Laser induced graphene and Cu nanoparticles functionalized microtextured chemiresistive sensor for the fast detection of aqueous Hg²⁺

A phenol-formaldehyde co-polymeric film patterned with laser induced graphene (LIG) microchannels (100 µm wide × 100 µm height with 400 µm interspacing) was synthesized and used as a chemiresistive sensor for mercuric ions (Hg²⁺) in water. The LIG transformation of the microtextured region in the film enhanced the electrical conductivity (sheet resistance = 2.8 kΩ/sq) of the material. The microchannels intensified wettability of the film via a fast (∼1 min) passive capillary flow when the film was dipped in test sample for sensing. The Cu nanoparticles in situ included in the chemiresistive film served as the recognition element for Hg²⁺ ions via complexation formation. The sensor showed linear (R² > 0.995) responses over the low (2–30 ppb) as well as high (0.03–20 ppm) concentration ranges, with the sensitivities of 0.64 Ω/ppb and 66.92 Ω/ppm, respectively. The sensor also showed a fast response without interference from co-metal ions commonly present in wastewater. The method of fabricating the chemiresistive Hg²⁺ sensor in this study is easy, and its scope can be broadened to measure a wide range of analytes by functionalizing the substrate with a suitable recognition element.