An electrical characterisation system for the real-time acquisition of multiple independent sensing parameters from organic thin film transistors

The presence of multiple independent sensing parameters in a single device is the key conceptual advantage of sensor devices based on an organic thin film transistor (OTFT) over simple organic chemiresistors. Practically, however, these multiple parameters must first be extracted from the electrical characteristics of the OTFTs and, thus, they are not immediately apparent. To exploit the advantage of OTFT sensors, we require a measurement technology to extract these parameters in real time. Here, we introduce an efficient, cost-effective system that is a faster and more compact alternative to the expensive and cumbersome laboratory-based instruments currently available. The characterisation system presented here records the electric behaviour of OTFTs in the form of its “saturated transfer characteristics” multiple times per second for virtually unlimited periods of time, with the option to multiplex up to 20 devices in parallel. By applying a bespoke algorithm to the measured transfer characteristics, the system then extracts, in real time, several underlying transistor parameters (on- and off-current, threshold voltage, and charge carrier mobility). Tests were conducted on the example of a poly(thieno[3,2-b]thiophene) (PBTTT) OTFT exposed to ethanol vapour. The system extracts the underlying OTFT parameters with very low noise without introducing apparent correlations between independent parameters as an artefact

Electrochemical gating of a hydrophobic organic semiconductor with aqueous media

We show that even the highly hydrophobic semiconducting polymer poly [2,5-bis(3-tetradecylthiophen-2-yl) thieno[3,2-b]thiophene] (PBTTT) can operate in organic electrochemical transistor (OECT) rather than field effect (OFET) mode when gated with aqueous media. The required bulk penetration of anions into the semiconducting film within the electrochemical window of water is here enabled by the choice of anion, namely, picric acid (PA). OECT mode operation in PBTTT films or its analogues had previously been seen only when gated with solid electrolytes with a larger electrochemical window, or for PBTTT analogues with hydrophilic sidechains. We assign the ability of PA anions to penetrate bulk PBTTT from their similarity to PBTTT solvents (chlorinated benzenes), in the sense that they both display an electron-deficient π electron system. In control experiments, we confirm that OECT mode is not observed when gating PBTTT with another organic acid (acetic acid) that does not display such π electron system, and that the gating mechanism indeed is electrochemical doping rather than a charge transfer mechanism. OECT mode is observed only at rather high PA concentrations in an aqueous gate medium (50 mM or more), but when it is, it leads to conductivities of ≈80 S/cm, slightly larger than for a PBTTT analogue with hydrophilic side chains gated with chloride anions

Adaptive and sensitive fibre-optic fluorimetric transducer for air- and water-borne analytes

A sensitive fibre optic fluorescence intensity meter has been designed and built as a transducer to detect quenching of conjugated polymer fluorescence with minimum adjustment between air- and waterborne analytes. Only generic, commercially available parts including optical fibres, solvents, airbrush, standard optical and electronic parts, and a digital lock-in amplifier have been used, avoiding the need for a fluorescence spectrometer. To test the instrument, optical fibres were sensitised with the generic fluorescent poly(phenylene-vinylene) derivative MDMO-PPV and exposed to a variety of vapour pressures, and concentrations in water, of the nitroaromatic explosive 2,4 dinitrotoluene (DNT). We establish dimensionless Stern-Volmer constants (KSV) and limit-of-detection (LoD) for air- and water-borne DNT as KSV(air) = 1.4 × 107 vs. KSV(water) = 5.8 × 106 and LoD(air) = 10.9 ppb and LoD(water) = 56 ppb. These LoDs compare favourably to prior reports. We consider our study of the MDMO-PPV/DNT system as a successful test of our transducer design and recommend its wider use

Transport Properties of Highly Aligned Polymer Light-Emitting-Diodes

We investigate hole transport in polymer light-emitting-diodes in which the emissive layer is made of liquid-crystalline polymer chains aligned perpendicular to the direction of transport. Calculations of the current as a function of time via a random-walk model show excellent qualitative agreement with experiments conducted on electroluminescent polyfluorene demonstrating non-dispersive hole transport. The current exhibits a constant plateau as the charge carriers move with a time-independent drift velocity, followed by a long tail when they reach the collecting electrode. Variation of the parameters within the model allows the investigation of the transition from non-dispersive to dispersive transport in highly aligned polymers. It turns out that large inter-chain hopping is required for non-dispersive hole transport and that structural disorder obstructs the propagation of holes through the polymer film.Comment: 4 pages, 5 figure

Including a Cold Pool Representation in a Convection Parameterization and Simulating Its Impacts on the Spatial and Temporal Variability of the Precipitation in the NASA GEOS GCM

We developed and implemented a simple representation of a cold pool in the Grell-Freitas (GF) convection parameterization. The cold pool parameterization is based on the observation that convective-scale downdrafts produce a local deficit of the moist static energy (MSE). This information is advected and becoming downwind available to trigger and intensify new convection. The cold pool is dissipated by a simple exponential decay using a lifetime of a few hours, or by interacting with the underneath surface by exchanging latent and sensible heat fluxes. Preliminary results show some improvement of the simulation of the diurnal cycle of the precipitation over the land, mainly during the nighttime

Water-gated transistor using ion exchange resin for potentiometric fluoride sensing

We introduce fluoride-selective anion exchange resin sorbents as sensitisers into membranes for water-gated field effect transistors (WGTFTs). Sorbents were prepared via metal (La or Al)-loading of a commercial macroporous aminophosphonic acid resin, PurometTM MTS9501, and were filled into a plasticised poly(vinyl chloride) (PVC) phase transfer membrane. We found a potentiometric response (membrane potential leading to WGTFT threshold shift) to fluoride following a Langmuir–Freundlich (LF) adsorption isotherm with saturated membrane potential up to ~480 mV, extremely low characteristic concentration c1/2 = 1/K, and picomolar limit of detection (LoD), even though ion exchange did not build up charge on the resin. La-loading gave a superior response compared to Al-loading. Membrane potential characteristics were distinctly different from charge accumulating sensitisers (e.g., organic macrocycles) but similar to the Cs+ (cation) selective ion-exchanging zeolite mineral ‘mordenite’. We propose a mechanism for the observed threshold shift and investigate interference from co-solutes. Strong interference from carbonate was brought under control by ‘diluting’ metal loading in the resin. This work sets a template for future studies using an entirely new ‘family’ of sensitisers in applications where very low limit of detection is essential such as for ions of arsenic, mercury, copper, palladium, and gold

Design, Synthesis and Catalytic Activity of (Cyclopentadienone)iron Complexes Containing a Stereogenic Plane and a Stereogenic Axis

Herein, we report the synthesis and characterization of several chiral (cyclopentadienone)iron complexes (CICs) featuring either two (R)-BINOL-derived stereoaxes or a combination of one (R)-BINOL-derived stereoaxis and a stereogenic plane. The stereoplane-containing CICs were obtained as epimer mixtures, which were separated by flash column chromatography and assigned an absolute configuration based on XRD analysis, NMR and order of elution. The library was tested in the asymmetric hydrogenation of ketones showing good catalytic activity and a moderate stereoselectivity which, notably, is mostly imparted by the stereogenic plane. Indeed, the two epimers of each CIC possessing a stereoplane show opposite and equally strong stereochemical preference.Winning plane: chiral (cyclopentadienone)iron complexes (CICs) featuring a combination of an (R)-BINOL-derived stereoaxis and a stereogenic plane were synthesized in diastereoisomerically pure form, characterized and tested in the asymmetric hydrogenation of ketones. The new CICs showed good catalytic activity and, remarkably, the stereoplane epimers displayed similar and opposite stereochemical preference

PREP-CHEM-SRC – 1.0: a preprocessor of trace gas and aerosol emission fields for regional and global atmospheric chemistry models

The preprocessor PREP-CHEM-SRC presented in the paper is a comprehensive tool aiming at preparing emission fields of trace gases and aerosols for use in atmospheric-chemistry transport models. The considered emissions are from the most recent databases of urban/industrial, biogenic, biomass burning, volcanic, biofuel use and burning from agricultural waste sources. For biomass burning, emissions can be also estimated directly from satellite fire detections using a fire emission model included in the tool. The preprocessor provides emission fields interpolated onto the transport model grid. Several map projections can be chosen. The inclusion of these emissions in transport models is also presented. The preprocessor is coded using Fortran90 and C and is driven by a <i>namelist</i> allowing the user to choose the type of emissions and the databases

Quality Improvement in Pediatric Head Trauma with PECARN Rules Implementation as Computerized Decision Support

Background: For the 1.4 million emergency department (ED) visits for traumatic brain injury (TBI) annually in the United States, computed tomography (CT) may be over utilized. The Pediatric Emergency Care Applied Research Network developed 2 prediction rules to identify children at very low risk of clinically important TBI. We implemented these prediction rules as decision support within our electronic health record (EHR) to reduce CT. Objective: To test EHR decision support implementation in reducing CT rates for head trauma at 2 pediatric EDs. Methods: We compared monthly CT rates 1 year before [preimplementation (PRE)] and 1 year after [postimplementation (POST)] decision support implementation. The primary outcome was change in CT use rate over time, measured using statistical process control charts. Secondary analyses included multivariate comparisons of PRE to POST. Balancing measures included ED length of stay and returns within 7 days after ED release. Results: There were 2,878 patients with head trauma (1,329 PRE and 1,549 POST) included. Statistical process control charts confirmed decreased CT rates over time POST that was not present PRE. Secondary statistical analyses confirmed that CT scan utilization rates decreased from 26.8% to 18.9% (unadjusted Odds Ratio [OR], 0.64; 95% Confidence Interval [CI], 0.53 -0.76; adjusted OR, 0.71; 95% CI, 0.58 -0.86). Length of stay was unchanged. There was no increase in returns within 7 days and no significant missed diagnoses. Conclusions: Implementation of EHR-integrated decision support for children with head trauma presenting to the ED is associated with a decrease in CT utilization and no increase in significant safety events