Electrochromic Sensors Research Articles

Exploring Zr-based Metal-Organic Frameworks as Smart Electrochromic Sensors by Coordination-Driven Surface Engineering.

As emerging stimuli-responsive materials, electrochromic metal-organic frameworks (MOFs) are still not utilized in sensing applications due to difficulties in water stability, facile synthesis and functionalization, and efficient translation of specific recognition events. Here, we firstly find that a Zr-based MOF furnished with postsynthetically created viologen-like electron-deficient moiety was electrochromic active. With a coordination-driven surface engineering strategy where phosphate-containing biomolecules are tethered to Zr nodes of the MOF, fine tuning the interface electron transfer was readily achieved, thus benefitting for constructing smart electrochromic sensors through the combination of the sensitivity of electrochemistry with the visuality of colorimetry. Particularly, MOF-coated conductive films enabled label-free detection of phosphoproteins, and aptamer-functionalized ones responded specifically to the target. In two cases distinct color changes allow for visual quantification. This study represents the first example of MOF-based electrochromic sensors developed by an efficient strategy, indicating the generality to electrochromic counterparts for various sensing applications.

Dual Direct Z-Scheme Heterojunction with Stable Electron Supply to a Au/PANI Photocathode for Ultrasensitive Photoelectrochemical and Electrochromic Visualization Detection of Ofloxacin in a Microfluidic Sensing Platform.

A novel dual-mode microfluidic analytical device integrating self-powered photoelectrochemical (PEC) sensing with electrochromic visualization analysis was developed for ultrasensitive ofloxacin (OFL) detection. First, an advanced dual direct Z-scheme BiVO4@Ni-ZnIn2S4/Bi2S3 (BVZIS) heterojunction was designed as a photoanode matrix to steadily provide electrons. The dual Z-scheme structure formed in photoactive BVZIS composites greatly accelerated the migration of electrons. In addition, the doping of Ni in ZnIn2S4 markedly enhanced the optical absorption and promoted the separation of the photocarrier. Second, electrochromic material polyaniline-modified Au (Au/PANI) was first electrodeposited on the photocathode for immobilizing aptamers and realizing visualized readout. On the one hand, Au/PANI with excellent conductivity could receive electrons from the photoanode without external energy supply. On the other hand, PANI would be rapidly reduced by the received electrons and change its color from blue to green obviously. With the increase in OFL, the increased steric hindrance resulted in the significant decline in the PEC signal and RGBgreen value. Third, wide linear ranges of PEC (0.05 pg/mL to 150 ng/mL) and electrochromic technique (0.1 pg/mL to 100 ng/mL) as well as low detection limits of PEC (18 fg/mL) and electrochromic (30 fg/mL) sensors could achieve the ultrasensitive detection of OFL in milk and river water.

Simple electrochromic sensor for the determination of amines based on the proton sensitivity of polyaniline film

The lack of simple strategies for the design and fabrication of electrochromic (EC) sensors has obstructed the extensive application of these efficient devices in analytical chemistry. Herein, we introduced a novel EC sensor based on the proton sensitivity of conducting polyaniline (PANI) film to determine amines as model analytes. Firstly, the EC behavior of fluorine-doped tin oxide modified with PANI film (FTO/PANI) in both the absence and presence of different amines was studied. The results indicated that amines can interfere with the EC process of PANI. The change in the EC response of PANI at the wavelengths of 420 nm, 620 nm, and 750 nm enables the in-direct determination of amines. It should be emphasized that the absorption spectrum of amines exhibits no peaks in the visible regime. The present method exhibits triethylamine (as an amine) detection in the linear dynamic range of 0.10–7.01 µmol L−1 with a limit of detection of 0.06 µmol L−1. The EC mechanism of PANI towards amines was carefully studied using field emission scanning electron microscope (FESEM), Fourier-transform infrared (FT–IR), X-ray diffraction (XRD), and time-depended density functional theory (TD-DFT) techniques. Finally, as a practical application, the EC sensor was utilized to monitor the spoilage of beef and fish samples in the gaseous phase. The present assay can pave the way for the development of simple and efficient EC sensors.

Evaluation of Electrochromic Properties of Polypyrrole/Poly(Methylene Blue) Layer Doped by Polysaccharides.

Polypyrrole (Ppy) and poly(methylene blue) (PMB) heterostructure (Ppy-PMB) was electrochemically formed on the indium tin oxide (ITO) coated glass slides, which served as working electrodes. For electropolymerization, a solution containing pyrrole, methylene blue, and a saccharide (lactose, sucrose, or heparin) that served as dopant was used. The aim of this study was to compare the effect of the saccharides (lactose, sucrose, and heparin) on the electrochromic properties of the Ppy-PMB layer. AFM and SEM have been used for the analysis of the surface dominant features of the Ppy-PMB layers. From these images, it was concluded that the saccharides used in this study have a moderate effect on the surface morphology. Electrochromic properties were analyzed with respect to the changes of absorbance of the layer at two wavelengths (668 nm and 750 nm) by changing the pH of the surrounding solution and the potential between +0.8 V and −0.8 V. It was demonstrated that the highest absorbance changes are characteristic for all layers in the acidic media. Meanwhile, the absorbance changes of the layers were decreased in the more alkaline media. It was determined that the Ppy-PMB layers with heparin as a dopant were more mechanically stable in comparison to the layers doped with lactose and sucrose. Therefore, the Ppy-PMB layer doped with heparin was selected for the further experiment and it was applied in the design of electrochromic sensors for the determination of three xanthine derivatives: caffeine, theobromine, and theophylline. A linear relationship of ΔA (∆A = A+0.8V − A−0.8V) vs. concentration was determined for all three xanthine derivatives studied. The largest change in optical absorption was observed in the case of theophylline determination.

A review on bio-synthesized Co3O4 nanoparticles using plant extracts and their diverse applications

Developing a rapid, reliable and eco-accommodating methodology for the synthesis of metal/metal oxide nanoparticles (NPs) is an important step in the area of nanotechnology. Cobalt oxide nanoparticles (Co3O4 NPs) have been widely studied due to their potential applications including, antibacterial, antifungal, electrochromic sensors, heterogeneous catalysis, and energy storage devices. Due to the large rate of perilous chemicals employed in the physical and chemical production of these NPs, green methods employing the use of plants, fungus, algae, and bacteria have been adopted. However, plant-mediated synthesis of metal NPs has been developed as a substitute to defeat the restrictions of conventional synthesis approaches such as physical and chemical methods. Biomolecules, such as tannins, saponins, proteins, amino acids, steroids, enzymes, flavonoids, and vitamins from several plant extracts have been used as a stabilizing and reducing agents for the synthesis of Co3O4 NPs. Recently, several attempts were made to develop plant-mediated synthesis methods to produce stable, cost-effective, and eco-accommodating Co3O4 NPs. In this review, a comprehensive study was conducted on synthesis, characterization, and various applications of Co3O4 NPs produced using various plant sources.

Electrochromic sensors: Innovative devices enabled by spectroelectrochemical methods

Abstract Electrochromic sensors are electrochemical devices exploiting colour changes as a means to simplify device construction and instrumentation requirements. Despite their advantages, electrochromic sensors have begun to emerge only recently. Mainly based on the works appeared in the literature over the past 2 years, we describe the construction and operation of these devices. A simple framework is proposed to understand and classify these devices more easily. This is based on the sensor architecture, their power source, and how information is displayed. Despite being new, electrochromic sensors are already demonstrated in a number of applications, mostly related to health and point-of-care devices.

Ultrathin W18O49 Nanowire Assemblies for Electrochromic Devices

Ordered W18O49 nanowire thin films were fabricated by Langmuir-Blodgett (LB) technique in the presence of poly(vinyl pyrrolidone) coating. The well-organized monolayer of W18O49 nanowires with periodic structures can be readily used as electrochromic sensors, showing reversibly switched electrochromic properties between the negative and positive voltage. Moreover, the electrochromism properties of the W18O49 nanowire films exhibit significant relationship with their thickness. The coloration/bleaching time was around 2 s for the W18O49 nanowire monolayer, which is much faster than the traditional tungsten oxide nanostructures. Moreover, the nanowire devices display excellent stability when color switching continues, which may provide a versatile and promising platform for electrochromism device, smart windows, and other applications.

Poly(styrene)s with oligo(ethylene oxide) side chains as ionic conducting matrices

Solid phase ion conductors have been the object of studies during the last years for their potential use as conducting polymer matrices in electrochromic devices, sensors, photovoltaic and dry batteries. Comb polymers of poly(styrene) with oligo(ethylene oxide) side chains were investigated. They show reasonable conductivity of about 10−7–10−5 siemens/cm at ambient temperature and lithiumperchlorate as salt electrolyte. A dependence of the conductivity from the side chain length and the amount of added salt was found.