Template-Free In Situ Encapsulation of Enzymes in Hollow Covalent Organic Framework Capsules for the Electrochemical Analysis of Biomarkers

Although capsule-like materials as host carriers for enzyme encapsulation have been a hot topic in recent years, creating an ideal microenvironment for enhanced enzymatic performance is still a formidable challenge. Herein, we created a template-free method to in situ encapsulate natural enzymes in hollow covalent organic framework (COF) capsules at room temperature. The COF crystallites migrated from the inner core and self-assembled at the outside walls during the inside-out Ostwald ripening process, retaining the enzymes in the cavity. The adjustable hollow structure of the enzyme@COF capsule allowed the basic vibration of the enzyme to maintain a certain degree of freedom, thus significantly enhancing the enzymatic bioactivity. The hollow enzyme@COF capsule has large mesoporous tunnels allowing the efficient transport. In addition, the enzyme encapsulated in the capsule showed superior activity and ultrahigh stability under various extreme conditions that may lead to enzyme inactivation, such as high temperature, organic solvents, chelates, and the denaturing agent. Finally, the prepared hollow GOx@COF capsule was used for electrochemical sensing of glucose in human serum, and the electrochemical sensor exhibited high selectivity and satisfactory test results. This research not only provides a new way for COFs to encapsulate enzymes but also has potential applications in biocatalysis and biosensing, making artificial organelles possible.

One-pot synthesis of trypsin-based magnetic metal-organic frameworks for highly efficient proteolysis

Immobilization of enzymes onto metal-organic frameworks (MOFs) through a biomimetic mineralization approach can preserve biological functionality in harsh environments. Despite the success of this approach, the alkaline environment of the reaction system, which is caused by the organic monomers of MOFs, makes it unsuitable for some pH-sensitive enzymes, especially for trypsin. Herein, we reported a facile approach for the one-pot synthesis of trypsin-immobilized magnetic zeolite imidazolate framework-8 (iron oxide@ZIF-8@trypsin), where the growth of ZIF-8 around the citric acid-modified iron oxide and immobilization of trypsin occurred simultaneously when the pH of the reaction system was changed to some extent. With a large specific surface area and a high enzyme loading capacity, the resultant iron oxide@ZIF-8@trypsin exhibited 2.6 times higher enzymatic activity than free trypsin. Moreover, it showed a favourable magnetic response (43 emu g^-1) which made the operation and recycling easy and convenient. In addition, iron oxide@ZIF-8@trypsin could be applied as an immobilized enzyme microreactor (IMER) to rapidly and efficiently digest proteins and complex human serum samples with satisfactory results, showing great promise for application in proteomic analysis.

A hollow microshuttle-shaped capsule covalent organic framework for protein adsorption

A hollow microshuttle-shaped capsule COF was prepared using a template-free procedure for the first time and has demonstrated the highest adsorption capacity (550.82 mg g⁻¹) for hemoglobin so far.

A new sample preparation method for the absolute quantitation of a target proteome using 18O labeling combined with multiple reaction monitoring mass spectrometry

A new sample preparation method for target proteome absolute quantitation using ¹⁸O labeling-MRM MS.

Accelerating trypsin digestion: the immobilized enzyme reactor

Sample preparation has lagged far behind the evolution of instrumentation used in mass-linked protein analysis. Trypsin digestion, for example, still takes a day, as it did 50 years ago, while mass spectral analyses are achieved in seconds. Higher order structure of proteins is frequently modified by varying digestion conditions: shifting the initial points of trypsin cleavage, changing digestion pathways, accelerating peptide bond demasking and altering the distribution of miscleaved products at the completion of proteolysis. Reduction and alkylation are even circumvented in many cases. This review focuses on immobilized enzyme reactor technology as a means to achieve accelerated trypsin digestion by exploiting these phenomena.

Enzymes immobilized in mesoporous silica: a physical-chemical perspective

Mesoporous materials as support for immobilized enzymes have been explored extensively during the last two decades, primarily not only for biocatalysis applications, but also for biosensing, biofuels and enzyme-controlled drug delivery. The activity of the immobilized enzymes inside the pores is often different compared to that of the free enzymes, and an important challenge is to understand how the immobilization affects the enzymes in order to design immobilization conditions that lead to optimal enzyme activity. This review summarizes methods that can be used to understand how material properties can be linked to changes in enzyme activity. Real-time monitoring of the immobilization process and techniques that demonstrate that the enzymes are located inside the pores is discussed by contrasting them to the common practice of indirectly measuring the depletion of the protein concentration or enzyme activity in the surrounding bulk phase. We propose that pore filling (pore volume fraction occupied by proteins) is the best standard for comparing the amount of immobilized enzymes at the molecular level, and present equations to calculate pore filling from the more commonly reported immobilized mass. Methods to detect changes in enzyme structure upon immobilization and to study the microenvironment inside the pores are discussed in detail. Combining the knowledge generated from these methodologies should aid in rationally designing biocatalyst based on enzymes immobilized in mesoporous materials.

pH and ion strength modulated ionic species loading in mesoporous silica nanoparticles

Mesoporous silica nanoparticles (MSN) have emerged as appealing host materials to accommodate guest molecules for biomedical applications, and recently various methods have been developed to modulate the loading of guest molecules in the silica matrix. Herein, it was demonstrated that pH and ion strength showed great influence on the loading of charged species into the nanoparticles, taking MCM-41 as a host MSN model and methylviologen (MV(2+)) and 1,5-naphthalene disulfonate (NDS(2-)) as typical charged ionic guest molecules. As the pH increased from 3.0 to 8.0, the loading amount of MV(2+) increased gradually, while on the contrary, it decreased gradually for NDS(2-), for the solution pH changed the electrostatic interaction between the silica matrix and the ionic guest molecules. Additionally, the adding of NaCl reduced the electrostatic interaction, which resulted in a decreasing of the electrostatic rejection and electrostatic accumulation for the molecules carrying the same and the opposite charge to the particle respectively. Thus, pH and ion strength can be employed as simple approaches to modulate the loading of charged molecules and permselectivity in MSN. This work has a definite guidance function for molecule loading, transport modulation, controlled release as well as sensors based on MSN.