Ternary metal oxide engineering of screen-printed electrodes for wearable morphine sensing

Reliable, in-situ detection of opioid drugs remains a critical challenge for healthcare, forensic analysis, and public safety. Herein, we report for the first time a morphine sensor based on a newly designed ternary metal oxide (TMO) with the formula of Mg_0.50Ni_0.25Zn_0.25O. The TMO stabilizing six-coordinated Zn-O in rock-salt MgO and NiO matrix by short-range disorder, exhibits excellent sensitivity, selectivity, and long-term stability towards the electrochemical detection of morphine. The TMO-based morphine sensor shows robust performance across variable environments, in particular a two-fold higher sensitivity than the bare SPCE and achieves a limit of detection (LoD) as low as 0.11 μM with a dynamic range of 0.24 - 54.22 μM. By introducing a hydrogel interface to solvate and diffuse solid-state morphine to the TMO-modified flexible sensor electrode, our sensor is further integrated into a small form factor wearable platform capable of in-situ, non-invasive detection of solid-state morphine on surfaces such as skin, showing low sensitivity of 2.56 μA cm² nmol^-1 and LoD of 0.28 nmol cm^-2 in the dynamic range of 1- 6 nmol cm^-2.