Fast tailoring the ZIF-8 surface microenvironment at ambient temperature to boost glucose oxidase-like activity of AuNPs for biosensing.

Abstract

Rational design and tailoring of the surface microenvironment surrounding the catalytic sites, such as noble metal nanoparticles, is an effective way to enhance the catalytic activity of mimicking enzymes. However, it remains on-going challenges to regulate the microenvironment of the catalytic sites due to the lack of tunable variability in structural precision of conventional solid catalysts. Herein, three types of zeolitic imidazolate framework-8 (ZIF-8) with different major crystal facet orientations, i.e., cubic with (100) facets (denoted ZIF-8_c), truncated dodecahedral with (100), (110) facets (denoted ZIF-8_tr), and dodecahedral with (110) facets (denoted ZIF-8_r), were developed facilely using an electrochemical method by switching the potential at ambient temperature. Because the Zn²⁺ nodes were predominantly exposed on the (100) facets of ZIF-8, while the ligands were mainly exposed on the (110) facets. Hence, gold nanoparticles (AuNPs) showed differential glucose oxidase (GOx)-like activities when anchored in situ on different crystal facets of ZIF-8 and obeyed the following order ZIF-8_c/Au>ZIF-8_tr/Au>ZIF-8_r/Au. Notably, both the metal nodes and aromatic linkers of ZIF-8 interacted with AuNPs through coordination and π-π interactions. The Zn²⁺ nodes facilitated the formation of the electron-deficient Au species. The electron transfer from AuNPs to Zn²⁺ sites effectively boosted the catalytic activity. It was known that directly tailoring the microenvironment at the supporting sites of noble metal catalysts to boost catalysis through a facile electrochemical method was not reported. Based on the favorable GOx-like activity and long-term stability of ZIF-8_tr/Au, a highly sensitive electrochemical biosensing platform for assaying squamous cell carcinoma antigen (SCCA) was developed. It enabled fg-level detection of cancer marker.