Electrochemical sensor for nitrite detection in water samples using flexible laser-induced graphene electrodes functionalized by CNT decorated by Au nanoparticles

This paper reports on a sensitive, selective and reproducible electrochemical sensor for nitrite detection based on laser-induced graphene (LIG) electrode patterned onto a flexible poly(imide) substrate and further modified by COOH functionalized multiwalled carbon nanotubes (f-MWCNT) and gold nanoparticles (AuNPs) films. According to Raman spectroscopy, photoluminescence spectroscopy and scanning electron microscopy, the laser induced photothermal reactions produce ultrathin graphene-like sheets emerging from the substrate, which stay connected to the surface forming a three-dimensional microporous structure. This process permits to scribe in a single step and mask-free, working, counter and reference electrodes on a polymeric substrate. Cyclic voltammetry and electrochemical impedance spectroscopy performed in ferri-ferrocyanide redox pair show that the electroactive area of LIG modified by f-MWCNT- AuNPs is increased and the charge-transfer resistance is diminished in comparison to the modification by each nanomaterial alone. The sensor has a linear characteristic (R2 = 0.996) in the nitrite concentration range from 10 μM to 140 μM and a limit of detection of 0.9 μM following the 3Sb/m method. In presence of typical interfering ions, added in 100-fold excess, the sensor shows a relative standard deviation less than 10%. The results show that a single LIG/f-MWCNT-AuNPs electrode can perform electrochemical detection of nitrite for at least seven consecutive runs with a low signal variation of 2.63% corresponding to a nitrite concentration of 90 μM. Furthermore, seven different electrodes fabricated in the same batch performed identically, with a low signal variation of 2.80% corresponding to a nitrite concentration of 90 μM.