Defect Induced Structural Transition and Lipase Immobilization in Mesoporous Aluminum Metal-Organic Frameworks.

The transition from disorder to order and structural transformation are distinctive metal-organic framework (MOF) features. How to adapt or control both behaviors in MOF has rarely been studied. In this case, we demonstrate that our successful synthesis of [Al(OH)(PDA)]n (AlPDA-53-DEF, AlPDA-53-H, and AlPDA-68) with H2PDA=4,4'-[1,4-phenylenebis(ethyne-2,1-diyl)]-di benzoic acid has shown the intricate world of Aluminum Metal-Organic Frameworks (Al-MOFs). It offers profound insights into defect structures to order and transformations. AlPDA-53-DEF, in particular, revealed a fascinating interplay of various pore sizes within both micro and mesoporous regions, unveiling a unique lattice rearrangement phenomenon upon solvent desorption. Defects and disorders emerged as crucial impacts of transforming AlPDA-53-DEF, with its initially imperfect crystallinity, into the highly crystalline, hierarchically porous AlPDA-53-H.

Exploring the potential of iron-based metal-organic frameworks as peroxidase nanozymes for glucose detection with various secondary building units.

Finding materials in biosensing that balance enzyme-like reactivity, stability, and affordability is essential for the future. Because of their unique peroxidase properties, including variable pore size, surface area, and Lewis acid active sites, iron-based metal-organic frameworks (MOFs) have evolved as viable possibilities. In this study, we constructed a Fe-MOF and tested its peroxidase-like activity and responsiveness toward H2O2 colorimetric techniques. Using encapsulation, we incorporated glucose oxidase into the ZIF-90 PVP MOF and conducted a sequential reaction with the Fe-MOF to detect glucose. The results showed better peroxidase catalytic activity of the MIL-88B(Fe) (1,4-NDC) MOF and similar secondary building unit (SBU) Fe-MOFs were studied in other peroxidase nanozyme studies. When combined with an enzyme-encapsulating ZIF-90 PVP MOF, they could be sequentially employed for glucose detection purposes. This study highlights the potential of nanozymes as an alternative to natural enzymes, with promising applications in biosensing and beyond.

A bioinspired copper-based coordination polymer for the detection of pheochromocytoma biomarkers.

Oxidase-mimicking (catechol oxidase/laccase) nanozymes provide outstanding specificity in the detection of epinephrine (Epi) for the assessment of pheochromocytoma; however, epinephrine (Epi) and norepinephrine (NE) co-existing in the same systems will reduce the selectivity of the biosensor. In the current study, we synthesized copper-based coordination polymer (Cu-CP) nanozymes capable of accelerating the oxidation of Epi with high specificity. Furthermore, the Cu-CP is able to detect Epi over a wide linear range of 0.5-100 µM with a low detection limit of 0.36 µM while providing excellent stability and recyclability. Furthermore, we employed colorimetric and fluorescence signals for sequential detection of the coexistence of Epi and NE for use in tracking the treatment outcomes of patients with pheochromocytoma. Experiments using artificial urine further confirmed the efficacy of the proposed system.

Cu-PyC MOF with oxidoreductase-like catalytic activity boosting colorimetric detection of Cr(VI) on paper.

Hexavalent chromium ions (Cr(VI)) are highly toxic and prone to bioaccumulation in the natural environment. This study sought to develop a facile and cost-effective approach to on-site monitoring Cr(VI) content in diverse environmental samples. We synthesized copper-based MOF nanozymes (Cu-PyC MOF) and developed a simple colorimetric method by which to detect Cr(VI) on paper-based devices. The colorimetric product is obtained using the MOF nanozyme as a catalyst, Cr(VI) as an oxidant, 3,3',5,5'-tetramethylbenzidine (TMB) as a chromogenic substrate to produce a bluish-green color observable by the naked eye or a UV-visible spectrophotometer. After Cu-PyC MOF was suspended in an acidic buffer, it remained stable and showed oxidoreductase-like catalytic activity, which in turn boosts Cr(VI) reduction. The proposed scheme enables the detection of Cr(VI) within 3 min over a linear range of 0.5-50 µM with a low detection limit of 0.051 µM. The proposed nanozyme-based colorimetric method exhibits excellent reusability and selectivity over other 27 interference ions and can be used in real sample analysis.

Sequential detection of dopamine and L-DOPA by a 2,3-dopa-dioxygenase from Streptomyces sclerotialus.

A variety of enzyme-based colorimetric biosensors have been developed for clinical practice; however, these methods will only become cost-effective when they are able to process multiple samples with a high degree of sensitivity. In this study, a novel heat-stable enzyme, 2,3-dopa-dioxygenase from the thermophilic bacterium Streptomyces sclerotialus (SsDDO), was used in the development of a protein- and cell-based biosensor for the detection of L-DOPA for the first time. SsDDO catalyzes the oxidative cleavage of L-DOPA forms linear semialdehyde (AHMS) and cyclizes to a 3-carboxy-3-hydroxyallylidene-3,4-dihydropyrrole-2-carboxylic acid (CHAPCA). We next derivatized CHAPCA by reacting with 3-aminobenzoic acid (MABA) to yield a red-fluorescent pigment. Overall, the detection of L-DOPA via the red fluorescent signal can be completed in only 30 min. We also developed a sequential analysis method to detect the coexistence of dopamine and L-DOPA with a high degree of sensitivity using the dual-fluorescent signals to monitor the therapy of patients with Parkinson's disease treated with L-DOPA. The robustness and applicability of the system were further validated in serum. In addition, paper microfluidics modified with chitosan was applied for fast and cost-effective analysis of dopamine and L-DOPA in the mixed solutions.

The bi-metallic MOF-919 (Fe-Cu) nanozyme capable of bifunctional enzyme-mimicking catalytic activity.

In this study, we report on a bi-metal organic framework, MOF-919 (Fe-Cu), capable of bifunctional-enzyme mimicking activity with oxidase- and peroxidase-like activities. The catalytic activities were examined by using o-phenylenediamine (OPD) as a chromogenic substrate to study oxidase- and peroxidase-like mimetics. Based on our findings, we developed a simple epinephrine colorimetric biosensor with a broad linear range (1-100 µM) and a low detection limit (0.298 µM). This approach provides evidence for transition metal-based pristine bi-metallic MOFs capable of reproducing both oxidase-peroxidase properties, which could be applied as new nanosensors.