A bio-bar-code assay based upon dithiothreitol-induced oligonucleotide release.

The recently developed bio-bar-code assay for the PCR-less detection of protein and nucleic acid targets has been shown to be extraordinarily sensitive, exhibiting low attomolar sensitivity for protein targets and high zeptomolar sensitivity for nucleic acid targets. In the case of DNA detection, the original assay relies on three distinct oligonucleotide strands on a single nanoparticle for target identification and signal amplification. Herein, we report the development of a new nanoparticle probe that can be used in the bio-bar-code assay, which requires only one thiolated oligonucleotide strand. This new assay relies on the ability to liberate the adsorbed thiolated oligonucleotides from the gold nanoparticle surface with dithiothreitol (DTT), which simplifies the assay and increases its quantitative capabilities. The utility of this new DTT-based system is demonstrated by detecting a mock mRNA target using both fluorescent and scanometric assay readouts. When the scanometric readout is used, the sensitivity of the assay is 7 aM and quantification can be accomplished over the low-attomolar to the mid-femtomolar concentration range.