Expanding the synergy between MOFs and solid-state nanochannels: robust anchoring of enzymes for iontronic biosensing

We present the development of an innovative nanofluidic biosensor that integrates solid-state nanochannels modified with a metal-organic framework (MOF) for the detection of urea through enzymatic activity. The Zr-based MOF chosen was UiO-66-NH₂, synthesized within bullet-shaped nanochannels in track-etched polyethylene terephthalate (PET) membranes. Post-synthetic modification was employed to attach divinyl sulfone (DVS) to the amino moieties present, thus facilitating the covalent immobilization of the urease enzyme. Enzymatic hydrolysis of urea generates local pH changes within the nanochannels, which can be translated into measurable modulations of ionic transport due to the pH-sensitive surface charge of the MOF. The biosensor exhibited a detection limit of 10 μM for urea, excellent stability, reversibility, and specificity. This work represents the first report, to the best of our knowledge, of a nanofluidic sensor that utilizes a MOF covalently bonded with an enzyme for urea detection through ionic transport changes. The incorporation of post-synthetic modification techniques highlights the versatility of MOF-functionalized nanochannels in creating robust and sensitive biosensors, opening new avenues for advanced nanofluidic sensing applications.