Cascade-Gates Guarded Asymmetrical Nanochannel Membrane: An Interference-Free Device for Straightforward Detection of Trace Biomarker in Undiluted Serum

The tightest self-assembled ruthenium metal-organic framework combined with proximity hybridization for ultrasensitive electrochemiluminescence analysis of paraquat

Metal-organic frameworks (MOFs), as porous materials, have great potential for exploring high-performance electrochemiluminescence (ECL) probes. However, the constrained applicability of MOFs in the realm of ECL biosensing is primarily attributed to their inadequate water stability, which consequently impairs the overall ECL efficiency. Herein, we developed a competitive ECL biosensor based on a novel tightest structural ruthenium-based organic framework emitter combining the proximity hybridization-induced catalytic hairpin assembly (CHA) strategy and the quenching effect between the Ru-MOF and ferrocene for detecting paraquat (PQ). Through a simple hydrothermal synthesis strategy, ruthenium and 2,2'-bipyrimidine (bpm) are head-to-head self-assembled to obtain a novel tightest structural Ru-MOF. Due to the metal-ligand charge-transfer (MLCT) effect between ruthenium and the bpm ligand and the connectivity between the internal chromophore units, the Ru-MOF exhibits strong ECL emissions. Meanwhile, the coordination-driven Ru-MOF utilizes strong metal-organic coordination bonds as building blocks, which effectively solves the problem of serious leakage of chromophores caused by water solubility. The sensitive analysis of PQ is realized in the range of 1 pg/mL to 1 ng/mL with a detection limit of 0.352 pg/mL. The tightest structural Ru-MOF driven by the coordination of ruthenium and bridging ligands (2,2'-bipyrimidine, bpm) provides new horizons for exploring high-performance MOF-based ECL probes for quantitative analysis of biomarkers.

Pore-Forming Toxin-Driven Recovery of Peroxidase-Mimicking Activity in Biomass Channels for Label-Free Electrochemical Bacteria Sensing

The development of sensitive, selective, and rapid methods to detect bacteria in complex media is essential to ensuring human health. Virulence factors, particularly pore-forming toxins (PFTs) secreted by pathogenic bacteria, play a crucial role in bacterial diseases and serve as indicators of disease severity. In this study, a nanochannel-based label-free electrochemical sensing platform was developed for the detection of specific pathogenic bacteria based on their secreted PFTs. In this design, wood substrate channels were functionalized with a Fe-based metal-organic framework (FeMOF) and then protected with a layer of phosphatidylcholine (PC)-based phospholipid membrane (PM) that serves as a peroxidase mimetic and a channel gatekeeper, respectively. Using Staphylococcus aureus (S. aureus) as the model bacteria, the PC-specific PFTs secreted by S. aureus perforate the PM layer. Now exposed to the FeMOF, uncharged 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) molecules in the electrolyte undergo oxidation to cationic products (ABTS•+). The measured transmembrane ionic current indicates the presence of S. aureus and methicillin-resistant S. aureus (MRSA) with a low detection limit of 3 cfu mL-1. Besides excellent specificity, this sensing approach exhibits satisfactory performance for the detection of target bacteria in the complex media of food.

The Challenges and Opportunities for TiO2 Nanostructures in Gas Sensing

Chemiresistive gas sensors based on metal oxides have been widely applied in industrial monitoring, medical diagnosis, environmental pollutant detection, and food safety. To further enhance the gas sensing performance, researchers have worked to modify the structure and function of the material so that it can adapt to different gas types and environmental conditions. Among the numerous gas-sensitive materials, n-type TiO2 semiconductors are a focus of attention for their high stability, excellent biosafety, controllable carrier concentration, and low manufacturing cost. This Perspective first introduces the sensing mechanism of TiO2 nanostructures and composite TiO2-based nanomaterials and then analyzes the relationship between their gas-sensitive properties and their structure and composition, focusing also on technical issues such as doping, heterojunctions, and functional applications. The applications and challenges of TiO2-based nanostructured gas sensors in food safety, medical diagnosis, environmental detection, and other fields are also summarized in detail. Finally, in the context of their practical application challenges, future development technologies and new sensing concepts are explored, providing new ideas and directions for the development of multifunctional intelligent gas sensors in various application fields.

PdPtB Electrochemiluminescence Nanoenhancer and SiC@Au-PEDOT Nanowires-Based Detection of β-Amyloid Oligomers in Alzheimer's Disease

β-Amyloid oligomers (AβOs) are promising biomarkers for the diagnosis of Alzheimer's disease (AD). The present research introduces a novel electrochemiluminescence (ECL) immunosensor based on PdPtB nanoenhancer and SiC@Au-PEDOT nanowires (NWs) for the specific and ultrasensitive detection of AβOs. The PdPtB nanoenhancer exhibited excellent oxidase-like catalytic activity with in situ generation of reactive oxygen species (ROS) to enhance luminol ECL in neutral media. In addition, SiC@Au-PEDOT NWs were utilized as a biocompatible and conductive substrate for the modification of the glassy carbon electrode (GCE). With this design, the ECL immunosensor showed outstanding AβOs analytical performance without exogenous coreactant. The ECL immunosensor demonstrated a favorable linear range of 20 pM to 20 nM and a detection limit of 10 pM under optimized conditions with potential straightforward clinical application. In general, the developed ECL immunosensor provides a promising strategy for the early diagnosis of AD.

Target-Driven Z-Scheme Heterojunction Formation for ppb H2S Detection from Exhaled Breath at Room Temperature

As a biomarker of periodontitis, sensitive and timely monitoring of hydrogen sulfide (H2S) in exhaled breath at room temperature (RT) is important for the early intervention of oral diseases. However, the required high operation temperature to achieve high sensitivity is still a technical challenge for directly monitoring exhaled breath. In this study, by integrating metal-organic frameworks (MOFs) into self-aligned TiO2 nanotube arrays (NTs), a chemiresistor gas sensor with outstanding sensitivity and selectivity was constructed for the detection of H2S at RT. The precise regulation of a Co(III)-based MOF CoBDC-NH2 (BDC-NH2 = 2-aminoterephthalic acid) not only induced more active surface for the preconcentration of the target gas but also caused a buildup of Z-scheme heterojunctions in the H2S atmosphere that induced an ultrahigh sensitivity at RT via 365 nm light-emitting diode irradiation. The response and recovery times decreased to ∼50 and ∼28%, respectively, when this system was exposed to UV light. The sensing chips based on the as-prepared TiO2/CoBDC-NH2 NTs exhibited the highest-ranking H2S sensing performance, i.e., a limit of detection of 1.3 ppb and excellent selectivity even to 100 times high concentration of interference gases, owing to the synergistic chemical environment provided by NH2-functionalized Co-MOFs and abundant photogenerated electrons provided by Z-scheme heterojunctions. This sensing chip was also used in a practical application for the timely monitoring of halitosis from direct exhaled breath. This study provides a reliable and sensitive design for clinically aiding the timely detection of H2S in a complex oral environment.

Recent Progress in MOF-Based Electrochemical Sensors for Non-Enzymatic Glucose Detection

In recent years, substantial advancements have been made in the development of enzyme-free glucose sensors utilizing pristine metal-organic frameworks (MOFs) and their combinations. This paper provides a comprehensive exploration of various MOF-based glucose sensors, encompassing monometallic MOF sensors as well as multi-metal MOF combinations. These approaches demonstrate improved glucose detection capabilities, facilitated by the augmented surface area and availability of active sites within the MOF structures. Furthermore, the paper delves into the application of MOF complexes and derivatives in enzyme-free glucose sensing. Derivatives incorporating carbon or metal components, such as carbon cloth synthesis, rGO-MOF composites, and core-shell structures incorporating noble metals, exhibit enhanced electrochemical performance. Additionally, the integration of MOFs with foams or biomolecules, such as porphyrins, enhances the electrocatalytic properties for glucose detection. Finally, this paper concludes with an outlook on the future development prospects of enzyme-free glucose MOF sensors.

Target Recognition-Triggered Peroxidase-Mimicking Activity Depression in Homochiral Nanochannels for Identifying Cystine Enantiomers

Enantioselective identification of chiral molecules is of paramount importance in medical science, biochemistry, and pharmaceutics owing to the configuration-dependent activities of enantiomers. However, the identical physicochemical properties of enantiomers remain challenging in chiral sensing. In this study, inspired by the peroxidase-mimicking activity of Fe(III)-based nanomaterials, an enantioselective artificial architecture is constructed on TiO₂ nanochannels. Homochiral Ti-based metal-organic frameworks (MOFs) use a 2,2'-bipyridine-5,5'-dicarboxylic acid ligand as the artificial enzyme skeleton, Fe(III) as peroxidase-mimicking centers, and l-tartaric acid (TA) as a chiral recognition selector. Using l-/d-cystine as model enantiomers, the chiral moieties of l-TA on Ti-MOFs allow stereoselective recognition of guest molecules through hydrogen bonds formed between chiral cystine and the host. In a tris(2-carboxyethyl)phosphine hydrochloride-containing environment, the disulfide bonds in cystine molecules are further cleaved, and the HS-tails react with Fe(III) active sites, causing the loss of peroxidase-like performance of nanochannels. Benefitting from the nanochannel architecture's current-potential (I-V) properties, the selective recognition of cystine enantiomers is directly monitored through the peroxidase-like activity change-induced ionic current signatures. This study provides a new and universal strategy for distinguishing disulfide- and thiol-containing chiral molecules.

Rational design of mesoporous chiral MOFs as reactive pockets in nanochannels for enzyme-free identification of monosaccharide enantiomers

Monosaccharides play significant roles in daily metabolism in living organisms. Although various devices have been constructed for monosaccharide identification, most rely on the specificity of the natural enzyme. Herein, inspired by natural ionic channels, an asymmetrical MOF-in-nanochannel architecture is developed to discriminate monosaccharide enantiomers based on cascade reactions by combining oxidase-mimicking and Fenton-like catalysis in homochiral mesoporous CuMOF pockets. The identification performance is remarkably enhanced by the increased oxidase-mimicking activity of Au nanoparticles under a local surface plasmon resonance (LSPR) excitation. The apparent steady-state kinetic parameters and nano-fluidic simulation indicate that the different affinities induced by Au-LSPR excitation and the confinement effect from MOF pockets precipitate the high chiral sensitivity. This study offers a promising strategy for designing an enantiomer discrimination device and helps to gain insight into the origin of stereoselectivity in a natural enzyme.