NIR-II live imaging study on the degradation pattern of collagen in the mouse model.

The degradation of collagen in different body parts is a critical point for designing collagen-based biomedical products. Here, three kinds of collagens labeled by second near-infrared (NIR-II) quantum dots (QDs), including collagen with low crosslinking degree (LC), middle crosslinking degree (MC) and high crosslinking degree (HC), were injected into the subcutaneous tissue, muscle and joints of the mouse model, respectively, in order to investigate the in vivo degradation pattern of collagen by NIR-II live imaging. The results of NIR-II imaging indicated that all tested collagens could be fully degraded after 35 days in the subcutaneous tissue, muscle and joints of the mouse model. However, the average degradation rate of subcutaneous tissue (k = 0.13) and muscle (k = 0.23) was slower than that of the joints (shoulder: k = 0.42, knee: k = 0.55). Specifically, the degradation rate of HC (k = 0.13) was slower than LC (k = 0.30) in muscle, while HC showed the fastest degradation rate in the shoulder and knee joints. In summary, NIR-II imaging could precisely identify the in vivo degradation rate of collagen. Moreover, the degradation rate of collagen was more closely related to the implanted body parts rather than the crosslinking degree of collagen, which was slower in the subcutaneous tissue and muscle compared to the joints in the mouse model.

In Vivo Precision Evaluation of Lymphatic Function by SWIR Luminescence Imaging with PbS Quantum Dots.

Advancements in lymphography technology are essential for comprehensive investigation of the lymphatic system and its function. Here, a shortwave infrared (SWIR) luminescence imaging of lymphatic vessels is proposed in both normal and lymphatic dysfunction in rat models with PbS quantum dots (PbS Qdots). The lymphography with PbS Qdots can clearly and rapidly demonstrate the normal lymphatic morphology in both the tail and hind limb. More importantly, compared to ICG, SWIR luminescence imaging with PbS Qdots can easily identify the dominant lymphatic vessel and node with higher luminescence signal in rats. Moreover, lymphatic pump is identified as segment contracting sections with a size of ≈1 cm in rat by in vivo SWIR lymphograhy, which propose a direct feature for precise evaluation of lymphatic function. Notably, in vivo SWIR luminescence imaging with PbS Qdots also clearly deciphers the in vivo pattern of morphological and function recovery from lymphatic system in rat model. In summary, SWIR luminescence imaging with PbS Qdots can improve the lymphography and thus deepen the understanding of the morphology and structure of the lymphatic system as well as lymphatic function such as lymphatic pump, which will facilitate the diagnosis of lymphatic dysfunction in the future.

Highly thermal stable RNase A@PbS/ZnS quantum dots as NIR-IIb image contrast for visualizing temporal changes of microvasculature remodeling in flap.

Surgeons face great challenges in acquiring high-performance imaging because fluorescence probes with desired thermal stability remains rare. Here, hybrid lead sulfide/zinc sulfide quantum dots (PbS/ZnS QDs) nanostructures emitting in the long-wavelength end of the second near-infrared (NIR-IIb) window were synthesized and conjugated with Ribonuclease-A (RNase A). Such formed RNase A@PbS/ZnS QDs exhibited strong NIR IIb fluorescence and thermal stability, as supported by the photoluminescent emission assessment at different temperatures. This will allow the RNase A@PbS/ZnS QDs to provide stable fluorescence signals for long-time intraoperative imaging navigation, despite often happened, undesirable thermal accumulation in vivo. Compared to NIR-IIa fluorescence imaging, NIR-IIb vascular fluorescence imaging achieved larger penetration depth, higher signal/background ratios and nearly zero endogenous tissue autofluorescence. Moreover, these QDs illustrate the reliability during the real-time and long-time precise assessment of flap perfusion by clearly visualizing microvasculature map. These findings contribute to intraoperative imaging navigation with higher precision and lower risk.

Ultraviolet Carbon Nanodots Providing a Dual-Mode Spectral Matching Platform for Synergistic Enhancement of the Fluorescent Sensing.

The sensing of chromium(VI) (Cr(VI)) is highly desired, due to its toxic and carcinogenic effects upon human health. Fluorescent probes, especially carbon nanodots (CNDs), have been widely used for Cr(VI) sensing via the inner filter effect (IFE). However, improving the sensitivity of these probes remains a difficult issue. In this work, CNDs derived from ß-Lactoglobulin were applied as an ultrasensitive fluorescent probe for Cr(VI). With 260 nm excitation, the CNDs showed multi-band emission, including an ultraviolet 360 nm peak. The spectral matching of the CNDs with Cr(VI) led to synergistic suppression of both the excitation and emission light in the fluorescent sensing. As a consequence, the CNDs showed high sensitivity toward Cr(VI), the detection limit reaching as low as 20 nM. Moreover, taking advantage of the multi-emissive property of the CNDs, the synergistic effect was proven in an IFE-based sensing system, which might be extended to the design of other kinds of fluorescent probes.

Selective determination of acetone by carbon nanodots based on inner filter effect.

Fluorescent sensing of acetone has been achieved taking advantage of the unique optical property of acetone. However, the complicated synthesis process of the fluorescent probes limited their application. Here, carbon nanodots (CNDs) derived from glucose were chosen as the sensing material for the first time, which could be obtained by a one-pot microwave-assisted synthesis within 2 min. The CND had ultraviolet excitation spectrum, resulting in an obvious overlap between its excitation band with the absorption band of acetone. The fluorescent quenching occurred via inner filter effect with fast response. The CNDs showed sensitive response to acetone with a detection limit of 0.09 vol%, which was comparable to most previously reported MOF probes. The results of our work indicated the feasibility of IFE-based sensing method, and demonstrated an efficient and convenient way for acetone detection.

Nontoxic fluorescent carbon nanodot serving as a light conversion material in plant for UV light utilization.

In this study, water-soluble fluorescent carbon nanodots (CNDs) were directly injected into the leaf of nicotiana tabacum. With the help of UV-to-blue light conversion nanomaterial, the photosynthetic rate of the leaf was improved 18% upon additional 6 W UV irradiation. The photostability and toxicity of different kinds of CNDs were discussed. The results showed that CNDs functionalized with NH2-groups on their surfaces could maintain good fluorescence in plant leaf, and CNDs with complex surface groups tended to have high toxicity to the plant. The NH2-functionalized CNDs with non-toxicity and good photostability were used as in vivo light conversion material for direct utilization of UV light in the solar energy.

Microwave-assisted synthesis of water-dispersed CdTe/CdSe core/shell type II quantum dots.

A facile synthesis of mercaptanacid-capped CdTe/CdSe (core/shell) type II quantum dots in aqueous solution by means of a microwave-assisted approach is reported. The results of X-ray diffraction and high-resolution transmission electron microscopy revealed that the as-prepared CdTe/CdSe quantum dots had a core/shell structure with high crystallinity. The core/shell quantum dots exhibit tunable fluorescence emissions by controlling the thickness of the CdSe shell. The photoluminescent properties were dramatically improved through UV-illuminated treatment, and the time-resolved fluorescence spectra showed that there is a gradual increase of decay lifetime with the thickness of CdSe shell.

Ultra-photostable, non-cytotoxic, and highly fluorescent quantum nanospheres for long-term, high-specificity cell imaging.

A new class of fluorescent quantum nanospheres (QNs) is directly achieved in aqueous phase through a facile one-pot microwave irradiation (MWI) strategy. Multi-color QNs with maximum emission wavelengths ranging from 525 to 610 nm and PLQY of 30-60% are facilely prepared through this new MWI strategy. In addition to strong fluorescence, these QNs possess excellent photostability, preserving ∼90% of the original intensity after 70 min high-power UV irradiation (100 W Xeon lamp). In sharp contrast, the fluorescence of CdTe/CdS/ZnS core-shell-shell quantum dots (QDs), recognized as established fluorescent probes with robust photostability, decrease to ∼50% under the same conditions. Besides, cytotoxicity assessment demonstrates that the prepared QNs exhibit favorable cytocompatibility to K562 cells with high concentration (3 µmol) and long-time incubation (24 h). Furthermore, cellular imaging results demonstrate that the as-prepared QNs are remarkably efficacious for long-term and high-specificity immunofluorescent cellular labeling, and multi-color cell imaging. Our systematical investigation clearly shows that these high-performance QNs may serve as practical and powerful tools for various biological researches, such as in vivo and in vitro imaging.

The cytotoxicity of cadmium based, aqueous phase - synthesized, quantum dots and its modulation by surface coating.

In this report, we evaluated the cytotoxicity of a series of quantum dots (QDs) directly synthesized in aqueous phase, i.e., thiols-stabilized CdTe, CdTe/CdS core-shell structured and CdTe/CdS/ZnS core-shell-shell structured QDs, with a variety of cell lines including K562 and HEK293T. We have demonstrated that the CdTe QDs are highly toxic for cells due to the release of cadmium ions. Epitaxial growth of a CdS layer reduces the cytotoxicity of QDs to a small extent. However, the presence of a ZnS outlayer greatly improves the biocompatibility of QDs, with no observed cytotoxicity even at very high concentration and long-time exposure in cells. Our systematic investigation clearly shows that the cytotoxicity of QDs can be modulated through elaborate surface coatings and that the CdTe/CdS/ZnS core-shell-shell structured QDs directly synthesized in aqueous phase are highly promising biological fluorescent probes for cellular imaging.

Synthesis of CdTe nanocrystals through program process of microwave irradiation.

A novel method, the program process of microwave irradiation (PPMI), which commendably integrates good qualities of microwave irradiation and a programmed heating process, is presented to synthesize high-quality CdTe nanocrystals in aqueous solution. Microwave irradiation, which acts as the heating mode of PPMI, is highly favorable for a narrow size distribution and low concentration of surface defects of nanocrystals. On the other hand, two correlative processes (the first process and the second process) are utilized in PPMI to actualize the programmed heating process, which is an effective strategy to improve the quality of nanocrystals. Thus, a series (diameters approximately 2-4 nm) of highly luminescent (PLQY approximately 30-68%) CdTe nanocrystals were rapidly prepared (reaction time approximately 1-30 min) in aqueous phase through PPMI.

Microwave-assisted growth and characterization of water-dispersed CdTe/CdS core-shell nanocrystals with high photoluminescence.

A novel microwave-assisted method of growth of high-quality CdTe/CdS core-shell nanocrystals in the aqueous phase is presented in this paper. The photoluminescence quantum yield (PLQY) is greatly enhanced by epitaxial growth of the CdS shell. Under optimum conditions, the PLQY of as-prepared nanocrystals reaches as high as 75% without any post-treatment. Furthermore, these investigations demonstrate that microwave irradiation is tremendously useful for fast epitaxial growth of nanocrystals due to its special characteristics. As a result, the microwave synthesis is sufficiently time-economizing (only five minutes are required) to obtain optimum amounts of CdTe/CdS core-shell nanocrystals in comparison to the conventional illumination method (several days are required). Therefore, this current research not only provides a rapid microwave synthesis for producing highly fluorescent CdTe/CdS core-shell nanocrystals, but also it presents some advantages of the microwave synthesis in comparison to the illumination method.