Abstract
Near-infrared (NIR) imaging technology has been widely used for biomedical research and applications, since it can achieve deep penetration in biological tissues due to less absorption and scattering of NIR light. In our research, polymer nanoparticles with NIR fluorophores doped were synthesized. The morphology, absorption/emission features and chemical stability of the fluorescent nanoparticles were characterized, separately. NIR fluorescent nanoparticles were then utilized as bright optical probes for macro in vivo imaging of mice, including sentinel lymph node (SLN) mapping, as well as distribution and excretion monitoring of nanoparticles in animal body. Furthermore, we applied the NIR fluorescent nanoparticles in in vivo microscopic bioimaging via a confocal microscope. Under the 635 nm-CW excitation, the blood vessel architecture in the ear and the brain of mice, which were administered with nanoparticles, was visualized very clearly. The imaging depth of our one-photon microscopy, which was assisted with NIR fluorescent nanoprobes, can reach as deep as 500 μm. Our experiments show that NIR fluorescent nanoparticles have great potentials in various deep-tissue imaging applications.
Highlights
Fluorescence imaging technique occupies an important and unique position in life sciences and medicine [1], due to its advantages for noninvasive study of biological tissues
The fluorescence signal of IR-820 doped polymer nanoparticles mainly located in the “optical transmission window” of biological tissue (700 - 900 nm), which demonstrates that the NIR fluorescent nanoparticles have the deep-tissue imaging potentials
Some nanoparticles [37,38,39] (e.g. quantum dots (QDs) and gold nanoparticles) have already been used for sentinel lymph node (SLN) mapping, and we present another approach in this work. 50 μl of IR-820 doped polymer nanoparticles in PBS (1X, pH = 7.4) was injected intradermally into the left forepaw of nude mice, and the mice were imaged with the in vivo optical imaging system under the 704 nm excitation
Summary
Fluorescence imaging technique occupies an important and unique position in life sciences and medicine [1], due to its advantages for noninvasive study of biological tissues. Polymer nanoparticles made up of biocompatible hydrophobic-hydrophilic copolymers (e.g. phospholipids-PEG), are very promising and more suitable for in vivo applications [28] They can be facilely synthesized and conjugated with biomolecules to target certain parts of live animal body (e.g. tumors) [29,30]. Relying on the absorption of two or more NIR photons by fluorophores at once, multiphoton microscopy is capable of achieving better focusing, deeper tissue penetration and efficient light detection noninvasively. It has been widely used in thick-tissue and in vivo bioimaging [32,33]. An optically clear suspension containing IR-820 doped polymer nanoparticles was obtained, which can be used for further experiments
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