A sensitive DNA electrochemical biosensor based on magnetite with a glassy carbon electrode modified by muti-walled carbon nanotubes in polypyrrole

A novel sensitive electrochemical biosensor based on magnetite nanoparticle for monitoring DNA hybridization by using MWNT-COOH/ppy-modified glassy carbon electrode is described. In this new detection system, mercapatoacetic acid (RSH)-coated magnetite nanoparticles, capped with 5′-(NH₂) oligonucleotide, is used as DNA probe to complex 29-base polynucleotide target (a piece of human porphobilinogen deaminase PBGD promoter from 170 to 142). Target sequence hybridized with the probe results in the decrease of the reduction peak current of daunomycin connected with probe. The response of non-complementary sequence was almost the same as the blank, and the response of three-base mismatched sequence within 29-base polynucleotide was obviously distinguished from complementary sequence, which can easily identify point mutation of DNA. The equation of calibration plot is i_p (μA) = 0.8255 − 0.0847c_{target oligonucleotide} × 10¹³ in the range of 6.9 × 10⁻¹⁴ to 8.6 × 10⁻¹³ mol/L, and correlation coefficient is 0.9974. The detective limit is 2.3 × 10⁻¹⁴ mol/L of target oligonucleotide. This device can be optimized for the detection of complex sequence.