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Abstract
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In recent years, increasing interest has focused on gold nanoparticle-core spherical nucleic acids (AuNP-core SNAs), in which AuNPs are densely functionalized with linear DNA or RNA.[1] AuNP-core SNAs can be programmed base by base to accurately assemble themselves, resulting in the SPR-related color change. This observable color change can provide appropriate platforms for target-responsive nucleic acid detection. [2-4] MicroRNAs (miRNAs) are a broad family of non-coding, single-stranded RNA molecules with a length of about 22 nucleotides that regulate a wide range of biological activities.[5] They have been found as biomarkers for the early identification and screening of cancer. So, MiRNA analysis is extremely useful in cancer treatment and monitoring. In this study, hairpin DNA-coated gold nanoparticles known as hairpin spherical nucleic acids (H-SNAs) are described to identify miRNA-30a as a candidate biomarker. The target miRNA induces single-component assembly of H-SNAs and provides a target-responsive colorimetric strategy. In the absence of the target miRNA a hairpin secondary structure is formed by a four-nucleotide palindromic sequence flanking the recognition loop on each side. However, the presence of the target miRNA which is complementary to the hairpin recognition loop breaks the stem-loop secondary structure, exposing the outer edge of the stem sequence (outer palindromic arm) and favoring single component assembly formation and subsequent red to blue colorimetric response. The colorimetric signal from the single-component assembly of H-SNAs was converted into measurable intensities associated to the three primary colors, red, green, and blue (RGB) using a smartphone. The data was then processed using the principal component analysis (PCA), and the first PC values were used as a calibration response and plotted against the concentration of the miRNA-30a in the samples. The obtained quantification limit was 5 nM and a linear response established for
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