Synthesis of Polymethylene Blue Nanoparticles and their Application to Label-Free DNA Detection

Polymethylene blue nanoparticles were prepared using a reverse microemulsion system with ammonium persulfate as the oxidant at room temperature. Polymethylene blue nanoparticles (50nm diameter) with enhanced electroactivity were superior to methylene blue and polymethylene blue obtained by electrochemical polymerization. To further verify the electrochemical behavior of the polymethylene blue nanoparticles, a label-free DNA sensor was fabricated with direct immobilization of the nanoparticles. This approach increased the number of redox probes and further amplified the signal. The current of polymethylene blue nanoparticles on the electrode surface was dependent on the access of counterions to the electrode surface. Upon hybridization of DNA, the transfer of the counterion was partially blocked, which resulted in a decrease in current. The reduction of the current was directly proportional to the concentration of DNA from 0.2PM to 0.2fM, with a detection limit of 0.087fM. The label-free electrochemical biosensor provided good selectivity, favorable stability, and reproducibility.