Molecular fingerprinting of nanoparticles in complex media with non-contact photoacoustics: beyond the light scattering limit

Abstract

Optical instruments can probe physical systems even to the level of individual molecules. In particular, every molecule, solution, and structure such as a living cell has a unique absorption spectrum representing a molecular fingerprint. This spectrum can help identify a particular molecule from others or quantify its concentration; however, scattering limits molecular fingerprinting within a complex compound and must be overcome. Here, we present a new, non-contact photoacoustic (PA)-based method that can almost completely remove the influence of background light scattering on absorption measurements in heterogeneous highly scattering solutions and, furthermore, separate the intrinsic absorption of nanoscale objects from their scattering. In particular, we measure pure absorption spectra for solutions of gold nanorods (GNRs) as an example of a plasmonic agent and show that these spectra differ from the extinction measured with conventional UV-VIS spectrophotometry. Finally, we show how the original GNR absorption changes when nanoparticles are internalized by cells.

Calibrated Photoacoustic Spectrometer Based on a Conventional Imaging System for In Vitro Characterization of Contrast Agents

“…Other PA spectrometers based on dedicated single-element detectors place fewer constraints related to the ultrasound frequency response of the detector. They evaluate the optical absorption coefficient using calibration with a known reference solution [12,13]. For these PA spectrometers, small sample volumes (3 µL [13] and 200 µL [12]) are placed in optically transparent cells, and SPP is performed on the same sample to concurrently measure the optical attenuation.…”

Mechanisms of Silver Nanoparticle Uptake by Embryonic Zebrafish Cells

“…The absorption spectra measured by UV-Vis were also strongly influenced by the biological medium; in the complex media, the samples exhibited significant scattering increase (compared to in UPW) and a second peak, revealing the presence of proteins in the sample. These results can be related to the fact that a considerable fraction of transmitted light does not reach the UV-Vis detector due to the complex nature of the cell medium, recording a higher absorption for these samples [41].…”

Photoacoustic Imaging in Gastroenterology: Advances and Needs

“…Conventional piezoelectric transducers limit the potential axial resolution of broadband PA signals. Note that all-optical detectors of PA signal are wideband and have significant advantage in these terms [22,23].…”

“…Petrova et al [55] demonstrated that generation of PA response from blood in terms of its thermoelastic properties depends on compartmentalization of hemoglobin within erythrocyte. Recently, Pelivanov et al [22] showed that localization of nanoagents in extracellular and/or intracellular matrix can affect the resultant absorption spectrum of nanoagents (Figure 8).…”

“…(C and D) absorption spectra of PEG-coated gold nanoparticles localized in extracellular matrix (HUVEC+GNRout)and internalized by HUVEC cells (HUVEC+GNRin) as detected by all-optical, narrow-beam PA spectrophotometer. Reproduced from open-source publication[22].…”