One-Step Assembly of Fluorescence-Based Cyanide Sensors from Inexpensive, Off-The-Shelf Materials.

We report a simple and versatile approach to assemble sensitive and selective fluorescence "turn-on" sensors for cyanide by combining three off-the-shelf materials; namely fluorescent dye, 1-vinyl imidazole polymer, and cupric chloride. The cyanide-sensing species is a non-fluorescent fluorophore-polymer-Cu2+ complex; which forms as a result of the imidazole polymer's ability to bind both fluorophore and fluorescence quencher (Cu2+). Cyanide removes Cu2+ from these complexes; thereby "turning-on" sensor fluorescence. These sensors are water-soluble and have a detection limit of ~2.5 µM (CN-) in water. Our ternary complex-based sensing approach also enables facile emission tuning; we demonstrate the convenient, synthesis-free preparation of blue and green-emitting sensors using distyrylbiphenyl and fluorescein fluorophores, respectively. Furthermore; these ternary complexes are easily immobilized using agarose to create cyanide-sensing hydrogels; which are then used in a simple; novel microdiffusion apparatus to achieve interference-free cyanide analysis of aqueous media. The present study provides an inexpensive approach for portable; interference-free cyanide detection.

Pyoverdine Assay for Rapid and Early Detection of Pseudomonas aeruginosa in Burn Wounds.

Infection is responsible for up to 60% of deaths in burn patients, and Pseudomonas aeruginosa (PA) has the highest mortality rate among all causes of bacteremia. These aggressive and virulent infections are often not detected until there is a positive blood culture for PA, meaning the patient already has bacteremia. An assay that rapidly detects PA while it is still present at low numbers within the burn wound could therefore be transformative, as it would allow for early and more effective treatment intervention. Pyoverdine, an Fe3+ chelating fluorescent molecule, is produced by PA to overcome the problem of limited iron availability and is essential for PA to cause acute infections. Here, we report the development and use of a simple qualitative pyoverdine assay for detection of PA in a clinically relevant in vivo burn wound model. In contrast with the 24 h quantitative culture approaches currently used, the pyoverdine assay is complete within 15 min. The assay has a PA detection limit of ∼106 colony forming units/(g of tissue) and detects the PA-specific biomarker pyoverdine within burn wounds before the pathogen disseminates within the body, evidence that the assay can detect lower, prebacteremic levels of PA within burn wounds.

Spatially controlled reversible colloidal self-assembly.

We studied the localized self-assembly of colloidal crystals on a topographically patterned substrate. A competition between particle and pattern interactions provided the ability to reversibly assemble quasi-two-dimensional colloidal crystals on a periodic landscape. The assembly process was visualized and controlled in real-space and real-time using video microscopy. Independent measurements and computer simulations were used to quantify all interactions controlling self-assembly. Steady-state studies characterized spatially inhomogeneous, coexisting fluid and crystal microstructures at various stages of assembly. Microstructures arise from a balance of local sedimentation equilibria within potential energy features and a tunable pairwise depletion attraction between colloids. Transient colloidal crystal self-assembly occurred via a quasiequilibrium process as characterized by continuously evolving spatial profiles of local density, bond orientational order, and self-diffusivities.

Interfacial colloidal crystallization via tunable hydrogel depletants.

We demonstrate an approach using temperature-dependent hydrogel depletants to thermoreversibly tune colloidal attraction and interfacial colloidal crystallization. Total internal reflection and video microscopy are used to measure temperature-dependent depletion potentials between approximately 2 microm silica colloids and surfaces as mediated by approximately 0.2 microm poly-N-isopropylacrylamide (PNIPAM) hydrogel particles. Measured depletion potentials are modeled using the Asakura-Oosawa theory while treating PNIPAM depletants as swellable hard spheres. Monte Carlo simulations using the measured potentials predict reversible, quasi-2D crystallization and melting at approximately 27 degrees C in quantitative agreement with video microscopy images of measured microstructures (i.e., radial distribution functions) over the temperature range of interest (20-29 degrees C). Additional measurements of short-time self-diffusivities display excellent agreement with predicted diffusivities by considering multibody hydrodynamic interactions and using a swellable hard sphere model for the PNIPAM solution viscosity. Our findings demonstrate the ability to quantitatively measure, model, and manipulate kT-scale depletion attraction and phase behavior as a means of formally engineering interfacial colloidal crystallization.

Equivalent temperature and specific ion effects in macromolecule-coated colloid interactions.

Ensemble total internal reflection microscopy is used to measure reversible temperature- and specific-ion-mediated interaction potentials between macromolecule-coated colloids and surfaces. Potentials are measured between PEO-PPO-PEO (poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)) block copolymers adsorbed to hydrophobically modified silica colloids and glass or gold planar surfaces. Conditions investigated include temperatures from 20 to 47 degrees C and MgSO4 concentrations from 0.2 to 0.5 M. The solvent-quality-mediated copolymer layer collapse inferred by comparing measured potentials and the predicted van der Waals attraction, including effects of the adsorbed copolymer and surface roughness, displays good agreement with expected limits based on the PEO block contour length and the bulk PEO density. Superposition of all PEO layer collapse measurements onto a single universal curve, via a transformed temperature scale relative to a reference temperature in each case, indicates an equivalence of increasing temperature and increasing MgSO4 concentration when layer interactions and dimensions are mediated. Accurate knowledge of nanometer- and kT-scale interactions of copolymer-coated colloids as a function of temperature and MgSO4 concentration provides the ability to reversibly control the stability, phase behavior, and self-assembly of such particles.