In-situ label-free optical biosensing with plasmonic enhanced ellipsometry using partially-embedded bimetallic Ag-Au alloy nanoparticles

This work presents a label-free optical biosensing platform by integrating the localized surface plasmon resonance (LSPR) and in-situ ellipsometry technique. A sensor chip composed of partially embedded Au-Ag alloy nanoparticles was fabricated on a glass substrate by the thermal dewetting method. The sensor chip was characterized using spectroscopic ellipsometry to determine the optical constant. The bulk RI resolution estimated from the ellipsometry phase (Delta) signal was found to be 4.62 x 10-7 RIU for the bare sensor chip. Also, the biosensing experiment toward protein detection gives a detection limit of 23 pM. Further, hexagonal-boron nitride nanosheets (h-BNNS) modified sensor chip shows enhanced sensitivity with the detection limit down to 4.2 pM. The protein adsorption coefficients obtained from the fitting of kinetics data give values of 4.6 x 104 mol- 1s- 1 and 2.65 x 105 mol-1 s- 1 for bare, and h-BNNS modified sensor chips, respectively. A theoretical simulation performed with COMSOL shows good agreement with our experimental outcomes. We believe that our proposed sensor chip enables the features of high stability, surface-sensitive, non-destructive, label-free, easy to fabricate, and cost-effectiveness, which make it feasible for large-scale production and commercialization in biomedical applications.

Automated summary

This work introduces a label-free optical biosensing platform that combines localized surface plasmon resonance (LSPR) with in-situ ellipsometry technique. The sensor chip, fabricated via the thermal dewetting method, consists of partially embedded Au-Ag alloy nanoparticles on a glass substrate. Spectroscopic ellipsometry was used to characterize the sensor chip and determine its optical constant. The proposed sensor chip demonstrates high stability, surface sensitivity, non-destructiveness, label-free detection, ease of fabrication, and cost-effectiveness, making it suitable for large-scale production and commercialization in biomedical applications.