Photothermal Lens Detection of Gold Nanoparticles: Theory and Experiments

Abstract

An approach for mode-mismatched two-beam (pump-probe) photothermal lens detection of multipoint light-absorbing targets in solution (e.g., gold nanoparticles) is developed for continuous-wave intensity-modulated laser-excitation mode. A description of the blooming of the thermooptical element (thermal lens) upon absorption of the excitation laser radiation is based on the summation of individual thermal waves from multiple heat sources. This description makes it possible to estimate the irregularities of the temperature (and, thus, the refractive index) profile for a discrete number of nanoparticles in the irradiated area and a change in the concentration and particle size parameters. Experimental results are in good agreement with theoretical dependences of the photothermal signal on nanoparticle size and concentration and excitation laser power. Calibration plots for particles from 2 to 250 nm show long linear ranges, limits of detection of gold nanoparticles at the level of hundreds of nanoparticles with the current setup, and the photothermal-lens sensitivity coefficient increases as a cubic function of particle size. Further improvements are discussed, including increasing the sensitivity thresholds up to one nanoparticle in the detected volume.

Ultrasensitive label‐free photothermal imaging, spectral identification, and quantification of cytochrome c in mitochondria, live cells, and solutions

“…The achieved sensitivity of detection and quantification cyt c detection in mitochondria and released from them is significantly increased compared to conventional absorption spectroscopy. The potential application of this technique/approach may include spectral identification and quantitative detection of highly localized cellular proteins in single cells in vitro and in vivo in batch and flow condition [60] in blood, lymph, and other biological liquids, as PT immunoaggregation assays [56], detection of biomolecules labeled with conventional organics labels or advanced nanoparticles [38, 80] with potential to detect single molecules. And these measurements can be complemented with PT imaging.…”

Pump-probe optical microscopy for imaging nonfluorescent chromophores

“…Photothermal microscopy, which has long been used for imaging absorbing microscopic objects (especially metal nanoparticles), can be regarded as a special version of pump-probe microscopy [20][21][22][23][24]. In its popular implementation, a pump beam (pulsed or CW) is used to excite the molecules and to induce local heating, and the resulting temperature-dependent refractive index gradient is then read out as a transparent phase object by a second probe beam.…”

“…In its popular implementation, a pump beam (pulsed or CW) is used to excite the molecules and to induce local heating, and the resulting temperature-dependent refractive index gradient is then read out as a transparent phase object by a second probe beam. Various specific microscopy arrangements have been developed such as thermal lens detection and heterodyne interference [20][21][22][23][24].…”

Au nanostructures: an emerging prospect in cancer theranostics

“…Au nanoparticles are ideal candidates for photoacoustic imaging because of their SPR-based light absorption. SPR leads to both light absorption and scattering enhancement [24], so relatively large nanoparticles are preferred because they possess higher absorption/scattering ratios [42]. Li and co-workers [43] demonstrated photoacoustic imaging in vivo using Au nanorods conjugated with antibodies targeting cancer cells.…”