Label-free detection of live cancer cells and DNA hybridization using 3D multilayered plasmonic biosensor

Three-dimensional (3D) multilayered plasmonic nanostructures consisting of Au nanosquares on top of SU-8 nanopillars, Au asymmetrical nanostructures in the middle, and Au asymmetrical nanoholes at the bottom were fabricated through reversal nanoimprint technology. Compared with two-dimensional and quasi-3D plasmonic nanostructures, the 3D multilayered plasmonic nanostructures showed higher electromagnetic field intensity, longer plasmon decay length and larger plasmon sensing area, which are desirable for highly sensitive localized surface plasmonic resonance biosensors. The sensitivity and resonance peak wavelength of the 3D multilayered plasmonic nanostructures could be adjusted by varying the offset between the top and bottom SU-8 nanopillars from 31% to 56%, and the highest sensitivity of 382 and 442 nm/refractive index unit were observed for resonance peaks at 581 and 805 nm, respectively. Live lung cancer A549 cells with a low concentration of 5 × 10³ cells ml^-1 and a low sample volume of 2 μl could be detected by the 3D multilayered plasmonic nanostructures integrated in a microfluidic system. The 3D plasmonic biosensors also had the advantages of detecting DNA hybridization by capturing the complementary target DNA in the low concentration range of 10^-14-10^-7 M, and providing a large peak shift of 82 nm for capturing 10^-7 M complementary target DNA without additional signal amplification.