and solid substrate is reduced by the incorporation of DSPE-PEG-PDP tethering groups. From the determined Young’s modulus values, the PEG chain conformation is found to dominate tLBM rigidity at concentrations above 6 mol %. Analysis of AFM force spectroscopy data indicates that the poly(ethylene glycol) (PEG) mushroom to brush transition occurs near 6 mol %, and this leads to first softening and then abrupt stiffening of tLBMs at higher DSPE-PEG-PDP concentration associated with the transition. When DSPE-PEG-PDP concentration is increased to 24 mol %, AFM topography and Young’s modulus appear correlated with another phase transition; AFM topography images are consistent with a bilayer disk structure with DSPE-PEG-PDP segregated at the rim of the disk.

A three-dimensional gyroid-inspired architecture composed of turbostratic graphene was fabricated using colloidal self-assembly and chemical vapor deposition.