Dual-form iron on carbon nanohorns for wide-pH-range electrochemical sensing of levodopa

Levodopa is a first-line therapeutic agent for Parkinson's disease, and real-time monitoring of its plasma concentration is crucial for optimizing personalized treatment strategies. In this study, iron/carbon nanohorn composites (Fe/CNHs(2)) featuring a dual-form Fe structure, in which atomically or sub-nanocluster dispersed Fe species coexist with Fe nanoparticles, were synthesized via a one-step positive-pressure arc-discharge method. The fabricated Fe/CNHs(2)-based sensing electrode exhibited excellent electrocatalytic activity toward levodopa, achieving a high sensitivity of 0.062 µA µM⁻¹ and a low detection limit of 0.75 µM. Moreover, the sensor enabled stable levodopa detection over a broad pH range of 3.6-9.5. Kinetic studies revealed that the wide pH tolerance originated from the enhanced structural stability provided by strong Fe-C interfacial interactions, together with an adsorption-controlled reaction process in which the rate-determining step showed limited dependence on proton concentration. Theoretical calculations further confirmed that the introduction of Fe active centers substantially decreased the reaction energy barrier. This work provides a new design strategy for metal-carbon composites with dual-functional synergy, and the developed sensor holds considerable potential for monitoring levodopa levels during Parkinson's disease treatment.