Fabrication of a paper-based sensor from graphene quantum dots coated with a polymeric membrane for the determination of gold(III) ions.

A novel paper-based sensor using graphene quantum dots (GQDs) as a colorimetric probe for Au3+ determination has been developed. The paper sensor was fabricated by the adsorption of GQDs onto cellulose filter paper and then coating with a PVC membrane. The PVC membrane was plasticized with o-NPOE containing potassium tetrakis(4-chlorophenyl)borate (KTpClPB) as a lipophilic cation-exchanger. According to the ion-exchanged mechanism between the lipophilic phase and aqueous phase, Au3+ in the aqueous solution was extracted to the lipophilic phase on the paper layer. Then, adsorbed GQDs on the paper could selectively reduce Au3+ to elemental gold (Au0). The generated gold nanoparticles (AuNPs) resulted in the color of the paper turning from pale yellow to pink, which was recorded by using CIE L*a*b* color space. Under optimized conditions, the change in the color difference (ΔE) was related to the concentration of Au3+ in a working linear range of 200-1000 μM and the detection limit was found to be 70 μM. The proposed sensor was successfully applied to the determination of Au3+ in real water samples. The results were in favorable agreement with standard inductively coupled plasma-optical emission spectrometry (ICP-OES) results.