Precise imaging of the cell surface of fluorescently labeled bacteria requires super-resolution methods because the size-scale of these cells is on the order of the diffraction limit. In this work, we present a photocontrollable small-molecule rhodamine spirolactam emitter suitable for non-toxic and specific labeling of the outer surface of cells for three-dimensional (3D) super-resolution (SR) imaging. Conventional rhodamine spirolactams photoswitch to the emitting form with UV light; however, these wavelengths can damage cells. We extended photoswitching to visible wavelengths >400 nm by iterative synthesis and spectroscopic characterization to optimize the substitution on the spirolactam. Further, an N-hydroxysuccinimide-functionalized derivative enabled covalent labeling of amines on the surface of live Caulobacter crescentus cells. Resulting 3D SR reconstructions of the labeled cell surface reveal uniform and specific sampling with thousands of localizations per cell and excellent localization precision in x, y, and z. The distribution of cell stalk lengths (a sub-diffraction-sized cellular structure) was quantified for a mixed population of cells. Pulse-chase experiments identified sites of cell surface growth. Covalent labeling with the optimized rhodamine spirolactam label provides a general strategy to study the surfaces of living cells with high specificity and resolution down to 10–20 nm.

We report computational chemistry-guided designs of chemoresponsive liquid crystals (LCs) with pyridine or pyrimidine groups that bind to metal cation-functionalized surfaces to provide improved selective responses to targeted vapor species (dimethylmethylphosphonate (DMMP)) over non-targeted species (water). We test the LC designs against experiments by synthesizing 4-(4-pentyl-phenyl)pyridine and 5-(4-pentyl-phenyl)-pyrimidine and quantifying LC responses to DMMP and water. Consistent with the computations, pyridine-containing LCs bind to metal cation-functionalized surfaces too strongly to permit a response to either DMMP or water whereas pyrimidine-containing LCs undergo a surface-driven orientational transition in response to DMMP without interference from water. The computation predictions are not strongly dependent on assumptions regarding the degree of coordination of the metal ions but are limited in their ability to predict LC responses when using cations with mostly empty d orbitals. Overall, this work identifies a promising new class of chemoresponsive LCs based on pyrimidine that exhibits enhanced tolerance to water, a result that is important because water is a ubiquitous and particularly challenging chemical interferent in chemical sensing strategies based on LCs. The work also provides further evidence of the transformative utility of computational chemistry methods to design of LC materials that exhibit selective orientational responses in specific chemical environments.Received: ((will be filled in by the editorial staff))Revised: ((will be filled in by the editorial staff))

Surface-supported liquid crystals (LCs) that exhibit orientational and thus optical responses upon exposure to ppb concentrations of Cl gas are reported. Computations identified Mn cations as candidate surface binding sites that undergo redox-triggered changes in the strength of binding to nitrogen-based LCs upon exposure to Cl gas. Guided by these predictions, μm-thick films of nitrile- or pyridine-containing LCs were prepared on surfaces decorated with Mn binding sites as perchlorate salts. Following exposure to Cl , formation of Mn (in the form of MnO microparticles) was confirmed and an accompanying change in the orientation and optical appearance of the supported LC films was measured. In unoptimized systems, the LC orientational transitions provided the sensitivity and response times needed for monitoring human exposure to Cl gas. The response was also selective to Cl over other oxidizing agents such as air or NO and other chemical targets such as organophosphonates.

We report the use of computational chemistry methods to design a chemically responsive liquid crystal (LC). Specifically, we used electronic structure calculations to model the binding of nitrile-containing mesogens (4′-n-pentyl-4biphenylcarbonitrile) to metal perchlorate salts (with explicit description of the perchlorate anion), which we call the coordinately saturated anion model (CSAM). The model results were validated against experimental data. We then used the CSAM to predict that selective fluorination can reduce the strength of binding of nitrile-containing nematic LCs to metalsalt-decorated surfaces and thus generate a faster reordering of the LC in response to competitive binding of dimethylmethylphosphonate (DMMP). We tested this prediction via synthesis of fluorinated compounds 3-fluoro-4′-pentyl[1,1′-biphenyl]-4-carbonitrile and 4-fluoro-4′-pentyl-1,1′-biphenyl, and subsequent experimental measurements of the orientational response of LCs containing these compounds to DMMP. These experimental measurements confirmed the theoretical predictions, thus providing the first demonstration of a chemoresponsive LC system designed from computational chemistry.

The development of stimuli-responsive materials suitable for use in wearable sensors is a key unresolved challenge. Liquid crystals (LCs) are particularly promising, as they do not require power, are light-weight, and can be tuned to respond to a range of targeted chemical stimuli. Here, an advance is reported in the design of LCs for chemical sensors with the discovery of LCs that assume parallel orientations at free surfaces and yet retain their chemoresponsiveness. The resulting LC-based sensors are more sensitive and exhibit faster responses than previous LC sensor designs.