Bioelectrochemical synthesis of gluconate by glucose oxidase immobilized in a ferrocene based redox hydrogel

Enzymatic bioelectrodes based on ferrocene-modified metal-organic layers for electrochemical glucose detection

Metal-organic frameworks (MOFs) are often applied for enzyme immobilization, while they are limited for bioelectrochemical applications due to poor electronic conductivity. Two-dimensional (2D) metal-organic layers (MOLs) with an ultra-thin lamellar structure can effectively shorten the electron transport path and improve the electron transfer rate. In this study, ferrocene as an electron mediator is covalently bound to a 2D-MOL (Fc-NH2-Hf-BTB-MOL) to accelerate electron transfer between the electrode surface and enzyme. Glucose oxidase (GOx) is immobilized on the electrode modified with Fc-NH2-Hf-BTB-MOL with the addition of chitosan and carboxylated carbon nanotubes. Electrochemical tests such as cyclic voltammetry are carried out on the glucose biosensor, which shows linear detection ranges of 5 ~ 400 μM and 3 ~ 9 mM, with a detection limit of 3.9 μM (S/N = 3). Therefore, this strategy of construction of an enzyme electrode based on 2D-MOLs with enhanced electron transfer results in a biosensor with excellent specificity and activity for practical glucose detection.

COFcap2, a recyclable tandem catalysis reactor for nitrogen fixation and conversion to chiral amines

Two or more catalysts conducting multistep reactions in the same reactor, concurrent tandem catalysis, could enable (bio)pharmaceutical and fine chemical manufacturing to become much more sustainable. Herein we report that co-immobilization of metal nanoparticles and a biocatalytic system within a synthetic covalent organic framework capsule, COFcap-2, functions like an artificial cell in that, whereas the catalysts are trapped within 300-400 nm cavities, substrates/products can ingress/egress through ca. 2 nm windows. The COFcap-2 reactor is first coated onto an electrode surface and then used to prepare eleven homochiral amines using dinitrogen as a feedstock. The amines, including drug product intermediates and active pharmaceutical ingredient, are prepared in >99% enantiomeric excess under ambient conditions in water. Importantly, the COFcap-2 system is recycled 15 times with retention of performance, addressing the relative instability and poor recyclability of enzymes that has hindered their broad implementation for energy-efficient, low waste production of chemicals and (bio)pharmaceuticals.

Probing the influence of crosslinkers on the properties, response, and degradation of enzymatic hydrogels for electrochemical glucose biosensing through fluorescence analysis

Drop-cast crosslinked hydrogels are a common platform for enzymatic electrochemical biosensors. Despite the widespread use of these complex systems, there are still several questions about how their physicochemical properties affect their performance, stability, and reproducibility. In this work, first-generation faradaic biosensors composed of glucose oxidase and branched polyethyleneimine (BPEI) are prepared using either glutaraldehyde (GA) or ethylene glycol diglycidyl ether (EGDGE) as crosslinkers. While EGDGE gels present an increasing electrochemical response with increasing crosslinker concentration, the current of GA gels decreases at high crosslinker concentration probably due to the hampered diffusion on tightly networked gels. We compared different strategies to use fluorescence microscopy to gain insight into the gel structure either by labeling the gel components with fluorophores or taking advantage of the intrinsic fluorescence of the imines formed upon crosslinking with GA. By monitoring the fluorescence of the crosslinking bonds and the electrochemical response, we demonstrate that hydrolysis, a common hydrogel degradation mechanism, is not responsible for the loss of electrical current over time in gels prepared with glutaraldehyde. Most hydrogel-based electrochemical biosensor studies do not perform specific experiments to determine the cause of the degradation and instead just infer it from the dependence of the current on the preparation conditions (most commonly concentrations). We show that, by taking advantage of several analytical techniques, it is possible to gain more knowledge about the degradation mechanisms and design better enzymatic biosensors.