Investigation of the photoacoustic signal dependence on laser power

2007 ◽  
Author(s):  
Jan Niemi ◽  
Torbjörn Löfqvist ◽  
Per Gren
Keyword(s):  
Laser Power ◽  
Photoacoustic Signal ◽  
Signal Dependence

scholarly journals Photoacoustic Properties of Polypyrrole Nanoparticles

Nanomaterials ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 2457
Author(s):  
Peter Keša ◽  
Monika Paúrová ◽  
Michal Babič ◽  
Tomáš Heizer ◽  
Petr Matouš ◽  
...  
Keyword(s):  
Contrast Agent ◽  
Photoacoustic Imaging ◽  
Particle Surface ◽  
Photoacoustic Signal ◽  
Ammonium Persulphate ◽  
Coated Nanoparticles ◽  
Polypyrrole Nanoparticles ◽  
Signal Dependence

Photoacoustic imaging, an emerging modality, provides supplemental information to ultrasound imaging. We investigated the properties of polypyrrole nanoparticles, which considerably enhance contrast in photoacoustic images, in relation to the synthesis procedure and to their size. We prepared polypyrrole nanoparticles by water-based redox precipitation polymerization in the presence of ammonium persulphate (ratio nPy:nOxi 1:0.5, 1:1, 1:2, 1:3, 1:5) or iron(III) chloride (nPy:nOxi 1:2.3) acting as an oxidant. To stabilize growing nanoparticles, non-ionic polyvinylpyrrolidone was used. The nanoparticles were characterized and tested as a photoacoustic contrast agent in vitro on an imaging platform combining ultrasound and photoacoustic imaging. High photoacoustic signals were obtained with lower ratios of the oxidant (nPy:nAPS ≥ 1:2), which corresponded to higher number of conjugated bonds in the polymer. The increasing portion of oxidized structures probably shifted the absorption spectra towards shorter wavelengths. A strong photoacoustic signal dependence on the nanoparticle size was revealed; the signal linearly increased with particle surface. Coated nanoparticles were also tested in vivo on a mouse model. To conclude, polypyrrole nanoparticles represent a promising contrast agent for photoacoustic imaging. Variations in the preparation result in varying photoacoustic properties related to their structure and allow to optimize the nanoparticles for in vivo imaging.

What are the ranges and basis of auxeticity in the phases of cellulose microfibrils?

2017 ◽  
Author(s):  
Akwasi Asamoah
Keyword(s):  
Bacterial Cellulose ◽  
Raman Spectra ◽  
Laser Power ◽  
Microfibrillated Cellulose ◽  
Glass Slide ◽  
Flax Fibre ◽  
Cellulose Microfibrils

<p>One sample of 1D bundle of cellulose microfibrils in the form of lignified flax fibre (0.10526 mm x 10 mm), and one 2D networks of cellulose microfibrils in the form of tunicate cellulose (0.07 mm x 5 mm x 10 mm), bacterial cellulose (0.135 mm x 5 mm x 10 mm) and microfibrillated cellulose (0.08 mm x 5 mm x 10 mm) were put on a glass slide parallel to the principal spectrometer axis. Raman spectra were measured all round in-plane under both half (in 5° steps) polarisation from 0° to 360° in extended mode between 100 cm<sup>-1</sup> and 1150 cm<sup>-1</sup> in 3 accumulations at 10s exposure and 100% laser power. The cursor was placed at the peak of the 1095 cm<sup>-1</sup> band, and intensity read.</p>

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