Nanomedicine is just starting to reshape clinical practice and since the last decade magnetic nanoparticles have drawn increasing attention to the development of different types of magnetic biosensors. This is because of their high physical and chemical stability and that they are not generally affected by reagent chemistry or exposure to light. Magnetic nanoparticle-based biosensors offer an attractive and cost-effective route for detection of biomolecules, since they are relatively inexpensive to produce and easily made biocompatible.
We have developed a diagnostic method, based on oligonucleotide-functionalized magnetic nanoparticles, for detection of specific DNA sequences. These DNA sequences are amplified through an isothermal amplification technique called rolling circle amplification (RCA) which generates micrometer sized RCA products after one hour of amplification. The oligonucleotides attached to the surface of the magnetic nanoparticles are complementary to repeating sequences of the RCA products. In a high salt and high temperature environment, the oligonucleotide-functionalized magnetic nanoparticles bind to the RCA products and forms large aggregates visible to the naked eye. This allows for simple qualitative detection of specific DNA sequences where there is no need for complicated and expensive readout instrumentation.
Our developed method yields visible aggregates in the presence of at least 1 amol of DNA target in less than 2 hours; targeting the antibiotic resistance gene sul1. Specificity tests shows that there is no non-specific aggregation detected in samples containing up to 20 fmol of non-complementary amplified DNA.
This method is a versatile and simple tool for detecting pathogenic DNA with no read-out equipment required.