Single-atomic-ion detection with plasmon-enhanced whispering-gallery-mode microlasers.

Area of Science:

• Photonics and Nanotechnology
• Analytical Chemistry
• Biomedical Sensing

Background:

• Whispering-gallery-mode (WGM) microlasers are effective for label-free biosensing.
• Current WGM microlaser sensitivity is limited to detecting nanoparticles >10 nm.
• There is a need for higher sensitivity in detecting smaller analytes like atomic ions.

Purpose of the Study:

• To develop a plasmon-enhanced WGM microlaser for detecting single atomic ions.
• To achieve unprecedented sensitivity in label-free biosensing.
• To demonstrate real-time monitoring of ion interactions.

Main Methods:

• Integration of gold nanorods onto ytterbium-doped silica microspheres.
• Reduction of effective mode volume by ~1,000-fold.
• Enhancement of local electromagnetic field.
• Self-heterodyne detection of beatnote frequency shifts.

Main Results:

• Detection of single atomic ions (Zn²⁺ and Cd²⁺) in solution.
• Achieved peak sensitivities with beatnote shifts of 3.7 fm for Zn²⁺ and 7.2 fm for Cd²⁺.
• Demonstrated amplified signal-to-noise ratio due to plasmonic enhancement.

Conclusions:

• Plasmon-enhanced WGM microlasers offer a pathway to atomic-scale sensing.
• This technology has potential for single-molecule detection and in vivo probing.
• The developed system significantly surpasses previous sensitivity limits in WGM biosensing.