Assessment of microRNA-21 using gold nanoparticle-DNA conjugates based on colorimetric and fluorescent detection

The miR-21 detection is essential for the accurate and early diagnosis or prognosis of most diseases. In the current study, the miR-21 detection method was performed based on the exploitation of the simple colorimetric biosensor due to the unique surface plasmon resonance (SPR) absorption of gold nanoparticles. AuNPs were functionalized with the specific DNA probes on the gold surface by Au-SH bond. Two strategies are proposed to detect the miR-21. In the first strategy, probes (DNA1 and DNA2) were complementary to the sequence of the miR-21. When miR-21 is introduced, the hybridization reaction is triggered between the golden nanoparticles- (GNP)-DNA conjugates and targets, resulting in changes in SPR absorption band and macroscopic color of the AuNPs solution. In the second strategy, we used a fluorescence sequence (DNA3-FAM), which was complimentary of DNA1. The DNA3-FAM was released after hybridization of miR-21 with DNA1 and DNA2. The free DNA3-FAM sequences in plate wells containing 1% agarose gel were assessed by fluorescent microscope. The combination of two strategies and conventional equipment such as UV–Vis spectrometers and fluorescent microscopes could be useful in detecting the desired miRNAs (miR-21).