A simple and rapid chemiluminescence assay for on-site analysis of paraquat using a portable luminometer

Diagnostic Aspects of Paraquat in the Forensic Toxicology: A Systematic Review

Background

Paraquat (N, N-dimethyl-4,4-bipyridinium dichloride) is a nonselective, fast-acting, and contact chemical herbicide used extensively for weed control. It has high acute oral toxicity, the ability to accumulate in the lungs, and a high potential for pulmonary fibrosis after its intoxication. The present systematic review focuses on evaluating diagnostic aspects of paraquat (PQ) in forensic toxicology.

Methods

Evaluation of the literature according to the following criteria: only human studies published from February 1971 to March 2022 which are in English on the following databases: 1) Medline/PubMed/MeSH search words: ((Methyl viologen [Title/Abstract]) OR (paraquat [MeSH Terms])) AND (forensic [Title/Abstract]); 2) Scopus Keywords related to the study aim included forensic toxicology, paraquat, Methyl viologen; 3) Web of Science. Keywords related to the study aim included forensic toxicology, paraquat, and Methyl viologen.

Results

Thirty full-text articles were included. The results of our review indicate plasma and urine are more used for identifying PQ, and liver, lung, and gastric fluid are important in postmortem cases. Preparation methods, including liquid-liquid extraction (LLE), solid-phase extraction, and acetonitrile-precipitated protein, are often required for removing interfering substances. Chromatographic methods, among other analytical techniques, are more sensitive, specific, and applicable.

Conclusion

Our review suggests that plasma, urine, and lungs should be prioritized in sampling. Solid-phase extraction has better recovery than LLE in many samples. Colorimetric methods are not used much today, and radioimmunoassay (RIA) has limited application despite its high sensitivity. Gas and liquid chromatography methods appear to offer the best approach for the analysis of PQ.

A supramolecular hybrid sensor based on cucurbit[8]uril, 2D-molibdenum disulphide and diamond nanoparticles towards methyl viologen analysis

We develop an electrochemical sensor by using 2D-transition metal dichalcogenides (TMD), specifically MoS₂, and nanoparticles stabilized with cucurbit[8]uril (CB[8]) incorporated together with them. Two different nanoparticles are assayed: diamond nanoparticles (DNPs) and gold nanoparticles (AuNp). 0D materials, together with TMD, provide increased conductivity and active surface while the macrocycle CB[8] affords selectivity towards the guest methyl viologen (MV²⁺), also named paraquat. Glassy Carbon (GC) electrodes are modified by drop-casting of suspensions of MoS₂, followed by either a CB[8]-DNPs hybrid dispersion or a CB[8]-AuNp suspension. Atomic force microscopy is employed for the morphological characterization of the electrochemical sensor surface while cyclic voltammetry and electrochemical impedance spectroscopy techniques allow the electrochemical characterization of the sensor. The well-stablished signals of CB[8]-encapsulated MV²⁺ arise in voltammetric measurements when the macrocycle modifies the 0D-materials. Once the sensor construction and differential pulse voltammetry parameters have been optimized for quantification purposes, calibration procedures are performed with the platform GC/MoS₂/CB[8]-DNPs. This sensing platform shows linear relations between peak intensity and the MV²⁺ concentration in the linear concentration range of (0.73-8.0) · 10^-6 M with a limit of detection of 2.2 · 10^-7 M. Analyses of river water samples fortified with MV²⁺ at the μM level shows recoveries of 100% with RSD values of 6.4% (n = 3).

[Chemiluminescence assay for the investigation of reactive oxygen species generator]

Quinones play critical roles in biological systems, but are also regarded as a class of toxins that can cause oxidative stress in living cells, and the involvement of quinone-based reactive oxygen species in oxidative stress has been reported. In biological systems, quinones are reduced to semiquinone radicals by the enzyme NADPH:quinone reductase. Next, semiquinone radicals react with dissolved oxygen to form superoxide anion, which reacts with biological molecules to cause oxidative stress. On the other hand, chemiluminescence reagents such as luminol can emit chemiluminescence after oxidation by reactive oxygen species. Therefore, chemiluminescence reagents have been used widely to investigate reactive oxygen species. We have developed a sensitive and selective assay for quantifying quinones using luminol chemiluminescence. This chemiluminescence assay is based on the generation of reactive oxygen species through the redox reaction between quinone and dithiothreitol, a reductant, followed by detection of the generated reactive oxygen by luminol. Additionally, this assay can be used to quantify the toxic herbicide, paraquat, which produces reactive oxygen species in the same manner as quinones. This review describes the development of a sensitive and selective chemiluminescence assay for investigating quinones and paraquat by utilizing their ability to generate reactive oxygen species.

Information processing through a bio-based redox capacitor: signatures for redox-cycling

Redox-cycling compounds can significantly impact biological systems and can be responsible for activities that range from pathogen virulence and contaminant toxicities, to therapeutic drug mechanisms. Current methods to identify redox-cycling activities rely on the generation of reactive oxygen species (ROS), and employ enzymatic or chemical methods to detect ROS. Here, we couple the speed and sensitivity of electrochemistry with the molecular-electronic properties of a bio-based redox-capacitor to generate signatures of redox-cycling. The redox capacitor film is electrochemically-fabricated at the electrode surface and is composed of a polysaccharide hydrogel with grafted catechol moieties. This capacitor film is redox-active but non-conducting and can engage diffusible compounds in either oxidative or reductive redox-cycling. Using standard electrochemical mediators ferrocene dimethanol (Fc) and Ru(NH3)6Cl3 (Ru(3+)) as model redox-cyclers, we observed signal amplifications and rectifications that serve as signatures of redox-cycling. Three bio-relevant compounds were then probed for these signatures: (i) ascorbate, a redox-active compound that does not redox-cycle; (ii) pyocyanin, a virulence factor well-known for its reductive redox-cycling; and (iii) acetaminophen, an analgesic that oxidatively redox-cycles but also undergoes conjugation reactions. These studies demonstrate that the redox-capacitor can enlist the capabilities of electrochemistry to generate rapid and sensitive signatures of biologically-relevant chemical activities (i.e., redox-cycling).