Isothermal methods, such as helicase-dependent amplification (HDA), have an advantage over polymerase chain reaction for DNA amplification owing to their ease of operation. Here, we developed a new HDA method that is nanoparticle-assisted, termed nanoHDA. This method uses gold nanoparticles (AuNPs) to improve the sensitivity and specificity of the isothermal method. In HDA, the denaturation of DNA templates is mediated by helicases, but this method is limited by the low denaturation efficiency of helicases. In this report, AuNPs with preferential affinity for single-stranded DNA (ssDNA) were utilized to improve the denaturation efficiency of helicases. The same affinity property of nanoparticles can also enhance specificity by suppressing primer-dimer formation. This nanoHDA method was employed to genotype the KRAS gene in genomic DNA samples from colorectal cancer patients, as achieved by the hybridization of nanoHDA amplicons using the NanoBioArray chip.

Here, we report a method that uses gold nanoparticles (AuNPs) to enhance the specificity of DNA hybridization without reducing its detection sensitivity. The conventional stringent wash method utilizes high-temperature/low-salt conditions to enhance the specificity of DNA hybridization-based assays. This method creates a destabilizing environment for base pairing that affects specific and nonspecific duplexes. Therefore, specificity is achieved at the expense of signal intensity or sensitivity. However, in the proposed wash method, AuNPs predominantly destabilize nonspecific duplexes, offering specificity without compromising sensitivity. This AuNP wash technique has proven to be effective in detecting single nucleotide polymorphisms (SNPs) in genomic samples even at room temperature in a CD-like NanoBioArray (CD-NBA) chip. This method is also robust with sequence variation and is compatible with multiplex DNA analyses on microarrays. Thus, the AuNP wash method could potentially be useful for improving the accuracy of DNA hybridization results.