Microbubble resonators for scattering-free absorption spectroscopy of nanoparticles.

Area of Science:

• Nanotechnology
• Spectroscopy
• Biomedical Engineering

Background:

• Plasmonic nanoparticles offer unique optical properties for sensing.
• Accurate spectral analysis of nanoparticles in turbid media remains challenging.
• Microbubble resonators provide a sensitive platform for optical measurements.

Purpose of the Study:

• To develop a proof-of-concept for reconstructing absorbance spectra of plasmonic nanoparticles.
• To demonstrate scattering-insensitive spectral detection using photothermal conversion.
• To validate the system's performance with turbid samples.

Main Methods:

• Utilizing photothermal conversion within a microbubble resonator to detect absorbance.
• Comparing spectra of gold nanorod suspensions with and without milk powder to assess scattering insensitivity.
• Interrogating small sample volumes (below 40 nl) with low-intensity excitation (around 20 µW).

Main Results:

• Accurate reconstruction of absorbance spectra for plasmonic nanoparticle suspensions was achieved.
• The photothermal detection method proved insensitive to light scattering effects.
• The system successfully analyzed small sample volumes with low optical power.

Conclusions:

• Microbubble resonators coupled with photothermal detection offer a robust method for nanoparticle spectral characterization.
• This technique is suitable for analyzing turbid biological fluids due to its scattering insensitivity.
• The system's compatibility with microfluidics and potential for miniaturization are promising for portable devices.