Abstract
A cost-effective, stable and ultrasensitive localized surface plasmon resonance (LSPR) sensor based on gold nanoparticles (AuNPs) partially embedded in transparent substrate is presented. Partially embedded AuNPs were prepared by thermal annealing of gold thin films deposited on glass at a temperature close to the glass transition temperature of the substrate. Annealed samples were optically characterized by using spectroscopic ellipsometry and compare with theoretical modeling to understand the optical responses from the samples. By combining the partially-embedded AuNPs substrate with a microfluidic flow cell and dove prism in an ellipsometry setup, an ultrasensitive change in the LSPR signal can be detected. The refractive index sensitivity obtained from the phase measurement is up to 1938 degrees/RIU which is several times higher than that of synthesized colloidal gold nanoparticles. The sample is further used to investigate the interactions between primary and secondary antibodies. The bio-molecular detection limit of the LSPR signal is down to 20 pM. Our proposed sensor is label free, non-destructive, with high sensitivity, low cost, and easy to fabricate. These features make it feasible for commercialization in biomedical applications.
Highlights
The optical response of metallic nanoparticles with size of few tens of nanometers can lead to localized surface plasmon resonance (LSPR) resulting from the coupling of collective excitation of the conduction electrons with the incident light
Optical responses from partially-embedded AuNPs in glass substrate prepared by thermally annealed Au films show a clear transition from LSPR to SPR mode as the film thickness increases
The proposed plasmonic bio-chip was tested for bulk sensitivity response by using a prism-assisted spectroscopic ellipsometry and its sensitivity was compared to that of the gold nanoparticles immobilized on the glass substrate
Summary
The optical response of metallic nanoparticles with size of few tens of nanometers can lead to localized surface plasmon resonance (LSPR) resulting from the coupling of collective excitation of the conduction electrons with the incident light. The position and intensity of LSPR frequency is sensitive to the size, shape and inter-particle distance, and refractive indices of the surrounding materials [2,3] This particular property has fostered applications in bio-medical sensors, which detect local refractive index changes of the medium near the nanoparticle surface as a consequence of bio-molecular binding. Plasmonic biosensor based on gold nanoparticles with different shape prepared through various techniques such as colloidal lithography, electron beam lithography, nanosphere lithography and nano-imprint lithography etc., have been studied for decades [4,5,6,7]. Colloidal synthesized metal nanoparticles are more promising in the areas of biological sensing and
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