Understanding Baseline Drift in Laser-Induced Graphene Electrodes and Its Impact on Heavy Metal Detection by Anodic...

The planar Laser-Induced Graphene (LIG) patterned electrochemical sensor device was fabricated with a CO₂ infrared laser on a commercial polyimide film. We investigated the dynamic surface and baseline current changes in LIG versus Glassy carbon (GC) electrodes after multiple square wave voltammetry (SWV) scans in 0.1 M acetate buffer (pH 4.5), using OCP and EIS techniques. Additionally, bismuth-film coated on LIG (Bi/LIG) and GC (Bi/GC) electrode were characterized and compared for detection of heavy metal ions using anodic stripping voltammetry (ASV). The electrochemical deposition and stripping processes of Pb, Cu, Zn and Cd on these Bi/LIG were studied to obtain mechanistic insights. Results show that the nature and condition of the LIG substrates have a profound effect upon the nucleation and growth of the bismuth deposit. A simple baseline correction strategy was used on LIG device for detection of multiple heavy metal ions (i.e. Pb²⁺, Cd²⁺, Cu²⁺ and Zn²⁺) in 0.1 M acetate buffer (pH 4.5) with square wave anodic stripping voltammetry (SWASV) and the corresponding limit of detections (LOD) are found to be 14.82 ppb (Zn²⁺), 12.11 ppb (Cd²⁺), 11.55 ppb (Pb²⁺), and 14.64 ppb (Cu²⁺) respectively. The Bi/LIG sensor device was further tested for metal analysis in a real-world sample. Results show that baseline correction provides accurate Pb²⁺ detection despite limitations towards other metal ions. LIG electrodes also provide better detection for Zn²⁺ and Cu²⁺ than GC electrode. This study provides the methods and mechanistic understandings for the use of porous and heterogeneous LIG materials in the analytical detection of multiple heavy metals.