Activatable Semiconducting Oligomer Amphiphile for Near-Infrared

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Activatable Semiconducting Oligomer Amphiphile for Near-Infrared Luminescence Imaging of Biothiols Chen Xie, Yan Lyu, Xu Zhen, Qingqing Miao, and Kanyi Pu ACS Appl. Bio Mater., Just Accepted Manuscript • DOI: 10.1021/acsabm.8b00353 • Publication Date (Web): 06 Sep 2018 Downloaded from http://pubs.acs.org on September 6, 2018

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ACS Applied Bio Materials

Activatable Semiconducting Oligomer Amphiphile for Near-Infrared Luminescence Imaging of Biothiols Chen Xie, Yan Lyu, Xu Zhen, Qingqing Miao and Kanyi Pu* School of Chemical and Biomedical Engineering, Nanyang Technological University, 637457, Singapore Keywords: polymer nanoparticles, molecular imaging, biothiols, near-infrared fluorescence

Abstract: Abnormal level of biothiols such as cysteine (Cys) and homocysteine (Hcy) is associated with many pathological diseases. However, most fluorescence probes for biothiols sensing rely on visible fluorescence which are not optimized for in vivo imaging because of the shallow tissue penetration. We herein synthesize a hydrophobic oligo(phenylenevinylene) (OPV) based semiconducting oligomer amphiphile that can emit both fluorescence and afterglow luminescence and evaluate its ability for detection of biothiols. Such an amphiphile is used to encapsulate a hydrophobic near-infrared (NIR) dye through π-π stacking and hydrophobic interaction to develop a near-infrared (NIR) fluorescence nanoprobe (OPVN0.2). Because the OPV backbone has the benzaldehyde end groups that can specifically react with biothiols, the fluorescence of OPVN0.2 is enhanced in the presence of biothiols; however, its afterglow luminescence of OPVN0.2 remained nearly the same due to the different luminescence mechanism. Such a nanoprobe permits sensitive detection of biothiols both in vitro and in vivo.

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INTRODUCTION Cysteine (Cys) and homocysteine (Hcy) are two important biothiols which impact variety of physiological and biological processes such as detoxification, post-translational modification, protein synthesis and cellular homeostasis.1,2 For instance, deficiency of Cys may lead to lethargy, edema, slowed growth and liver damage.3-5 Abnormal level of Hcy is involved in Alzheimer’s, coronary heart and cardiovascular diseases.6-8 Due to their importance in physiology, sensing of Cys and Hcy has been the focus of large numbers of studies.9 Among numerous detection methods, optical techniques especially fluorescence imaging has been widely studied because of its significant advantages including high sensitivity, simplicity, low cost and real-time sensing capability.10 Based on fluorescence imaging, a variety of fluorescence probes have been designed for sensing of Cys and Hcy.11-14 However, most of such fluorescence probes rely on visible fluorescence as the signal rather than near-infrared (NIR) fluorescence, which significantly restrict their in vivo applications due to the shallow tissue penetration. Thus, development of NIR fluorescence probe for Cys and Hcy detection is highly demanded. Semiconducting polymer nanoparticles (SPNs) have shown great potential in the field of optical imaging because of their good biocompatibility and outstanding optical property.15-17 SPNs have been utilized for fluorescence imaging, photoacoustic (PA) imaging and photothermal therapy due to their NIR absorption, and high photothermal conversion efficiencies.18-25 Until now, fluorescent SPNs have been applied for tumor imaging,26,27 cell imaging,28,29 and ultrafast imaging of blood flow.30 SPNs have also been used for detecting druginduced hepatotoxicity31 and acute neuroinflammation32 through chemiluminescence imaging. Meanwhile,

poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]

(MEHPPV)-based


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SPNs have been found to continuously emit luminescence long after removal of light excitation. Such afterglow luminescence behavior permits ultrasensitive in vivo imaging due to the elimination of tissue autofluorescence.33,34 Because of the structural versatility, SPNs-based activatable nanoprobes have been designed for imaging of reactive oxygen and nitrogen species (RONS),35,36 metal ions,37,38 enzyme,39 pH40 and temperature,41 showing their great potential in molecular imaging. Although SPNs have shown great promise for activatable fluorescence imaging, SPNs are mainly prepared by encapsulation of semiconducting polymers (SPs) into amphiphilic block copolymers such as polystyrene-b-poly(acrylic acid) (PS-b-PAA)42 and poly(ethylene glycol)-bpoly(propylene glycol)-b-poly(ethylene glycol) (PEG-b-PPG-b-PEG).43 These SPNs are binary micelles and thus they encounter the potential issue of dissociation.44 Such disadvantage can further lead to the poor biodistribution and changed optical properties in vivo.45 Thus, alternative approaches for SPN-based activatable probes are highly desired. We herein report the design and synthesis of a semiconducting oligomer amphiphile (OPVPEG) to detect Cys and Hcy. Such an amphiphile is composed of a hydrophobic oligo(phenylenevinylene) (OPV) with two benzaldehyde groups and hydrophilic poly(ethylene glycol) (PEG) chains. The OPV segment acts as the signal source and the sensing component for Cys and Hcy, while two hydrophilic PEG chains provide water solubility to OPV. In addition, a NIR-absorbing photosensitizer, 2,3-naphthalocyaninato-bis(trihexylsiloxy)silane (NCBS), can be encapsulated into OPV-PEG to develop OPVN into a NIR fluorescent activatable nanoprobe for detection of Cys and Hcy. At last, the proof-of-concept imaging of Cys and Hcy is demonstrated both in cells and in living animals.


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Scheme 1. Synthetic route for OPV-PEG.

(i) 1,6-dibromohexane, sodium methoxide in methanol (25 wt%), ethanol, reflux, 2 h; (ii) polyoxymethylene, hydrobromic acid in acetic acid (33 wt%), glacial acetic acid, 70 °C, 4 h; (iii) triphenylphosphine, anhydrous toluene, reflux, 3 h; (iv) 2,5-dimethoxyterephthalaldehyde, lithium ethanolate, anhydrous dichloromethane (DCM), 25 °C, 4 h; (v) iodine, DCM, room temperature, overnight; (vi) NaN3, DCM/N,N-dimethylformamide (DMF), 30 °C, 48 h; (vii) mPEG-alkyne, CuBr, N,N,N’,N’’,N’’’-pentamethyldiethylenetriamine (PMDETA), tetrahydrofuran (THF), room temperature, 48 h.

RESULTS AND DISCUSSION OPV-PEG was synthesized by conjugating PEG onto a dialdehyde-modified OPV (Scheme 1). Hydroquinone (compound 1) was reacted with 1,6-dibromohexane to give compound 2 with two alkyl bromide groups. Compound 2 was then treated with polyoxymethylene and hydrobromic acid to give compound 3. Triphenylphosphine was reacted with compound 3 to afford compound 4 with phosphonium bromide which was a substrate for Wittig reaction. Then, compound 4 was reacted with 2,5-dimethoxyterephthalaldehyde by Wittig reaction to give OPV-Br, and then the alkyl bromide of OPV-Br was substituted by sodium azide to afford OPV-N3. The structures of


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OPV-Br and OPV-N3 were confirmed by proton nuclear magnetic resonance (1H NMR),

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NMR and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDITOF MS) (Figures S1-S4). The substitution of bromide by azide was confirmed by the shift of the characteristic peak from 3.41 ppm (–CH2Br) into 3.28 ppm (–CH2N3). Finally, OPV-N3 was conjugated with propargyl end-functionalized methoxy-PEG (mPEG-alkyne) (Mn = 2000 g/mol) via copper-catalyzed click reaction to give OPV-PEG. 1H NMR was also used to confirm the structure of OPV-PEG, the resonance peaks of OPV segment (10.45-10.34, 7.62-6.86, 4.46-3.76, 1.77-1.28 ppm) and the PEG repeating unit (3.64 ppm) were all clearly observed (Figure S5). In addition, gel permeation chromatography (GPC) result demonstrated the successful conjugation of PEG onto OPV because of the much higher molecular weight (6416 g mol-1) for OPV-PEG as compared with OPV-Br and OPV-N3 (Figure S6). These results clearly demonstrated the successful synthesis of OPV-PEG. Because of the conjugation of PEG, OPV-PEG had good solubility in aqueous solution and can form small nanoparticles through self-assembly. Transmission electron microscope (TEM) images indicated the spherical morphology of OPV-PEG nanoparticles. Dynamic light scattering (DLS) results indicated that the hydrodynamic size of OPV-PEG was 8.1 ± 1.5 nm, which remained almost the same after addition of Cys (7.5 ± 1.5 nm) (Figure 1a). The optical properties of OPV-PEG were then studied. The maximum absorption of OPV-PEG was at 445 nm, and its emission range was from 500 to 800 nm with the maximum at ~600 nm. OPV-PEG had a fluorescence quantum yield of 0.86%. After adding Cys, both the maximum absorption and emission of OPV-PEG showed obvious blue-shifts to 420 nm and 500 nm, respectively (Figure 1b and 1c). In addition, the fluorescence of OPV-PEG at 500 nm increased linearly upon adding Cys (Figure 1d), indicating the ability for quantification of Cys. The saturation point was


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detected at the concentration of 900 µM, and the fluorescence of OPV-PEG at 500 nm was increased by 25.2-fold compared with its original. The limit-of-detection (LOD) was calculated as 12.3 µM, which was lower than the physiological concentration of Cys (30 - 200 µM).46 In the structure of OPV moiety, the aldehyde groups acted as not only the electron-withdrawing groups but also reactive groups for Cys and Hcy. Thus, the intramolecular charge transfer (ICT) from phenylenevinylene to aldehyde groups could be switched off after the reaction of aldehyde groups with Cys/Hcy, which resulted in the blue-shift in absorption and emission of OPV-PEG. The blue-shifted absorption and fluorescence spectra as well as the enhanced fluorescence intensity indicated that Cys could react with the aldehyde groups in the structure of OPV-PEG, forming the thiazolidine adduct (Figure 1e).47 Because phenylenevinylene-containing structures could have afterglow signal after light irradiation based on our previous literatures,33,34 the afterglow intensities of OPV-PEG were then tested. The afterglow intensity of OPV-PEG remained nearly the same after addition of Cys (Figure 1f). Such a difference intensity change from fluorescence was reasonable, because afterglow had a unique luminescence mechanism that was distinct from fluorescence. Based on our studies, the afterglow luminescence mechanism can be proposed as follows: OPV can generate singlet oxygen (1O2) under light irradiation, the generated 1O2 can further oxidize the double bonds in the structure of phenylenevinylene to give the unstable dioxetane intermediate. Such intermediate degrades while emitting photons.33 In addition to fluorescence intensity, generation of 1O2 upon light irradiation was an important factor for afterglow luminescence intensity. Singlet oxygen sensor green (SOSG) was thus used to detect the ability to generate 1O2 before and after treatment of Cys. It showed that OPV-PEG generated less 1O2 after treatment with Cys (Figure 1g), and thus led to slightly decrease afterglow intensity despite the increase


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fluorescence. In conclusion, these data indicated that OPV-PEG had good responsiveness to Cys, and was a good candidate for the preparation of activatable nanoprobe for Cys.

Figure 1. In vitro characterization of OPV-PEG. (a) Size distribution of OPV-PEG (8 µg mL-1) in phosphate buffer solution (PBS) before and after addition of Cys (1 mM). Inset is the representative TEM image of OPV-PEG before adding Cys. The scale bar represents 30 nm. Absorption (b) and fluorescence (c) spectra of OPV-PEG (8 µg mL-1) before and after adding Cys (1 mM). (d) Fluorescence intensities of OPV-PEG (8 µg mL-1) at 500 nm under different Cys concentrations in 1×PBS (pH = 7.4). Excitation: 450 nm. (e) Proposed mechanism for Cys imaging by OPV-PEG. (f) Afterglow intensities of OPV-PEG (200 µg mL-1) before and after adding Cys (5 mM) recorded by IVIS. (g) Enhancement of fluorescence intensity (F/F0) for SOSG (1 µM) incubated with OPV-PEG (1 µg mL-1) at 528 nm before and after adding Cys as a function of irradiation time by white light (1 W cm-2). The afterglow signals were collected by using bioluminescence mode after 1 min white light irradiation (1 W cm-2). Error bars show standard deviations (SDs) (n = 3). n.s. indicates no statistically significant difference. After confirming that OPV-PEG had good cytocompatibility and stability in physiological conditions (Figure 2a and Figure S7), OPV-PEG was applied to detect Cys in living cells. Hela


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cells were divided into three groups with different pretreatment. For the Cys group, Cys was used to pretreat the cells to increase the intracellular concentration of Cys. For the NEM+cys group, N-ethylmaleimide (NEM), a thiol scavenger, was first used to pretreat the cells, followed by the addition of Cys. After incubating OPV-PEG with cells, only weak green fluorescence signal could be detected for the cells without any treatment (Control group), which indicated the relatively low concentration of Cys in Hela cells (Figure 2b). In contrast, such fluorescence intensity for Cys group was significantly higher (1.7-fold) than that of control cells (Figure 2c). Such enhancement in the fluorescence signal was attributed to the activation of OPV-PEG by Cys in the living cells. In addition, for the NEM+cys group, the fluorescence intensity was almost identical to the control group, because the increased Cys concentration in living cells was compromised by NEM (Figure 2b and 2c). These data indicated that OPV-PEG effectively monitored the concentration of Cys in living cells.

Figure 2. Imaging of Cys in cell using OPV-PEG. (a) Cell viability of Hela cells after incubation of OPV-PEG in various concentrations for 24 h. (b) Confocal images of Hela cells with different pretreatments after incubation with OPV-PEG (30 µg mL-1) for 24 h. 4’,6-diamidino-2phenylindole (DAPI) was used to stain the cell nuclei (blue). The scale bar represents 20 µm. (c) Comparison of green fluorescence intensities of Hela cells with different pretreatments after


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incubation with OPV-PEG (30 µg mL-1) for 24 h. Error bars show SDs (n = 3). Double asterisks indicate p < 0.01. To redshift the fluorescence and afterglow signals of OPV-PEG into the NIR region, a NIRabsorbing photosensitizer, NCBS, was doped into OPV-PEG to afford OPVN (Figure 3a). The doping amount was optimized from 0.2% to 4% w/w, and 0.2% w/w (OPVN0.2) was chosen as the candidate because of its smaller size, relatively high NIR fluorescence and afterglow intensities compared with other OPVNs (Figure S8a-S8c). For OPVN0.2, its average diameter (~7.7 nm) and morphology were almost the same compared with those of OPV-PEG (Figure 3b). Different from OPV-PEG, OPVN0.2 had an emerged absorption peak at 775 nm, the decreased fluorescence intensity around 600 nm and increased fluorescence intensity at 776 nm (Figure 3c and 3d). OPVN0.2 had a fluorescence quantum yield of 0.78%. Obvious spectral overlap existed in the range of 600 to 750 nm between the absorption of NCBS and the emission of OPV-PEG (Figure S8d). These results demonstrated the successful encapsulation of NCBS and efficient fluorescence resonance energy transfer (FRET) from OPV to NCBS within OPVN0.2. The afterglow intensity of OPVN0.2 under white light irradiation was 3.2-fold higher than that of OPV-PEG, and such afterglow intensity can further increase 3.8-fold under 808 nm laser irradiation. Furthermore, the afterglow intensity of OPVN0.2 was 7.7-fold higher than that of OPV-PEG under laser irradiation at 808 nm (Figure 3e). These phenomena were consistent with our previous studies, as NCBS can generate more 1O2 than OPV-PEG under white light irradiation, and even more 1O2 can be generated under 808 nm laser irradiation for NCBS.33,34 These data indicated that doping NCBS was able to efficiently redshift the emission of OPVN to NIR region and enhance the afterglow intensity of OPVN.


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Figure 3. Synthesis and characterization of the NIR fluorescent probe. (a) Schematic diagram for the preparation of OPVNs. (b) Size distributions of OPV-PEG and OPVN0.2 in 1×PBS buffer (pH = 7.4). The inset image is the representative TEM image of OPVN0.2, the scale bar represents 30 nm. Absorption (c) and fluorescence (d) spectra of OPV-PEG and OPVN0.2 in 1×PBS buffer (pH = 7.4). (e) Afterglow intensities of OPV-PEG and OPVN0.2 (200 µg mL-1) under white light or laser irradiation at 808 nm. The afterglow signals were collected by bioluminescence mode after white light or 808 nm laser irradiation (1 W cm-2) for 1 min. Error bars indicate SDs (n = 3). The sensing response of OPVN0.2 towards biothiols was then studied. Upon adding Cys, the emission of OPVN0.2 at 780 nm under 710 nm excitation linearly increased (Figure 4a and 4b), validating the feasibility for quantification of Cys. The saturation point was detected at the concentration of 600 µM, and the fluorescence of OPVN0.2 at 780 nm was increased by 2.2-fold compared with its original. The LOD was calculated as 39.5 µM under the probe concentration of 8 µg mL-1 (Figure 4b). Such LOD was in the range of physiological concentration of Cys.46


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Similar fluorescence enhancement at 780 nm was detected when 450 nm was used as the excitation wavelength (Figure 4c and Figure S9a). Such phenomenon can be attributed to the efficient FRET from OPV to NCBS, leading to the fluorescence enhancement at 780 nm rather than at 500 nm. Similar to OPV-PEG, the afterglow intensity of OPVN0.2 showed no obvious change before and after addition of Cys (Figure 4d). Such phenomenon should be ascribed to the fact that the less amount of 1O2 was generated from OPVN0.2 after treatment of Cys (Figure 4e), which canceled out the increase luminescence intensity. Selectivity studies indicated that except Cys and Hcy, other amino acids tested herein could not enhance the fluorescence of OPVN0.2, demonstrating its high specificity to Cys and Hcy. Similarly, the detection could be conducted upon excitation at 450 nm (Figure S9b). The afterglow intensity of OPVN0.2 remained almost unchanged for all amino acids in the study (Figure 4f and Figure S9c). These data demonstrated that OPVN0.2 specifically detected Cys and Hcy and was promising for in vivo experiments because of its NIR emission.

Figure 4. In vitro detection of Cys using OPVN0.2. (a) Fluorescence spectra of OPVN0.2 (8 µg mL-1) under different concentrations of Cys in 1×PBS (pH = 7.4). Excitation: 710 nm. (b)


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Fluorescence intensities of OPVN0.2 at 780 nm under different Cys concentrations in 1×PBS (pH = 7.4). Excitation: 710 nm. (c) Fluorescence spectra of OPVN0.2 (8 µg mL-1) under different concentrations of Cys in 1×PBS (pH = 7.4). Excitation: 450 nm. (d) Fluorescence and afterglow images of OPVN0.2 (8 µg mL-1 for fluorescence, 200 µg mL-1 for afterglow) before and after adding Cys (600 µM for fluorescence, 5 mM for afterglow). (e) F/F0 for SOSG (1 µM) incubated with OPVN0.2 (1 µg mL-1) at 528 nm before and after addition of Cys with different irradiation time by 808 nm laser (1 W cm-2). (f) Afterglow and fluorescence intensities of OPVN0.2 (8 µg mL-1 for fluorescence, 200 µg mL-1 for afterglow) incubated with Cys, Hcy and other amino acids (600 µM for fluorescence, 5 mM for afterglow) in 1×PBS (pH = 7.4). 1: Control, 2: arginine, 3: asparagine, 4: glutamine, 5: glycine, 6: lysine, 7: methionine, 8: proline, 9: serine, 10: valine, 11: GSH, 12: Hcy, 13: Cys. The fluorescence images were acquired using 710 nm as excitation wavelength and 780 nm as emission wavelength. The afterglow images were collected by using bioluminescence mode after 1 min laser irradiation (1 W cm-2) at 808 nm. Error bars indicate SDs (n = 3). After verifying the cytocompatibility and stability in physiological condition (Figure S10), OPVN0.2 was then applied for in vivo imaging experiments. Nude mice were divided into three groups for the experiments. Lipopolysaccharide (LPS) was intraperitoneally pre-injected into mice to induce peritonitis, which could reduce the concentration of Cys.48,49 On the contrary, Cys was intraperitoneally injected into mice for the Cys group to increase the Cys concentration. At t = 4 h or 30 min post-injection of LPS or Cys, respectively, OPVN0.2 was intraperitoneally injected into mice, imaging experiments were then carried out after injection of OPVN0.2 for 3 h. The fluorescence intensity for Cys-treated mice was significantly higher (1.4 fold) than the control mice, while a 23% intensity reduction was observed for fluorescence of LPS-treated mice


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compared with that of control mice (Figure 5a and 5b). In contrast, the afterglow intensities showed no statistically significant difference among all the three groups, which was consistent with previous results (Figure 5b vs 4d). Such unchanged afterglow signal of OPVN0.2 allowed to track the probe location in living mice. In addition, afterglow signal had a significantly higher signal-to-background ratio (SBR) than fluorescence signal (Figure 5c), confirming that afterglow signal was more suitable for tracking the location of probe. The fluorescence enhancement upon Cys treatment and its reduction upon LPS treatment demonstrated that OPVN0.2 was able to monitor the change of Cys concentration in living animals.

Figure 5. In vivo imaging. (a) Representative fluorescence and afterglow images of mice intraperitoneally injected with OPVN0.2 (400 µg mL-1, 200 µL) for 4 h. The mice were pretreated with saline (0.2 mL), LPS (1 mg mL-1, 0.2 mL) or Cys (1 M, 0.2 mL) through intraperitoneal injection. (b) Quantifications of fluorescence and afterglow intensities for the images in (a). (c) SBRs of fluorescence and afterglow signals for the in vivo images in (a). Error bars indicate standard error of mean (n = 3). Single asterisk indicates p < 0.05. n.s. indicates no statistically significant difference. CONCLUSION In summary, an OPV-based amphiphilic semiconducting oligomer (OPV-PEG) which contains hydrophobic OPV moiety and hydrophilic PEG chains was prepared. The OPV-PEG was


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characterized and can be applied for detecting Cys. In addition, the amphiphilic structure of OPV-PEG allowed OPV-PEG to encapsulate a NIR-absorbing photosensitizer (NCBS) to give OPVN0.2 with the NIR emission for in vivo imaging of Cys. Both OPV-PEG and OPVN0.2 had good selectivity towards Cys owing to the benzaldehyde groups in the OPV backbone. In addition, OPVN0.2 showed enhanced afterglow signal (7.7-fold) compared with OPV-PEG because of the encapsulation of NCBS, allowing the feasibility of in vivo afterglow tracking of the probe location. With good biocompatibility, OPV-PEG and OPVN0.2 were successfully applied for intracellular and in vivo imaging of Cys, respectively.

ASSOCIATED CONTENT Supporting Information. The supporting information is available free of charge on the ACS Publications website. Experimental section, additional figures as indicated in the text (Figures S1 – S10); 1H NMR, GPC, DLS, fluorescence spectra, fluorescence and afterglow intensities, cell viability. AUTHOR INFORMATION Corresponding Author *Email: [email protected]. ORCID Kanyi Pu: 0000-0002-8064-6009 Notes The authors declare no competing financial interest.


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ACKNOWLEDGMENT K.P. thanks Singapore Ministry of Education (Academic Research Fund Tier 1: 2015-T1-002091; and Tier 2: MOE2016-T2-1-098) and Nanyang Technological University (Start-Up grant: M4081627.120) for the financial support. REFERENCES (1) Weerapana, E.; Wang, C.; Simon, G. M.; Richter, F.; Khare, S.; Dillon, M. B. D.; Bachovchin, D. A.; Mowen, K.; Baker, D.; Cravatt, B. F. Quantitative Reactivity Profiling Predicts Functional Cysteines in Proteomes. Nature 2010, 468, 790-795. (2) Reddie, K. G.; Carroll, K. S. Expanding the Functional Diversity of Proteins Through Cysteine Oxidation. Curr. Opin. Chem. Biol. 2008, 12, 746-754. (3) Shahrokhian, S. Lead Phthalocyanine as a Selective Carrier for Preparation of a CysteineSelective Electrode. Anal. Chem. 2001, 73, 5972-5978. (4) Zhang, W.; Yin, C.; Zhang, Y.; Chao, J.; Huo, F. A Turn-on Fluorescent Probe Based on 2,4-Dinitrosulfonyl Functional Group and Its Application for Bioimaging. Sensor Actuat. BChem. 2016, 233, 307-313. (5) Zhou, X.; Jin, X.; Sun, G.; Wu, X. A Sensitive and Selective Fluorescent Probe for Cysteine Based on a New Response-Assisted Electrostatic Attraction Strategy: The Role of Spatial Charge Configuration. Chem. Eur. J. 2013, 19, 7817-7824. (6) Wang, Y.; Liu, S.; Ling, W.; Peng, Y. A Fluorescent Probe for Relay Recognition of Homocysteine and Group IIIA Ions Including Ga(III). Chem. Commun. 2016, 52, 827-830. (7) Lv, H.; Yang, X.; Zhong, Y.; Guo, Y.; Li, Z.; Li, H. Native Chemical Ligation Combined with Spirocyclization of Benzopyrylium Dyes for the Ratiometric and Selective Fluorescence Detection of Cysteine and Homocysteine. Anal. Chem. 2014, 86, 1800-1807.


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Graphical Abstract


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Activatable Semiconducting Oligomer Amphiphile for Near-Infrared

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