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      Rational design of small indolic squaraine dyes with large two-photon absorption cross section†

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          Abstract

          Assisted by theoretical analysis, we designed a small indolic squaraine with δ > 8000 GM at 780 nm, which is ideal for both in vitro and in vivo bio-imaging applications.

          Abstract

          Small organic dyes with large two-photon absorption (TPA) cross sections ( δ) are more desirable in many applications compared with large molecules. Herein, we proposed a facile theoretical method for the fast screening of small organic molecules as potential TPA dyes. This method is based on a theoretical analysis to the natural transition orbitals (NTOs) directly associated with the TPA transition. Experimental results on the small indolic squaraine dyes (ISD) confirmed that their TPA cross sections is strongly correlated to the delocalization degree of the NTOs of the S 2 excited states. Aided by this simple and intuitive method, we have successfully designed and synthesized a small indolic squaraine dye (ISD) with a remarkable δ value above 8000 GM at 780 nm. The ISD dye also exhibits a high singlet oxygen generation quantum yield about 0.90. The rationally designed TPA dye was successfully applied in both two-photon excited fluorescence cell imaging and in vivo cerebrovascular blood fluid tracing.

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          Most cited references 38

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          Deep tissue two-photon microscopy.

          With few exceptions biological tissues strongly scatter light, making high-resolution deep imaging impossible for traditional-including confocal-fluorescence microscopy. Nonlinear optical microscopy, in particular two photon-excited fluorescence microscopy, has overcome this limitation, providing large depth penetration mainly because even multiply scattered signal photons can be assigned to their origin as the result of localized nonlinear signal generation. Two-photon microscopy thus allows cellular imaging several hundred microns deep in various organs of living animals. Here we review fundamental concepts of nonlinear microscopy and discuss conditions relevant for achieving large imaging depths in intact tissue.
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            Relative and absolute determination of fluorescence quantum yields of transparent samples.

            Luminescence techniques are among the most widely used detection methods in the life and material sciences. At the core of these methods is an ever-increasing variety of fluorescent reporters (i.e., simple dyes, fluorescent labels, probes, sensors and switches) from different fluorophore classes ranging from small organic dyes and metal ion complexes, quantum dots and upconversion nanocrystals to differently sized fluorophore-doped or fluorophore-labeled polymeric particles. A key parameter for fluorophore comparison is the fluorescence quantum yield (Φf), which is the direct measure for the efficiency of the conversion of absorbed light into emitted light. In this protocol, we describe procedures for relative and absolute determinations of Φf values of fluorophores in transparent solution using optical methods, and we address typical sources of uncertainty and fluorophore class-specific challenges. For relative determinations of Φf, the sample is analyzed using a conventional fluorescence spectrometer. For absolute determinations of Φf, a calibrated stand-alone integrating sphere setup is used. To reduce standard-related uncertainties for relative measurements, we introduce a series of eight candidate quantum yield standards for the wavelength region of ∼350-950 nm, which we have assessed with commercial and custom-designed instrumentation. With these protocols and standards, uncertainties of 5-10% can be achieved within 2 h.
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              Proliferation of parenchymal microglia is the main source of microgliosis after ischaemic stroke.

              Stroke induces rapid activation and expansion of microglia, but the main source of microgliosis is controversial. Here we investigated the formation of microgliosis and infiltration of circulating cells in a photothrombosis stroke model by taking advantage of parabiosis and two-photon microscopy. We found that a small population of blood-derived CX3CR1(GFP/+) cells infiltrated the cerebral parenchyma, but these cells did not proliferate and were phenotypically distinguishable from resident microglia. CX3CR1(GFP/+) infiltrating cells also displayed different kinetics from reactive microglia. The number of CX3CR1(GFP/+) infiltrating cells peaked on Day 5 after stroke and then decreased. The decline of these infiltrating cells was associated with an active apoptotic process. In contrast, reactive microglia were recruited to the ischaemic area continuously during the first week after stroke induction. Immunohistology and in vivo two-photon imaging revealed that cells involved in the process of microgliosis were mainly derived from proliferating resident microglia. Expansion of microglia exhibited a consistent pattern and our in vivo data demonstrated for the first time that microglia underwent active division in regions surrounding the ischaemic core. Together, these results indicated that CX3CR1(GFP/+) infiltrating cells and reactive microglia represented two distinct populations of cells with different functions and therapeutic potentials for the treatment of stroke.
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                Author and article information

                Journal
                Chem Sci
                Chem Sci
                Chemical Science
                Royal Society of Chemistry
                2041-6520
                2041-6539
                1 January 2015
                7 October 2014
                : 6
                : 1
                : 761-769
                Affiliations
                [a ] State Key Laboratory of Applied Organic Chemistry (SKLAOC) , College of Chemistry and Chemical Engineering , Lanzhou University , Lanzhou 73000 , P. R. China . Email: haoli.zhang@ 123456lzu.edu.cn
                [b ] Beijing National Laboratory for Molecular Sciences (BNLMS) Institute of Chemistry , Chinese Academy of Sciences , Beijing 100190 , P. R. China
                [c ] School of Life Sciences , Lanzhou University , Lanzhou 73000 , P. R. China
                [d ] School of Basic Medical Sciences , Lanzhou University , Lanzhou 730000 , P. R. China
                [e ] Department of Chemistry , Capital Normal University , Beijing 100048 , P. R. China
                Article
                c4sc02165g
                10.1039/c4sc02165g
                5590541
                This journal is © The Royal Society of Chemistry 2014

                This is an Open Access article distributed under the terms of the Creative Commons Attribution 3.0 Unported License ( http://creativecommons.org/licenses/by/3.0/) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                Categories
                Chemistry

                Notes

                †Electronic supplementary information (ESI) available: Synthetic procedures and structural characterization of compounds, all the NTOs, time-resolved fluorescence spectra and the video of microscopy (Video-S1 and S2). See DOI: 10.1039/c4sc02165g

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