Directly printed plasmonic sensors of gold micro/nano-structures for biochemical detection

Abstract

Plasmonics is an emerging technology that has many important applications, such as biochemical detection. Especially in recent years, with the development of micro/nano fabrication technology and numerical simulation tools, research on the mechanism and application of localized surface plasmon resonance (LSPR) has attracted more attention. One of the most important optical effects of LSPR is the localization of the electromagnetic field at certain regions of the nanostructure's surface (or, in other words, the local field is "enhanced"). The tight confinement of local electromagnetic fields by metallic nanostructures can lead to many novel optical effects and provide opportunities for light-matter interactions at the nanometer-scale level. Such a unique property can be harnessed to develop high-performance optical biosensing technologies, such as LSPR label-free biosensing and plasmonic substrates for plasmonically-enhanced IRAS biodetection. In this thesis, we develop two kinds of directly printed plasmonic biosensors for LSPR label-free biosensing and plasmonically-enhanced IRAS biochemical detection, respectively. Firstly, an optical fiber-tip biosensor based on micropatterns of gold nanoparticles is developed. The flat end-face of optical fiber makes it a uniquely ultrasmall substrate which provides opportunities for the development of many ultrasmall optical sensors and devices. Its small size allows the access to space-restricted environments, while its good biocompatibility, chemical resistance, and mechanical robustness make it very suitable for biosensing applications. After printing of plasmonic structures upon optical fiber end-face, a highly compact and sensitive biosensor can be fabricated. We developed an in-situ precision photoreduction technology to directly print plasmonic nanoparticles on the fiber end-face and thereby fabricate optical fiber-tip plasmonic biosensors. The fabricated sensors have been successfully demonstrated to detect the antibody and SARS-CoV-2 mimetic DNA sequence at the concentration levels of less than 100 ng/mL and 0.8 pM, respectively. Secondly, a plasmonic substrate of periodic gold micro-flake array is developed for plasmonically-enhanced infrared absorption-spectroscopy biodetection. Plasmonic gold micro-flakes are directly printed by using precision photoreduction technology. Their spectral peaks of plasmonic resonances are tuned by the geometric parameters of the structure to match with the absorption peak of target molecules in the infrared region. The spectral responses of such plasmonic substrates are measured and compared with numerical results simulated by using COMSOL. A plasmonically enhanced infrared absorption-spectroscopy has been demonstrated by using the fabricated plasmonic substrate to detect BSA at the concentration level of 10 nM.