New water-soluble colorimetric pH and metal ione sensor based on graphene quantum dot modified with alizarine red S

A new colorimetric sensor was designed for the screening pH changes in solutions, as well as, detection of some cations. The sensor preparation includes the chemical binding of alizarine red S (ARS) as a sensor of pH and cation to graphene quantum dots (GQD). Loading ARS on GQD led to the formation of water soluble sensor which finally responded to the colorimetric detection of some cations in water. Solubility and stability of the sensor in water indicate that the sensor is an ideal system for the biological and environmental applications. To demonstrate the applicability of the new sensor, the colorimetric responds of sensor were examined for some cations including Fe3+, Co2+, Ca2+, As3+, Cd2+, Hg2+, Pb2+, Sn2+, Al3+, and Cr3+. The colorimetric detections of all the ions were performable individually in a solution. In addition, GQD-ARS as a colorimetric sensor detected Co2+ at pH < 0.6 with limit of quantification 0.08 mM and Fe3+ at 0.6 < pH < 4.0 with limit of quantification 0.03 mM in the mixture of cations.