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This work presents a polyene bridging strategy on Rhodamine-type dye analogues (Rh824, Rh926, and Rh1029) for tuning absorption and emission wavelengths from the first near-infrared window (NIR-I; 750–900 nm) to the unprecedented second near-infrared window (NIR-II; 1000–1700 nm). Phosphatidylcholine (PC) enclosures of the dyes improve water solubility and triple the fluorescent quantum yields. The representative NIR-II fluorophore Rh1029-PC presents significantly higher spatial resolution, compared to NIR-I fluorophore Rh824-PC, when performing in vivo vascular imaging. We construct a mouse vascular hemorrhage model and apply Rh1029-PC as the angiography agent in NIR-II window for the first time. The images show superior clarity of the hemorrhage positions in the NIR-II window, suggesting the successful application of the hybrid Rhodamine-derived dye in NIR-II fluorescent bioimaging.

limited by either the few choices of fluorophores [8,9] or the difficulty of aqueous modification, [10] which is especially true when NIR absorption and emission are required. [11,12] Moreover, the above-mentioned fluorophores mostly interact with analytes in a quenching scheme which can be easily affected in complex biological media such as cytoplasm or body fluid, making it more challenging to produce reliable in vivo lifetime signals. [13] Alternatively, thanks to the well-shielded 4f-4f transition, the lifetime of rare-earthdoped nanocrystals is less likely to fluctuate in those conditions once the emitters are well protected, [14][15][16] and NIR-emissive Tm 3+ , Er 3+ , Yb 3+ , or Nd 3+ has been widely applied in in vivo imaging. [17][18][19][20][21] The longer lifetime of rare-earth-doped nanocrystals also benefits background-free bioimaging as the short-lived autofluorescence can be filtered by time gate. [22][23][24] However, the commonly used rareearth-doped nanoparticles usually have to be passivated by an inert shell to prevent the quenching of activators and emitters (Yb 3+ , Tm 3+ ), [25][26][27][28][29] while the fluorescence energy transfer is most sensitive of distance. [30] This causes a dilemma; when a thicker shell increases the fluorescence intensity, the energy transfer efficiency inevitably drops. Therefore, it is necessary to design a luminescent lifetime probe which can take both the strong luminescence signal and the appropriate energy transfer distance into account thus meeting the requirements of detection in vivo. Recently, we reported a family of rare-earth nanocrystals with the absorption and emission at the same energy level, which has inspired our design. With time-domain filtering technique, the NIR light transducers have strong luminescence and high quantum yield compared to upconversion materials, NIR dyes, or quantum dots. [31] Based on these findings, a highly luminescent (182 times compared to core upconversion particles and 33 times compared to core-shell upconversion particles under low power density, as shown in Figure 3) and lifetime-responsive LRET nanocomposite was built for effective in vivo sensing (Figure 1). NaYF 4 :Tm nanocrystal, which absorbs and emits photons in the same transition ( 3 H 6 -3 H 4 ), was employed as the donors (Figure 1b). It was further combined with a commercially available IR-820 dye as acceptors, which has a specific response to ClO − , forming an NIR ClO − -responsive LRET nanocomposite. The lifetime was affected by the number of window (660-950 and 1000-1500 nm). Herein, this work reports a lifetimeresponsive nanocomposite with both excitation and emission in the NIR I window (800 nm) and lifetime in the microsecond region. The incorporation of Tm 3+ -doped rare-earth nanocrystals and NIR dye builds an efficient energy transfer pathway that enables a tunable luminescence lifetime range. The NaYF 4 :Tm nanocrystal, which absorbs and emits photons at the same energy level, is found to be 33 times brighter than optimized core-shell upconversi...

No abstract

We report a technique for coherence transfer of laser light through a fiber link, where the optical phase noise induced by environmental perturbation via the fiber link is compensated by remote users with passive phase noise correction, rather than at the input as is conventional. Neither phase discrimination nor active phase tracking is required due to the open-loop design, mitigating some technical problems such as the limited compensation speed and the finite compensation precision as conventional active phase noise cancellation. We theoretically analyze and experimentally demonstrate that the delay effect introduced residual fiber phase noise after noise compensation is a factor of 7 higher than the conventional techniques. Using this technique, we demonstrate the transfer laser light through a 145-km-long, lab-based spooled fiber. After being compensated, the relative frequency instability in terms of overlapping Allan deviation is 1.9 × 10 −15 at 1s averaging time and scales down 5.3×10 −19 at 10,000 s averaging time. The frequency uncertainty of the light after transferring through the fiber relative to that of the input light is (−0.36 ± 2.6) × 10 −18 . As the transmitted optical signal remains unaltered until it reaches the remote sites, it can be transmitted simultaneously to multiple remote sites on an arbitrarily complex fiber network, paving a way to develop a multi-node optical frequency dissemination system with post automatic phase noise correction for a number of end users.Index Terms-Fiber-optic radio frequency transfer, optical frequency transfer, metrology.

It is very challenging to probe the temperature in a nanoscale because of the lack of detection technique. Temperature-sensitive luminescent probes at a nanoscale provide the possibility to solve this problem. Herein, we fabricated a model, which combined two kinds of temperature sensitive nanoprobes and gold nanoparticle heater within mesoporous silica nanoparticles. Upconverting nanoparticles and quantum dots located at different positions inside 110 nm nanoparticles reported different temperatures when the gold nanoparticles generated heat by 532 nm laser irradiation. The temperature difference between two probes with an average distance of 55 nm can reach about 30 °C. Our results prove that the temperature distribution at a nanoscale can be measured, and it will be noteworthy if a nano-heater is applied.

Luminescence imaging, exhibiting noninvasive, sensitive, rapid, and versatile properties, plays an important role in biomedical applications. It is usually unsuitable for direct biodetection, because the detected luminescence intensity can be influenced by various factors such as the luminescent substance concentration, the depth of the luminescent substance in the organism, etc. Ratiometric imaging may eliminate the interference due to the luminescent substance concentration on the working signal. However, the conventional ratiometric imaging mode has a limited capacity for in vivo signal acquisition and fidelity due to the highly variable and wavelength-dependent scattering and absorption process in biotissue. In this work, we demonstrate a general imaging mode in which two signals with the same working wavelength are used to perform ratiometric sensing ignoring the depth of the luminescent substance in the organism. Dual-channel decoding is achieved by time-gated imaging technology, in which the signals from lanthanide ions and fluorescent dyes are distinguished by their different luminescent lifetimes. The ratiometric signal is proven to be nonsensitive to the detection depth and excitation power densities; thus, we could utilize the working curve measured in vitro to determine the amount of target substance (hypochlorous acid) in vivo .

Hypoxia has been identified to contribute the pathogenesis of a wide range of liver diseases, and therefore, quantitative mapping of liver hypoxia is important for providing critical information in the diagnosis and treatment of hepatic diseases. However, the existing imaging methods are unsuitable to quantitatively assess liver hypoxia due to the need of liver‐specific contrast agents and be easily affected by other imaging factors. Here, a time‐resolved lifetime‐based imaging method is established for quantitative mapping of the distribution of hypoxia in the livers of mice by combining a wide‐field luminescence lifetime imaging system with an oxygen‐sensitive nanoprobe. It is shown that the method is suitable for real‐time quantification of the change of oxygen pressure in the process of hepatic ischemia‐reperfusion of the mouse. Moreover, the developed lifetime imaging methodology is used to quantitatively map liver hypoxia regions in the mouse model of orthotopic liver tumor, where the average oxygen pressure in tumorous liver is far below the normal liver.