Biodegradable asparagine–graphene oxide free chlorine sensors fabricated using solution-based processing

Chlorine is used as a powerful disinfectant in several water-related industries and in the food industry to remove bacteria and other harmful contaminants. In this paper, we present a solution-based fabrication process for biodegradable free chlorine sensors using asparagine that is functionalized onto graphene oxide (GO). An ink solution of asparagine, NaOH, and GO was mixed at room temperature for 24 h before being centrifuged and washed with deionized (DI) water and ethanol, then stored in a solution of equal parts DI water and ethanol. The formulated ink was drop-casted onto a screen-printed carbon electrode (SPCE), spin-coated to achieve a uniform film, and then dried. The sensor showed high sensitivity of 0.30 μA ppm^-1 in a linear range of 0 to 8 ppm with a hysteresis-limited resolution of 0.2 ppm, very high selectivity in the presence of commonly interfering ions, and an operating voltage well below the reduction potential of dissolved oxygen. The sensor response time to achieve a steady state was 50 s, and it showed little change in its drift response over 16 h and over a temperature range of 10 to 45 °C.