Combination of a Sample Pretreatment Microfluidic Device with a Photoluminescent Graphene Oxide Quantum Dot Sensor for Trace Lead Detection

A novel trace lead ion (Pb2+) detection platform by combining a microfluidic sample pretreatment device with a DNA aptamer linked photoluminescent graphene oxide quantum dot (GOQD) sensor was proposed. The multilayered microdevice included a microchamber which was packed with cation exchange resins for preconcentrating metal ions. The sample loading and recovery were automatically actuated by a peristaltic polydimethylsiloxane micropump with a flow rate of 84 mu L/min. Effects of the micropump actuation time, metal ion concentration, pH, and the volumes of the sample and eluent on the metal ion capture and preconcentration efficiency were investigated on a chip. The Pb2+ samples whose concentrations ranged from 0.48 nM to 1.2 mu M were successfully recovered with a preconcentration factor value between 4 and 5. Then, the preconcentrated metal ions were quantitatively analyzed with a DNA aptamer modified GOQD. The DNA aptamer on the GOQD specifically captured the target Pb2+ which can induce electron transfer from GOQD to Pb2+ upon UV irradiation, thereby resulting in the fluorescence quenching of the GOQD. The disturbing effect of foreign anions on the Pb2+ detection and the spiked Pb2+ real samples were also analyzed. The proposed GOQD metal ion sensor exhibited highly sensitive Pb2+ detection with a detection limit of 0.64 nM and a dynamic range from 1 to 1000 nM. The on-chip preconcentration of the trace metal ions from a large-volume sample followed by the metal ion detection by the fluorescent GOQD sensor can provide an advanced platform for on-site water pollution screening.