A novel fluorescence aptamer biosensor for trace Pb(II) based on gold-doped carbon dots and DNAzyme synergetic catalytic amplification

Gold-doped carbon dots (CDAu) and carbon dots (CD) were quickly prepared by microwave irradiation procedure, using glucose as carbon source and HAuCl4 as doped reagent. Both CDAu and DNAzyme of Pb(II)-aptamer (Apt)-heme exhibit catalysis of the new fluorescence indicator reaction of H2O2-3,3',5,5'-tetramethylbenzidine (TMB) to produce the oxidized TMB (TMBOX) with a fluorescent peak at 404 nm. The Apt can be adsorbed on the CDAu surface to form a CDAu-Apt conjugate to inhibit the catalysis to cause the fluorescence intensity decreasing. The target for Pb(II) combined with the Apt to form stable G-quadruplex complex and free CDAu, in which G-quadruplex reacted with heme to form G-quadruplex/heme DNAzyme. Both the free CDAu and DNAzyme catalyzed in synergetic to produce TMBOX, and the fluorescence enhanced greatly. Thus, a new and highly sensitive synergetic catalytic fluorescence method for the determination of 0.0005-0.46 mu mol/L Pb(II) was established, with a detection limit of 0.25 nmol/L, its sensitivity is several orders of magnitude higher than most previously reported Pb2+ sensors. Compared with the CD, the CDAu has a quantum yield increase of 150%.