Interfacial engineering of graphenic carbon electrodes by antimicrobial polyhexamethylene guanidine hydrochloride for ultrasensitive bacterial detection

Pathogenic bacteria are severe threats to public health. Existing bacterial detection methods are often time-consuming and costly. Impedance-based electrochemical sensors using carbon electrodes have been explored for bacterial detection. However, the pristine carbon surface is inefficient in attracting bacterial cells. Here, we demonstrate an interfacial engineering method for graphenic carbon (GC) electrodes by using a common antibacterial material to achieve ultrasensitive bacterial detection. Polyhexamethylene guanidine hydrochloride (PHMG) is a broad-spectrum antimicrobial material. We first conjugated perylene bisimide (PBI) with PHMG to form a new PBI-PHMG compound. PBI-PHMG with an optimal PBI content can retain PHMG's intrinsic antibacterial activity while PBI anchors PBI-PHMG on the GC surface via strong pi-pi interactions. The resulting PBI-PHMG modified GC electrodes have positively charged surfaces, which effectively attract and inactivate bacterial cells. Cytoplasm materials released from damaged cells change the impedance of GC electrodes significantly, leading to considerably enhanced bacterial detection sensitivity down to 2 CFU mL⁻¹ for both E. coli and S. aureus within 30 min of incubation time. The facile preparation, short detection time and high sensitivity of the impedance sensors based on the modified GC electrodes are promising for practical applications such as portable devices for point-of-use bacterial detection.