Quantum Dots Meet Enzymes: Hydrophobicity of Surface Ligands and Size Do Matter.

Colloidal quantum dots (QDs) are a class of representative fluorescent nanomaterials with tunable, bright, and sharp fluorescent emission, with promising biomedical applications. However, their effects on biological systems are not fully elucidated. In this work, we investigated the interactions between QDs with different surface ligands and different particle sizes and α-chymotrypsin (ChT) from the thermodynamic and kinetic perspectives. Enzymatic activity experiments demonstrated that the catalytic activity of ChT was strongly inhibited by QDs coated with dihydrolipoic acid (DHLA-QDs) with noncompetitive inhibitions, whereas the QDs coated with glutathione (GSH-QDs) had weak effects. Furthermore, kinetics studies showed that different particle sizes of DHLA-QDs all had high suppressive effects on the catalytic activity of ChT. It was found that DHLA-QDs with larger particle sizes had stronger inhibition effects because more ChT molecules were bound onto the surface of QDs. This work highlights the importance of hydrophobic ligands and particle sizes of QDs, which should be considered as the primary influencing factors in the assessment of biosafety. Meanwhile, the results herein can also inspire the design of nano inhibitors.

A sandwich-type photoelectrochemical aptasensor using Au/BiVO4 and CdS quantum dots for carcinoembryonic antigen assay.

A novel sandwich-type photoelectrochemical (PEC) aptasensor for the carcinoembryonic antigen (CEA) assay was fabricated using the CEA aptamer, Au/BiVO4 and CdS quantum dots (CdS QDs). In virtue of the localized surface plasmon resonance effect of Au nanoparticles, Au/BiVO4 showed an effective utilization of visible light and excellent photoactivity, and was employed as the photoanode. After CdS QDs were conjugated to Au/BiVO4 through the sandwich structure based on the hybridization of the CEA aptamer with two partially complementary single-stranded DNA molecules, the photocurrents were further enhanced by a resonance energy transfer between CdS QDs and Au nanoparticles. Meanwhile, the consumption of the photo-induced holes by ascorbic acid could also retard the combination of the electron-hole pairs and cause an increase of the photocurrents. However, the specific recognition of CEA by the CEA aptamer could destroy the sandwich structure and remarkably weaken the photocurrent response. Thus, the quantitative detection of CEA was connected with the decrease of the photocurrent. Benefitting from the above methods for signal enhancement, the PEC aptasensor showed a wide sensing range of 0.0001-10 ng mL-1 and a low detection limit of 0.047 pg mL-1 for CEA detection. The specificity, stability and recoveries of the PEC aptasensor were also excellent. Therefore, the construction of the present PEC aptasensor provides a universal and practical method for sensing other substances.

Thermodynamics, Kinetics and Mechanisms of Noncompetitive Allosteric Inhibition of Chymotrypsin by Dihydrolipoic Acid-Coated Gold Nanoclusters.

Enzymes are an important class of biomacromolecules which catalyze many metabolic processes in living systems. Nanomaterials can be synthesized with tailored sizes as well as desired surface modifications, thus acting as promising enzyme regulators. Fluorescent gold nanoclusters (AuNCs) are a representative class of ultrasmall nanoparticles (USNPs) with sizes of ∼2 nm, smaller than most of proteins including enzymes. In this work, we chose α-chymotrypsin (ChT) and AuNCs as the model system. Activity assays and inhibition kinetics studies showed that dihydrolipoic acid (DHLA)-coated AuNCs (DHLA-AuNCs) had a high inhibitory potency (IC50 = 3.4 µM) and high inhibitory efficacy (>80%) on ChT activity through noncompetitive inhibition mechanism. In distinct contrast, glutathione (GSH)-coated AuNCs (GSH-AuNCs) had no significant inhibition effects. Fluorescence spectroscopy, agarose gel electrophoresis and circular dichroism (CD) spectroscopy were conducted to explore the underlying mechanisms. A two-step interaction model was proposed. First, both DHLA-AuNCs and GSH-AuNCs might be bound to the positively charged sites of ChT through electrostatic forces. Second, further hydrophobic interactions occurred between three tyrosine residues of ChT and the hydrophobic carbon chain of DHLA, leading to a significant structural change thus to deactivate ChT on the allosteric site. On the contrary, no such interactions occurred with GSH of zwitterionic characteristic, which explained no inhibitory effect of GSH-AuNCs on ChT. To the best of our knowledge, this is the first example of the allosteric inhibition of ChT by nano regulators. These findings provide a fundamental basis for the design and development of nano regulators.

The Influence of Retreated Lithium Slag with a High Content of Alkali, Sulfate and Fluoride on the Composition and the Microstructure of Autoclaved Aerated Concrete.

In this paper, the possibility of retreated lithium slag (RTLS) with a high content of alkali, sulfate and fluoride as a partial replacement for fly ash (FA) to produce autoclaved aerated concrete (AAC) was investigated. The influence of the RTLS dosage on the AAC performance were examined. The composition and microstructure of hydrates as well as the microstructure of the RTLS-FA-based AAC compositions were determined by XRD, FTIR, TG-DSC and SEM. The results illustrated that the incorporation of RTLS changed the crystal structure and the microstructure of the tobermorite. With increased RTLS contents, the morphology of tobermorite was changed, and the grass-like tobermorite gradually transformed into network-like tobermorite. The newly formed tobermorite improved the mechanical performance of the AAC. Compared with the RTLS10, the content of tobermorite in the RTLS30 increased by 8.6%.