Most bacteria in nature exist as biofilms, which support intercellular signaling processes such as quorum sensing (QS), a cell-to-cell communication mechanism that allows bacteria to monitor and respond to cell density and changes in the environment. Because QS and biofilms are involved in the ability of bacteria to cause disease, there is a need for the development of methods for the non-invasive analysis of QS in natural bacterial populations. Here, by using surface-enhanced resonance Raman scattering spectroscopy, we report rationally designed nanostructured plasmonic substrates for the in-situ, label-free detection of a QS signaling metabolite in growing Pseudomonas aeruginosa biofilms and microcolonies. The in situ, non-invasive plasmonic imaging of QS in biofilms provides a powerful analytical approach for studying intercellular communication on the basis of secreted molecules as signals.

Three series of cationic oligo p-phenyleneethynylenes (OPEs) have been synthesized to study their structure-property relationships and gain insights into the transition from molecular to macromolecular properties. The absorbance maxima and molar extinction coefficients in all three sets increase with increasing number of repeat units; however, the increase in λ(max) between the oligomers having 2 and 3 repeat units is very small, and the oligomer having 3 repeat units shows virtually the same spectra as a p-phenyleneethynylene polymer having 49 repeat units. A computational study of the oligomers using density functional theory calculations indicates that while the simplest oligomers (OPE-1) are fully conjugated, the larger oligomers are nonplanar and the limiting "segment chromophore" may be confined to a near-planar segment extending over three or four phenyl rings. Several of the OPEs self-assemble on anionic "scaffolds", with pronounced changes in absorption and fluorescence. Both experimental and computational results suggest that the planarization of discrete conjugated segments along the phenylene-ethynylene backbone is predominantly responsible for the photophysical characteristics of the assemblies formed from the larger oligomers. The striking differences in fluorescence between methanol and water are attributed to reversible nucleophilic attack of structured interfacial water on the excited singlet state.

Hybrid nanostructures composed of metal nanoparticles and metal-organic frameworks (MOFs) have recently received increasing attention toward various applications due to the combination of optical and catalytic properties of nanometals with the large internal surface area, tunable crystal porosity and unique chemical properties of MOFs. Encapsulation of metal nanoparticles of well-defined shapes into porous MOFs in a core-shell type configuration can thus lead to enhanced stability and selectivity in applications such as sensing or catalysis. In this study, the encapsulation of single noble metal nanoparticles with arbitrary shapes within zeolitic imidazolate-based metal organic frameworks (ZIF-8) is demonstrated. The synthetic strategy is based on the enhanced interaction between ZIF-8 nanocrystals and metal nanoparticle surfaces covered by quaternary ammonium surfactants. High resolution electron microscopy and tomography confirm a complete core-shell morphology. Such a well-defined morphology allowed us to study the transport of guest molecules through the ZIF-8 porous shell by means of surface-enhanced Raman scattering by the metal cores. The results demonstrate that even molecules larger than the ZIF-8 aperture and pore size may be able to diffuse through the framework and reach the metal core.

Plasmonic supercrystals and periodically structured arrays comprise a class of materials with unique optical properties that result from the interplay of plasmon resonances, as well as near- and far-field coupling. Controlled synthesis of such hierarchical structures remains a fundamental challenge, as it demands strict control over the assembly morphology, array size, lateral spacing, and macroscale homogeneity. Current fabrication approaches involve complicated multistep procedures lacking scalability and reproducibility, which has hindered the practical application of plasmonic supercrystal arrays. Herein, these challenges are addressed by adding an organic solvent to achieve kinetic control over the template-assisted colloidal assembly of nanoparticles from aqueous dispersion. This method yields highly regular periodic arrays, with feature sizes ranging from less than 200 nm up to tens of microns. A combined experimental/computational approach reveals that the underlying mechanism is a combination of the removal of interfacial surfactant micelles from the particle interface and altered capillary flows. Assessing the efficacy of such square arrays for surface-enhanced Raman scattering spectroscopy, we find that a decrease of the lattice periodicity from 750 nm down to 400 nm boosts the signal by more than an order of magnitude, thereby enabling sensitive detection of analytes, such as the bacterial quorum sensing molecule pyocyanin, even in complex biological media.

This article reports an investigation of the photophysical properties and the light- and dark-biocidal activity of two poly(phenyleneethynylene) (PPE)-based conjugated polyelectrolytes (CPEs) bearing cationic imidazolium solubilizing groups. The two polymers feature the same PPE-type backbone, but they differ in the frequency of imidazoliums on the chains: PIM-4 features two imidazolium units on every phenylene repeat, whereas PIM-2 contains two imidazolium units on every other phenylene unit. Both polymers are very soluble in water and polar organic solvents, but their propensity to aggregate in water differs with the density of the imidazolium units. The polymers are highly fluorescent, and they exhibit the amplified quenching effect when exposed to a low concentration of anionic electron-acceptor anthraquinone disulfonate. The CPEs are also quenched by a relatively low concentration of pyrophosphate by an aggregation-induced quenching mechanism. The biocidal activity of the cationic imidazolium CPEs was studied against both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus bacteria in the dark and under blue-light illumination. Both polymers are effective biocides, exhibiting greater than 3 log kill with 30-60 min of light exposure at concentrations of ≤10 μg mL(-1).

Optical manipulation techniques are important in many fields. For instance, they enable bottom-up assembly of nanomaterials and high-resolution and in situ analysis of biological cells and molecules, providing opportunities for discovery of new materials, medical diagnostics, and nanomedicines. Traditional optical tweezers have their applications limited due to the use of rigorous optics and high optical power. New strategies have been established for low-power optical manipulation techniques. Optothermal manipulation, which exploits photon-phonon conversion and matter migration under a light-controlled temperature gradient, is one such emerging technique. Elucidation of the underlying physics of optothermo-matter interaction and rational engineering of optical environments are required to realize diverse optothermal manipulation functionalities. This Account covers the working principles, design concepts, and applications of a series of newly developed optothermal manipulation techniques, including bubble-pen lithography, opto-thermophoretic tweezers, opto-thermoelectric tweezers, optothermal assembly, and opto-thermoelectric printing. In bubble-pen lithography, optical heating of a plasmonic substrate generates microbubbles at the solid-liquid interface to print diverse colloidal particles on the substrates. Programmable bubble printing of semiconductor quantum dots on different substrates and haptic control of printing have also been achieved. The key to optothermal tweezers is the ability to deliver colloidal particles from cold to hot regions of a temperature gradient or a negative Soret effect. We explore different driving forces for the two types of optothermal tweezers. Opto-thermophoretic tweezers rely on an abnormal permittivity gradient built by structured solvent molecules in the electric double layer of colloidal particles and living cells in response to heat-induced entropy, and opto-thermoelectric tweezers exploit a thermophoresis-induced thermoelectric field for the low-power manipulation of small nanoparticles with minimum diameter around 20 nm. Furthermore, by incorporating depletion attraction into the optothermal tweezers system as particle-particle or particle-substrate binding force, we have achieved bottom-up assembly and reconfigurable optical printing of artificial colloidal matter. Beyond optothermal manipulation techniques in liquid environments, we also review recent progress of gas-phase optothermal manipulation based on photophoresis. Photophoretic trapping and transport of light-absorbing materials have been achieved through optical engineering to tune particle-molecule interactions during optical heating, and a novel optical trap display has been demonstrated. An improved understanding of the colloidal response to temperature gradients will surely facilitate further innovations in optothermal manipulation. With their low-power operation, simple optics, and diverse functionalities, optothermal manipulation techniques will find a wide range of applications in life sciences, colloidal...

A novel class of phenylene ethynylene polyelectrolyte oligomers (OPEs) has been found to be effective biocidal agents against a variety of pathogens. The mechanism of attack is not yet fully understood. Recent studies have shown that OPEs cause catastrophic damage to large unilamellar vesicles. This study uses classical molecular dynamics (MD) simulations to understand how OPEs interact with model lipid bilayers. All-atom molecular dynamics simulations show that aggregates of OPEs inserted into the membrane cause significant structural damage and create a channel, or pore, that allows significant leakage of water through the membrane on the 0.1 μs time scale.

Recent advances in chemical sciences have enabled the tailorable synthesis of colloidal particles with variable composition, size, shape and properties. Building superstructures with colloidal particles as building blocks is appealing for the fabrication of functional metamaterials and nanodevices. Optical nano-printing provides a versatile platform to print various particles into arbitrary configurations with nanometric precision. In this review, we summarize recent progress in optical nano-printing of colloidal particles and its related applications. Diverse techniques based on different physical mechanisms, including optical forces, light-controlled electric fields, optothermal effects, laser-directed thermo-capillary flows, and photochemical reactions, are discussed in detail. With its flexible and versatile capabilities, optical nano-printing will find promising applications in numerous fields such as nanophotonics, energy, microelectronics, and nanomedicine.