Graphene Encapsulated Diamond Nanoneedles as Sensitive Electrochemical Paraquat Sensor for <i>Amaranthus</i> Leaves

Ensuring food security often requires the use of pesticides, which can lead to significant ecological and human health risks due to toxicity. Paraquat (PQ), one of the most dangerous herbicides, poses severe threats to human health, including organ failure and neurological damage. Electrochemical detection methods have demonstrated significant promise for accurate and sensitive detection of PQ. Nonetheless, conventional methods for fabricating electrodes are typically complex and time-consuming, which hinders their applicability in fast and efficient sensing systems. In this study, graphene-encapsulated diamond nanoneedles (GDNs) were synthesized as robust electrodes using a microwave plasma-enhanced chemical vapor deposition system. The microstructural analysis revealed that the diamond nanoneedles were encapsulated by graphene sheaths. The GDNs demonstrated desirable conductivity and electrochemical activity, attributed to the coexistence of the diamond and graphite phases. Using these GDN electrodes, differential pulsed anodic stripping voltammetry in a 0.1 M phosphate buffer solution enabled impressive detection of PQ, achieving a limit of detection as 0.002 μM and 2.97 μA/μM sensitivity at an optimal condition in the linearity range of 0.1-0.8 μM. The electrodes demonstrated high repeatability, selectivity, and remarkable recovery in real samples, including seawater and washed water from Amaranthus leaves, highlighting potential as a sensing material for the real-time monitoring of PQ.