Analytical Sciences最新文献

Glutathione (GSH) is a tripeptide and natural reducing agent composed of glutamic acid, glycine, and cysteine. Its level in the human body is closely linked to human health, such as diabetes, Alzheimer's disease, and cancer. The supplementation of exogenous GSH could bring health benefits and GSH detection in food is of considerable importance. However, the existing assays for GSH detection such as high-performance liquid chromatography/mass spectrometry, electrochemiluminescence and fluorescent nanoprobe were not satisfactory because of the disadvantages of equipment and site requirements. In this study, a multiple-colorimetric detection assay for GSH was developed based on GSH's reaction with gold nanorods. During the reaction with varying concentrations of GSH, the gold nanorods degraded into spherical nanoparticles with multiple color changes, which could be used to determine GSH concentrations. The transverse surface plasmon resonance absorption peak of gold nanorods (AuNRs) significantly shifted, indicating a novel mechanism distinct from etching or surface coating, which typically altered the longitudinal surface plasmon absorption peak. Under optimized conditions, the assay exhibited commendable specificity and reliability in actual samples. The assay accurately quantified GSH ranging from 1 to 10 µM, with detection limits of 439 nM and 260 nM for spectrophotometry and visual analysis, respectively. It was firstly to use GSH as a reducing agent to react with AuNRs in the presence of AgNO₃ and the mechanism was different from etching or surface coating. The study's assay shows potential for detecting GSH in food samples and provides an alternative approach for the development of colorimetric detection assays based on AuNRs.

The diverse functional roles of RNA within cells have led to a growing interest in developing RNA-binding fluorescent probes to investigate RNA functions. In particular, the probes for double-stranded RNA (dsRNA) structures are of significant value given the importance of the secondary and tertiary RNA structures on their biologic functions. This review highlights our recent efforts on the development of triplex-forming peptide nucleic acid (TFP)-based probes for fluorescence sensing of dsRNA structures. We demonstrated that the forced intercalation of asymmetric cyanine dyes integrated as base surrogate within the probes was useful for achieving significant light-up response toward target dsRNAs. We also showed that the TFP probes conjugated with small RNA-binding molecules facilitated the fluorescence sensing of biologic relevant dsRNAs containing unpaired nucleobases. The binding and fluorescence signaling functions of such probes were discussed, emphasizing their potential as analytical tools for studying dsRNA structures.

A digital-movie-based flow colorimetry for pH measurement using a universal indicator has been applied to the end point detection of acid-base titrations. A two-channel flow system of feedback-based flow ratiometry, primarily consisting of two peristaltic pumps, a digital microscope-based detector, and a laptop computer, was constructed; a Visual Basic.NET program written in-house was used for automating the analytical processes. While maintaining the total flow rate (F_T) constant, a titrand solution was merged with a titrant solution, both containing the same concentration of Van Urk's universal indicator, under varying flow ratios. Downstream, the video image was captured with a digital microscope and its color was expressed as RGB values, hue, and luminance. The end point was determined from the rapid change of hue reflecting the color transition of the universal indicator around the equivalence point. A stepwise titration of multivalent acid (i.e., H₃PO₄) was also possible by setting hue values corresponding to the first (1st) and second (2nd) equivalence points as criteria to determine the respective end points. The hue-based approach was validated by the titrations of CH₃COOH and H₃PO₄ (1st and 2nd equivalence points) with 0.1 mol dm^-3 NaOH and to those of NaOH and NH₃ with 0.1 mol dm^-3 HCl. The method was applied to determine Japanese Pharmacopoeia (JP) borax and JP citric acid. The respective assay results were 100.0 ± 0.0% and 100.0 ± 0.0%, both meeting the JP specifications. The developed method is simple, high throughput (1 titration/min), versatile, and does not require indicator replace depending on the equivalence point pH.

"Liquid gold" has been traditionally used for over a century to decorate ceramicware, but its chemical composition has not been thoroughly investigated. One of the keys to successfully characterizing liquid gold, which is a complex mixture, is to distinguish Au-containing products from other chemicals. In this paper, we propose a separation based on the difference in collision cross section, of which chemicals with heavy atoms are relatively smaller than those without in ion mobility-mass spectrometry (IM-MS). Chemicals containing a single Au atom (and Pt atom) were successfully separated from other species in the two-dimensional distribution map for IM-MS. By a detailed analysis of the spectra obtained by IM-MS/MS with collision-induced dissociation before and after IM separation, we found that liquid gold (gold resinate) was a mixture of a series of (1) Au reacted with α-pinene-related units and (2) Au reacted with abietic acid units. α-Pinene and abietic acid are the main components of turpentine and rosin, the raw materials of liquid gold as reported previously (Anal. Sci. 2024, 40, 133-139). All Au-containing species contain sulfur atoms. Species of Au reacted with α-pinene-related units with different degrees of unsaturation and oxidation have also been identified. Liquid gold, a complex mixture of chemicals containing Au, has been successfully analyzed compositionally.

A biosensor for biochemical oxygen demand (BOD) was developed based on intracellular 5'-adenosine triphosphate (ATP) measurements in Saccharomyces cerevisiae. Intracellular ATP was measured using an engineered protein named ATeam, comprising a bacterial F₀F₁-ATP synthase ε subunit sandwiched between cyan fluorescent protein and mVenus, a modified yellow fluorescent protein. Because the binding of ATP to ATeam induces changes in the fluorescence spectra owing to Fӧrster resonance energy transfer, S. cerevisiae expressing ATeam is expected to show spectral changes owing to the intracellular ATP produced by the metabolism of the BOD sample. A glycogen phosphorylase knockout S. cerevisiae strain expressing ATeam was prepared, and the fluorescence spectra of the strain were analyzed. Changes in the fluorescence spectra of glucose in the medium were observed, which exhibited a linear relationship with the glucose concentration (0-100 mg/L, R² = 0.970). Responses to lactose, fructose, sucrose, Glu, Asp, His, and Gly were evaluated and compared with typical BOD measurements. The results of this comparison suggest that a BOD biosensor based on intracellular ATP can be used for BOD measurements. A BOD standard solution comprising glucose and glutamic acid (GGA) was calibrated across a concentration range of 0 to 100 mg/L. Finally, simulated real samples were prepared using real pond water and GGA was measured. The correlation between the BOD value evaluated using intracellular ATP and that evaluated using the 5-day BOD test showed a linear relationship with R² = 0.944.

In recent years, wearable sweat sensors have garnered significant attention for real-time monitoring of human physiological information because of their ability to continuously and non-invasively detect multiple sweat biomarkers. Among these, potentiometric sensors stand out for their low power consumption, low cost, compact design, and real-time monitoring capabilities, making them an ideal alternative for sweat analysis. However, enhancing the sensitivity of ion-selective electrodes (ISEs), a critical parameter of potentiometric sensors, remains a challenging research focus. In this work, the sensitivity of K⁺ ISEs was significantly enhanced by doping two-dimensional nanoparticles graphitic carbon nitride (g-C₃N₄) into the ion-to-electron transducer of the electrode via electrodeposition. The calibration curve slope of the K⁺ potentiometric sensors with doped g-C₃N₄ reached 59.6 mV/dec, representing a 33% increase in sensitivity compared to the control sensor without g-C₃N₄. Furthermore, the developed sensors demonstrated excellent repeatability, and anti-interference capabilities. Finally, the feasibility of the prepared sensors was further validated in artificial sweat. The large specific surface area of g-C₃N₄ combined with the excellent conductivity of PEDOT: PSS, significantly improved the sensitivity of ISEs in this study. This innovative approach paves a new avenue for the application of two-dimensional materials in potentiometric sensors, potentially advancing the field of real-time sweat analysis.

The human BK channel (hBK) is an essential membrane protein that regulates various biological functions, and its dysfunction leads to serious diseases. Understanding the biophysical properties of hBK channels is crucial for drug development. Artificial lipid bilayer recording is used to measure biophysical properties at the single-channel level. However, this technique is time-consuming and complicated; thus, its measurement efficiency is very low. Previously, we developed a novel technique to improve the measurement efficiency by rapidly forming lipid bilayer membranes and incorporating ion channels into the membrane using a hydrophilically modified gold probe. To further improve our technique for application to the hBK channel, we combined it using the gold probe with a liposome fusion method. Using a probe on which liposomes containing hBK channels were immobilized, the channels were efficiently incorporated into the lipid bilayer membrane, and the measured channel currents showed the current characteristics of the hBK channel. This technique will be useful for the efficient measurements of the channel properties of hBK and other biologically important channels.