Conjugated polymer dots emerge as attractive molecular imaging nanoprobes in living animals for their excellent optical properties including bright fluorescence intensity, excellent photostability, high emission rates, and low intrinsic cytotoxicity. This mini-review summarizes recent advances on near-infrared-emitting poly[2-methoxy-5- (2-ethylhexyloxy)-1,4-phenylenevinylene] polymer dots for in vivo bioimaging. The preparation of near-infrared MEH-PPV polymer dots is firstly discussed, followed by some examples of their applications ranging from lymph node mapping and tumor imaging to long-term tumor tracking.

Lymphatic vasculature system has attracted extensive attention due to its important role in some pathological changes such as lymphedema, immune dysfunction, gut malabsorption and lymph node metastasis, etc. With the continuous development of fluorescence imaging technology, it has been widely used in the study of lymphatic vessels structure, morphology, and function both in preclinical and clinical. Fluorescence imaging can help researchers and clinicians to know the morphological and functional status of lymphatic vessels, explore the role of lymphatic vessels in various lymph-related diseases, and help diagnosis the state of lymphatic vessels in patients and formulate further treatment plan. Herein, we describe the usage and recent advances of fluorescence imaging technology including immune fluorescence imaging, optical coherence tomography, near-infrared fluorescence imaging in ex vivo and in vivo lymphangiography, and discuss the future applications of fluorescence imaging in lymphatic vasculature imaging.

In vivo biological imaging in first near-infrared window (NIR-I, 700-900 nm) and the second near-infrared window (NIR-II, 1000-1700 nm) using conjugated polymers have recently attracted great interest. Compared with imaging in visible region (400-700 nm), NIR bioimaging can provide deeper tissue penetration and higher spatial resolution due to fewer scattering of longer-wavelength photons. Moreover, most of NIR-I and NIR-II conjugated copolymers have been reported with tunable excitation and emission of fluorophores through modification of their donor-acceptor structures. In this minireview, we focus on the recent advances on chemical synthesis of conjugated polymers and their biological imaging in NIR-I and NIR-II windows.