Self-Assembled Optofluidic 3D Chemical Sensors

Most plasmonic-based sensors are designed on two-dimensional (2D) planar surfaces with an enhanced electromagnetic field close to it. The enhancement effect decays in exponential form as samples move away from the surface. This results in a tiny nanoscale sensing area where long distances between the sensing position and the micro/nano specimen is undesired. Here, we introduce a method that enforces the specimen to be located close to the sensing area (plasmonic structures) using three-dimensional (3D) nano architectures self-assembled with nanoscale precision. A sensor (nanosplit rings) patterned on the inner surface of nano tubular 3D structures allows a strong interaction between the specimen and the optical sensor. The self-assembly process offers great flexibility in scaling tube diameters from 500 nm down to 100 nm. The proposed method also bridges the large gap between nanofluidics and nanoplasmonics. Here, a dynamically optofluidic sensing behavior can be achieved during biomolecular transportation in the tube, at the same time, these biomolecules can be detected via nanosplit rings inducing an electromagnetic field enhancement effect. Different 3D plasmonic structures, including nanocylinders, parallel plates, and prisms, were self-assembled and simulated. The results indicate that nanocylinders have the highest optical enhancement. Tests were first carried out to verify the nanotubes’ ability to flow liquid inside them then hemoglobin was used as the target biomolecule and was flowed in the fabricated 3D plasmonic tubular structures. Raman result demonstrates that a 22 times higher enhancement intensity was realized for hemoglobin fingerprints in the 3D structure compared to a 2D planar surface. This result shows the power of utilizing 3D architectures in nanoscale, leading to enhanced physical (optical) properties.