The accurate quantification of free acidic species occluded within metal–organic frameworks (i.e., UiO-66) is essential for evaluating synthesis completeness, material purity, and post-synthetic processing. In this work, a rapid and automated headspace gas chromatography (HS‑GC) method was developed for the determination of total free acids in MOFs. The strategy couples ultrasound‑assisted methanolic extraction with a selective phase‑conversion reaction: the extracted carboxylic acids react stoichiometrically with bicarbonate in a sealed headspace vial to liberate carbon dioxide, which is then detected by HS‑GC. Under systematically optimized conditions, the method exhibited excellent linearity, high sensitivity with a low limit of detection, and satisfactory precision. Accuracy was confirmed by near‑quantitative spike recoveries and by close agreement with a well‑established spectrophotometric reference method. Leveraging the automated headspace platform, the procedure substantially reduced sample cycle time and enabled high‑throughput operation while markedly decreasing organic solvent consumption relative to conventional wet‑chemical protocols. This approach provides a reliable, efficient, and environmentally favorable tool for routine monitoring of free acid content in MOFs (i.e., UiO-66), facilitating quality control in both laboratory‑scale research and scaled‑up synthesis.
Accurate trace-level H2O2 detection is critical across a wide range of fields, including biomedical, food, and industrial monitoring, yet a catalase-based platform combining a sub-nanomolar detection limit with high sensitivity, robust operational stability, and reproducibility remains a major unmet need and an area of strong demand. Herein, we present a third-generation H2O2 biosensor in which bovine liver catalase (CAT) is immobilized on a hierarchically engineered glassy carbon electrode (GCE), with a TiO2-carboxylated multiwalled carbon nanotube (TiO2-cMWCNTs) hybrid sandwiched between a cysteine-gold nanoparticle (Cys-AuNPs) anchoring layer and a thin Nafion (NF) permselective overlayer (NF/CAT/TiO₂-cMWCNTs/Cys-AuNPs/GCE). Characterization (TEM, SEM, SEM-EDS, FTIR) confirmed uniform TiO2 distribution and direct –COOH/TiO2 coupling, with carboxylate and hydrogen-bonding signatures indicating a chemically integrated network that provides an oxygen-rich, hydrophilic microenvironment, stabilizing CAT against subunit dissociation and activity loss while preserving a continuous, conductive direct electron-transfer (DET) pathway. Within this architecture H2O2 drives the turnover, the heme generates the analytical signal, and the surrounding layers anchor, host, wire, and shield the enzyme. Mechanistically, whereas catalase-based biosensors typically invoke the Compound I/Compound II cycle only schematically, we anchor this cycle, the H2O2-turnover mechanism of catalase that proceeds through two high-valent heme intermediates, in deposited crystal structures through a PDB-guided active-site analysis (bovine catalase 3RE8, cross-validated against 3NWL, with sub-ångström RMSD to the experimentally resolved Compound I (1MQF) and Compound II ferryl-hydroxo (2CAG) intermediates). This ties the directly observed Nernstian 1e⁻/1H⁺ proton-coupled electron transfer to a structurally grounded DET pathway and introduces a structure-informed route to mechanism integration in sub-nanomolar H2O2 biosensing. Electrochemical analyses (CV, EIS, SWV, DPV, LSV) confirmed rapid, quasi-reversible DET (Ip.a./Ipc = 1.001, E°′ = −410 mV vs. Ag/AgCl, Ks = 38.59 s− 1), high sensitivity (57.5 µA·µM− 1), and an LOD of 0.3 nM over a 0.001–1 µM linear range. Benchmarked against reported catalase biosensors, the platform delivers the lowest detection limit among those reporting both sensitivity and LOD. It further shows high selectivity against common electroactive and matrix interferents, RSDs of 1.85
Legionella pneumophila is a harmful Gram-negative aquatic pathogen that causes Legionnaires’ disease, and sensitive detection of this bacterium is essential for epidemiological investigation. Herein, a photoelectrochemical (PEC) biosensor based on 3,4,9,10-perylenetetracarboxylic acid (PTCA) as the photoactive material and tetraphenylporphyrin cobalt (CoPP) as the signal quencher was constructed for the detection of the macrophage infectivity potentiator (mip) gene fragment from Legionella pneumophila. PTCA with favorable optoelectronic properties and film-forming capacity provided a strong initial photocurrent response. Gold nanoparticles (Au NPs) were electrodeposited on the electrode surface to immobilize DNA S1 through Au-S interactions. After target-induced DNA hybridization, CoPP was intercalated into the formed DNA duplex, which efficiently quenched the PEC signal of PTCA. Benefiting from the signal quenching effect of CoPP towards PTCA, the proposed biosensor achieved quantitative detection of the mip gene fragment in the range from 100 fmol/L to 1 µmol/L with a detection limit of 33.3 fmol/L. This work provides an analytical tool and shows promise for practical screening of the mip gene fragment of Legionella pneumophila in respiratory specimens with high bacterial loads.
Rapid sensors for choline detection in food samples are highly desired. Three quinoline-based sensors (KL-1/2/3) were synthesized, among which KL-1 with favorable chemiluminescence performance was selected. For the first time, quinoline skeletons were utilized to construct TMB-free dual-mode colorimetric-chemiluminescence sensors. Choline oxidase produces H₂O₂ from choline, triggering simultaneous luminescence and color fading on KL-1. This sensor quantifies choline linearly from 10 to 100 μM with LOD of 6.32 μM, while the colorimetric mode shows linear response within 0–200 μM with an instrumental LOD of 18.4 μM and a naked-eye detection limit of 50 μM. This dual-mode sensor tolerates milk-matrix interferences and provides satisfactory recoveries upon simple sample dilution. This work offers a simple dual-mode sensor for rapid food choline detection.
Chemiluminescence (CL) quantification of hydrogen peroxide (H2O2) by conventional flash‑type systems is hindered by the short emission window, which compromises the accuracy and reproducibility. Here we report a chitosan‑stabilized CL capsule (LHB@CS) platform for sustained and reliable detection of H2O2. The capsules are prepared via a one‑pot ultrasonication‑assisted method, in which luminol and hemin are co‑encapsulated within the oil phase and chitosan (CS) is adsorbed as a colloidal stabilizer. Upon addition of H2O2, H2O2 diffuses into the oil phase and triggers the hemin-catalyzed CL reaction, producing a sustained emission for about 200 s with approximately 85
