Mesoporous Silica-gold Films for Straightforward, Highly Reproducible Monitoring of Mercury Traces in Water

A Graphene-Coated Silicon Wafer Plate Improves the Sensitivity and Reproducibility of MALDI-TOF MS Analysis of Proteins

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) is widely used to analyze small and large molecules. However, proteins are difficult to analyze with MALDI-TOF MS in clinical applications because of their low ionization efficiency and heterogeneous crystallization with the matrix on the sample spots. Here, we investigate the potential of a customized graphene-coated silicon wafer (G/SiO2) plate for MALDI-TOF MS analysis of a clinically important protein, KPC-2, in comparison with a conventional stainless steel (SUS) plate. Our results demonstrate that the G/SiO2 plate outperforms the SUS plate in terms of sensitivity, reproducibility, and mass accuracy/precision across a wide range of molecular weights, even with highly complex samples. Furthermore, a five-day robustness test confirms the practical applicability of the G/SiO2 plate for the reliable identification of target protein(s) in MALDI-TOF MS analysis. Overall, our findings suggest that the use of the G/SiO2 plate holds great potential for improving the sensitivity and reproducibility of MALDI-TOF MS analysis for the identification of proteins, making it a promising tool for clinical applications.

Photoactive Titanium Dioxide Films with Embedded Gold Nanoparticles for Quantitative Determination of Mercury Traces in Humic Matter-Containing Freshwaters

Mercury detection in humic matter-containing natural waters is often associated with environmental harmful substances for sample preparation. Herein we report an approach based on photoactive titanium dioxide films with embedded gold nanoparticles (AuNP@TiO₂ dipstick) for chemical-free sample preparation and mercury preconcentration. For this purpose, AuNPs are immobilized onto a silicon wafer and further covered with a thin photoactive titanium dioxide layer. The AuNPs allow the preconcentration of Hg traces via amalgamation, while TiO₂ acts as a protective layer and, at the same time, as a photocatalyst for UV-C radiation-based sample pretreatment. Humic matter, often present in natural waters, forms stabile complexes with Hg and so hinders its preconcentration prior to detection, causing a minor recovery. This problem is solved here by irradiation during Hg preconcentration onto the photoactive dipstick, resulting in a limit of detection as low as 0.137 ng L^-1 using atomic fluorescence spectrometry (AFS). A 5 min preconcentration step is sufficient to obtain successful recovery of Hg traces from waters with up to 10 mg L^-1 DOC. The feasibility of the approach was demonstrated by the determination of Hg traces in Danube river water. The results show no significant differences in comparison with standard cold vapor-atomic fluorescence spectrometry (CV-AFS) measurements of the same sample. Hence, this new AuNP@TiO₂ dipstick provides a single-step sample preparation and preconcentration approach that combines sustainability with high analytical sensitivity and accuracy.

Addition of thiourea and hydrochloric acid: Accurate nanogram level analysis of mercury in humic-rich natural waters by inductively coupled plasma mass spectrometry

An analytical method was developed for the direct determination of total mercury in natural waters at low ng L^-1 level by inductively coupled plasma mass spectrometry (ICP-MS). The presented method overcomes previously observed problems relating to poor spike recoveries by adding 0.12% thiourea in addition to 3% HCl to all samples and standards. The sample preparation is fast and easy to perform by the developed method since it requires only the addition of HCl and thiourea to the water samples. A very low instrument detection limit (0.4 ng L^-1) was obtained without time-consuming preconcentration procedures. The accuracy and precision of the developed method were found excellent by the analysis of a certified groundwater reference material (ERM-CA615). The determined Hg concentration of 38.6 ± 0.5 ng L^-1 was within the 95% confidence interval of the certified concentration of 37 ± 4 ng L^-1. The analysis of natural water samples showed that total mercury levels ranged from concentrations lower than the method detection limit (2.0 ng L^-1) to 10.9 ng L^-1. Excellent recoveries of 96-108% for inorganic mercury (iHg) and 102-110% for methylmercury (MeHg) were obtained for spiked humic-rich natural water samples. To our knowledge, the developed method is the first ICP-MS method for the analysis of humic-rich natural water samples at ng L^-1 concentrations without the need for hyphenated techniques or preconcentration procedures.

Growth and Functionalization of Particle-Based Mesoporous Silica Films and Their Usage in Catalysis

We report the formation of mesoporous films consisting of SBA-15 particles grown directly onto substrates and their usage as catalysts in esterification of acetic acid and ethanol. The film thickness was altered between 80 nm and 750 nm by adding NH₄F to the synthesis solution. The salt also affects the formation rate of the particles, and substrates must be added during the formation of the siliceous network in the solution. Various substrate functionalizations were tested and hydrophobic substrates are required for a successful film growth. We show that large surfaces (> 75 cm²), as well as 3D substrates, can be homogenously coated. Further, the films were functionalized, either with acetic acid through co-condensation, or by coating the films with a thin carbon layer through exposure to furfuryl alcohol fumes followed by carbonization and sulfonation with H₂SO₄. The carbon-coated film was shown to be an efficient catalyst in the esterification reaction with acetic acid and ethanol. Due to the short, accessible mesopores, chemical variability, and possibility to homogenously cover large, rough surfaces. the films have a large potential for usage in various applications such as catalysis, sensing, and drug delivery.