A review of nanocomposite-modified electrochemical sensors for water quality monitoring

Electrochemical sensors play a significant role in detecting chemical ions, molecules, and pathogens in water and other applications. These sensors are sensitive, portable, fast, inexpensive, and suitable for online and in-situ measurements compared to other methods. They can provide the detection for any compound that can undergo certain transformations within a potential window. It enables applications in multiple ion detection, mainly since these sensors are primarily non-specific. In this paper, we provide a survey of electrochemical sensors for the detection of water contaminants, i.e., pesticides, nitrate, nitrite, phosphorus, water hardeners, disinfectant, and other emergent contaminants (phenol, estrogen, gallic acid etc.). We focus on the influence of surface modification of the working electrodes by carbon nanomaterials, metallic nanostructures, imprinted polymers and evaluate the corresponding sensing performance. Especially for pesticides, which are challenging and need special care, we highlight biosensors, such as enzymatic sensors, immunobiosensor, aptasensors, and biomimetic sensors. We discuss the sensors’ overall performance, especially concerning real-sample performance and the capability for actual field application

Synthesis and characterization of organic-inorganic colorants

New colorant materials have been found with the interaction of organic dyes and metal alkoxides. Changes in the hue are observed as indigo dye or thioindigo dyes are combined with the ASB (aluminum tri-secbutoxide), when compared to the original indigo or thioindigo dye, due to the binding and geometry change between dye and metal alkoxide. These dyes are combined with the ASB in two different methods of hydrolysis, namely in the air and in water. Similarly, when TTIP (Titanium tetraisopropoxide) is hydrolyzed using the sol gel process, along with the incorporation of thioindigo dye, hue changes were observed. X-ray diffraction of these colorants indicates that these dyes are absorbed on the surface of the inorganic compounds, which are produced from their respective organometallic precursors. Uv-Vis and IR spectrum studies showed that there is a binding mechanism involved between the organic dye and Al atom from the ASB and Ti atom from the TTIP

Modeling the conductivity response to NO2 gas of films based on MWCNT networks

This work proposes a model describing the dynamic behavior of sensing films based on functionalized MWCNT networks in terms of conductivity when exposed to time-variable concen-trations of NO2 and operating with variable working temperatures. To test the proposed model, disordered networks of MWCNTs functionalized with COOH and Au nanoparticles were exploited. The model is derived from theoretical descriptions of the electronic transport in the nanotube net-work, of the NO2 chemisorption reaction and of the interaction of these two phenomena. The model is numerically implemented and then identified by estimating all the chemical/physical quantities involved and acting as parameters, through a model fitting procedure. Satisfactory results were obtained in the fitting process, and the identified model was used to further the analysis of the MWCNT sensing in dynamical conditions

Copper(I) Ethylene Complexes Supported by 1,3,5-Triazapentadienyl Ligands with Electron-Withdrawing Groups

The fluorinated 1,3,5-triazapentadienyl ligands [N­{(C₃F₇)­C­(2-(NO₂)­C₆H₄)­N}₂]⁻, [N­{(C₃F₇)­C­(4-(NO₂)­C₆H₄)­N}₂]⁻, [N­{(C₃F₇)­C­(2-(CF₃)­C₆H₄)­N}₂]⁻, and [N­{(C₃F₇)­C­(2-F,6-(CF₃)­C₆H₃)­N}₂]⁻ have been used as supporting ligands in copper­(I) ethylene chemistry. [N­{(C₃F₇)­C­(2-(NO₂)­C₆H₄)­N}₂]­Cu­(C₂H₄) (<b>7</b>), [N­{(C₃F₇)­C­(4-(NO₂)­C₆H₄)­N}₂]­Cu­(C₂H₄) (<b>8</b>), [N­{(C₃F₇)­C­(2-(CF₃)­C₆H₄)­N}₂]­Cu­(C₂H₄) (<b>9</b>), and [N­{(C₃F₇)­C­(2-F,6-(CF₃)­C₆H₃)­N}₂]­Cu­(C₂H₄) (<b>10</b>) are easily isolable, thermally stable solids and display their ethylene proton and carbon resonances in the δ 3.68–3.48 and 85.2–87.6 ppm regions, respectively. X-ray crystal structures reveal that <b>7</b>–<b>10</b> feature trigonal-planar copper sites and κ²-bonded, U-shaped triazapentadienyl ligands. The Cu­(I) carbonyl adducts [N­{(C₃F₇)­C­(2-(NO₂)­C₆H₄)­N}₂]­Cu­(CO)­(NCCH₃) (<b>16</b>) and [N­{(C₃F₇)­C­(4-(NO₂)­C₆H₄)­N}₂]­Cu­(CO)­(NCCH₃) (<b>17</b>) have also been synthesized, and they have pseudotetrahedral copper sites. The CO stretching frequencies of the compounds <b>16</b> and <b>17</b> and ethylene ¹³C NMR chemical shift data of <b>7</b>–<b>10</b> suggest that these molecules have rather acidic copper sites and weakly donating triazapentadienyl ligands

Layer-by-Layer Deposited Multi-Modal PDAC/rGO Composite-Based Sensors

Different environmental parameters, such as temperature and humidity, aggravate food spoilage, and different volatile organic compounds (VOCs) are released based on the extent of spoilage. In addition, a lack of efficient monitoring of the dosage of pesticides leads to crop failure. This could lead to the loss of food resources and food production with harmful contaminants and a short lifetime. For this reason, precise monitoring of different environmental parameters and contaminations during food processing and storage is a key factor for maintaining its safety and nutritional value. Thus, developing reliable, efficient, cost-effective sensor devices for these purposes is of utmost importance. This paper shows that Poly-(diallyl-dimethyl ammonium chloride)/reduced Graphene oxide (PDAC/rGO) films produced by a simple Layer-by-Layer deposition can be effectively used to monitor temperature, relative humidity, and the presence of volatile organic compounds as indicators for spoilage odors. At the same time, they show potential for electrochemical detection of organophosphate pesticide dimethoate. By monitoring the resistance/impedance changes during temperature and relative humidity variations or upon the exposure of PDAC/rGO films to methanol, good linear responses were obtained in the temperature range of 10–100 °C, 15–95% relative humidity, and 35 ppm–55 ppm of methanol. Moreover, linearity in the electrochemical detection of dimethoate is shown for the concentrations in the order of 102 µmol dm−3. The analytical response to different external stimuli and analytes depends on the number of layers deposited, affecting sensors’ sensitivity, response and recovery time, and long-term stability. The presented results could serve as a starting point for developing advanced multi-modal sensors and sensor arrays with high potential for analytical applications in food safety and quality monitoring

Pharmacodynamic Evaluation of a Single Dose versus a 24-Hour Course of Multiple Doses of Cefazolin for Surgical Prophylaxis

The optimal perioperative duration for the administration of cefazolin and other prophylactic antibiotics remains unclear. This study aimed to describe the pharmacodynamics of cefazolin for a single 2 g dose versus a 24 h course of a 2 g single dose plus a 1 g eight-hourly regimen against methicillin-susceptible Staphylococcus aureus. Static concentration time–kill assay and a dynamic in vitro hollow-fibre infection model simulating humanised plasma and interstitial fluid exposures of cefazolin were used to characterise the pharmacodynamics of prophylactic cefazolin regimens against methicillin-sensitive Staphylococcus aureus clinical isolates. The initial inoculum was 1 × 105 CFU/mL to mimic a high skin flora inoculum. The static time–kill study showed that increasing the cefazolin concentration above 1 mg/L (the MIC) did not increase the rate or the extent of bacterial killing. In the dynamic hollow-fibre model, both dosing regimens achieved similar bacterial killing (~3-log CFU/mL within 24 h). A single 2 g dose may be adequate when low bacterial burdens (~104 CFU/mL) are anticipated in an immunocompetent patient with normal pharmacokinetics

Copper(I) Ethylene Complexes Supported by 1,3,5-Triazapentadienyl Ligands with Electron-Withdrawing Groups

The fluorinated 1,3,5-triazapentadienyl ligands [N­{(C₃F₇)­C­(2-(NO₂)­C₆H₄)­N}₂]⁻, [N­{(C₃F₇)­C­(4-(NO₂)­C₆H₄)­N}₂]⁻, [N­{(C₃F₇)­C­(2-(CF₃)­C₆H₄)­N}₂]⁻, and [N­{(C₃F₇)­C­(2-F,6-(CF₃)­C₆H₃)­N}₂]⁻ have been used as supporting ligands in copper­(I) ethylene chemistry. [N­{(C₃F₇)­C­(2-(NO₂)­C₆H₄)­N}₂]­Cu­(C₂H₄) (<b>7</b>), [N­{(C₃F₇)­C­(4-(NO₂)­C₆H₄)­N}₂]­Cu­(C₂H₄) (<b>8</b>), [N­{(C₃F₇)­C­(2-(CF₃)­C₆H₄)­N}₂]­Cu­(C₂H₄) (<b>9</b>), and [N­{(C₃F₇)­C­(2-F,6-(CF₃)­C₆H₃)­N}₂]­Cu­(C₂H₄) (<b>10</b>) are easily isolable, thermally stable solids and display their ethylene proton and carbon resonances in the δ 3.68–3.48 and 85.2–87.6 ppm regions, respectively. X-ray crystal structures reveal that <b>7</b>–<b>10</b> feature trigonal-planar copper sites and κ²-bonded, U-shaped triazapentadienyl ligands. The Cu­(I) carbonyl adducts [N­{(C₃F₇)­C­(2-(NO₂)­C₆H₄)­N}₂]­Cu­(CO)­(NCCH₃) (<b>16</b>) and [N­{(C₃F₇)­C­(4-(NO₂)­C₆H₄)­N}₂]­Cu­(CO)­(NCCH₃) (<b>17</b>) have also been synthesized, and they have pseudotetrahedral copper sites. The CO stretching frequencies of the compounds <b>16</b> and <b>17</b> and ethylene ¹³C NMR chemical shift data of <b>7</b>–<b>10</b> suggest that these molecules have rather acidic copper sites and weakly donating triazapentadienyl ligands

Ultra-Sensitive and Fast Humidity Sensors Based on Direct Laser-Scribed Graphene Oxide/Carbon Nanotubes Composites

In this paper, the relative humidity sensor properties of graphene oxide (GO) and graphene oxide/multiwalled nanotubes (GO/MWNTs) composites have been investigated. Composite sensors were fabricated by direct laser scribing and characterized using UV-vis-NIR, Raman, Fourier transform infrared, and X-ray photoemission spectroscopies, electron scanning microscopy coupled with energy-dispersive X-ray analysis, and impedance spectroscopy (IS). These methods confirm the composite homogeneity and laser reduction of GO/MWNT with dominant GO characteristics, while ISresults analysis reveals the circuit model for rGO-GO-rGO structure and the effect of MWNT on the sensor properties. Although direct laser scribing of GO-based humidity sensor shows an outstanding response (|ΔZ|/|Z| up to 638,800%), a lack of stability and repeatability has been observed. GO/MWNT-based humidity sensors are more conductive than GO sensors and relatively less sensitive (|ΔZ|/|Z| = 163,000%). However, they are more stable in harsh humid conditions, repeatable, and reproducible even after several years of shelf-life. In addition, they have fast response/recovery times of 10.7 s and 9.3 s and an ultra-fast response time of 61 ms when abrupt humidification/dehumidification is applied by respiration. All carbon-based sensors’ overall properties confirm the advantage of introducing the GO/MWNT hybrid and laser direct writing to produce stable structures and sensors

End-On and Side-On π‑Acid Ligand Adducts of Gold(I): Carbonyl, Cyanide, Isocyanide, and Cyclooctyne Gold(I) Complexes Supported by N‑Heterocyclic Carbenes and Phosphines

N-Heterocyclic carbene ligand SIDipp (SIDipp = 1,3-bis­(2,6-diisopropylphenyl)­imidazolin-2-ylidene) and trimesitylphosphine ligand have been used in the synthesis of gold­(I) cyanide, <i>t</i>-butylisocyanide, and cyclooctyne complexes (SIDipp)­Au­(CN) (<b>3</b>), (Mes₃P)­Au­(CN) (<b>4</b>), [(Mes₃P)₂Au]­[Au­(CN)₂] (<b>5</b>), [(SIDipp)­Au­(CN^<i>t</i>Bu)]­[SbF₆] (<b>[6]­[SbF</b>_<b>6</b><b>]</b>), [(SIDipp)­Au­(cyclooctyne)]­[SbF₆] (<b>[8]­[SbF</b>_<b>6</b><b>]</b>), and [(Mes₃P)­Au­(cyclooctyne)]­[SbF₆] (<b>[9]­[SbF</b>_<b>6</b><b>]</b>). A detailed computational study has been carried out on these and the related gold­(I) carbonyl adducts [(SIDipp)­Au­(CO)]­[SbF₆] (<b>[1]­[SbF</b>_<b>6</b><b>]</b>), [(Mes₃P)­Au­(CO)]­[SbF₆] (<b>[2]­[SbF</b>_<b>6</b><b>]</b>), and [(Mes₃P)­Au­(CN^<i>t</i>Bu)]⁺ (<b>[7]</b>^<b>+</b>). X-ray crystal structures of <b>3</b>, <b>5</b>, <b>[6]­[SbF</b>_<b>6</b><b>]</b>, <b>[8]­[SbF</b>_<b>6</b><b>]</b>, and <b>[9]­[SbF</b>_<b>6</b><b>]</b> revealed that they feature linear gold sites. Experimental and computational data show that the changes in π-acid ligand on (SIDipp)­Au⁺ from CO, CN^–, CN^<i>t</i>Bu, cyclooctyne as in <b>[1]</b>⁺, <b>3</b>, <b>[6]</b>⁺, and <b>[8]</b>⁺ did not lead to large changes in the Au–C_carbene bond distances. A similar phenomenon was also observed in Au–P distance in complexes <b>[2]</b>⁺, <b>4</b>, <b>[7]</b>⁺, and <b>[9]</b>⁺ bearing trimesitylphosphine. Computational data show that the Au–L bonds of “naked” [Au–L]⁺ or SIDipp and Mes₃P supported [Au–L]⁺ (L = CO, CN^–, CN^<i>t</i>Bu to cyclooctyne) have higher electrostatic character than covalent character. The Au←L σ-donation and Au→L π-back-donation contribute to the orbital term with the former being the dominant component, but the latter is not negligible. In the Au–CO adducts <b>[1]</b>⁺and <b>[2]</b>⁺, the cationic gold center causes the polarization of the C–O σ and π orbitals toward the carbon end making the coefficients at the two atoms more equal which is mainly responsible for the large blue shift in the CO stretching frequency. The SIDipp and Mes₃P supported gold­(I) complexes of cyanide and isocyanide also exhibit a significant blue shift in υ̅_CN compared to that of the free ligands. Calculated results for Au­(CO)Cl and Au­(CF₃)­CO suggest that the experimentally observed blue shift in ν̅_CO of these compounds may at least partly be caused by intermolecular forces