Construction of Peroxidase-like Metal-Organic Frameworks in TiO2 Nanochannels: Robust Free-Standing Membranes for Diverse Target Sensing.

Abstract

The high cost and easy denaturation of natural enzymes under environmental conditions hinder their practical usefulness in sensing devices. In this study, peroxidase (POD)-like metal-organic frameworks (MOFs) were in situ grown in the nanochannels of an anodized TiO2 membrane (TiO2NM) as an electrochemical platform for multitarget sensing. By directly using a nanochannel wall as the precursor of metal nodes, Ti-MOFs were in situ derived on the nanochannel wall. Benefitting from the presence of bipyridine groups on the ligands, the MOFs in the nanochannels provide plenty of sites for Fe3+ anchoring, thus endowing the resulting membrane (named as Fe3+:MOFs/TiO2NM) with remarkable POD-like activity. Such Fe3+-induced POD-like activity is very sensitive to thiol-containing molecules owing to the strong coordination effect of thiols on Fe3+. Most importantly, the POD-like activity of nanochannels can be in situ characterized by the current-potential (I-V) properties via catalyzing the oxidation of 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) substrate to the corresponding positively charged product ABTS•+. As a proof-of-concept application, the free-standing POD-like membranes were applied as a label-free assay in sensing cysteine, as well as monitoring acetylcholinesterase (AChE) activity through the generated thiol-containing product. Furthermore, based on the toxicity effect of organophosphorus (OP) compounds on AChE, the robust membranes were successfully utilized to evaluate the toxicity of diverse OP compounds. The POD-like nanochannels open up an innovative way to expand the application of nanochannel-based electrochemical sensing platforms in drug inspection, food safety, and environmental pollution.