Colorimetric detection of urea nitrate: the missing link

Novel Self-assembly Pd(II)-Schiff Base Complex Modified Glassy Carbon Electrode for Electrochemical Detection of Paracetamol

A self-assembly Pd-Schiff base complex was synthesized and used as an electrochemical sensor in phosphate buffer solution, where it enhanced the electrocatalytic activity toward the paracetamol detection. The Schiff base {(HL) = (4-(((Z)-3-(hydroxyimino) butan-2-ylidene) amino)-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one)} was selected to prepare Pd-based complexes due to its high antimicrobial activity. A linear calibration curve was constructed using GC/Pd-SB in paracetamol concentration range of 1–50 μM and its detection limit was calculated as 0.067 μM. The modified electrode, GC/Pd-SB, could successfully determine the paracetamol concentration in human blood serum and commercial drug tablets with high sensitivity. The prepared metal complex was characterized using techniques, namely, X-ray diffraction (XRD) and scanning electron microscope (SEM). In addition, electrochemical studies were performed using different electrochemical techniques like cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS). DFT calculations were used to estimate the equilibrium geometry, molecular orbital, ground-state properties, and interaction energy between paracetamol and palladium.

Graphical Abstract

Colorimetric sensors and nanoprobes for characterizing antioxidant and energetic substances

The development of analytical techniques for antioxidant compounds is important, because antioxidants that can inactivate reactive species and radicals are health-beneficial compounds, also used in the preservation of food and protection of almost every kind of organic substance from oxidation. Energetic substances include explosives, pyrotechnics, propellants and fuels, and their determination at bulk/trace levels is important for the safety and well-being of modern societies exposed to various security threats. Most of the time, in field/on site detection of these important analytes necessitates the use of colorimetric sensors and probes enabling naked-eye detection, or low-cost and easy-to-use fluorometric sensors. The use of nanosensors brings important advantages to this field of analytical chemistry due to their various physico-chemical advantages of increased surface area, surface plasmon resonance absorption of noble metal nanoparticles, and superior enzyme-mimic catalytic properties. Thus, this critical review focuses on the design strategies for colorimetric sensors and nanoprobes in characterizing antioxidant and energetic substances. In this regard, the main themes and properties in optical sensor design are defined and classified. Nanomaterial-based optical sensors/probes are discussed with respect to their mechanisms of operation, namely formation and growth of noble metal nanoparticles, their aggregation and disaggregation, displacement of active constituents by complexation or electrostatic interaction, miscellaneous mechanisms, and the choice of metallic oxide nanoparticles taking part in such formulations.

Trace Detection and Chemical Analysis of Homemade Fuel-Oxidizer Mixture Explosives: Emerging Challenges and Perspectives

The chemical analysis of homemade explosives (HMEs) and improvised explosive devices (IEDs) remains challenging for fieldable analytical instrumentation and sensors. Complex explosive fuel-oxidizer mixtures, black and smokeless powders, flash powders, and pyrotechnics often include an array of potential organic and inorganic components that present unique interference and matrix effect difficulties. The widely varying physicochemical properties of these components as well as external environmental interferents and background challenge many sampling and sensing modalities. This review provides perspective on these emerging challenges, critically discusses developments in sampling, sensors, and instrumentation, and showcases advancements for the trace detection of inorganic-based explosives.

Surface modified colloidal silica nanoparticles: Novel aspect for complete identification of explosive materials

Terrorism by means of explosives has become a crucial threat. Nanoparticles with distinctive properties can offer novel aspects for instant detection of explosive materials. Common explosives are organic compounds that contain nitro group (NO₂) along with carbon and hydrogen elements. This study demonstrates complete identification of nitramine explosives (RDX & HMX) using colloidal silica nanoparticles. Sustainable fabrication of colloidal silica was conducted via hydrothermal processing technique. Explosive identification involves a digestion of the tested material using strong acid. The digestion process results in the development of nitro group and corresponding formaldehyde segment. The identification of the nitro group was performed using colloidal silica nanoparticles functionalized with secondary amine to develop a characteristic dark blue colour. Simultaneous identification of formaldehyde segment was performed using colloidal silica functionalized with aromatic phenol to develop a red colour. This robust explosive detection technology can find wide applications on site where instant identification to assess potential threat is a crucial demand. Thanks to hydrothermal processing, sustainable fabrication and surface modification of colloidal silica particles can be obtained.

Electrochemical Sensors Containing Schiff Bases and their Transition Metal Complexes to Detect Analytes of Forensic, Pharmaceutical and Environmental Interest. A Review

Schiff bases and their transition metal complexes are inexpensive and easy to synthesize. These compounds display several structural and electronic features that allow their application in numerous research fields. Over the last three decades, electroanalytical scientists of various areas have developed electrochemical sensors from many compounds. The present review discusses the applicability of Schiff bases, their transition metal complexes and new materials containing these compounds as electrode modifiers in sensors to detect analytes of forensic, pharmaceutical and environmental interest. In forensic sciences, Schiff bases are mainly used to analyze illicit drugs: chemical reactions involving Schiff bases can help to elucidate illicit drug production and to determine analytes in seized samples. In the environmental area, given that most methodologies provide Limit of Detection (LOD) values below the values recommended by regulatory agencies, Schiff bases constitute a promising strategy. As for pharmaceutical applications, Schiff bases represent an approach for analysis of complex biological samples containing low levels of the target analytes in the presence of a large quantity of interfering compounds. This review will show that new highly specific materials can be synthesized based on Schiff bases and applied in the pharmaceutical industry, toxicological studies, electrocatalysis and biosensors. Most literature papers have reported on Schiff bases combined with carbon paste to give a chemically modified electrode that is easy and inexpensive to produce and which displays specific and selective sensing capacity for different applications.

Combining ultrasound-assisted extraction and a microliter colorimetric assay for the streamlined determination of urea in animal feedstuff

This paper proposes a novel analytical strategy for the routine determination of urea in animal feedstuffs, combining an ultrasound-assisted miniaturized extraction protocol with a microplate colorimetric assay based on the reaction between 4-dimethylaminobenzaldehyde and urea. In order to accelerate the extraction, we introduced an ultrasound-assisted miniaturized protocol and compared it with both classic and miniaturized alternatives. The potential interference of amino acids was bypassed by shifting the detection wavelength from 435 to 450 nm. Urea could be quantified in the range 0.05-1.00% (w/w) with high precision (RSD < 5%). The results were in agreement with a commercial enzymatic method, demonstrating the accuracy and selectivity of the assay. The miniaturization led to a 50 times downscale when compared to the official method, resulting in a reduction of at least 90% in chemical consumption per determination, contributing to a more "green" and sustainable analytical methodology.