Dual Linear Range Laser-Induced Graphene-Based Sensor for 4-Nitrophenol Detection in Water

Electrochemical sensors provide an excellent platform for in situ water pollutant detection. Graphene-based electrochemical sensors have been effective in the analysis of different genres of pollutants. However, the complex, chemically intensive steps of graphene fabrication and its modification pose challenges to the large-scale application of these sensors. Laser-induced graphene (LIG) is a promising technology with a simple, rapid, chemical-free, mask-free, and scalable solution to produce graphene-based electrochemical sensors. Among a diverse array of water pollutants, 4-nitrophenol (4-NP) is a critical pollutant owing to its acute toxicity and adverse health effects on humans and other living organisms. It is known to have carcinogenic, mutagenic, and teratogenic effects on aquatic life, plants, and human beings at very low concentrations. This work demonstrated a simple nonreceptor-based electrochemical sensor for 4-NP detection by laser-induced graphene (LIG) printed on polyimide (PI) films. The laser irradiation of polymeric films results in 3D porous graphene structure formation, which increases the electron transfer rate as well as the electrochemically active surface area. The LIG sensor was fabricated by optimizing laser settings and characterized by SEM, TEM, XRD, Raman spectroscopy, XPS, TGA, and EDS analysis. Using linear sweep voltammetry, the LIG sensors demonstrated linear behavior in two concentration ranges from 0.15 to 1 μM and 2.5 to 100 μM with a detection limit of 95 nM. A higher sensitivity was observed for the lower concentration range, which could be attributed to increased electrochemical sites for 4-NP in the porous LIG. The sensor showed good selectivity toward 4-NP in the presence of its isomers and other phenolic compounds. Furthermore, it showed good selectivity in sewage samples spiked with different 4-NP concentrations. The enhanced sensitivity of LIG toward 4-NP at a lower concentration range could pave the way for high-performance sensors using LIG for environmental and other applications.