Engineering Active Metal Oxide Interfaces on MOF‐Derived 3D Carbon Architecture for Small‐Molecule Biosensing

ABSTRACT The sensitivity of bioelectronic interfaces relies on maximizing electroactive surface area, motivating porous architectures with strong electrical transport. Laser‐induced graphene (LIG) provides a direct route to 3D carbon networks, yet its relatively inert surface requires tailored functionalization to immobilize biorecognition elements. Incorporating metal oxides can increase surface reactivity, but metal‐salt precursor routes often lead to aggregation and weak adhesion. Although metal—organic frameworks (MOFs) can improve precursor uniformity, most MOF‐derived graphene/oxide systems target gas‐phase analytes rather than biomolecules in electrolyte environments. Here, we report an ultrafast MOF‐assisted laser‐writing method that forms nanoscale copper oxide (CuO) domains within a 3D graphene network in a single step. The resulting CuO/LIG interface presents Cu─O surface functionalities that facilitate silanization and aptamer immobilization. Integrated into an extended‐gate field‐effect transistor, the CuO/LIG interface enables quantitative cortisol detection from 1 p M to 1 µM with a 1.3 pM detection limit and strong selectivity against serotonin, glucose, and progesterone. Device transfer curves show only minor threshold‐voltage drift over 5 days. This patternable approach integrates MOF chemistry with laser writing, profviding a generalizable route to robust hybrid interfaces for aqueous biosensing.