Electrochemical detection of heavy metal ions using plasma treated laser-induced graphene

Abstract

There is a growing need to develop in-field, rapid, and reliable heavy metal ion sensors as their pollution from industrial and other processes has led to an increase in health and environmental issues worldwide. In particular, lead and cadmium are concerning because they are extremely bioavailable, soluble in water, and prevalent in aquatic and terrestrial systems, leading to contamination. Electrochemical sensors are economical, able to detect multiple heavy metal ion species, exhibit rapid response rates, and have a high ease-of-use. Ion selective electrodes can measure heavy metal ions, but they lack the portability and versatility to simultaneously detect multiple heavy metal ion species. Additionally, there is a need to be able to detection these heavy metals in a variety of environmental media. Herein, we report the first example of an oxygen plasma-treated, laser-induced graphene (LIG) platform that performs electrochemical sensing of cadmium and lead. The sensors are created through a scalable, direct-write laser fabrication process that converts polyimide into LIG, simplifying fabrication and eliminating the need for biological and chemical functionalization. The electrodes exhibited low detection limits (Cd-33.6nM and Pb-6.83nM) using differential pulse voltammetry (DPV) without the need for functionalization. The relative capacitance of the LIG electrodes steadily increased from 42.13F/g without oxygen plasma treatment to 91.86 F/g after 180 seconds treatment. Interference testing and recovery testing did not exhibit a negative effect on the sensitivity of target heavy metal ion species. These functionalization-free graphene sensors have the potential to detect of heavy metal ions across multiple environmental applications.