Sustainable Rice Husk‐Derived Biochar‐Based Composite as Conductive Recognition Interface for Selective Electrochemical Sensing of Dopamine

Sensitive and selective determination of dopamine (DA) is important for neurochemical analysis, but electrochemical detection in complex matrices remains limited by interfacial passivation and interference from coexisting electroactive species. Here, rice husk‐derived biochar (RHB) was integrated with UiO‐66‐NH ₂ through an in situ solvothermal process to construct a conductive composite interface for DA sensing. The RHB scaffold provides an interconnected carbon network for charge transport and increases the accessible electrode/electrolyte interface, whereas incorporation of the UiO‐66‐NH ₂ precursor modifies the interfacial environment relevant to DA accumulation and electrooxidation. Control experiments using bare GCE, RHB/GCE, UiO‐66‐NH ₂ precursor/GCE, and the composite‐modified electrode showed that the composite produced the highest DA current response under identical conditions. Post‐electrochemical X‐ray diffraction revealed disappearance of the characteristic UiO‐66‐NH ₂ reflections after operation in phosphate‐buffered saline (PBS), demonstrating loss of long‐range metal–organic framework (MOF) crystallinity. UiO‐66‐NH ₂ is therefore regarded as a structural precursor rather than as the persistent electroactive MOF phase during sensing in PBS. Under optimized conditions, the resulting RHB‐based composite/GCE (RHB composite/GCE) exhibited two linear ranges between 0.07–7.0 and 7.0–70.0 μM with a detection limit of 10.24 nM. In diluted human urine, recoveries of 99.4% (relative standard deviation (RSD) = 1.3%, n  = 3) and 102.3% (RSD = 1.8%, n  = 3) were obtained for DA additions of 1.0 and 5.0 μM, respectively. These results demonstrate that biomass‐derived conductive carbon can effectively improve the electrochemical performance of a UiO‐66‐NH ₂ ‐derived sensing interface and provide a practical route for incorporating agricultural waste‐derived carbon into electrochemical sensor design.