A laser-induced graphene (LIG) modified with chitosan (Chit) and conducting polymer polyfolate (PFA) was used as a base to develop a flat and flexible pH sensor. LIGs were formed using two different irradiation wavelengths of 355 nm and 532 nm. Depending on the wavelengths, the obtained electrodes were named LIG355 and LIG532. Microscopic imaging revealed that the bare LIG electrode surface had rough structures after laser treatment giving hydrophilic properties, and that PFA forms fibre-like structures on Chit coated LIG. Electrochemical investigation with the redox probe demonstrated that diffusion is a limiting process at the bare and modified LIG electrodes. A capacitive behaviour was observed from electrochemical impedance spectra at bare electrodes, showing a rather rough interface at LIG355 but a microporous one at LIG532. The developed flat and flexible electrode was sensitive to pH in the region from 6.0 to 9.0. In the studied pH range, the sensitivity was 27.86 ± 0.81 for PFA/Chit/LIG355 and 30.32 ± 0.50 mV/pH for PFA/Chit/LIG532 with moderate stability for a period of more than two months.

Determination of pesticides is important for human health. Sensors are one of the best solutions because they do not require a long sample preparation and can be used not only in a laboratory. Electrochemical sensors can be easily minimised and employed for the detection of pesticides in liquid samples such as ground or wastewater. Conducting polymers have a few roles in electrochemical sensors, therefore, they can be good candidates for sensor development. Electrochemically co-polymerised folic acid and riboflavin as well as folic acid and L-lysine were employed for the detection of atrazine using square wave voltammetry. The co-polymer composition was optimised and characterised electrochemically and spectroscopically. The optimal composition of polyfolic acid and poly-L-lysine co-polymer electrosynthesised from the monomer ratio 1:10 was the best in terms of stability and sensitivity to atrazine. The best method was the square wave voltammetry showing the best sensitivity to atrazine 198 ± 1 μA/μM cm2, and the limit of detection was 14.8 nM. However, the sensitivity in tap water was significantly lower but still suitable for atrazine detection by the spike method.

Applications of conductive polymers in sensors