Abstract

Optical microresonators based on Whispering Gallery Modes have been extensively investigated as unique tools for fundamental studies and as core components in several applications. Specifically, microbubbles resonators (MBR) made from glass capillaries combine high optical and mechanical Q-factors together with intrinsic microfluidics, and in this work we demonstrate them as unique platforms for photoacoustic (PA) detection and photothermal (PT) spectroscopy. In a first configuration, we employed a MBR as an optical transducer to detect the PA signal generated by a suspension of gold nanorods (GNRs) placed within the MBR, demonstrating all-optical PA detection and high sensitivity towards nanoparticles optical absorption. The MBR acts both as the ultrasound sensor and as the microvial, enabling the inspection of submicroliter samples without the need for impedance-matching media. We then present a flow cytometry experiment where the GNRs run through the MBR, and we estimate PA intensity by a Fourier analysis of the read-out signal. The sharp MBR mechanical eigenmodes allowed to easily decouple the environmental noise from the PA contributions. In a second proof-of-concept experiment using a similar setup, we implemented the MBR transducer to reconstruct the GNRs absorption spectrum through the photothermal conversion. The high sensitivity of the MBR towards temperature variations allowed for the interrogation of small samples while using a low-intensity beam for their excitation. This thermal detection produces spectra that are insensitive towards light scattering in the sample, as proved experimentally by comparing the spectra of aqueous GNR suspensions in the presence or absence of milk powder.

Microbubble resonators for scattering-free absorption spectroscopy of nanoparticles

Gabriele Frigenti, Lucia Cavigli, Fulvio Ratto, Sonia Centi, Tatyana V. Murzina, Daniele Farnesi, Stefano Pelli, Silvia Soria, and Gualtiero Nunzi Conti
Opt. Express 29(20) 31130-31136 (2021)

Flexible microbubble-based Fabry–Pérot cavity for sensitive ultrasound detection and wide-view photoacoustic imaging

Jun Ma, Yang He, Xue Bai, Li-Peng Sun, Kai Chen, Kyunghwan Oh, and Bai-Ou Guan
Photon. Res. 8(10) 1558-1565 (2020)

Photothermal and photoacoustic Raman cytometry in vitro and in vivo

Evgeny V. Shashkov, Ekaterina I. Galanzha, and Vladimir P. Zharov
Opt. Express 18(7) 6929-6944 (2010)

Optically induced resonance of nanoparticle-loaded microbubbles

Jacob D. Dove, Mark A. Borden, and Todd W. Murray
Opt. Lett. 39(13) 3732-3735 (2014)

TT-type resonator-based differential photoacoustic spectroscopy for trace gas detection

Fupeng Wang, Liyan Fu, Jianguo Zhang, Ze Han, Shuo Pang, Qingsheng Xue, Diansheng Cao, Qian Li, and Qiang Wang
Opt. Lett. 49(8) 2173-2176 (2024)