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Herein, oxidized 3,3′,5,5′-tetramethylbenzidine (oxTMB) nanobelts were developed to enhance the colorimetric and paper-based sensing of H₂O₂. It was found that the minor component of Fe²⁺ in Na₂SO₄ reagent could catalyze the oxidization of TMB by H₂O₂ into positively charged oxTMB, which was further assembled into dark blue oxTMB nanobelts via electrostatic interaction with SO₄²⁻. The extinction originating from the absorption and scattering of oxTMB nanobelts was utilized to quantitatively detect H₂O₂ with a wide linear detection range (1.0–300 μM) and a low limit of detection (0.48 μM). In addition, no coffee-ring effect was observed in the test zone of the paper-based colorimetric array, which was beneficial to judge the color by naked eye. Finally, the colorimetric method was applied to detect H₂O₂ in contact lens care solution. This work not only proposed a new colorimetric sensing platform for H₂O₂, but also highlighted the minor component in the reagent might influence the experimental result.

Accurately monitoring H₂O₂ concentrations in 3D cell clusters is challenging due to limited diffusion and rapid degradation of H₂O₂ in the culture medium. Despite the incorporation of three-dimensional cell culture approaches, the detection technology has largely remained as a 2D planar system. In this study, we present a versatile approach of 3D electrochemical sensing utilizing carbon nanotubes as conductive scaffolds for in-situ monitoring of H₂O₂ in cell clusters. These scaffolds enabled direct contact between H₂O₂ released from cells and the electrodes, thereby improving sensitivity and ensuring biocompatibility for cell aggregates. The scaffolds exhibited electrocatalytic behavior with a limit of detection of 6.7 nM H₂O₂. Additionally, the electrochemical responses of cell clusters with the scaffolds exhibited significantly higher current compared to clusters without scaffolds when stimulated with model drugs. This study underscores the potential of conductive scaffolds for real-time monitoring of H₂O₂ released from cell clusters in 3D microenvironments.

Cation exchange membranes (CEMs) are widely used in many applications. The fixed anionic groups e.g., COO⁻, –SO₃^-, etc. in the polymer matrix ideally allows the passage only of oppositely charged cations, driven by a potential or a concentration gradient. Anions, charged negative, the same as the membrane matrix, cannot pass through the membrane due to electrostatic repulsion. Such “Donnan-forbidden” passage can, however, occur to some degree, if the electrical or concentration gradient is high enough to overcome the “Donnan barrier”. Except for salt uptake/transport in concentrated salt solutions, the factors that govern such Forbidden Ion Transport (FIT) have rarely been studied. In most applications of transmembrane ion transport, whether electrically driven as in electrodialysis, or concentration-driven, it is the transport of the counterion to the fixed charged groups, such as that of the proton through a CEM, that is usually of interest. Nevertheless, CEMs are also of interest in analytical chemistry, specifically in suppressed ion chromatography. As used in membrane suppressors, both transport of permitted ions and rejection of forbidden ions are important. If the latter is indeed governed by electrostatic factors, other things being equal, the primary governing factor should be the charge density of the membrane, tantamount to its ion exchange capacity (IEC). In fabricating microscale suppressors, we found useful to synthesize a new ion exchange polymer that can be easily molded to make tubular microconduits. Despite a high IEC of this material, FIT was also found to be surprisingly high. We measured several relevant properties for thirteen commercial and four custom-made membranes to discover that while FIT is indeed linearly related to 1/IEC for a significant number of these membranes, for very high water-content membranes, FIT may be overwhelmingly governed by the water content of the membrane. In addition, FIT through all CEMs differ greatly among strong acids, they may still be transported as the molecular acids and the extent is in the same order as the expected activity of the molecular acid in the CEM. These results are discussed with the perspective that even for strong acids, the transport does take place as un-ionized molecular acids.

Herein, we developed a platinum-copper nano-enzyme-linked immunosorbent assay (NLISA) based split diagnostic platform for the ultrasensitive detection of cardiac troponin I (cTnI). The PtCu nanozyme synthesized by one-pot synthesis exhibited ultra-high peroxidase-like activity (35.17 U mg⁻¹), which was about 4.5 times higher than that of the unmodified Pt nanozyme (8.83 U mg⁻¹). Due to the efficient peroxidase-like activity of the copper-platinum complexed nanozyme, transduction and sequential amplification of cTnI biological signals were achieved in combination with a liposome-embedded amplification strategy. The encapsulation efficiency was calculated by introducing a liposomal bilayer model, which showed that the introduction of a single liposomal molecule could amplify the signal up to 870-fold, thus promising a high sensitivity test. Notably, the dynamic response of cTnI was in the range of 0.1–5000 pg mL⁻¹ with an ultra-low detection limit (0.048 pg mL⁻¹). The developed NLISA analysis system provides a new way to discover efficient and sensitive alternatives to ELISA kits, which can meet the practical needs of community healthcare testing conditions and rapid testing in hospitals.

Fluorescent probes have been reported for monitoring urinary albumin (u-ALB) to enable early diagnosis of kidney diseases and facilitate regular point-of-care testing (POCT) for chronic kidney disease (CKD) patients. However, the albumin can bind hydrophobic drugs through host-guest interactions, which may result in decreased accuracy of probes at regular drug sites and hamper POCT of albuminuria since CKD patients often need to take medications routinely. Herein, we reported a novel fluorescent probe (NC-2) by molecular engineering of a reported AIEgen (NC-1). The introduction of a non-conjugated ring moiety to the molecular rotor granted the NC-2 enhanced sensitivity with a limit of detection in urine of 8.7 mg/L, which is below l the threshold of microalbuminuria (30 mg/L). Moreover, the NC-2 was found to preferentially bind to the FA1 site of ALB, conferring it with excellent anti-interference capacities against exogenous drug molecules and metabolites. Simulation experiments using lab-spiked urine samples containing common drugs taken by CKD patients demonstrated that the probe could provide satisfied detecting accuracy (80–90 %). Furthermore, a paper-based device was constructed and achieved on-site detection of u-ALB in qualitative and semi-quantitative manners. Findings in this work were of great significance to the development of fluorescent probes for accurate detection of ALB in complex urine samples and the further achievement of fluorescence-based POCT for CKD.

The group B Streptococcus (GBS) can generate vertical transmission to infants during delivery, has been seriously threatening the health of infants. Rapid and accurate prenatal GBS diagnosis for pregnant women is a deterministic blueprint to avoid infant viruses. Here, we developed an extraction-free nucleic acid isothermal amplification/CRISPR-Cas12a cutting one-pot system for GBS diagnostic assay by using suboptimal protospacer adjacent motifs, effectively avoiding multiple handling steps and uncapping contamination. The GBS diagnosis assay based on a one-pot system was validated by using fluorescent technique and lateral flow assay strips, exhibited fantastic specificity, accuracy and sensitivity with a limit of detection of 32 copies per reaction (0.64 copies/μL). Moreover, a portable device was constructed and integrated with the one-pot system to realize the GBS detection without professional and scene restrictions, it showed excellent performance in clinical sample detection, which achieved optical and portable GBS detection for point-of-care testing or home-self testing.

As we all know, SERS (Surface-enhanced Raman spectroscopy) is widely used in sensing, analysis and detection. The covalent organic frameworks (COFs) have performed well as a material for supporting metal nanoparticles and facilitating analyte adsorption in SERS, which may greatly enhance the detection sensitivity and reproducibility. The synthesis of traditional metal/COFs composites involved chemical reduction methods, however, the resulting metallic NPs exhibited reduced capacity to enhance SERS due to their small particle sizes (usually <20 nm). This paper presented a novel photoreduction method for the facile growth of AuNPs (diameters: 75 nm) on COFs matrix under light control, which represents the first report of such synthesis on COF. Subsequently, the photoreduction deposition induced AuNPs/COFs composites, which served as highly sensitive and reproducible SERS-active substrates for capturing the spectral information of four types of macrolide antibiotics. The detection limits for the four macrolide antibiotics were determined to be 3.30 × 10⁻¹¹, 3.43 × 10⁻¹⁰, 1.10 × 10⁻¹⁰ and 5.78 × 10⁻¹¹ M, respectively, exhibiting excellent linear relationships within the concentration range of 10⁻¹⁰ to 10⁻³ M. Therefore, our proposed SERS method opens up a new idea for the development of SERS substrates and environmental safety monitoring, and it has great potential for ensuring food safety in the future.

Metal–organic frameworks (MOFs), especially bimetallic MOFs, have attracted widespread attention for simulating the structure and function of natural enzymes. In this study, different morphologies of bimetallic Cu–Zn-MOF with different peroxidase (POD)-like activities were prepared by simply controlling the molar ratio of Cu²⁺ and Zn²⁺. Among them, the doughnut-shaped Cu₉–Zn₁-MOF exhibited the largest POD-like activity. Cu₉–Zn₁-MOF was combined with glucose oxidase to construct a sensitive and selective glucose colorimetric biosensor with a linear detection range of 10–300 μM and a detection limit of 7.1 μm. Furthermore, Cu₉–Zn₁-MOF can efficiently convert hydrogen peroxide (H₂O₂) into hydroxyl radicals that effectively kill both gram-negative and gram-positive bacteria at low H₂O₂ level. The results of this study may promote the synthesis of bimetallic MOFs and broaden their applications in the biomedical field.