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A comprehensive comparative validation for two different types of dissolved oxygen (DO) analyzers, amperometric and optical, is presented on two representative commercial DO analyzers. A number of performance characteristics were evaluated including drift, intermediate precision, accuracy of temperature compensation, accuracy of reading (under different measurement conditions), linearity, flow dependence of the reading, repeatability (reading stability), and matrix effects of dissolved salts. The matrix effects on readings in real samples were evaluated by analyzing the dependence of the reading on salt concentration (at saturation concentration of DO). The analyzers were also assessed in DO measurements of a number of natural waters. The uncertainty contributions of the main influencing parameters were estimated under different experimental conditions. It was found that the uncertainties of results for both analyzers are quite similar but the contributions of the uncertainty sources are different. Our results imply that the optical analyzer might not be as robust as is commonly assumed; however, it has better reading stability, lower stirring speed dependence, and typically requires less maintenance. On the other hand, the amperometric analyzer has a faster response and wider linear range. Both analyzers seem to have issues with the accuracy of temperature compensation. The approach described in this work will be useful to practitioners carrying out DO measurements for ensuring reliability of their measurements.

Increasing trace levels of antibiotics and hormones in the environment and food samples are concerning and pose a threat. Opto-electrochemical sensors have received attention due to their low cost, portability, sensitivity, analytical performance, and ease of deployment in the field as compared to conventional expensive technologies that are time-consuming and require experienced professionals. Metal-organic frameworks (MOFs) with variable porosity, active functional sites, and fluorescence capacity are attractive materials for developing opto-electrochemical sensors. Herein, the insights into the capabilities of electrochemical and luminescent MOF sensors for detection and monitoring of antibiotics and hormones from various samples are critically reviewed. The detailed sensing mechanisms and detection limits of MOF sensors are addressed. The challenges, recent advances, and future directions for the development of stable, high-performance MOFs as commercially viable next-generation opto-electrochemical sensor materials for the detection and monitoring of diverse analytes are discussed.

As hazardous environmental pollutants, residual tetracycline (TC) and acetone are harmful to the ecosystem. Therefore, it is necessary to detect the presence of these pollutants in the environment. In this work, using Zn (II) salt, 4-(4-carboxy phenoxy) phthalic acid (H3L), and 3,5-bis(1-imidazolyl) pyridine (BMP), a new metal–organic framework (Zn-MOF) known as [Zn3(BMP)2L2(H2O)4]·2H2O was synthesized using a one-pot hydrothermal method. The Zn-MOF has a three-dimensional framework based on the [Zn1N2O2] and [Zn2N2O4] nodes linked by a tridentate bridge BMP ligand and an L ligand with the μ1:η1η0/μ1:η1η0/μ0:η0η0 coordination mode. There were two kinds of left- and right-handed helix chains, Zn1-BMP and Zn1-BMP-Zn1-L. The complex was stable in aqueous solutions with pH values of 4–10. The Zn-MOF exhibited a strong emission band centered at 385 nm owing to the π*→π electron transition of the ligand. It showed high luminescence in some common organic solvents as well as in the aqueous solutions of pH 4–10. Interestingly, TC and acetone effectively quenched the luminescence of the Zn-MOF in aqueous solution and enabled the Zn-MOF to be used as a sensor to detect TC and acetone. The detection limits of TC and acetone were observed to be 3.34 µM and 0.1597%, respectively. Even in acidic (pH = 4) and alkaline (pH = 10) conditions, the Zn-MOF showed a stable luminescence sensing capability to detect TC. Luminescence sensing of the Zn-MOF for TC in urine and aquaculture wastewater systems was not affected by the interfering agent. Furthermore, the mechanism of sensing TC was investigated in this study. Fluorescence resonance energy transfer and photoinduced electron transfer were found to be the possible quenching mechanisms via UV–Vis absorption spectra/the excitation spectra measurements and DFT calculations.

Water conductivity sensing relies universally on electrical measurements, which are subject to corrosion of the electrodes and subsequent signal drift in prolonged in situ uses. Furthermore, they cannot provide contactless sensing or remote readout. To this end, a novel device for water conductivity monitoring has been developed by employing a microenvironment-sensitive ruthenium complex, [Ru(2,2′-bipyridine-4,4′-disulfonato)3]4−, embedded into a quaternary ammonium functionalized cross-linked polymer support. The degree of swelling of the latter, which leads to a change in the emission lifetime, depends on the water conductivity. The sensor displays a reversible response (2 min ≤ t90 ≤ 3 min) and has been shown to be stable for >65 h of continuous monitoring of 0.8–12.8 mS cm−1 KCl solutions. Changes to the cation do not affect the sensor response, while changes to the anion type induce small effects. Variations in the dissolved O2 or temperature require corrections of the response. The sensor can be interrogated alongside dissolved O2 and pH luminescent sensors based on the same family of indicator dyes to exploit the definite advantages of luminescence lifetime-based detection.

A new Ni coordination polymer [Ni(MIP)(BMIOPE)]n (1) was constructed (BMIOPE = 4,4′-bis(2-methylimidazol-1-yl)diphenyl ether, and H2MIP = 5-methylisophthalic acid), possessing two-dimensional (2D) twofold parallel interwoven net structure with a 44∙62 point symbol. Complex 1 has been successfully obtained based on mixed-ligand strategy. The fluorescence titration experiments revealed that complex 1 could act as multifunctional luminescent sensor to simultaneously detect UO22+, Cr2O72− and CrO42−, and NFT (nitrofurantoin). The limit of detection (LOD) values for complex 1 are 2.86 × 10−5, 4.09 × 10−5, 3.79 × 10−5 and 9.32 × 10−5 M for UO22+, Cr2O72−, CrO42− and NFT. The Ksv values are 6.18 × 103, 1.44 × 104, 1.27 × 104 and 1.51 × 104 M−1 for NFT, CrO42−, Cr2O72− and UO22+. Finally, the mechanism of its luminescence sensing is studied in detail. These results manifest that complex 1 is a multifunctional sensor for sensitive fluorescent UO22+, Cr2O72−, CrO42− and NFT detection.

In this manuscript, recent advancements in the area of minimally-invasive transdermal biosensing and drug delivery are reviewed. The administration of therapeutic entities through the skin is complicated by the stratum corneum layer, which serves as a barrier to entry and retards bioavailability. A variety of strategies have been adopted for the enhancement of transdermal permeation for drug delivery and biosensing of various substances. Physical techniques such as iontophoresis, reverse iontophoresis, electroporation, and microneedles offer (a) electrical amplification for transdermal sensing of biomolecules and (b) transport of amphiphilic drug molecules to the targeted site in a minimally invasive manner. Iontophoretic delivery involves the application of low currents to the skin as well as the migration of polarized and neutral molecules across it. Transdermal biosensing via microneedles has emerged as a novel approach to replace hypodermic needles. In addition, microneedles have facilitated minimally invasive detection of analytes in body fluids. This review considers recent innovations in the structure and performance of transdermal systems.

Metal–organic frameworks (MOFs), as a class of crystalline hybrid architectures, consist of metal ions and organic ligands and have displayed great potential in luminescent sensing applications due to their tunable structures and unique photophysical properties. Until now, many studies have been reported on the development of MOF-based luminescent sensors, which can be classified into two major categories: MOF chemosensors based on reversible host–guest interactions and MOF chemodosimeters based on the irreversible reactions between targets with a probe. In this review, we summarize the recently developed luminescent MOF-based chemodosimeters for various analytes, including H2S, HClO, biothiols, fluoride ions, redox-active biomolecules, Hg2+, and CN−. In addition, some remaining challenges and future perspectives in this area are also discussed.

Carboxymethyl cellulose (CMC) films, derived from sugarcane bagasse agricultural waste (SCB) incorporated with Betalains-nitrogen-doped carbon dots (Betalains-N–CQDs), derived from beet root waste (BR), offer a sustainable, smart and naked-eye sensor for strawberry packaging due to their excellent fluorescent and shape memory properties. These CMC-Betalains-N–CQDs aim to enhance strawberry preservation and safety by enabling visual detection of common food contaminants such as bacteria, fungi and Pb(II). Crucially, the CMC-Betalains-N–CQD film also exhibits excellent shape memory properties, capable of fixing various shapes under alkaline conditions and recovering its original form in acidic environments, thereby offering enhanced physical protection for delicate produce like strawberries. Optical studies reveal the Betalains-N–CQDs’ pH-responsive fluorescence, with distinct emission patterns observed across various pH levels, highlighting their potential for sensing applications. Scanning Electron Microscopy (SEM) confirms the successful incorporation of Betalains-N–CQDs into the CMC matrix, revealing larger pores in the composite film that facilitate better interaction with analytes such as bacteria. Crucially, the CMC-Betalains-N–CQD film demonstrates significant antibacterial activity against common foodborne pathogens like Escherichia coli, Staphylococcus aureus, and Candida albicans, as evidenced by inhibition zones and supported by molecular docking simulations showing strong binding interactions with bacterial proteins. Furthermore, the film functions as a fluorescent sensor, exhibiting distinct color changes upon contact with different microorganisms and Pb(II) heavy metals, enabling rapid, naked-eye detection. The film also acts as a pH sensor, displaying color shifts (brown in alkaline, yellow in acidic) due to the betalains, useful for monitoring food spoilage. This research presents a promising, sustainable, and multifunctional intelligent packaging solution for enhanced food safety and extended shelf life.

A new metal–organic framework based on cadmium(II) cations, di(p-carboxyphenyl)sulphone and 4,7-di(imidazol-1-yl)-2,1,3-benzothiadiazole was prepared, and its crystal structure was determined using single-crystal XRD analysis. MOF demonstrated bright luminescence with a maximum near 500 nm and quantum yield reaching 20%. In addition, this MOF demonstrated sensing properties towards antibiotics and a toxic natural polyphenol gossypol through effective luminescence quenching in an ethanol suspension. The determined detection limit for gossypol was among the lowest reported so far (0.65 µM), and did not significantly change in the interference experiments with cottonseed oil as background, indicating the possibility of using this MOF as a sensor for the detection and determination of gossypol in real-life samples.

Gold nanoclusters (Au NCs) are promising luminescent nanomaterials due to their outstanding optical properties. However, their relatively low quantum yields and environment-dependent photoluminescence properties have limited their biological applications. To address these problems, we developed a novel strategy to prepare chitosan oligosaccharide lactate (Chi)-functionalized Au NCs (Au NCs@Chi), which exhibited emission with enhanced quantum yield and elongated emission lifetime as compared to the Au NCs, as well as exhibited environment-independent photoluminescence properties. In addition, utilizing the free amino groups of Chi onto Au NCs@Chi, we designed a FRET-based sensing platform for the detection of hydrogen sulfide (H 2 S). The Au NCs and the specific H 2 S-sensitive merocyanine compound were respectively employed as an energy donor and acceptor in the platform. The addition of H 2 S induced changes in the emission profile and luminescence lifetime of the platform with high sensitivity and selectivity. Utilization of the platform was demonstrated to detect exogenous and endogenous H 2 S in vitro and in vivo through wavelength-ratiometric and time-resolved luminescence imaging (TLI). Compared to previously reported luminescent molecules, the platform was less affected by experimental conditions and showed minimized autofluorescence interference and improved accuracy of detection. Optical sensors: Gold nanoclusters detect H 2 S Functionalized gold nanoclusters can be used as highly sensitive optical sensors of hydrogen sulfide (H 2 S), both in vitro and in vivo . Researchers in China treated gold nanoclusters, which consisted of a few hundred gold atoms, with chitosan oligosaccharide lactate to improve their emission lifetime and quantum yield. They also added a merocyanine compound that is sensitive to H 2 S. The presence of H 2 S induces spectral and lifetime changes in the green and red light emissions from the probe, which can be detected by wavelength-ratiometric or time-resolved photoluminescence imaging microscopy. Exogenous and endogenous H 2 S was measured both in vitro and in vivo . Compared to other approaches using luminescent probes, the probe offers improved sensitivity and accuracy, which are less affected by changes in concentration or laser power.