Hundreds-fold Sensitivity Enhancement of Photothermal Microscopy in Near-Critical Xenon

Abstract

Photothermal absorption microscopy of single Au nanoparticles was conducted at temperatures and pressures near the critical point of Xenon (Tc = 16.583 °C, Pc = 5.842 MPa). The divergence of the thermal expansion coefficient at the critical point makes the refractive index highly sensitive to changes in temperature, which directly translates to a large enhancement of the photothermal signal. We find that measurements taken near the critical point of Xe give a signal enhancement factor of up to 440 ± 130 over those taken in glycerol. The highest sensitivity recorded here corresponds to power dissipation of 64 pW, achieving a signal-to-noise ratio of 9.4 for 5 nm Au nanoparticles with an integration time of 50 ms, making this the most sensitive of any absorption microscopy technique reported to date. Enhancing the sensitivity of absorption microscopy lowers the operating heating power, allowing the technique to be more compatible with absorbers with absorption coefficient and photochemical stability lower than that of Au.

Single Nanoparticle Detection Using Optical Microcavities

“…However, a greater number of publications report single nanoparticle detection using WGM microcavities, such as microspheres and microtoroids. [21][22][23][24] For example, single gold nanoparticles with a radius of 2.5 nm [24] and single BSA molecules (66 kDa) [22] have been . Techniques such as hybrid plasmonic-photonic mode, active microcavity and mode locking have been developed, and have pushed the detection limit to a radius of 2.5 nm.…”

“…Compared to microcavity sensing, iSCAT requires an ultra-stable light source and photothermal microscopy needs critical temperature and pressure conditions, [24] and the two techniques provide the spatial information of the target analyte. Compared to microcavity sensing, iSCAT requires an ultra-stable light source and photothermal microscopy needs critical temperature and pressure conditions, [24] and the two techniques provide the spatial information of the target analyte.…”

“…The monitoring of the nanoparticles in air is necessary for safety control, because nanoscale particles generated from vehicles and industrial processes can penetrate the lungs and spread to other organs, resulting in serious respiratory and cardiac diseases. While optical sensing with a detection limit down to single nanoparticles has been achieved by various methods, such as scattering interferometric [21,22] and photothermal microscopy [23,24] and nanofiber sensors, [25][26][27][28][29] microcavity sensing attracts much attention, because their high quality factors (Q factor) and small mode volumes (V m ) enable significant enhancement of light-matter interactions. Various methods designed for sensing applications, such as nanostructured materials, [4][5][6] metafilms, [7] carbon dots, [8,9] electrodes [10,11] and elastic nanocomposite cilia structures, [12] and wearable sensors have been reported.…”

Absorption and Quantum Yield of Single Conjugated Polymer Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) Molecules

“…34 The high pressure was applied to xenon gas through thin steel tubes and controlled with an auxiliary device. The temperature of the whole cell was also controlled with a feedback device (see ref (34) for more details).…”

“…34 The high pressure was applied to xenon gas through thin steel tubes and controlled with an auxiliary device. The temperature of the whole cell was also controlled with a feedback device (see ref (34) for more details). We varied the temperature and pressure of xenon close to its critical point to achieve optimal sensitivity, and we used 20 nm diameter gold nanoparticles to calibrate the photothermal signal (see Figure S1b and c in the Supporting Information).…”