A highly sensitive, dual-readout assay based on self-assembly of two functional nanoparticles for homogeneous detection of protein biomarkers

Rapid, simple, and accurate quantitation of protein biomarkers is of great importance for biomedical diagnostics. Herein, we describe a dual-readout (colorimetric and potential) sensing strategy, which allows homogeneous detection of protein biomarkers with an ultrabroad detection range. To do so, two functional nanoparticles are prepared, including an antifouling magnetic nanoparticle (ANP) serving as a scaffold and a DNA-modified gold nanoparticle (DNA-GNP) used to generate both color and potential signal. In the presence of target protein, it will induce the conformation switch of DNA probes and thus mediate the assembly of two nanoparticles through strong hydrophobic interaction. Then, the resulting core-shell nanostructures can be analyzed by either optical or potential signal because of the self-assembly of highly negatively charged GNPs onto zwitterionic ANPs. The colorimetric mode enables simple, straightforward, and cost-effective detection of interferon-γ (IFN-γ) at nanomolar concentration by the naked eye. While plenty of negatively charged groups carried by DNA-GNPs can produce amplified potential signals, making the detection limit down to 78.8 fM. Compared with other reported strategies for IFN-γ detection, this homogeneous, dual-readout detection platform is composed just of two functional nanoparticles, providing a rather simple and low-cost method for cytokine assay.