Question

In regard to a colorimetric biosensor using gold nanoparticles modified with single-stranded DNA (DNA-AuNP Hybridization Sensor), what limit of detection and sensitivity are. In other words, explain the limit of detection and sensitivity in complete and clear manner. Then explain what good sensitivity and LOD would look like in such an experiment.

Additional information:

AuNps are attached to the Thio group at the end of DNA strands.

-S-(5')GCG CTA GAG TCG TTT CCT ATC GAC CAT GCT(3')-5- (3')CGC GAT CTC AGC AAA GGA TAG CTG GTA CGA(5') Figure 3. Simplified illustration of nanoparticles (yellow circles) connected via hybridized DNA strands Since each nanoparticle will be modified with more than one DNA strand, presence of "Comp" will lead to an aggregation of many nanoparticles. The aggregation of the nanoparticles can lead to a detectable colour change from red to purple/blue. Comp DNIA Red Solution Purple Solution Figure 4. Illustration of nanoparticle aggregation resulting from hybridization with Comp DNA. Black circles represent nanoparticles, and the squiggles represent DNA monomers. Colour change may not be obvious by eye and requires UV-vis spectroscopy for careful analysis.

Answer 1

A novel, high sensitive and specific DNA assay based on gold nanoparticles (AuNP) colorimetric detection and hybridization chain reaction (HCR) amplification has been demonstrated in this article. Two hairpin auxiliary probes were designed with single-stranded DNA (ssDNA) sticky ends which stabilize AuNPs and effectively prevent them from salt-induced aggregation. The target DNA hybridized with the hairpin auxiliary probes and triggered the formation of extended double-stranded DNA (dsDNA) polymers through HCR. As a result, the formed dsDNA polymers provide less stabilization without ssDNA sticky ends, and AuNPs undergo aggregation when salt concentration is increased. Subsequently, a pale purple-to-blue color variation is observed in the colloid solution. The system is simple in design and convenient in operation. The novel strategy eliminates the need of enzymatic reactions, separation processes, chemical modifications, and sophisticated instrumentations. The detection and discrimination process can be seen with the naked eye. The detection limit of this method is lower than or at least comparable to previous AuNP-based methods. Importantly, the protocol offers high selectivity for the determination between perfectly matched target oligonucleotides and targets with single base-pair mismatches.

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