Ultrafast Response and High Selectivity of Diethylamine Gas Sensors at Room Temperature Using MOF-Derived 1D CuO Nano-Ellipsoids.

Environmental and health monitoring requires low-cost, high-performance diethylamine (DEA) sensors. Materials based on metal-organic frameworks (MOFs) can detect hazardous gases due to their large specific surface area, many metal sites, unsaturated sites, functional connectivity, and easy calcination to remove the scaffold. However, developing facile materials with high sensitivity and selectivity in harsh environments for accurate DEA detection at a low detection limit (LOD) at room temperature (RT) is challenging. In this study, p-type semiconducting porous CuOx sensing materials were synthesized using a simple solvothermal process and annealed in an argon atmosphere at three different temperatures (x = 400, 600, and 800 °C). Significant variations in particle size, specific area, crystallite size, and shape were noticed when the annealing temperature was elevated. Cu-MIL-53 annealed at 400 °C (CuO-400) has a typical nanoellipsoid (NEs) shape with a length of 61.5 nm and a diameter of 33.2 nm. Surprisingly, CuO-400 NEs showed an excellent response to DEA with an ultra-LOD (Rg/Ra = 7.3 @ 100 ppb, 55% relative humidity), excellent selectivity and sensitivity (Rg/Ra = 236 @ 15 ppm), exceptional long-term stability and repeatability, and a fast response/recovery period at RT, outperforming most previously reported materials. CuO-400 NEs have outstanding gas-sensing characteristics due to their high porosity, 1D nanostructure, unsaturated Cu sites (Cu+ and Cu2+), large specific surface area, and numerous oxygen vacancies. This study presents a generic approach to produce future CuO derived from Cu-MOFs-sensitive materials, revealing new insights into the design of effective sensors for environmental monitoring at RT.

Much Stronger Chemiluminescence of 9-Mesityl-10-methylacridinium Ion than Lucigenin at Neutral Conditions for Co2+ Detection.

9-Mesityl-10-methylacridinium ion (Acr+-Mes) is a donor-acceptor molecule with a much longer lifetime and a higher energy electron transfer excited state than natural photosynthetic reaction centers. Unlike lucigenin with a coplanar geometry, Acr+-Mes has an orthogonal geometry. There is no π conjugation between Acr+ and Mes. Due to its special electron donor-acceptor structure, it does not rely on strong alkalinity to generate an electron transfer state like lucigenin, which makes it possible to achieve chemiluminescence (CL) under weakly alkaline or neutral conditions. In this study, we report Acr+-Mes CL for the first time. Acr+-Mes generates about 400 times stronger CL intensity than lucigenin under neutral conditions (pH = 7) using KHSO5 as the coreactant. Moreover, Co2+ can enhance Acr+-Mes/KHSO5 CL remarkably. Acr+-Mes/KHSO5 CL enables Co2+ detection with a linear range of 0.5-500 nM and a limit of detection of 28 pM (S/N = 3). This method was tested for the detection of Co2+ in lake water, and the standard recovery rate of 96.8-107% was achieved. This study provides a new way to develop efficient CL systems in neutral solutions.

Remarkably Enhanced Luminol/H2O2 Chemiluminescence with Excellent Peroxidase-like Activity of FeCoNi-based Metal-Organic Xerogels for the Sensitive Detection of Dopamine.

Metal-organic gels (MOGs) are a category of metal-organic smart soft materials with large specific surface areas, loose porous structures, and open metal active sites. In this work, trimetallic Fe(III)Co(II)Ni(II)-based MOGs (FeCoNi-MOGs) were synthesized at room temperature via a simple and mild one-step procedure. Fe3+, Co2+, and Ni2+ were the three central metal ions in it, while 1,3,5-benzenetricarboxylic acid (H3BTC) served as the ligand. The solvent enclosed in it was then removed by freeze-drying to get the corresponding metal-organic xerogels (MOXs). The as-prepared FeCoNi-MOXs have excellent peroxidase-like activity and can significantly enhance luminol/H2O2 chemiluminescence (CL) by more than 3000 times, which is very effective compared with other reported MOXs. Based on the inhibitory effect of dopamine on the CL of the FeCoNi-MOXs/luminol/H2O2 system, a simple, rapid, sensitive, and selective CL method for dopamine detection was established with a linear range of 5-1000 nM and a limit of detection of 2.9 nM (LOD, S/N = 3). Furthermore, it has been effectively used for the quantitative measurement of dopamine in dopamine injections and human serum samples, with a recovery rate of 99.5-109.1%. This research brings up prospects for the application of MOXs with peroxidase-like activity in CL.

A high-efficiency cathodic sodium nitroprusside/luminol/H2O2 electrochemiluminescence system in neutral media for the detection of sodium nitroprusside, glucose, and glucose oxidase.

Sodium nitroprusside (SNP) is an anti-hypertension drug used in vascular surgery, chronic cardiovascular disease, and in the management of acute myocardial infarction by the spontaneous release of nitric oxide. Herein, for the first time, we extend its application to electrochemiluminescence (ECL). The NO generated from the electrochemical reduction of SNP reacts with H2O2 to generate reactive oxygen species, which subsequently reacts with luminol to produce intense ECL. The ECL signal of the new SNP/H2O2/luminol system under neutral conditions (pH 7.4) is almost equivalent to the classic luminol/H2O2 system at pH 10, making this system highly attractive for bioanalysis that directly or indirectly liberates H2O2 under neutral conditions. At the optimum experimental conditions, the ECL intensity increases proportionally with the log of H2O2 and SNP concentration over the range from 0.2 µM-1000 µM and 0.08 mM-1.8 mM with the detection limits of 0.078 µM and 0.038 mM, respectively. The RSD for ten analyses of H2O2 is 4.25%. Recoveries from 97.2% to 101.7% were obtained for real sample analysis. Since H2O2 participates in numerous important enzymatic reactions, the application of this system was further investigated using glucose oxidase (GODx) and glucose as a representative enzyme and substrate, respectively, thus liberating H2O2 as a reaction product. The concentrations of glucose and the activity of GODx were directly proportional to the ECL intensities over a range of 5-1000 µM and 0.0025-1 units per mL with the limits of detection of 2.65 µM and 0.0012 units per mL (S/N = 3), respectively.

Derivatization-free determination of carbonyl compounds using bifunctional chemiluminescence coreactant thiourea dioxide.

Uniquely, thiourea dioxide not only can reduce carbonyl compounds but also generate an oxidant to trigger luminol chemiluminescence. Herein, derivatization-free carbonyl compound detection using bifunctional chemiluminescence coreactant thiourea dioxide has been developed for the first time with the second most crucial flavor benzaldehyde as a representative.

Development of lucigenin-N-hydroxyphthalimide chemiluminescence system and its application to sensitive detection of Co2.

N-hydroxyphthalimide (NHPI) is an efficient organic catalyst and an important chemical raw material which can be used as an intermediate in organic synthesis of drugs and pesticides. In this study, NHPI has been used as a coreactant of lucigenin chemiluminescence (CL) for the first time. The CL of the developed system is significantly enhanced in the presence of Co2+. Therefore, we developed a novel lucigenin-NHPI CL method coupled with flow injection analysis for the sensitive, precise, and selective determination of Co2+. The linear range of this method is 1-1000 nM, and the detection limit is 67 pM (S/N = 3). In addition, this method has a good selectivity for Co2+. It has been applied to the detection of Co2+ in lake water, and the standard recovery rate is 95.9-103.2%, indicating that the method is feasible.

Improving the limit of detection in portable luminescent assay readers through smart optical design.

Critical biomarkers of disease are increasingly being detected by point-of-care assays. Chemiluminescence (CL) and electrochemiluminescence (ECL) are often used in such assays due to their convenience and that they do not require light sources or other components that could complicate or add cost to the system. Reports of these assays often include readers built on a cellphone platform or constructed from low-cost components. However, the impact the optical design has on the limit of detection (LOD) in these systems remains unexamined. Here, we report a theoretical rubric to evaluate different optical designs in terms of maximizing the use of photons emitted from a CL or ECL assay to improve the LOD. We demonstrate that the majority of cellphone designs reported in the literature are not optimized, in part due to misunderstandings of the optical tradeoffs in collection systems, and in part due to limitations imposed on the designs arising from the use of a mobile phone with a very small lens aperture. Based on the theoretical rubric, we design a new portable reader built using off-the-shelf condenser optics, and demonstrate a nearly 10× performance enhancement compared to prior reports on an ECL assays running on a portable chip.