Quantum dot-based immunoassay enhanced by high-density vertical ZnO nanowire array

• We propose new immunosensing scheme using high-density vertical ZnO nanowire array with photostable quantum dot labeling.
• ZnO nanowire array plays an important role of providing a large surface area for the immobilization of biomolecules.
• The energy transfer between the ZnO nanowire and quantum dot was reduced by biotin–streptavidin complex.
• We demonstrated sandwich immunoassay of carcinoembryonic antigen on new platform.
• Sandwich immunoassay of CEA on ZnO nanowire with QD labeling shows low detection limit (1 pg/mL) and large detection range up to 100 ng/mL.

In this paper, we report an efficient and high-performance immunoassay platform by combining high-density vertical ZnO nanowire array with photostable quantum dot (QD) labeling. The ZnO nanowire array provides a large surface area for the immobilization of biomolecules, which makes it an efficient substrate for the immunoreaction of biomolecules. When a sandwich immunoassay with QD label was conducted on various substrates, the ZnO nanowire substrate showed stronger fluorescence signal than ZnO thin film and bare glass substrates by 3.8 and 8.5 times, respectively. We found that the fluorescence resonance energy transfer (FRET) from QD to ZnO nanowire could be suppressed by extending their distance with multilayer biotin–streptavidin complex. In addition, we demonstrated the QD-based immunoassay of carcinoembryonic antigen (CEA) on a ZnO nanowire substrate, showing an excellent immunoassay performance with a very low detection limit (0.001 ng/mL) and a large detection range up to 100 ng/mL.