A novel strategy was developed to extract, detect, and quantify trace-level DNA. For the extraction step, a composite of methylene blue (MB), poly(acrylic acid) (PAA), and modified iron oxide magnetic nanoparticles (IOMNPs) (PAA/IOMNPs) was used to adsorb DNA from the sample. MB-PAA/IOMNPs with adsorbed DNA were then separated from the solution with an external magnet and MB-DNA was eluted from PAA/IOMNPs with acetic acid. In the detection step, MB-DNA was adsorbed on the surface of 3-aminopropyltriethoxysilane (APTES)-modified glassy carbon electrode via electrostatic force. DNA was quantified by measuring the oxidation peak of MB at a potential -0.13 V vs. Ag/AgCl using differential pulse voltammetry. Under the optimal experimental conditions, the DNA sensor showed linear ranges from 0.001 to 0.005 pg μL-1, 0.005 to 0.070 pg μL-1, and 0.070 to 0.400 pg μL-1 and a limit of detection of 0.87 fg μL-1. The proposed sensor detected trace DNA in real samples with recoveries that ranged from 80.4 to 90.4%.
Keywords: 3-aminopropyltriethoxysilane-modified electrode; Differential pulse voltammetry; Electrochemical sensor; Iron oxide magnetic nanoparticles; Methylene blue; Trace DNA.