Pollen-based natural nanostructures to realize nanoplasmonic biochips for single-molecule detection

In this work, a paradigm change in the development of the plasmonic-based bio/chemical sensing approaches is presented. The proposed idea is to use natural nanostructures instead of those fabricated by electron-beam lithography (EBL) tools. This sensing approach produces several advantages, such as high performances without an optimization step and a simple, low-cost, and eco-friendly production process with respect to other methods, which are still time-consuming with low scalability. In particular, pollen's nanostructures covered by gold nanofilms are used to realize gold nanogratings (GNG), similar to those made via EBL, to excite hybrid plasmonic phenomena. Bulk and binding sensitivities are evaluated and compared to nanoplasmonic sensors, particularly those achieved via an EBL-based chip. As proof of principle, an estrogen receptor (ERα) is immobilized on the plasmonic nanostructured surfaces of both EBL-based and pollen-based chips and interrogated by the same custom 3D-printed holder through a transmission-based experimental setup, exploiting polymer optical fibers (POFs). The experimental results demonstrate that the proposed pollen-based nanoplasmonic biosensor shows performance very similar to an EBL-based nanoplasmonic biosensor, indicating the equivalence between the two nanoplasmonic biosensors. The biosensor exhibited a detection limit better than 1 aM for the estradiol, demonstrating the capabilities of the proposed sensing approach towards single-molecule detection.