Metal enhanced fluorescence improved protein and DNA detection by zigzag Ag nanorod arrays

• Metal enhanced fluorescence of zigzag Ag nanorods array has been investigated.
• Zigzag Ag nanorods with the folding number 7 have the highest scattering intensity.
• A 14-fold enhancement factor (EF) is obtained for neutravidin protein detection.
• An EF of 28 is achieved for the oligonucleotides hybridization detection.
• The detection limit of the target oligonucleotide is 0.01 pM.

As metal nano-arrays show great potential on metal enhanced fluorescence (MEF) than random nanostructures, MEF of Ag zigzag nanorod (ZNR) arrays made by oblique angle deposition has been studied for biomolecule-protein interaction and DNA hybridization. By changing the folding number and the deposition substrate temperature, a 14-fold enhancement factor (EF) is obtained for biotin-neutravidin detection. The optimal folding number is decided as Z=7, owing to the high scattering intensity of Ag ZNRs. The substrate temperature T=25 °C and 0 °C slightly alters the morphology of Ag ZNRs but has no big difference in EF. Further, Ag ZNRs deposited on a layer of Ag film have been introduced to the DNA hybridization and a significant signal enhancement has been observed through the fluorescence microscope. Through a detailed quantitative EF analysis, which excludes the enhancing effect from the increased surface area of ZNRs and only considers the contribution of MEF, an EF of 28 is achieved for the hybridization of two single-stranded oligonucleotides with 33 bases. Furthermore, a limit of detection is determined as 0.01 pM. We believe that the Ag ZNR arrays can serve as a universal and sensitive bio-detection platform.