Photoacoustic tomography (PAT) has emerged as a hybrid, nonionizing imaging modality because of its satisfactory spatial resolution and high soft tissue contrast. Here, we demonstrate the application of a novel organic PAT contrast agent based on polypyrrole nanoparticles (PPy NPs). Monodisperse PPy NPs are ∼46 nm in diameter with strong absorption in the near-infrared (NIR) range, which allowed visualization of PPy NP-containing agar gel embedded in chicken breast muscle at a depth of ∼4.3 cm. Compared with PAT images based on the intrinsic optical contrast in mice, the PAT images acquired within 1 h after intravenous administration of PPy NPs showed the brain vasculature with greater clarity than hemoglobin in blood. Preliminary results showed no acute toxicity to the vital organs (heart, liver, spleen, lungs and kidneys) in mice following a single imaging dose of PPy NPs. Our results indicate that PPy NPs are promising contrast agents for PAT with good biocompatibility, high spatial resolution and enhanced sensitivity.
Polypyrrole nanoparticles conjugating gadolinium chelates were successfully fabricated for dual-modal magnetic resonance imaging (MRI) and photoacoustic imaging guided photothermal therapy of cancer, from a mixture of pyrrole and pyrrole-1-propanoic acid through a facile one-step aqueous dispersion polymerization, followed by covalent attachment of gadolinium chelate, using polyethylene glycol as a linker. ). After 24 h intravenous injection of Gd-PEG-PPy NPs, the tumor sites exhibited obvious enhancement in both T 1 -weighted MRI intensity and photoacoustic signal compared with that before injection, indicating the effi cient accumulation of Gd-PEG-PPy NPs due to the introduction of the PEG layer onto the particle surface. In addition, tumor growth could be effectively inhibited after treatment with Gd-PEG-PPy NPs in combination with near-infrared laser irradiation. The passive targeting and high MRI/photoacoustic contrast capability of Gd-PEG-PPy NPs are quite favorable for precise cancer diagnosing and locating the tumor site to guide the external laser irradiation for photothermal ablation of tumors without damaging the surrounding healthy tissues. Therefore, Gd-PEG-PPy NPs may assist in better monitoring the therapeutic process, and contribute to developing more effective "personalized medicine," showing great potential for cancer diagnosis and therapy.
[1] Concentrations of elemental carbon (EC), carbon monoxide (CO), and carbon dioxide (CO 2 ) were measured in Beijing between 2005 and 2006. EC was measured every hour with a semicontinuous thermal optical analyzer. The observed concentrations were rather uniform over a distance of about 50 km from the observation site. The annual average concentrations of EC and CO were 6.9 mgC m À3 and 1120 parts per billion by volume, respectively. The concentrations of these species increased with decreasing near-surface wind speed (WS). The slopes of the CO-CO 2 , EC-CO 2 , and EC-CO correlations are used to estimate major EC and CO sources. In the weak wind regime (WS 2.0 m s À1 ), the median EC, DEC/DCO 2 , and DEC/DCO (except for winter) increased in the late evening and remained high until early morning. The traffic of heavy duty diesel trucks during nighttime was about 20 times higher than that during daytime. These results indicate a dominant contribution of exhaust from diesel vehicles to the nighttime EC. In winter, the nighttime CO and DCO/DCO 2 ratio were largely higher than those in the other seasons. The most likely cause is the increase in the CO emissions from the exhaust of gasoline vehicles at low temperature. The DEC/DCO 2 ratio in winter was lower than that in fall, indicating no significant additional EC emissions. The diurnal variations of EC, CO, CO 2 , and DEC/DCO were similar between weekdays and weekends. The slopes of the CO-CO 2 -EC correlations are compared with the CO-CO 2 -EC ratios derived from a published emission inventory in the Beijing area.
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