Micro‐Scaling Metal‐Organic Framework Films through Direct Laser Writing for Chemical Sensing

Abstract

Abstract A zeolitic imidazolate framework (ZIF‐8) containing two enzymes that form a cascade biocatalyst has been integrated with 3D structures that are fabricated through a two‐photon polymerization using direct laser writing lithography. Glucose oxidase (GOx) and horseradish peroxidase (HRP) are encapsulated by the biomimetic self‐assembly process of ZIF‐8 to form the GOx/HRP/ZIF‐8 composite which grows in situ on the surface of microprinted carbon‐coated hexagonal substrates (cHS). The GOx/HRP/ZIF‐8/cHS film is applied to glucose detection through enzymatic oxidation of glucose to gluconic acid, forming H2O2, in the presence of GOx and the subsequent reduction of H2O2 to water in the presence of HRP and Amplex Red. This reaction is monitored using fluorimetry as the oxidation of Amplex Red with H2O2 catalyzed by HRP forms red‐emitting resorufin. The GOx/HRP/ZIF‐8/cHS film responds to glucose concentrations with a linear range of 10–200 µm, which correlates to the salivary glucose level in healthy humans. The GOx/HRP/ZIF‐8/cHS film shows more than eight times and 13 times enhanced activity than GOx/HRP/cHS (without ZIF‐8) and GOx/HRP/ZIF‐8 on a non‐3D patterned substrate, respectively. The GOx/HRP/ZIF‐8/cHS film retains more than 80% or 100% of its initial activity after being stored for over 2 months at ≤24 or 4 °C, respectively.

Keywords

• biocascade catalysis
• chemical sensing
• direct laser writing
• enzyme encapsulation
• fluorescence
• metal‐organic frameworks