During white-light exposure, the region outside of the hologram polymerized to form a random-phase segregated morphology referred to as the floodlit region. Film thickness was controlled by the addition of 10 lm diameter glass rods to the pre-polymer syrup. The diffraction efficiency of the grating was determined through the ratio of the intensity of diffracted light to incident light using a He-Ne (632 nm) laser. SEM images were collected with a Hitachi 900S operating at 1 keV. The PM597 was excited with the doubled output (532 nm) of a Nd:YAG that had a repetition rate of 10 Hz and pulse duration of 5-8 ns. Photoluminescence (PL) was collected perpendicular to the cell with an Ocean Optics CCD/spectrometer that had a resolution of 1.9 nm.

In the light of the significance and urgency for the recognition and sensing of anions specifically, especially those of biological relevance, herein, we wish to demonstrate a novel colorimetric avenue for highly selective iodide recognition and sensing using simple citrate-stabilized core/shell Cu@Au nanoparticles. No other ions than iodide can induce an appreciable color change of the Cu@Au nanoparticles solution from purple to red by transforming the interconnected, irregularly shaped nanoparticles to the single, separated, and nearly spherical ones, as confirmed by the transmission electron microscopy (TEM). On the basis of the optical spectra and TEM studies, a mechanism of iodide-induced aggregating/fusion, fragmentation, and reorganization of atoms is proposed. With this strategy, 6 μM (0.76 ppm) of iodide can be recognized within 20 min by naked-eye observation. This sensitive and selective colorimetric assay opens up a fresh insight of facile, rapid, and reliable detection of iodide and may find its future application in the analysis of the total iodine in edible salt as well as the clinical diagnosis of urinary iodide.

We report a rapid and specific aptamer-based method for one-step cocaine detection with minimal reagent requirements. The feasibility of aptamer-based detection has been demonstrated with sensors that operate via target-induced conformational change mechanisms, but these have generally exhibited limited target sensitivity. We have discovered that the cocaine-binding aptamer MNS-4.1 can also bind the fluorescent molecule 2-amino-5,6,7-trimethyl-1,8-naphthyridine (ATMND) and thereby quench its fluorescence. We subsequently introduced sequence changes into MNS-4.1 to engineer a new cocaine-binding aptamer (38-GC) that exhibits higher affinity to both ligands, with reduced background signal and increased signal gain. Using this aptamer, we have developed a new sensor platform that relies on the cocaine-mediated displacement of ATMND from 38-GC as a result of competitive binding. We demonstrate that our sensor can detect cocaine within seconds at concentrations as low as 200 nM, which is 50-fold lower than existing assays based on target-induced conformational change. More importantly, our assay achieves successful cocaine detection in body fluids, with a limit of detection of 10.4, 18.4, and 36 μM in undiluted saliva, urine, and serum samples, respectively.