Determination of hypoxia-inducible factor-1 by using a ratiometric colorimetric test based on click-mediated growth of gold nanoparticles

The authors describe a significantly improved colorimetric nanoprobe for the determination of transcription factors (TFs). It is making use of click-mediated growth of gold nanoparticles (AuNPs) to amplify the signal-to-noise ratio. Hypoxia-inducible factor-1 (HIF-1) is an important TF that acts as a mediator of cell response to hypoxia. So, the detection of HIF-1 was chosen as the model analyte. Specifically, target HIF-1 is designed to bind to the hypoxia response element within DNA duplex. The click chemistry between the DNA duplex and alkynyl-functionalized AuNPs (AF-AuNPs) is then inhibited because of significant steric hindrance. As a result, the AF-AuNPs grow into larger-sized highly-aggregated irregular nanostructures, which in turn enable colorimetric determination. The ratio of absorbances at 620 and 560 nm increases in the 0.5 to 10 nM HIF-1 concentration range, and the detection limit is 0.27 nM. This is better by a factor of 100 than that of aggregation-based colorimetric assays. The nanoprobe is selective and can be used in complex samples. Conceivably, it may also be extended to the determination of other TFs by simply changing the used DNA duplex. Graphical abstract Schematic of a nanoprobe for detecting hypoxia-inducible factor-1 (HIF-1). Three concepts are involved: the binding of HIF-1 and hypoxia response element, the Cu⁺-catalyzed click chemistry between P1/P2 duplex and alkynyl-functionalized AuNPs (AF-AuNPs), and the AuNPs growth with hydroxylamine and HAuCl₄.