Engineering a 3D-Printed PLA-Based Graphene-NiCo2S4 Electrochemical Platform for Simultaneous Detection of Cd2+, Pb2+, and Hg2+ in Fish and Water

We report a low-cost, portable, and sustainable electrochemical sensor was developed for the simultaneous determination of Cd2+, Pb2+, and Hg2+ by integration of a graphene−nickel cobalt sulfide (Gr−NiCo2S4) nanocomposite with a three-dimensional (3D)-printed polylactic acid electrode. The Gr−NiCo2S4 nanocomposite was synthesized using simple liquid-phase exfoliation and hydrothermal methods and characterized by XRD, Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), TEM, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The XRD data confirmed the successful synthesis of NCS and Gr-NCS. SEM analysis showed the hierarchical porous nature of Gr-NCS, which provided the sites for metal ion accumulation and enhanced electroactive sites. Using electrochemical impedance spectroscopy analysis, the lowest Rct (118 Ω) obtained for Gr-NCS showed comparatively better electrochemical performance than Gr and NCS. The customized 3D-printed electrode exhibited better conductivity and rapid electron transfer kinetics, enabling sensitive detection of heavy metals using differential pulse anodic stripping voltammetry (DPASV). Under optimized conditions, the sensor achieved detection limits of 0.005, 0.014, and 0.008 μg mL−1 for Cd2+, Pb2+, and Hg2+, respectively. The use of the 3D electrode demonstrated high selectivity against common interfering ions, good reproducibility (relative standard deviation <1.9%), and stable performance over 20 days. Good recovery values of 93−105% confirmed the accuracy of the method. The developed sensor was successfully applied for the determination of heavy metals in fish and water samples using DPASV, and the obtained results were found comparable with inductively coupled-mass spectrometry. Based on the literature survey, this is the first demonstration of Gr-NCS as a sensing material for simultaneous analysis of multiple metals using a 3D-PLA electrode. The combination of additive manufacturing with Gr-based multifunctional nanomaterials provided a scalable, customizable, and cost-effective platform for portable electrochemical sensing of metal ions.