Gold nanoparticles tune the activity of laccase in anionic reverse micelles

Chiral evolution of carbon dots and the tuning of laccase activity

Chirality has attracted extensive attention in many fields ranging from chemistry to life sciences. Carbon dots (CDs) with good biocompatibility and unique photochemical properties have become a new star in the nanocarbon family. Endowed with chirality, CDs will exhibit more marvellous properties and bridge the fields of material chemistry and life sciences tightly. Herein, we report a facile one-step alkali-assisted electrochemical method to fabricate chiral CDs from cysteine (cys). We showed the chiral evolution of CDs with highly symmetrical circular dichroism (CD) signals in the range from 205 to 350 nm. These chiral CDs have been further demonstrated to be capable of tuning the activity of laccase: the l-CDs can improve the activity of the enzyme up to 20.2%, whereas the d-CDs decrease the activity to 10.4%. A series of experiments confirm that it is the synergistic effect of nanosize and chirality of CDs that induces the change in the structure of laccase and thus leads to the tuning of the laccase activity.

Simultaneous Enhancement of Bioactivity and Stability of Laccase by Cu2+/PAA/PPEGA Matrix for Efficient Biosensing and Recyclable Decontamination of Pyrocatechol

Simultaneously enhancing the catalytic bioactivity and stability of enzyme is still an intractable issue in the enzymatic study. Herein, a facile and effective approach was designed to immobilize and modify laccase on a Cu²⁺-adsorbed pyrene-terminated block copolymer [poly(acrylic acid)/poly(poly(ethylene glycol) acrylate)] (PAA/PPEGA), which was prepared via well-controlled reversible addition-fragmentation chain transfer polymerization. PAA provided the supporting matrix for firm immobilization of Cu²⁺, an enzyme bioactivity inducer, onto the microstructure of laccase, while avoiding any contamination of the heavy metal Cu²⁺ into the following application system. The water-soluble, biocompatible, and nontoxic PPEGA was used as an ideal modifier to improve the laccase stability. Accordingly, the modified laccase exhibited enhanced catalytic bioactivity and stability simultaneously to 447% and 237%, respectively. The modified laccase was immobilized on the highly oriented pyrolytic graphite surface and large-area graphene papers through π-π stacking interactions between the pyrene moiety of PAA/PPEGA and the π-conjugated graphenelike surface. The as-prepared portable solid-state electrochemical laccase biosensor showed lowest detection limit of 50 nM (S/N ≥ 3) and long-term stability for pyrocatechol detection. Besides, the laccase immobilization on graphene paper provided efficient pyrocatechol decontamination platform with convenience and recyclability, which could retain the laccase bioactivity of 176% after 8 consecutive operations.

Study on the catalytic performance of laccase in the hydrophobic ionic liquid-based bicontinuous microemulsion stabilized by polyoxyethylene-type nonionic surfactants

To formulate a compatible green medium for the conversion of a hydrophobic substrate by a hydrophilic enzyme, we investigated the phase behavior of pseudo ternary hydrophobic ionic liquid (HIL)/buffer/polyoxyethylene-type nonionic surfactant (CnEm)/n-alcohol system and the effects of the components on the formulation of the HIL-based bicontinuous microemulsion. It is found that small head group of the surfactant, high concentration of n-alcohol (medium/long alkyl chain) and low cohesive energy density of the HIL result in low phase transition temperature. In the CnEm stabilized compatible bicontinuous microemulsion, the kinetics of laccase catalyzed oxidation of 2,6-dimethoxyphenol were also investigated. It is found that in addition to temperature, n-alcohol is the key parameter affecting the catalytic performance of laccase, and the optimum n-alcohol depends on the type of HIL as an oil phase. All the kinetic parameters, such as Km, kcat, kcat/Km, and Ea (apparent activation energy), indicate that the bicontinuous microemulsion consisting of [Omim]NTf2/buffer/CnEm/n-hexanol is a suitable medium for the laccase-catalyzed reaction. To the best of our knowledge, this is the first report on the formulation of HIL-based bicontinuous microemulsion for enzyme catalysis.

Visible-Light-Induced Effects of Au Nanoparticle on Laccase Catalytic Activity

A deep understanding of the interaction between the nanoparticle and enzyme is important for biocatalyst design. Here, we report the in situ synthesis of laccase-Au NP (laccase-Au) hybrids and its catalytic activity modulation by visible light. In the present hybrid system, the activity of laccase was significantly improved (increased by 91.2% vs free laccase) by Au NPs. With a short time visible light illumination (λ > 420 nm, within 3 min), the activity of laccase-Au hybrids decreased by 8.1% (vs laccase-Au hybrid without light), which can be restored to its initial one when the illumination is removed. However, after a long time illumination (λ > 420 nm, over 10 min), the catalytic activity of laccase-Au hybrids consecutively decreases and is not reversible even after removing the illumination. Our experiments also suggested that the local surface plasma resonance effect of Au NPs causes the structure change of laccase and local high temperature near the Au NPs. Those changes eventually affect the transportation of electrons in laccase, which further results in the declined activity of laccase.

Tuning laccase catalytic activity with phosphate functionalized carbon dots by visible light

The phosphate functionalized carbon dots (PCDs) with high biocompatibility and low toxicity can be used as efficient additives for the construction of laccase/PCDs hybrids catalyst. A series of experiments indicated that the activity of laccase/PCDs was higher than that of free laccase (increased by 47.7%). When laccase/PCDs hybrids catalyst was irradiated with visible light (laccase/PCDs-Light), its activity was higher than that of laccase/PCDs hybrids without light irradiation (increased by 92.1%). In the present system, the T1 Cu in laccase was combined with the phosphate group on PCDs, which can increase binding capacity of laccase/PCDs hybrids and substrate. Further, the visible light irradiation increased the donating and accepting electronic capability of the laccase/PCDs hybrids, improving their catalytic activity.