Unlike prism-based metallic film sensors, plasmonic nanostructure sensors exhibit stronger near-field confined capacity on the surface which have recently attracted their use in different areas such as medical diagnosis. Plasmonic nanostructures comprise surface plasmon resonance that can be directly excited by free space incident light which can lead to the development of ultra-compact and multiplexed sensing applications. This, however, requires significant improvement in the materials and design approach that will lead to more sensitive and relatively portable nanostructures relevant for emerging and future applications.
Lithography-based top-down nanofabrication technologies are currently used in the fabrication of most plasmonic nanostructure sensors. Even though these technologies are capable of producing products with high precision, stability and repeatability, they are generally expensive, time-consuming and produce low yields and small footprint sizes that are economically unviable. For instance, these shortcomings hinder the investigation of angle-depended to sensing properties. Alternatively, fabrication of low cost large-scale ordered nanostructure arrays has been affected by the low sensing properties of the sunken nanostructures. To this end, researchers have been looking for alternatives and have identified large-scale and low-cost biosensors with convex nanostructures as a promising solution.
Nanjing University researchers: Dr. Yuzhang Liang, Zhiyong Yu and Professor Ting Xu developed a low-cost innovative centimeter-scale and high sensitivity sensing platform. The platform was fabricated through a low-cost transfer nanoprinting technique based on an ultrathin anodic aluminum oxide membrane. Their work is currently published in the research journal, Advanced Optical Material.
The sensing substrate comprised of highly ordered hexagonal nanodisk arrays on an opaque gold film that was initially deposited on a silica substrate. The authors simultaneously observed two resonant modes in the plasmonic nanodisk structure at nonzero incident angles. This was attributed to the occurrence of the surface plasmon polariton Bloch modes bearing different diffraction orders. This difference further resulted in the disparate near field optical properties. As such, it was possible to investigate the dependence of the surface and bulk sensitivities on the incident angle under the two observed resonant modes. The results indicated that the incident angle can be generally optimized to improve the sensing performance of the sensor.
To prove the concept, the fabricated plasmonic nanostructure biosensor was used in monitoring and measuring the sensitivity of a protein binding at a dilute concentration in real-time. Additionally, this was conducted at different incident angles to help further understand the influence and role of the incident angles on the senor performance. For a longer wavelength resonant mode, lowest detection limit of 1.8 nanomolar was recorded at an incident angle of 100. This was significantly higher than that observed in prism-based commercial plasmonic sensors.
In a nutshell, the research team fabricated a large-scale, low-cost plasmonic sensing substrate using a rather simple fabrication process. The resulting plasmonic nanostructure sensing platform is, therefore, a promising approach in the development of low-cost and high throughput biosensing devices. This will advance new applications in various fields including medical diagnosis, environmental monitoring, and food safety.
Liang, Y., Cui, W., Li, L., Yu, Z., Peng, W., & Xu, T. (2019). Large‐Scale Plasmonic Nanodisk Structures for a High Sensitivity Biosensing Platform Fabricated by Transfer Nanoprinting. Advanced Optical Materials, 7(7), 1801269.Go To Advanced Optical Materials