Electrochemical gene sensor for Mycoplasma pneumoniae DNA using dual signal amplification via a Pt@Pd nanowire and horse radish peroxidase

A dually amplified DNA biosensor was constructed for the determination of the DNA of Mycoplasma pneumoniae (M. pneu). A gold electrode was modified with 3,4,9,10-perylenetetracarboxylic acid dianhydride (PTCDA; a π-stacking perylene semiconductor dye with outstanding electronic and optical properties), a layer of gold nanoparticles (nano-Au), and capture DNA. Pt@Pd nanowires served as carriers for the coimmobilization of complementary probe (CP2) and the mediator thionine (Thi). Horseradish peroxidase (HRP) acted as a blocking reagent and signal enhancer. Following base pairing, the modified Pt@Pd nanowires were captured on the surface of the gold electrode. After addition of H2O2, the Pt@Pd nanowires and HRP both catalyzed the reduction of H2O2 and promoted the electron transfer via the mediator Thi, resulting in an amplified electrochemical signal. The electrical signal, best measured at a working voltage of −200 mV (vs a SCE), is logarithmically related to the concentration of the M. pneu DNA in the 0.1 pM to 20 nM concentration range, and the detection limit (at an S/N ratio of 3) is 0.03 pM. The assay is robust, sensitive and specific. Conceivably, it is a cost-effective alternative to the established PCR method for the detection of M. pneu in clinical samples.