Current Analytical Chemistry - Volume 18, Issue 7, 2022

Background: Demand for alcohol-based products, including gel- and aqueous-type hand sanitizers, room sprays, and mouthwashes, has rapidly increased during the ongoing COVID-19 pandemic because of their microbicidal properties. However, toxic methanol can be found from the intentional addition of methanol by manufacturers and invariable production during the manufacturing of alcohol (ethanol). Although the FDA has recommended that such products should contain less than 630 ppm of methanol, it is only a temporary measure established specifically to regulate such products during the current COVID-19 pandemic and hence is not strictly regulated. Objective: This study aims to detect and quantify the level of methanol in alcohol-based products. However, some manufacturers unethically add methanol to their products and promote them as methanol-free. Besides, they do not provide proficiency and toxicity test results. Therefore, these kinds of products need to be analyzed to determine if they are acceptable to use. Methods: This study qualitatively and quantitatively investigates the amount of methanol in commercial alcohol-based products using a newly developed headspace gas chromatography/mass spectrometry method. Moreover, alcoholic beverages which contain methanol are analyzed to be compared with the levels of methanol in alcohol-based products and determine if their methanol levels are acceptable. Results: Methanol concentrations in gel-type hand sanitizers (517 ppm) and mouthwashes (202 ppm) were similar to those in white wine (429 ppm) and beer (256 ppm), respectively, while that of aqueous-type hand sanitizers (1139 ppm) was 1.5 times more than that of red wine (751 ppm). Conclusion: Methanol levels in most of the alcohol-based products did not exceed the FDArecommended limit.

Background: By using bimetal nanocomposite modified electrode, the electrochemical DNA biosensor showed the advantages of high sensitivity, low cost, rapid response and convenient operation, which was applied for disease diagnosis, food safety, and biological monitoring. Objective: A nanocomposite consisting of platinum (Pt)-gold (Au) bimetal and two-dimensional graphene (GR) was synthesized by hydrothermal method, which was modified on the surface of carbon ionic liquid electrode and further used for the immobilization of probe ssDNA related to Vibrio parahaemolyticus tlh gene to construct an electrochemical DNA sensor. Method: Potassium ferricyanide was selected as electrochemical indicator, cyclic voltammetry was used to study the electrochemical behaviours of different modified electrodes and differential pulse voltammetry was employed to test the analytical performance of this biosensor for the detection of target gene sequence. Results: This electrochemical DNA biosensor could detect the Vibrio parahaemolyticus tlh gene sequence as the linear concentration in the range from 1.0×10-¹³ mol L^-1 to 1.0×10^-6 mol L^-1 with the detection limit as 2.91×10^-14 mol L^-1 (3σ). Conclusion: This proposed electrochemical DNA biosensor could be used to identify the special gene sequence with good selectivity, low detection limit and wide detection range.

Aims: Here, we report a simple strategy for the preparation of thermally exfoliated graphite (EG) and its application to modify glassy carbon electrode (GCE) surfaces for electrochemical Cu²⁺ ion sensing. Method: The electrochemical Cu²⁺ sensor was constructed by a layer modification of a glassy carbon electrode (GCE) with exfoliated graphite (EG) and chitosan (CS) as a binder, and CS also supports a large number of -NH2 functional groups for Cu²⁺ capture. Result: Due to the creation of a three-dimensional (3D) structure, the EG/CS-coated GCE (EG/CS/GCE) electrode exhibited a higher sensitivity towards Cu²⁺ detection than that of modification by graphite/chitosan (GP/CS), chitosan (CS) or graphite intercalated compounds (GIC)/chitosan. Conclusion: The proposed method could detect Cu²⁺ in the range of 10 μM to 3 mM with a detection limit of 0.5 μM and sensitivity of 43.62 μA mM^-1.

Background: 5-Fluorouracil (5-FU) is a well-established anticancer drug. Several studies have also demonstrated the anticancer potential of Cannabidiol (CBD) against various malignancies, including skin cancer. Reported synergistic effects of this combination fascinate researchers to consider this for the management of skin cancer. Methods: A simple and robust HPLC method for simultaneous estimation of 5-FU and CBD at its single wavelength (237 nm) was developed and validated. The separation of these compounds was performed on Waters® HPLC system with Hypersil™ C18 RP-column using methanol and water in gradient flow as mobile phase. The method could effectively quantify the nanogram levels of both analytes simultaneously in plasma spiked samples and various nanoformulations. The analytical performance of the proposed method was validated in terms of various parameters, such as linearity, ruggedness, specificity, and few others. Results: 5-FU as well as CBD were successfully detected at 237 nm with retention time of 1.4 and 1.84 minutes, respectively. Calibration curves were found to be linear with R2 values of 0.985 and 0.984 for 5-FU and CBD, respectively. The method was linear, precise, specific and robust. Additionally, prepared method successfully determined concentration of both drugs in combitorial nanoformulations. Conclusion: The findings show that the developed method is simple, reliable, sensitive and economical. It could be employed for the simultaneous estimation of 5-FU and CBD in various in vitro and in vivo studies.

Background: Uric acid (UA) is an important metabolic intermediate of the human body. Abnormally high levels of UA will cause diseases. However, UA monitoring with commercial products relies on invasive blood collection, which not only causes pain in patients but also risks bacterial infections and skin irritation. In recent years, new models of noninvasive detection through body surface penetration have raised higher expectations for the sensitivity of uric acid detection, and rapid, accurate and highly sensitive UA sensors will become powerful tools for the diagnosis of UA-related diseases. Objective: This study aimed to identify the differences in catalytic efficiency between regular PB from spray crystallization (RPB) and irregular PB from electrodeposition (EDPB), which is used for fabricate a high sensitive uric acid sensor. Methods: Regular Prussian blue nanocrystals (RPB) were grown on graphene oxide flakes (GO), on the surface of a custom screen-printed carbon electrode (SPCE), using a spray method assisted by a constant magnetic field (CMF). After immobilizing uricase, the uric acid biosensor Uricase/RPB/CMF-GO/SPCE was obtained. Results: The detection range of the sensor response to UA was 0.005~2.525 mM, and the detection limit was as low as 3.6 μM. The cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) results showed that compared to amorphous electrodeposited Prussian blue (EDPB), RPB more favorably accelerated electron transport. Conclusion: This novel uric acid biosensor exhibits high sensitivity over a wide concentration range, strong anti-interference ability, and good stability and reproducibility. Thus, it has good application prospects for determining uric acid in physiological samples.

Background: Currently, carbon nanomaterials and carbon nanomaterials-based electrodes have illustrated significant electrocatalytic abilities. Methods: An electrochemical sensor was developed for vanillin using graphene (GR) decorated with gold nanoparticles (AuNPs) on a glassy carbon electrode (GCE) with two steps. AuNPs/GR/GCE, as the electrochemical sensor for determination of vanillin, included dropping GR onto the electrode and then electrodepositing AuNPs on GR/GCE. The structure and morphology of the synthesized nanocomposites (AuNPs/GR) on the electrode were confirmed by scanning electron microscopy (SEM). Results: Electrochemical studies revealed that modification of the electrode surface with AuNPs/GR nanocomposites significantly increases the oxidation peak currents of vanillin. The peak currents in differential pulse voltammetry (DPV) of vanillin increased linearly with their concentration in the range of 5-120 μM. The limit of detection was found to be 1.7 μM for vanillin. Also, the effect of some interfering compounds, such as NaCl, KCl, glucose, alanine, phenylalanine, glycine, and others, on the determination of vanillin was evaluated, and none of them had a significant effect on the assay recovery. Conclusions: A new electrochemical biosensor was fabricated with AuNPs/GR nanocomposites. The sensor was successfully used to detect vanillin in cookie samples.

Background: Recent studies demonstrate that titanium dioxide nanoparticles (TiO2 NPs) are an effective source of reactive oxygen species (ROS) for photodynamic therapy and radionuclide stimulated dynamic therapy (RaST). Unfortunately, tracking the in vivo distribution of TiO2 NPs noninvasively remains elusive. Objective: Given the use of gadolinium (Gd) chelates as effective contrast agents for magnetic resonance imaging (MRI), this study aims to (1) develop hybrid TiO2-Gd NPs that exhibit high relaxivity for tracking the NPs without loss of ROS generating capacity; and (2) establish a simple colorimetric assay for quantifying Gd loading and stability. Method: A chelate-free, heat-induced method was used to load Gd onto TiO2 NPs, which was coated with transferrin (Tf). A sensitive colorimetric assay and inductively coupled plasma mass spectrometry (ICP-MS) were used to determine Gd loading and stability of the TiO2-Gd-Tf NPs. Measurement of the relaxivity was performed on a 1.4 T relaxometer and a 4.7 T small animal magnetic resonance scanner to estimate the effects of magnetic field strength. ROS was quantified by activated dichlorodihydrofluorescein diacetate fluorescence. Cell uptake of the NPs and RaST were monitored by fluorescence microscopy. Both 3 T and 4.7 T scanners were used to image the in vivo distribution of intravenously injected NPs in tumor-bearing mice. Results: A simple colorimetric assay accurately determined both the loading and stability of the NPs compared with the expensive and complex ICP-MS method. Coating of the TiO2-Gd NPs with Tf stabilized the nanoconstruct and minimized aggregation. The TiO2-Gd-Tf maintained ROS-generating capability without inducing cell death at a wide range of concentrations but induced significant cell death under RaST conditions in the presence of F-18 radiolabeled 2-fluorodeoxyglucose. The longitudinal (r1 = 10.43 mM^-1s^-1) and transverse (r2 = 13.43 mM^-1s^-1) relaxivity of TiO2-Gd-Tf NPs were about twice and thrice, respectively, those of clinically used Gd contrast agent (Gd-DTPA; r1 = 3.77 mM^-1s^-1 and r2 = 5.51 mM^-1s^-1) at 1.4 T. While the r1 (8.13 mM^-1s^-1) reduced to about twice that of Gd-DTPA (4.89 mM^-1s^-1) at 4.7 T, the corresponding r2 (87.15 mM^-1s^-1) increased by a factor 22.6 compared to Gd-DTPA (r2 = 3.85). MRI of tumor-bearing mice injected with TiO2-Gd-Tf NPs tracked the NPs distribution and accumulation in tumors. Conclusion: This work demonstrates that Arsenazo III colorimetric assay can substitute ICP-MS for determining the loading and stability of Gd-doped TiO2 NPs. The new nanoconstruct enabled RaST effect in cells, exhibited high relaxivity, and enhanced MRI contrast in tumors in vivo, paving the way for in vivo MRI-guided RaST.

Background: Water contamination and its remediation are currently considered a major concern worldwide. Design of effective methods for water purification is highly demanded for the adsorption and removal of such pollutants. Objective: This study depicts the effectiveness of nickel oxide-copper oxide nanoparticles (NiO-CuO), which can extract and remediate ferric ions, Fe(III), from aqueous solutions. Methods: The NiO-CuO nanoparticles were simply prepared by the co-precipitation method and then used as adsorbent with respectable advantages of high uptake capacity and surface area. Results: Adsorption of Fe(III) onto NiO-CuO nanoparticles showed an uptake capacity of 85.86 mgg^-1 at pH 5.0. The obtained data from the carried-out experiment of Fe(III) adsorption onto NiO-CuO nanoparticles were well suited to the Langmuir isotherm and pseudo-second-order kinetic models. Moreover, different coexisting ions did not influence the adsorption of Fe(III) onto NiO-CuO nanoparticles. The recommended methodology was implemented on the adsorption and removal of several environmental water samples with high efficiency. Conclusion: The designed method displayed that NiO-CuO nanoparticles can be used as a promising material for the adsorptive removal of heavy metals from water.

Background: Detection of Vitamin C (Vc) is very important to protect human health. A lot of methods have been developed for the detection of Vc. However, many methods require complex material preparation and skilled operators. Thus, a simple, label-free biosensor is still urgently needed. Methods: In this work, N-methylmesoporphyrin IX (NMM)/G-quadruplex pair was used as a labelfree signal reporter. Without Vc, the G-quadruplex DNA and its incomplete complementary chain could form a duplex structure by T-Hg(II)-T mismatch. In this case, the G-quadruplex structure could not be formed. When Vc was added, the Hg²⁺ was reduced to Hg(0). Then, the G-quadruplex DNA became free and formed a G-quadruplex structure to emit fluorescence signals. Results: Under optimal conditions, this biosensor showed a good linear response in the range of 0.2 - 4.0 μM and a low limit of detection (19.9 nM). This biosensor also had good selectivity towards Vc. Meanwhile, the satisfactory recovery rates (93.2%-102.8%) suggested that this biosensor had potential for measuring Vc in real samples. Conclusion: In this work, a simple label-free fluorescent biosensor for the detection of Vc based on Hg²⁺-mediated DNA structural changes had been developed. The whole experiment was simple and all reagents were commercialized. The label-free detection was realized by NMM/G-quadruplex as a signal reporter. This biosensor was very sensitive with a low limit of detection. It had a potential practical application for Vc detection in milk powder.

Background: A rapid and specific detection of pathogens is of great importance from public health viewpoint as well as from economic perspectives. Genosensor based on sequence specific detection of Escherichia coli facilitates significant improvements in rapidity and specificity over traditional microbiological methods. Objective: The present study was aimed at identifying a sequence of xanQ genetic markers for designing the DNA sensing probe and fabricating a genosensor using the interdigitated gold electrode (IDE). Methods: A label-free genosensor for E. coli detection in water by a novel nucleic acid sensing probe, URecA1016 is reported. The URecA1016 sensing probe-functionalized gold-interdigitated electrode surface by covalent coupling using 11-Mercaptoundecanoic acid (crosslinker) to develop the electrochemical genosensor. Results: Upon DNA hybridization, the non-Faradaic sensing measurements showed a decreasing capacitance value with 10 min response time at 120 Hz frequency and 10 mV applied potential. The linearity range of the genosensor was between 1 and 1000 pg/mL for DNA of E. coli with a limit of quantification (LoQ) of 1.27 pg DNA/mL of E. coli (equivalent to approximately 150 CFU/mL) at 95% confidence. Whilst the genosensor was E. coli species-specific as has been tested for the detection of E. coli MTCC 3221, E. coli O157:H7 ATCC 43895, E. coli O78:H11 MTCC 723 any cross-reactivity could not be observed with DNA of Shigella flexneri MTCC 9543 and Bacillus subtilis MTCC 736. The capacitance change responses were also recorded and discussed. Conclusion: The URecA1016 sensing probe was found to be specific for the detection of different E. coli species spiked in water. The results obtained in our study demonstrated the possible application potential of genosensor for E. coli detection in real water samples.