Low Concentration Range Research Articles

Construction of two isomorphic multifunctional MOFs via a dual-ligand strategy for aromatic compounds detection and photocatalytic degradation performance

The development of multifunctional and structurally unique metal−organic frameworks (MOFs) presents a highly attractive yet challenging endeavor for chemists. In this study, we employ a dual-ligand strategy to synthesize two isomorphic Co/Zn MOFs, {[Co4(BMIP)3(MIP)4]·3DMF·H2O}n (SNUT-35-Co) and {[Zn4(BMIP)3(MIP)4]·2DMF·2H2O}n (SNUT-35-Zn). The photocatalytic performance of SNUT-35-Co and SNUT-35-Zn was evaluated using methylene blue (MB). Under UV/visible-light irradiation, the photocatalytic decolorization rates of MB for SNUT-35-Co and SNUT-35-Zn reached 95 % within 140 min and 120 min, respectively, indicating their superior degradation. Notably, SNUT-35-Zn demonstrated exceptional detection capabilities for aromatic compounds, such as aniline and nitrobenzene, at lower concentration range without interference from other components. The detection limits for these two small molecules were found to be 0.430 and 0.431 μM, respectively. Additionally, both MOFs exhibited large transient photocurrent and low impedance in electrochemical measurement. The results suggested that the photocatalytic activities of MOFs are influenced by their three-dimensional structures, which facilitate electrons passing due to the inherent semiconductor properties.

Bottom-up designing nanostructured oxide libraries under a lab-on-chip paradigm towards a low-cost highly-selective E-nose

BackgroundThe multisensor concept has been developed as a powerful alternative to well-known gas-analytical instrumentation for applications where a fast but accurate and reliable assessment of the environment is required. The concept follows a biology-inspired approach where the selectivity towards various gases/odors is attained via pattern recognition of multisensory signal vectors. Herein, we discuss how to design a selective multisensor library based on various metal oxide nanostructures like a lab-on-chip using a simple but efficient bottom-up growth of materials over the multi-electrode chip under robust dc electrochemical protocols. ResultsIn addition to a conventional growth of oxide layers over the metal electrodes, we show that the fine nanowall-like oxide structures appear as a quasi-matrixed percolation film over the SiO2 substrate surface in the inter-electrode gaps to constitute a chemiresistive film. We have tested two directions while applying the technique to grow Co, Ni, Mn, and Zn oxides to develop on-chip sensor arrays of, (i) monoxide type employing the oxide films with gradual change of growth time, and (ii) multi-oxide type based on the four oxides. The materials were thoroughly characterized by electron microscopy, X-ray diffraction, thermogravimetric analysis, and X-ray photoelectron spectroscopy/mapping to prove the composition and structure. Among tested oxides, ZnO readily appears not only at the electric potential-targeted chip zone but also in other areas to dope the films for yielding heterojunctions with other oxides that enhances a variability of functional properties in the on-chip sensor array. The gas-sensing performance of the chips has been tested versus various chemically akin alcohol vapors at the sub- and low ppm range of concentrations in a mixture with air. SignificanceWe show that the grown oxide nanostructures exhibit a high-sensitive chemiresistive signal which allows one to build a multisensor vector signal, selective to the kind of alcohols, even at sub-ppm concentrations. Moreover, the multi-oxide library yields options for a superior selectivity under LDA metrics than the gradient-grown mono-oxide one due to the versatility of materials while the low-cost growth protocols remain to be the same in both cases. The delivered method to produce multisensor arrays allows one producing low-cost but efficient electronic nose units for numerous applications.

Ultratrace CO/SF6 Detection System Based on Differential Fourier Transform Infrared Spectroscopy Combined with the Weighted Sine Spectral Reconstruction Convolutional Neural Network (WSSR-CNN) Model.

Carbon monoxide (CO), as an indicator gas for fault diagnosis of gas-insulated switchgear, has the strongest absorption coefficient in the mid-infrared region, making Fourier transform infrared (FTIR) spectroscopy an ideal method for its concentration detection. However, there is extremely abundant absorption of SF6 in this region, resulting in a great challenge for CO/SF6 detection. To address this challenge, we report a high sensitivity online detection system for ultratrace levels of CO, which combines differential Fourier transform infrared (DFTIR) spectroscopy with a weighted sine spectral reconstruction convolutional neural network (WSSR-CNN). The differential technique is first introduced into FTIR for baseline correction of CO absorption signals. The novel WSSR method achieves feature extraction and denoising of weak spectral signals in strong interference by discretizing interfering signals and enhancing target signals. On this basis, the detection of CO concentration is realized using the CNN model. Finally, WSSR-CNN is compared with four other methods. Results showed that WSSR-CNN outperforms all four models with evaluation index R2 reaching 0.99982 and 0.99999 in the range of low concentration (0.096-0.986 ppm) and high concentration (1.984-52.193 ppm) and mean absolute percentage error of 0.97% and 0.22%, respectively. The lowest detection limit of the system at 1σ is 13 ppb, which is the best result reported so far for detecting CO/SF6 concentration based on FTIR.

Cost-effective chemiresistive biosensor with MWCNT-ZnO nanofibers for early detection of tuberculosis (TB) lipoarabinomannan (LAM) antigen.

Thedevelopment of an affordable chemiresistive biosensor enhanced with a multi-walled carbon nanotube-zinc oxide (MWCNT-ZnO) nanofiber compositeis presented. The sensor leverages the precise interaction between lipoarabinomannan (LAM) tuberculosis (TB) antigens and antibodies to achieve high sensitivity and specificity. The MWCNT-ZnO nanofibers have a larger surface area and better electrical conductivity, which makes it easier for TB antibodies to stick to them. The binding of LAM TB antigens to the fixed Monoclonal Antibody-MBS320597 induces significant resistance changes in the chemiresistive sensor, enabling accurate TB detection. Performance evaluation reveals a linear detection range from 1.0 to 100.0pg/mL in the lower concentration range and up to 6.0ng/mL in the higher concentration range, with a sensitivity of 79.750mApgmL-1cm-2 and a lower limit of detection of 40.54fg/mL. The sensor exhibits a response time of 102s. Featuring rapid response time and high sensitivity, this biosensor is ideally suited for point-of-care (PoC) applications. The incorporation of MWCNT-ZnO nanofibers shows great potential for enhancing the development of sensitive and cost-effective TB diagnostic tools, which could play a crucial role in advancing global TB control and management efforts.

Evidence for a Griffiths Phase to Cluster Spin Glass Transition in the La2/3Sr1/3(Mn1-3 xAl2 xTix)O3 System.

The presence of Griffiths phase to cluster spin glass transition has theoretically been predicted in both classical and quantum systems. However, its detection in a classical system has been lacking for decades, which hinders a complete understanding of the relationship between the Griffiths phase and cluster spin glass. Here, the experimental discovery of the Griffiths phase to cluster spin glass transition is reported in a classical magnetic system, diluted ferromagnets La2/3Sr1/3(Mn1-3 xAl2 xTix)O3 (0 ≤ x ≤ 0.12). The phase diagram of the system shows a transition from the Griffiths phase into a ferromagnetic state in the low disorder concentration range (0.01 < x ≤ 0.09). In the high disorder concentration range (0.09 < x ≤ 0.12), a Griffiths phase to cluster spin glass transition is identified, which nicely matches that of disordered quantum systems. Moreover, the Griffiths phase is essentially an unfrozen cluster spin glass with partially broken ergodicity is demonstrated experimentally. These findings serve as crucial experimental references for understanding the glassy phenomena in disordered magnets, facilitating future exploration of their unique properties and functionalities.

B-178 A Sensitive LC-MS/MS Assay for Total Testosterone Quantification

Abstract Background Total testosterone immunoassay is a commonly ordered test for the diagnosis of gonadal disorders. However, immunoassays suffer from low specificity and sensitivity, which leads to inaccuracy especially in the low concentration range (&amp;lt; 100 ng/dL). As a result, commercial testosterone immunoassays have difficulties to accurately measure total testosterone levels for women, children, and hypogonadal men. LC-MS/MS has emerged as the method of choice for the accurate quantitation of steroid hormones. We presented here a sensitive laboratory-developed total testosterone assay, which was validated on two LC-MS/MS instruments. Methods An internal standard containing [2,3,4-13C3]-testosterone was added to each sample. The spiked serum sample was loaded on a supported liquid extraction (SLE) cartridge and eluted using methylene chloride. The elute was dried down under nitrogen and reconstituted in sample reconstitution buffer. Chromatographic separation was achieved using a Restek Ultra C18, 50 x 2.1 mm, 3µm analytical column and a total run time of each sample was 5 minutes. The assay was validated on two triple quadrupole mass spectrometers, API 6500 and API 4500. Results were compared with those of a reference laboratory. Results The assay was linear in the range of 1 to 1200 ng/dL for total testosterone and the AMR was set at 2-1200 ng/dL. The interday and intraday imprecision were less than 8%. Split sample comparison to a reference laboratory demonstrated acceptable accuracy with the slope of 1.053 and correlation coefficient (R2) of 0.991. The limit of detection (LOD) was 0.2 ng/dL and the limit of quantitation (LOQ) was 0.5 ng/dL. Results obtained from two instruments agreed well with the slope of 0.996 and the R2 of 0.999. No carryover or interferences was observed for this assay. Conclusions A LC-MS/MS based method was developed and validated for measuring total testosterone levels for female and children. This sensitive and specific assay will improve the diagnosis of hypogonadism and monitoring of testosterone-suppressing treatment.

Rapid formation of carbon dioxide hydrate governed by the natural nano-clay for effective carbon dioxide capture

Gas hydrate can separate and capture enormous carbon dioxide (CO2) only using water cages. Capturing CO2 in hydrate form is viewed as a green and effective technology to reduce the global CO2 emission. However, the sluggish kinetics and high cost of kinetics promotors of CO2 hydrate formation limited the application of hydrate-based CO2 capture technology. Here, we used the nano-clay prepared by cheap natural clay to promote the formation kinetics of CO2 hydrate. At the low concentration range, the formation period of CO2 hydrate in the two-dimensional nano-clay dispersion was significantly shorter than that of the one-dimensional nano-clay dispersion. The induction time (5 min) obtained in vermiculite nanoflakes dispersion was shorter than most solid promotors of CO2 hydrate formation kinetics in reported works. Besides, we found that the water molecules near the negatively charged two-dimensional nano-clay surface were more likely to form the cage-like structure than those around the one-dimensional nano-clay surface. The similar hydrogen-bonded structure of the cage-like water with CO2 hydrate made them favorable for the CO2 hydrate formation. These results shed light on the design of the effective kinetics promotors of CO2 hydrate and contribute to develop the hydrate-based CO2 capture technologies.

Probing aqueous diclofenac potassium: Unveiling molecular interactions through dielectric relaxation spectroscopy and MD simulation

Diclofenac potassium (DK) is a salt and undergoes ionization in an aqueous environment. The detailed information about the molecular structure and interactions of such aqueous ionic solutions holds substantial significance in the field of pharmaceutics. This comprehension facilitates the enhancement of pharmaceutical formulations, leading to improved bioavailability, stability, and therapeutic efficacy. It also contributes to the optimization of drug delivery systems. Molecular interactions in the aqueous solutions of DK were studied using dielectric relaxation spectroscopy (DRS) and molecular dynamic (MD) simulation. In DRS, complex dielectric permittivity, ε∗(f) for aqueous solutions of DK of varying concentrations were measured in the frequency range of 20 Hz to 2 MHz at five different temperatures ranging from 303.15 K to 323.15 K. Complex ac conductivity, σ∗(f) and dc conductivity (σdc) were determined from the complex dielectric permittivity. The effect of concentration and temperature on complex permittivity and allied parameters are discussed. The dielectric spectra of aqueous DK reveal dual relaxation processes i.e., normal (n) relaxation and alpha (α) relaxation. The dielectric strength is predominant for α-process and n-process in the low (0 < X ≤ 0.0299) and high (0.029 < X ≤ 0.0822) concentration range respectively. Moreover, Stoke’s relation between dielectric relaxation time, ion mobility and viscosity of the aqueous solutions is discussed. MD simulation at 303.15 K temperature has also been conducted to get additional information on molecular interactions between DK and/or H2O molecules through hydrogen bonding (HB).

Photochemical Fabrication of Ag‐Modified Hierarchical Cu@Cu2O/CuO Nanocomposite Toward Room Temperature NO2 Detection

Developing room temperature (RT) gas sensor based on metal oxide semiconductor material has long been challenging. Herein, a 1D hierarchical Ag‐modified Cu@Cu2O/CuO nanocomposite has been designed by low‐temperature etching self‐assembly combined with photochemical deposition method based on Cu nanowires (NWs). After a step of alkaline solution etching, the surface of Cu NWs is self‐assembled to form a hierarchical Cu@Cu2O/CuO, and then Ag nanoparticles are modified on its surface by photochemical deposition to obtain the desired material. All the preparation processes are carried out at RT and have good controllability. When applied as sensing material, the optimal Cu@Cu2O/CuO/Ag nanocomposite exhibits high response of ≈337.0 to 10 ppm NO2 with excellent selectivity and fast response/recovery (60/400 s) at 25 °C. It is worth noting that such a strategy of loading Ag nanoparticles improves its gas sensitivity by about 42.4 times, and the resulting sensor shows good sensitivity and screening ability to NO2 in the low concentration range. Finally, the nanostructure of the material is characterized systematically and the sensing mechanism is discussed.

Impact of weathered and virgin polyethylene terephthalate (PET) micro- and nanoplastics on growth dynamics and the production of extracellular polymeric substances (EPS) of microalgae

The ever-increasing plastic waste accumulation in the marine environment necessitates a deeper understanding of microalgae interactions with micro- and nanoplastics (MNP), and the role of extracellular polymeric substances (EPS). EPS, known for its adhesive properties and produced as an algal stress response, may facilitate aggregation of both algae and MNPs, thereby impacting ecological and hydrodynamic processes such as the trophic transfer or vertical transport of MNPs. Moreover, gaining a deeper understanding of the impact of weathering processes on the potential toxicological effects of plastic particles, and the comparative significance of plastic-specific effects relative to those of naturally occurring particles such as kaolin clay, is imperative. Therefore, this study investigated the impact of fragmented, polydisperse virgin polyethylene terephthalate (PET, Daverage = 910 nm) and weathered PET (Daverage = 1700 nm) on the growth and the production of EPS of Rhodomonas salina. Algae were exposed to a range of low MNP concentrations (10, 100 and 1000 and 10,000 MNPs ml-1) for 11 days. A natural particle control (kaolin, Daverage = 1600 nm) was deployed to differentiate particle effects from plastic effects. It was observed that exposure to both weathered PET and virgin PET resulted in initially increased growth rates (7.80 % and 7.28 % respectively), followed by significant decreases in algae cell density (−30.1 % and −11.2 % respectively). Furthermore, exposure to weathered PET caused a simultaneous elevation in cellular EPS production (76.51 %). The effects of plastics were significantly larger than the effect of kaolin. Also, the observed effects were amplified by the weathering of the plastics. These observations underscore the interactions between particle type, age and concentration, and their distinct impacts on algae density and growth inhibition. The observations indicate a role for EPS as an algal protection mechanism, potentially affecting the environmental fate of MNP – microalgae aggregates.

Ratiometric fluorescence sensing of triclosan by Lanthanide-Functionalized Metal–Organic frameworks

As a widely used antibacterial and antifungal agent in numerous personal care and consumer products, triclosan (TCS) is frequently detected in natural water bodies and has caused serious harm on human health and ecosystems. The quantitative and fast analysis of TCS is thus of paramount significance, however still remains challenging. In recent years, ratiometric fluorescence sensing has attracted vast interests in analyte detection due to the dual emission, which can effectively eliminate interference from environmental factors and improve the detection accuracy. Benefiting from the strong encapsulation capability and structural adjustability, metal organic frameworks (MOFs) are demonstrated to be a perfect platform to construct ratiometric fluorescence sensors. In the present study, we modify a zirconium MOF, UiO-67-bpy, to be a ratiometric fluorescence sensor by introducing Eu3+ and carbon dots sequentially via the post-synthetic method. The obtained hybrid system, CDs@Eu/UiO-67-bpy, shows two well separated emission peaks. With the addition of TCS, the red fluorescence from Eu3+ at 611 nm decreases while the blue fluorescence from carbon dots at 412 nm remains unchanged, resulting an excellent ratiometric response. Linear relationships of the fluorescence ratio (F412/F611) against the concentration of TCS are acquired in both low and high concentration range with detection of limit as low as 0.53 and 2.3 μM, respectively. Moreover, satisfactory recoveries of TCS levels from CDs@Eu/UiO-67-bpy are achieved in various water samples and personal care products. The composite of CDs@Eu/UiO-67-bpy also displays a fluorescence color changing from red to blue responsive to different concentration of TCS, demonstrating great potential in practical application of CDs@Eu/UiO-67-bpy for visualized monitoring TCS.

Competitive Adsorption of 4-Hydroxybenzaldehyde and Toluene onto High Silica Zeolites

To evaluate the ability of zeolites to remove natural low molecular organic substances, p-hydroxybenzaldehyde (p-HBA), a phenolic compound derived from lignin, was chosen as a representative of naturally occurring dissolved organic substances. Two distinct high-silica zeolite materials, namely ZSM-5 and Y, were utilised for the study, and the adsorption process was investigated under a wide range of conditions. It has been observed that p-HBA is adsorbed by both zeolites, and the pH significantly impacts the adsorption of p-HBA, particularly within the low concentration range, while exerting minimal influence on the saturation capacity. For both zeolites, various isotherm models were assessed to accurately describe the adsorption data obtained from aqueous solutions of p-HBA. In addition, to comprehend the selectivity of the adsorbents towards natural organic substances and xenobiotics, the competitive adsorption of mixtures of p-HBA and toluene (TOL) was investigated. The zeolite’s saturation capacity for p-HBA diminishes with increasing contaminant concentration. Conversely, the adsorption of toluene remains minimally affected by p-HBA, and it has been demonstrated that toluene can displace adsorbed p-HBA from the zeolites’ sites. This finding has been confirmed by diffractometric study that indicates that TOL and p-HBA occupy “the same” adsorption sites. Furthermore, Rietveld refinements reveal the formation of p-HBA complexes interacting with the framework and stabilising the guest structures within the zeolite porosity. The results obtained are important for the selection of proper adsorbent for the removal of hydrocarbons in environmental application (natural waters).

Effect of zinc oxide/graphene oxide nanocomposites on the cytotoxicity, antibacterial and mechanical properties of polymethyl methacrylate

BackgroundEnhancing the antibacterial properties of polymethyl methacrylate (PMMA) dental resins is crucial in preventing secondary infections following dental procedures. Despite the necessity for such improvement, a universally applicable method for augmenting the antibacterial properties of PMMA without compromising its mechanical properties and cytotoxicity remains elusive. Consequently, this study aims to address the aforementioned challenges by developing and implementing a composite material known as zinc oxide/graphene oxide (ZnO/GO) nanocomposites, to modify the PMMA.MethodsZnO/GO nanocomposites were successfully synthesized by a one-step procedure and fully characterized by TEM, EDS, FTIR and XRD. Then the physical and mechanical properties of PMMA modified by ZnO/GO nanocomposites were evaluated through water absorption and solubility test, contact angle test, three-point bending tests, and compression test. Furthermore, the biological properties of the modified PMMA were evaluated by direct microscopic colony count method, crystal violet staining and CCK-8.ResultsThe results revealed that ZnO/GO nanocomposites were successfully constructed. When the concentration of nanocomposites in PMMA was 0.2 wt. %, the flexural strength of the resin was increased by 23.4%, the compressive strength was increased by 31.1%, and the number of bacterial colonies was reduced by 60.33%. Meanwhile, It was found that the aging of the resin did not affect its antibacterial properties, and CCK-8 revealed that the modified PMMA had no cytotoxicity.ConclusionZnO/GO nanocomposites effectively improved the antibacterial properties of PMMA. Moreover, the mechanical properties of the resin were improved by adding ZnO/GO nanocomposites at a lower range of concentrations.

Invitro-Virucidal and Anti-Microbial Activities of Phytochemical Extracts from Garlic (Allium Sativum)

The findings of the present study had demonstrated that the plant extract possess anti-virucidal and anti-microbial activities according to standard screening tests and conventional accepted protocols. The results indicated that high yield of the extract was obtained at the end of the ethanol soxhlet extraction with the extract having greenish and smoothly textures. The phytochemical screening of methanolic and ethanolic extracts of Allium Sativum bulbs using soxhlet extraction method revealed the presence of tnnins, saponins and steroids in all the extracts. Flavonoid was present in ethanolic extract while alkaloid was present in methanolic extract. The results further revealed that SPyogenes was the most sensitive to the isolated compound while E. Coli was the least Kpneumonia showed high sensitivity to the isolated compound. The low concentration range for the MIC (2.1-uglml-4.0 uglml) and the MBC (2.uglml-18uglml) generally exhibited marked anti-bacterial activities and anti-virucidal potential against the susceptible organisms.

Generic method for the detection of short & long chain PFAS extended to the lowest concentration levels of SERS capability

The detection of the highly toxic per- and polyfluoroalkyl substances, PFAS, constitutes a challenging task in terms of developing a generic method that could be rapid and applicable simultaneously to both long and short-chain PFAS at ppt concentration level. In the present study, the method introduced by the USA Environmental Protection Agency, EPA, to detect surfactants, using methylene blue, MB, which is identified an ideal candidate for PFAS-MB ion pairing, is extended at the lowest concentration range by a simple additional step that involves the dissociation of the ion pairs in water. In this work, Surface Enhanced Raman Scattering, SERS, is applied via Ag nanocolloidal suspensions to probe MB and indirectly either/or both short-chain (perfluorobutyric acid, PFBA) and long-chain (perfluoloctanoic acid, PFOA) PFAS downt to 5 ppt. This method, which can be further optimized to sub-ppt level via a custom-made SERS-PFAS dedicated Raman system, offers the possibility to be applied to either specific PFAS (both short and long-chain) in a targeted analysis or to total PFAS in a non-targeted analysis at very low detection limits, following any type of MB detection method in aqueous solutions and obviously with any type of SERS substrate.

Study of ISFET for KCl sensing

This work presents the fabrication and electrical characterization of the Ion Sensitive Field Effect Transistor (ISFET) exposed to potassium chloride (KCl) solutions. The focus of the study is to compare two measurements methods and verify the effects of these methods in the device threshold voltage (VTH) sensitivity to the different KCl concentrations. First, a reference electrode (a platinum needle) is placed in the sample solution over the gate area of the device, demonstrating that the threshold voltage decreases with the increase of the KCl concentration. The method shows a sensitivity of 10.44 mV/mM for the low KCl concentration range (0 to 10 mM) and 0.5 mV/mM for the higher KCl concentration range (10 to 100 mM). The second method involves inserting a second platinum electrode into the solution on the field oxide. This method proposes the KCl electrolysis to increase the selectivity for potassium ions. The result allows the next steps for potassium sensing biosensor application with selective membranes.

Zr-based metalloporphyrin MOF probe for electrochemical detection of parathion-methyl

An electrochemical (EC) sensor based on metalloporphyrin metal-organic framework (MOF) for the detection of parathion-methyl (PM) has been developed. The prepared MOF-525(Fe) exhibits great signal enhancement toward the electrochemical detection of PM owing to its unique structural properties and electrochemical activities. Under optimal experimental conditions, the as-prepared MOF-525(Fe) based EC sensor exhibited excellent PM sensing performance with a wide linear detection range (0.1 μM–100 μM) and low limit of detection (LOD, 1.4 nM). Compared to its corresponding Fe metalloporphyrin (linker), MOF-525(Fe) exhibited a superior sensitivity (28.31 μA cm−2·μM−1), which is 3.7 times higher than the sensitivity of FeTCPP linker (7.56 μA cm−2·μM−1) towards PM. The improved performance is associated with the high specific surface area and the large pore channels of MOF-525(Fe) facilitating a better interaction between PM and the Fe metalloporphyrin active sites, especially in the lower concentration range. Moreover, a possible affinity of the PM molecules toward Zr6 clusters may also contribute to the selective enrichment of PM on MOF-525(Fe). This EC sensor further demonstrated high selectivity in the presence of interfering molecules. The recovery results further confirm accurate PM sensing in actual samples, which suggests promising applications for the rapid detection of environmental organophosphates by metalloporphyrin MOFs.

A dual-signals fluorometric and colorimetric peptide-based probe for Cu(II) and glyphosate detection and its application for bioimaging and water testing

A novel dual-signal fluorometric and colorimetric probe FMDH (5-FAM-Met-Asp-His-NH2), incorporating a tripeptide (Met-Asp-His-NH2) linked to 5-carboxyfluorescein (5-FAM), was firstly synthesised. FMDH demonstrated exceptional selectivity and sensitivity, rapid response, wide pH response range and robust anti-interference capabilities for monitoring Cu2+. This was achieved through a distinctive naked-eye colorimetric and fluorescent quenching behaviour. A good linearity within the range of 0–3 μM (R2 = 0.9914) was attained, and the limit of detection (LOD) for Cu2+ was 47.4 nM. Furthermore, the FMDH-Cu2+ ensemble responded to glyphosate with notable selectivity and sensitivity. A good linear correlation (R2 = 0.9926) was observed at the lower concentration range (2.4–7.8 μM) and achieving a detection limit as low as 29.9 nM. The response time of FMDH with Cu2+ and glyphosate were less than 20 s, and the pH range of 7–11 that was suitable for practical application under physiological pH conditions. MTT assays confirmed that FMDH offers good permeability and low toxicity, facilitating successful application in imaging analysis of Cu2+ and glyphosate in living cells and zebrafish. In addition, FMDH was employed in the detection of these analytes in real water samples. Cost-effective, highly sensitive and easily prepared FMDH-impregnated test strips were developed for the efficient visual detection of Cu2+ and glyphosate under 365 nm UV light. Increasing concentrations of Cu2+ and glyphosate resulted in notable colour changes under 365 nm UV light, enabling visual semi-quantitative analysis via a smartphone colour-analysis App.

Improved efficiency of ion trapping time-of-flight mass spectrometry for the analysis of pesticide residues and mycotoxins at trace levels in baby food

The analysis of pesticide residues and mycotoxins in baby food demands exceptionally low limits of quantitation, necessitating the use of highly sensitive instruments capable of conducting trace analyses. High-resolution instruments typically fail to detect such low levels. However, the latest advancements in liquid time-of-flight technology, when coupled with ion trapping, enable ion enrichment, thereby improving detection levels. This allows for the analysis of these substances at low concentration levels, benefiting from enhanced mass accuracy. Additionally, the use of mass accuracy data helped eliminate matrix interferences, thereby enabling high-confidence identification. We developed a multi-residue method to analyse 219 pesticide residues and 9 mycotoxin residues in baby food matrices. Utilizing a QuEChERS-based extraction method, the samples were then analysed using an LC-ZenoTOF 7600 system with mass window screening acquisition. For pesticides, the limit of quantitation was 0.001–0.003 mg/kg for 81 % of the evaluated compounds, 0.005 mg/kg for 13 %, 0.010 mg/kg for 4 % and 0.020–0.030 for 2 %; good linearities were obtained at these levels. Apparent recoveries were evaluated at 0.003, 0.005, and 0.010 mg/kg. At the lowest recovery level, 93 % of compounds showed recoveries between 70 and 120 %. The rest of the compounds were in the range of 63–129 %, with relative standard deviation values below 20 %. For mycotoxins, the limits of quantitation ranged from 0.0001 to 0.100 mg/kg, with matrix-matched concentrations assessed within this range. Recoveries were evaluated at low concentration range (0.001–0.003 mg/kg) and high range (0.020–0.050) with apparent recoveries values between 92 and 140 %. Finally, a total of 31 commercial baby food samples were analysed using this method. The results indicated that 16 samples contained pesticide residues, while two samples were found to have mycotoxins.

High-performance optical fiber differential urea sensing system for trace urea concentration detection with enhanced sensitivity using liquid crystals

A compact optical fiber differential sensing system consisting of microfiber interferometer (MFI) functionalized urease combined with stearic acid (SA)-doped 4-cyano-4′-pentylbiphenyl (5CB) and two fiber Bragg gratings (FBGs) for urea detection has been proposed and experimentally demonstrated. The SA-doped 5CB plays an important role of sensing signal amplification in urease specific recognition of urea. The hydrolysis reaction between urea and urease at the microfiber surface causes the deprotonation and self-assembly of SA, which further induces the reorientation of 5CB from planar alignment to homeotropic alignment. This process can be captured and transduced into the macroscopic wavelength shift of the MFI and power difference of two FBGs in the differential sensing system. The experimental results show that the differential sensing system can effectively detect urea in artificial urine, where the sensitivity of MFI is 3.85 nm/mM with a detection limit of 0.03 mM and the power difference sensitivity of two FBGs is 15.05 dB/mM with a detection limit of 0.01 mM within low concentration range of 0.01–0.1 mM. Furthermore, the differential sensing system has good selectivity, affordability, and temperature self-compensation. Therefore, the differential sensing system can be used as a sensitive method for urea detection and has potential applications in human health detection.