Specific bioanalytical optical and photoelectrochemical assays for detection of methanol in alcoholic beverages

Recent advancements in ubiquitous colorimetric and fluorometric sensors for the detection of methanol

Methanol, an aliphatic alcohol, is a widely recognized volatile organic compound (VOC) extensively used as a cost-effective solvent in various chemical, agricultural, and biological industries. However, the intentional adulteration of alcoholic beverages with inexpensive methanol for economic gain poses significant health hazards, including birth defects, respiratory illnesses, nervous system damage, and various chronic conditions. Prolonged exposure to methanol vapour can result in adverse effects such as eye inflammation, dizziness, headaches, insomnia, stomach problems, visual impairment, and even fatality. Notably, from 2017 to 2019, there were 7104 documented cases of methanol intoxication, resulting in 1888 fatalities across 306 recorded outbreaks of methanol poisoning. Notably, over 90% of these cases reported in Asia. Given the severe health risks associated with methanol, there is an urgent need for dependable detection methods to ensure public safety. One promising approach involves chemosensors capable of detecting methanol through changes in fluorescence or color. This review article provides a comprehensive overview of the latest advancements in methanol detection, categorizing sensors based on their materials, structural attributes, and detection mechanisms. In essence, the review highlights recent research progress in fluorometric and colorimetric methods for methanol detection.

A conductometric enzymatic methanol sensor based on polystyrene - PAMAM dendritic polymer electrospun nanofibers

Methanol (MeOH) is a solvent and cleaning agent used in industry, but it is poisonous when ingested. The recommended release threshold for MeOH vapor is 200 ppm. We present a novel sensitive micro-conductometric MeOH biosensor created by grafting alcohol oxidase (AOX) onto electrospun polystyrene-poly(amidoamine) dendritic polymer blend nanofibers (PS-PAMAM-ESNFs) on interdigitated electrodes (IDEs). The analytical performance of the MeOH microsensor was evaluated using gaseous MeOH, ethanol, and acetone samples collected from the headspace above aqueous solution with known concentration. The sensor's response time (t_Res) fluctuates from 13 s to 35 s from lower to higher concentrations. The conductometric sensor has a sensitivity of 150.53 μS.cm-1 (v/v) for MeOH and a detection limit of 100 ppm in the gas phase. The MeOH sensor is 7.3 times less sensitive to ethanol and 136.8 times less sensitive to acetone. The sensor was verified for detecting MeOH in commercial rubbing alcohol samples.

Differentiable detection of ethanol/methanol in biological fluids using prompt graphene-based electrochemical nanosensor coupled with catalytic complex of nickel oxide/8-hydroxyquinoline

Serious health hazards of volatile organic compounds such as methanol and ethanol for living species and their adverse effects on the environment raised a global requirement for developing a portable, precise, and sensitive detection platform capable of simultaneous and differentiable detection of alcohols in aquatic biological and non-biological fluids. Each year, methanol toxicity causes serious healthcare problems and leads to high mortalities in developing countries. Hence, designing and developing a practical nanosensor for diagnostic applications and environmental monitoring is crucial. Herein, we have addressed this demand by fabricating a portable, ultra-sensitive, and precise nanosensor capable of simultaneous and differentiable detection of methanol and ethanol in any aquatic specimen in about 1 min. The nanosensor is composed of the integrated graphene oxide (GO) flakes with the catalytic complex of NiOx and 8-hydroxyquinoline (8HQ) capable of identification of methanol and ethanol with an analytical sensitivity/detection limit of 30.66 μA(μmol/mL)-1.cm-2/6.87 nmol mL-1 and 118.99 μA(μmol/mL)-1.cm-2/1.80 nmol mL-1 using voltammetric assays between the linear range of 0.014-0.01 μmol mL-1 and 0.83-0.58 μmol mL-1, respectively. The outcome of the assessments exhibited the favorable capability of the prepared nanosensor for precise/prompt detection of alcohols in blood specimens and showed an ideal correlation with the outcome of the gold standard.

Design of a photoelectrochemical lab-on-a-chip immunosensor based on enzymatic production of quantum dots in situ

We present a new photoelectrochemical immunoassay based on a microfluidic device. Its operation employs enzymatic generation of CdS quantum dots.

Illicit Alcohol: Public Health Risk of Methanol Poisoning and Policy Mitigation Strategies

Illicit (unrecorded) alcohol is a critical global public health issue because it is produced without regulatory and market oversight with increased risk of safety, quality and adulteration issues. Undertaking iterative research to draw together academic, contemporary and historic evidence, this paper reviews one specific toxicological issue, methanol, in order to identify the policy mitigation strategies of interest. A typology of illicit alcohol products, including legal products, illegal products and surrogate products, is created. A policy landscape matrix is produced that synthesizes the drivers of illicit alcohol production, distribution, sale and consumption, policy measures and activity related signals in order to inform policy development. The matrix illustrates the interaction between capabilities, motivations and opportunities and factors such as access, culture, community norms and behavior, economic drivers and knowledge and information and gives insight into mitigation strategies against illicit alcohol sale and consumption, which may prove of value for policymakers in various parts of the world.

Development of portable CdS QDs screen-printed carbon electrode platform for electrochemiluminescence measurements and bioanalytical applications

In this work, a portable and disposable screen-printed electrode-based platform for CdS QDs electrochemiluminescence (ECL) detection is presented. CdS QDs were synthesized in aqueous media and placed on top of carbon electrodes by drop casting. The CdS QDs spherical assemblies consisted of nanoparticles about 4 nm diameters and served as ECL sensitizers to enzymatic assays. The nanoparticles were characterized by optical techniques, TEM and XPS. Besides, the electrode modification process was optimized and further studied by SEM and confocal microscopy. The ECL emission from CdS QDs was triggered with H₂O₂ as cofactor and enzymatic assays were employed to modulate the CdS QDs ECL signal by blocking the surface or generating H₂O₂ in situ. Thiol-bearing compounds such as thiocholine generated through the hydrolysis of acetylthiocholine by acetylcholinesterase (AChE) interacted with the surface of CdS QDs thus blocking the ECL. The biosensor showed a linear range up to 5 mU mL^-1 and a detection limit of 0.73 mU mL^-1 for AChE. Moreover, the inhibition mechanism of the enzyme was studied by using 1,5-bis-(4-allyldimethylammonium-phenyl)pentan-3-one dibromide with a detection limit of 79.22 nM. Furthermore, the natural production of H₂O₂ from the oxidation of methanol by the action of alcohol oxidase was utilized to carry out the ECL process. This enzymatic assay presented a linear range up to 0.5 mg L^-1 and a detection limit of 61.46 μg L^-1 for methanol. The reported methodology shows potential applications for the development of sensitive and easy to hand biosensors and was applied to the determination of AChE and methanol in real samples.

Quantum dots as nanosensors for detection of toxics: a literature review

Great advances have been made in sensor-based methods for chemical analysis owing to their high sensitivity, selectivity, less testing time, and minimal usage of chemical reagents. Quantum Dots (QDs) having excellent optical properties have been thoroughly explored for variety of scientific applications wherein light plays an important role. In recent years, there have been an increasing number of publications on the applications of QDs as photoluminescent nanosensors for the detection of chemicals and biomolecules. However, there has been hardly any publication describing the use of QDs in the detection of various toxic chemicals at one place. Hence, a literature survey has been made on the applications of QDs as chemosensors for the detection of gaseous, anionic, phenolic, metallic, drug-overdose, and pesticide poison so as to open a new perspective towards the role of sensors in analytical toxicology. In this review, the QD-based analysis of biospecimens for poison detection in clinical and forensic toxicology laboratories is highlighted.

Nitrogen-doped graphene quantum dot-based sensing platform for metabolite detection

A novel fluorescent sensing platform based on nitrogen-doped graphene quantum dots (N-GQDs) is presented, which is able to detect various metabolites (cholesterol, glucose, lactate, and xanthine) rapidly, sensitively, and selectively. Hg²⁺ can attach on the surface of N-GQDs, leading to the quenching of N-GQD fluorescence. In the presence of cysteine (Cys), Hg²⁺ is released from N-GQDs and associates with Cys. Then, the fluorescence of N-GQDs is recovered. Hydrogen peroxide, resulting from the enzymatic oxidation of metabolites, can convert two molecules of Cys into one molecule of cystine, which cannot bind with Hg²⁺. So, the fluorescence of N-GQDs quenched again. For cholesterol, glucose, lactate, and xanthine, the limits of detection are 0.035 μmol/L, 0.025 μmol/L, 0.07 μmol/L, and 0.04 μmol/L, respectively, and the linear ranges are 1-12 μmol/L, 0.06-3 μmol/L, 0.2-70 μmol/L, and 0.12-17 μmol/L, respectively. The presented method was applied to quantify metabolites in human blood samples with satisfactory results. Graphical abstract.

N-doped oxidized carbon dots for methanol sensing in alcoholic beverages

Methanol (MeOH) adulteration in alcoholic beverages resulting in irreparable health damage demands highly sensitive and cost-effective sensors for its quantification. As carbon dots are emerging as new biocompatible and sustainable light-emitting detectors, this work demonstrates the hydrothermally prepared nitrogen-doped oxidized carbon dots (NOCDs) as on-off fluorescent nanoprobes to detect MeOH traces in water and alcoholic beverages. The presence of 1% of MeOH in distilled water is found to decrease the NOCD fluorescent emission intensity by more than 90% whereas up to 70% ethanol (EtOH) content changes the signal to within 20% of its initial value. HR-TEM analysis reveals the agglomeration of the nanoprobes suspended in MeOH. Due to their selectivity towards MeOH, the fluorescent nanoprobes were successfully tested using a few MeOH spiked branded and unbranded Mexican alcoholic beverages. Varying degrees of signal quenching is observed from the fluorescent nanoprobes dispersed in different pristine beverages with a detection limit of less than 0.11 v%. Herein, we establish a new perspective towards economically viable non-toxic fluorescent probes as a potential alternative for the detection of MeOH in alcoholic beverages.

Herein, we establish a new perspective towards economically viable non-toxic fluorescent probes as a potential substitute of expensive alternative for the detection of MeOH in alcoholic beverages.

A rapid method to detect and estimate the activity of the enzyme, alcohol oxidase by the use of two chemical complexes - acetylacetone (3,5-diacetyl-1,4-dihydrolutidine) and acetylacetanilide (3,5-di-N-phenylacetyl-1,4-dihydrolutidine)

A rapid and sensitive method has been devised in order to detect and estimate the synthesis of the enzyme alcohol oxidase (AOX) by fungi, by way of the use of two chemical complexes, namely, acetylacetone (3,5-diacetyl-1,4-dihydrolutidine) and acetylacetanilide (3,5-di-N-phenylacetyl-1,4-dihydrolutidine). This method involves the use of the AOX enzyme that could specifically oxidize methanol, giving rise to equimolar equivalents each of formaldehyde (HCHO) and hydrogen peroxide (H₂O₂) as the end products. Further, the formaldehyde, thus produced was allowed to interact with the neutral solutions of acetylacetone and the ammonium salt, gradually developing a yellow color, owing to the synthesis and release of 3,5-diacetyl-1,4-dihydrolutidine (yellow product; λ = 420 nm; λ_ex/em = 390/470 nm) and the product, so generated was quantified spectrophotometrically by measureing its absorbance at 412 nm. In another set up, the amount of formaldehyde produced as a sequel to the oxidation of methanol by the AOX enzyme was determined by allowing it to react with the acetylacetanilide reagent, after which the volume of the fluorescent product - 3,5-di-N-phenylacetyl-1,4-dihydrolutidine (colorless product; λ_ex/em = 390/470 nm) that was generated was estimated by measuring its emission at 460 nm (excitation wavelength at 360 nm) in a spectrophotometer. Of the various substrates tested, a commercial source of the AOX enzyme appreciably oxidizes methanol, thereby generating formaldehyde, and further reacts with acetylacetone, to give rise to a bright yellow complex, displaying a maximum activity of 1402 U/mL. Determination of the AOX activity by the use of acetylacetone and acetylacetanilide could serve as a viable alternative to the conventional alcohol oxidase-peroxidase-2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid (AOX-POD-ABTS) based method. In view of this, this method appears to be invaluable for application at the various food, pharmaceutical, fuel, biosensor, biorefinery, biopolymer, biomaterial, platform chemical, and biodiesel industries.

Optical Sensors Based on II-VI Quantum Dots

Fundamentals of quantum dots (QDs) sensing phenomena show the predominance of these fluorophores over standard organic dyes, mainly because of their unique optical properties such as sharp and tunable emission spectra, high emission quantum yield and broad absorption. Moreover, they also indicate no photo bleaching and can be also grown as no blinking emitters. Due to these properties, QDs may be used e.g., for multiplex testing of the analyte by simultaneously detecting multiple or very weak signals. Physico-chemical mechanisms used for analyte detection, like analyte stimulated QDs aggregation, nonradiative Förster resonance energy transfer (FRET) exhibit a number of QDs, which can be applied in sensors. Quantum dots-based sensors find use in the detection of ions, organic compounds (e.g., proteins, sugars, volatile substances) as well as bacteria and viruses.

Cu2+-Modulated in situ growth of quantum dots for split-type photoelectrochemical immunoassay of prostate-specific antigen

A split-type photoelectrochemical immunosensor of PSA was developed using Cu²⁺-dependent catalytic oxidation for inhibiting the in situ growth of CdS QDs.