Highly Selective and Portable Fluorescence Turn-On Detection of Sc3+ in Ore and Water Based on Strong Lewis Acid-Base Coordination.

Detecting scandium (Sc) with high selectivity and sensitivity is a challenging task due to its chemical similarity to other rare earth ions. Our findings show that the fluorescence of the complex fluorescent indicator calcein (CL) is quenched under acidic conditions (pH = 2), and Sc3+ strongly inhibits this process. The results demonstrate that CL forms multimers and precipitates out of the solution under acidic conditions, while Sc3+ causes a significant decrease in the scattering intensity of the solution. Additional experiments revealed that the strong Lewis acid nature of Sc3+ complexes with the carboxyl groups of CL leads to increased dispersion of CL even under acidic conditions, thus enhancing its absorption and fluorescence. The complexation ratio of Sc3+ and CL was investigated through spectral titrations and theoretical calculations. The interaction between Sc3+ and CL is the strongest among rare earth and common metal ions due to the smallest ionic radius, resulting in high selectivity. The fluorescence turn-on strategy had a linear range of 0.04 to 2.25 µM under optimal conditions, with a detection limit of 20 nM for Sc3+. The combination of 3D printing and a smartphone program allows for portable on-site analysis of Sc3+. Mineral and water samples were used to demonstrate the potential of this strategy for the rapid, selective, and sensitive analysis of low levels of Sc3+.

Portable and Rapid Fluorescence Turn-On Detection of Total Pepsin in Saliva Based on Strong Electrostatic Interactions.

Salivary pepsin has been proposed as a promising diagnostic marker for gastroesophageal reflux disease (GERD). However, the activity of human pepsin is strongly influenced by pH, and the acidic condition (pH ∼ 2) is optimal, which is a contradiction for the pepsin detection kit based on its catalytic activity. Thus, its accurate quantification in saliva (neutral pH) by readily rapid tools with simplicity and low cost is still challenging. Herein, a convenient fluorescence assay has been developed for the rapid detection of pepsin at neutral pH based on its electrostatic interaction with SYBR Green (SG) rather than the bioactivity. At neutral pH, the positively charged SG fluorophore can be effectively adsorbed by the negatively charged pepsin due to the low isoelectric point (pI) and large molecular size of pepsin. Thus, the molecular rotation of SG is limited, and its fluorescence intensity is significantly increased. The strategy was further confirmed to have the same fluorescence response as that of normally active and inactivated pepsin. Due to the unique pI of pepsin, the fluorescence strategy is highly selective for pepsin compared to other proteins. On the basis of this strategy, a smartphone-based fluorescence capture device integrated with a programmed Python program was fabricated for both color recognition and the accurate detection of pepsin within 3 min. Under the optimal conditions, this turn-on sensor allowed for the on-site analysis of pepsin with a detection limit of 0.2 µg/mL. Moreover, this strategy was successfully used to assess salivary pepsin to aid in the noninvasive diagnosis of GERD.

Nanozyme's catalytic activity at neutral pH: reaction substrates and application in sensing.

Nanozymes exhibit their great potential as alternatives to natural enzymes. In addition to catalytic activity, nanozymes also need to have biologically relevant catalytic reactions at physiological pH to fit in the definition of an enzyme and to achieve efficient analytical applications. Previous reviews in the nanozyme field mainly focused on the catalytic mechanisms, activity regulation, and types of catalytic reactions. In this paper, we discuss efforts made on the substrate-dependent catalytic activity of nanozymes at neutral pH. First, the discrepant catalytic activities for different substrates are compared, where the key differences are the characteristics of substrates and the adsorption of substrates by nanozymes at different pH. We then reviewed efforts to enhance reaction activity for model chromogenic substrates and strategies to engineer nanomaterials to accelerate reaction rates for other substrates at physiological pH. Finally, we also discussed methods to achieve efficient sensing applications at neutral pH using nanozymes. We believe that the nanozyme is catching up with enzymes rapidly in terms of reaction rates and reaction conditions. Designing nanozymes with specific catalysis for efficient sensing remains a challenge.

Clematichinenoside (AR) Attenuates Hypoxia/Reoxygenation-Induced H9c2 Cardiomyocyte Apoptosis via a Mitochondria-Mediated Signaling Pathway.

Mitochondria-mediated cardiomyocyte apoptosis is involved in myocardial ischemia/reperfusion (MI/R) injury. Clematichinenoside (AR) is a triterpenoid saponin isolated from the roots of Clematis chinensis with antioxidant and anti-inflammatory cardioprotection effects against MI/R injury, yet the anti-apoptotic effect and underlying mechanisms of AR in MI/R injury remain unclear. We hypothesize that AR may improve mitochondrial function to inhibit MI/R-induced cardiomyocyte apoptosis. In this study, we replicated an in vitro H9c2 cardiomyocyte MI/R model by hypoxia/reoxygenation (H/R) treatment. The viability of H9c2 cardiomyocytes was determined by MTT assay; apoptosis was evaluated by flow cytometry and TUNEL experiments; mitochondrial permeability transition pore (mPTP) opening was analyzed by a calcein-cobalt quenching method; and mitochondrial membrane potential (ΔΨm) was detected by JC-1. Moreover, we used western blots to determine the mitochondrial cytochrome c translocation to cytosolic and the expression of caspase-3, Bcl-2, and Bax proteins. These results showed that the application of AR decreased the ratio of apoptosis and the extent of mPTP opening, but increased ΔΨm. AR also inhibited H/R-induced release of mitochondrial cytochrome c and decreased the expression of the caspase-3, Bax proteins. Conversely, it remarkably increased the expression of Bcl-2 protein. Taken together, these results revealed that AR protects H9c2 cardiomyocytes against H/R-induced apoptosis through mitochondrial-mediated apoptotic signaling pathway.

Preparation and Load-Bearing Capacity of Lattice Cell Warren Truss Slot Resin-Stiffener-Reinforced Foam Sandwich Material.

This study optimized and proposed a Warren truss slot-hole structure with a double-sided, square shallow slot and vertical and horizontal corrugated symmetry, achieved with inclined holes based on the stability and a good bearing capacity of an inclined strut truss structure. The tetrahedral truss lattice cells were obverse and reverse-staggered in the central core of the structure. Compared with the double-sided, square shallow groove cylindrical straight hole, the resin consumption of the Warren truss slot holes was similar to that of a vacuum-assisted resin infusion; however, the external flat compression force of the Warren truss slot holes on the resin stiffener structure doubled, and its bending contact force increased by approximately 1.5 times. Furthermore, the resulting Warren truss-slotted resin structure exhibited a late failure time. Compared with the double-sided, square shallow groove cylindrical straight hole foam-core sandwich composite, the Warren truss slot resin-stiffener-reinforced sandwich composite exhibited an increase of 4.7 kN in the flat compression load, an improvement of ~40% in flat compressive strength performance, an increase of ~0.58 kN in the bending load, and an improvement of ~60% in the bending strength, demonstrating its better bearing strength performance.

Light-activated carbon dot nanozyme with scandium for a highly efficient and pH-universal bio-nanozyme cascade colorimetric assay.

Nanozyme-based colorimetric assays have attracted much attention due to their cost-effectiveness, high stability, and sensitivity. In particular, the catalytic cascade imparted by the biological enzyme is highly selective. However, developing an efficient, one-pot, and pH-universal bio-nanozyme cascade remains challenging. Considering the tunable activity of the photo-activated nanozyme, we herein demonstrated a pH-universal colorimetric assay based on the Sc3+-boosted photocatalytic oxidation of carbon dots (C-dots). As a strong Lewis acid, Sc3+ shows ultra-fast complexation with OH- over a broad pH range and dramatically decreases the pH of the buffer solutions. In addition to regulating the pH, Sc3+ also binds to the C-dots to produce a persistent and strongly oxidizing intermediate based on photo-induced electron transfer. The proposed Sc3+-boosted photocatalytic system was successfully used in a cascade colorimetric assay with biological enzymes for assessing their activity as well as the detection of enzyme inhibitors at neutral and alkaline pH. Instead of designing new nanozymes for catalytic cascades, this work suggests that introducing promoters can be a convenient strategy in practical applications.

Immobilization of Lipase by Ionic Liquid-Modified Mesoporous SiO2 Adsorption and Calcium Alginate-Embedding Method.

Porcine pancreatic lipase (PPL) was immobilized onto functionalized ionic liquid-modified silica carrier using gelatinization and physical adsorption. The immobilized lipase was characterized with N2 adsorption-desorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FT-IR) before and after modification and immobilization. The results showed that the modification of the ionic liquid and the introduction of lipase had been successfully approved. The rate of enzymatic reaction and its influencing factors was primarily studied by enzymatic reaction kinetics. K m values of PPL-SiO2@CA and PPL-IM/BF4-SiO2@CA were 4.9 and 3.7 mg/ml, respectively. It indicated that the modification of the functionalized ionic liquid enhanced the affinity between the immobilized enzyme and the substrate. The immobilization efficiency, specific activity, optimum temperature, optimum pH, thermal stability, reusability, and storage stability of the immobilized enzyme were investigated. We found that the stability of the immobilized enzyme was significantly higher than that of the unmodified immobilized enzyme. Specially, PPL-IM/BF4-SiO2@CA maintained good thermal stability and retained more than 92% of its activity at 65 °C after preheating 3 h. Graphical Abstract Above, the immobilized lipase maintained more than 92% of its initial activity after incubating at 65 °C for 3 h.