Paper-Based, Hand-Drawn Free Chlorine Sensor with Poly(3,4-ethylenedioxythiophene):Poly(styrenesulfonate).

The concentration of free chlorine used for disinfecting drinking water, recreational water, and food processing water is critical for environmental and human health conditions, and should be controlled within stipulated ranges. This report, for the first time, describes a paper-based electrochemical free chlorine sensor fabricated by hand-drawing. The electrical resistivity of a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) chemoresistor increases when it is exposed to free chlorine in water due to oxidation reactions. Because the relative change of the electrical resistance represents the sensor's response, the sensor can be fabricated by hand-drawing with different shapes and dimensions. The fabrication steps are all at room temperature, require no instrumentation or equipment, and can be carried out by untrained personnel. The fabricated sensor is mechanically stable, reusable, has a wide sensing range, and can accurately measure free chlorine concentrations in real water samples. Therefore, the low-cost, hand-drawn free chlorine sensor is of great significance for water quality monitoring in less developed areas where fabrication facilities, analytical equipment, and trained personnel are limited, but the need for analytical devices is critical. In addition to the free chlorine sensor demonstrated in this study, other types of PEDOT:PSS-based sensors and electronic devices can be fabricated by the developed hand-drawing process.

Direct method of tracing the wetting states on nanocomposite surfaces.

Identifying the two distinctive wetting states on a nanostructured surface remains an open challenge. We report here a direct method of tracing the Wenzel and Cassie states by using Ag nanoparticles as tracing agents. The method provides an answer to the long-standing question of whether there is a transition from the Wenzel to Cassie state in the sliding angle drop on superhydrophobic nanocomposite thin films containing multiwalled carbon nanotubes.

Fully Integrated, Simple, and Low-Cost Electrochemical Sensor Array for in Situ Water Quality Monitoring.

Rapid, accurate and inexpensive monitoring of water quality parameters is indispensable for continued water safety, especially in resource-limited areas. Most conventional sensing systems either can only monitor one parameter at a time or lack user-friendly on-site monitoring capabilities. A fully integrated electrochemical sensor array is an excellent solution to this barrier. Electrochemical sensing methods involve transduction of water quality parameters where chemical interactions are converted to electrical signals. The challenge remains in designing low-cost, easy-to-use, and highly sensitive sensor array that can continuously monitor major water quality parameters such as pH, free chlorine, temperature along with emerging pharmaceutical contaminants, and heavy metal without the use of expensive laboratory-based techniques and trained personnel. Here, we overcame this challenge through realizing a fully integrated electrochemical sensing system that offers simultaneous monitoring of pH (57.5 mV/pH), free chlorine (186 nA/ppm), and temperature (16.9 mV/°C) and on-demand monitoring of acetaminophen and 17ß-estradiol (<10 nM) and heavy metal (<10 ppb), bridging the technological gap between signal transduction, processing, wireless transmission, and smartphone interfacing. This was achieved by merging nanomaterials and carbon nanotube-based sensors fabricated on microscopic glass slides controlled by a custom-designed readout circuit, a potentiostat, and an Android app. The sensing system can be easily modified and programmed to integrate other sensors, a capability that can be exploited to monitor a range of water quality parameters. We demonstrate the integrated system for monitoring tap, swimming pool, and lake water. This system opens the possibility for a wide range of low-cost and ubiquitous environmental monitoring applications.

Tailoring MWCNTs and ß-Cyclodextrin for Sensitive Detection of Acetaminophen and Estrogen.

Monitoring of trace amount of acetaminophen and estrogen in drinking water is of great importance because of their potential links to gastrointestinal diseases and breast and prostate cancers. The sensitive and accurate detection of acetaminophen and estrogen requires the development of advanced sensing materials that possess appropriate number of analyte-capturing sites and suitable signal conduction path. This can be achieved by implementing appropriate chemical attachment of multiwalled carbon nanotubes (MWCNTs) and ß-cyclodextrin (ßCD). Here, we report a systematic investigation of four types of modified MWCNT-ßCD: (1) physical mixing, (2) "click reaction", (3) thionyl chloride esterification, and (4) Steglich esterification. The Steglich esterification is a one-step approach with shorter reaction time, lower reaction temperature, and eliminates handling of air/moisture-sensitive reagents. MWCNT-ßCD prepared by Steglich esterification possessed moderate ßCD loading (5-10 wt %), large effective surface area, and fast electron transfer. The host-guest interaction of ßCD and redox properties of MWCNT enabled sensitive detection of acetaminophen and 17ß-estradiol (E2 is a primary female sex hormone) in the range of 0.005-20 and 0.01-15 µM, with low detection limits of 3.3 and 2.5 nM, respectively. We demonstrated accurate detection results of pharmaceutical compositions in water and urine samples. These results indicate that Steglich esterification method may be applied in fabricating pharmaceutical contaminants sensors for health and environmental applications.

Isomerism and Blue Electroluminescence of a Novel Organoboron Compound: BIII2 (O)(7-azain)2 Ph2.

Bright blue light with a maximum at 450 nm is emitted by both structural isomers of the novel, stable BIII2 (O)(7-azain)2 Ph2 (7-azain=7-azaindole anion) on irradiation with UV light. The isomer shown in the picture has approximate C2 symmetry (the other isomer approximate Cs symmetry) and electroluminesces when used as the emitting layer in an electroluminescent device.