Label-Free Quantification of Bilirubin Using a Refractive Index-Insensitive Nanolaminate SERS Substrate

Area of Science:

• Nanotechnology
• Spectroscopy
• Biomarker Detection

Background:

• Bilirubin is a biomarker for neurotoxicity, but detecting low unbound levels is difficult.
• Surface-enhanced Raman spectroscopy (SERS) offers label-free detection but suffers from signal fluctuations due to refractive index (RI) variations.
• Plasmonic hotspots in SERS can cause resonance detuning, limiting quantitative accuracy.

Purpose of the Study:

• To develop a refractive index-insensitive SERS substrate for robust and reliable bilirubin detection.
• To overcome the limitations of current SERS methods in quantifying low-level biomarkers.
• To demonstrate a general strategy for improving SERS quantitative reliability.

Main Methods:

• Fabrication of a multi-resonant nanolaminate SERS substrate with a metal-insulator-metal architecture.
• Utilizing vertically stacked layers to achieve broadband spectral overlap and consistent enhancement under varying RI conditions.
• Demonstrating label-free bilirubin detection and assessing quantitative linearity and reliability.

Main Results:

• The nanolaminate SERS substrate exhibited RI-insensitive and robust signal enhancement.
• Achieved highly linear label-free bilirubin detection from 10^-9 to 10^-4 M with R² = 0.99.
• Demonstrated improved quantitative reliability compared to single-resonant SERS substrates.

Conclusions:

• The developed RI-insensitive SERS substrate provides enhanced quantitative reliability for biomarker detection.
• This multi-resonant nanolaminate design offers a general strategy for robust SERS-based biosensing.
• The findings are crucial for accurate quantification of biomarkers in complex biological environments.