DNAzyme assisted recycling amplification method for ultrasensitive amperometric determination of lead(II) based on the use of a hairpin assembly on a composite prepared from nitrogen doped graphene, perylenetetracarboxylic anhydride, thionine and gold nanoparticles

A Pb(II)-DNAzyme is used in an amperometric method for the determination of Pb(II). The method is based on two feedback processes. In the first, the Pb(II)-DNAzyme initiates a reaction in presence of Pb(II) in a micro-tube to release a linear DNA (S-1). In the second, the S-1 triggers the recycling amplification between two types of hairpin-shaped DNA templates (H-1 and H-2) which consist of a primer sequence and a Pb(II)-DNAzyme substrate sequence. The Pb(II)-DNAzyme has excellent cleavage specificity toward the substrate sequence in S-1 that combined firstly with H-1 and then is linked to H-2. This process will connect H-1 and H-2. After hybridization with H-1 and H-2 to form two DNA complexes, S-1 is released and initiates the next recycling process. This results in efficient amplification. A glassy carbon electrode (GCE) was immersed into solution of HAuCl4 to electrodeposit a layer of gold nanoparticles. This is followed by the assembly of the hairpin probe H-1 on the GCE. In addition, a nanohybrid consisting of 3, 4, 9, 10-Perylenetetracarboxylic acid (PTCA) and nitrogen-doped graphene (NG) was loaded with electroactive thionine (Thi) and gold to form nanoparticles of type NG-PTCA-Thi-Au. This is responsible for generating the amperometric signal (best measured at around -0.30 V vs. SCE) and also acts as the reducing agent for synthesizing the NG-PTCA-Thi-Au nanohybrid. H-2 is immobilized on NG-PTCA-Thi-Au to form a new tracer label. The concentration of Pb(II) in a solution can be quantified by determination of the amount of cleaved S-1. The method has high sensitivity and selectivity for Pb(II). The detection limit is 0.42 pM (S/N = 3), and the detection range extends from 1 pM to 1000 nM. Graphical abstract Schematic representation of electrodes for the determination of the lead ions (Pb2+). The sensor is using Pb2+-DNAzyme assisted recycling amplification based on hairpin assembly on a composite prepared from nitrogen doped graphene, perylenetetracarboxylic anhydride, thionine and gold nanoparticles (NG-PTCA-Thi-Au). This versatile platform expands studies on the detection of heavy metal ions.