Design And Synthesis Of Redox-sensitive Optical Probes For Bioimaging Applications

It is necessary to maintain the balance of redox status within aerobic organisms.Uncontrolled doses of redox species have been demonstrated to be associated with many diseases.Thus increasing attentions have been drawn to design sensitive and selective sensors for detection of redox species.Luminescence imaging has attracted fast-growing interest owing to its advantages,such as noninvasiveness,high sensitivity and specificity through staining with a luminescent probe.Developing a luminescent probe for detection of redox species in biological samples has become one of the most important assay methods.Although many luminescent probes have been reported for quantification of redox species,commonly used probes are fluorescent organic compounds.In most cases,these compounds often undergo complicated synthesis process,and have small Stokes shift,poor photostability and water solubility,which limit their real biomedical applications.Additionally,most of these probes exhibit emission changes upon addition of analytes.The responses at a single detection window can be affected by experimental conditions,such as fluctuations of probe concentrations and excitation laser power.Importantly,when fluorescent probes are used for tissues or living small animals,the autofluorescence from endogenous compounds usually interferes the results of imaging and reduces the precision and accuracy for analysis.Hence,the design and preparation of novel luminescent probes for redox species are now chanllenging and necessary.In this thesis,we focus on the development of luminescent nanoprobes with imporved biocompatibility and photostability.Furthermore,the specific photophysical properites of nanoprobes,such as dual emission and long emission lifetime,have been investigated in detail.The combination of these probes with different optical imaging techniques has been applied for in vitro and in vivo imaging with high sensitivity and accuracy.The research content of the thesis includes the following parts: 1.Dual-emissive nanohybrid for ratiometric and lifetime imaging of intracellular hydrogen sulfideWe design a nanohybrid for the detection of hydrogen sulfide(H2S)based on mesoporous silica nanoparticles.A phosphorescent iridium(III)complex and a specific H2S-sensitive organic dye are embedded into the nanohybrid.It exhibits a unique dual emission which is ascribed to the iridium(III)complex and the organic dye,respectively.Upon addition of H2 S,the emission from the organic dye is quenched,while that from the iridium(III)complex is almost unchanged,which enables the ratiometric detection of H2 S.Additionally,the nanohybrid owns long luminescence lifetime and displays a significant change in luminescence lifetime in response to H2 S.Intracellular detection of H2 S is performed via ratiometric imaging and photoluminescence lifetime imaging microscopy.As far as we know,the nanoprobe is the first example to utilize lifetime-based method for intracellular H2 S detection,which provides a novel direction for investigation of physiological process.2.Luminescent gold nanocluster-based sensing platform for redox species detection in vitro and in vivo with improved accuracy and anti-interference abilityGold nanoclusters have emerged as promising luminescent nanomaterials because of their good water solubility,high photostability,easy bioconjugation and long emission lifetime.We used long-lived luminescent gold nanoclusters as a nanoplatform to construct two dual-emissive nanoprobes for detection of oxygen levels and H2 S in cells and zebrafishes.In the probe for oxygen levels,an O2-sensitive phosphorescent iridium(III)complex was modified on the suface of gold nanoclusters with a convenient method.The nanoprobe exhibits high sensitivity,selectivity and excellent reversibility,and has been empolyed for hypoxia imaging in vitro and in vivo.In the probe for H2 S,chitosan oligosaccharide lactate is used as the bridge to connect gold nanoclusters and a H2S-sensitive merocyanine compound.Gold nanoclusters and the specific H2S-sensitive merocyanine compound have been used as energy donor and acceptor,respectively.Addition of H2 S induces changes in emission profile and luminescence lifetime of the platform with high sensitivity and selectivity.Both nanoprobes have been demonstrated to be self-calibrating and less affected by the probe concentration and incident excitation power through luminescence ratio-based assay.Additionally,through utilization of time-resolved luminescence imaging techniques,probes have been proved to show minimized autofluorescence interference and improved accuracy of detection,espcially in in vivo imaging.Both nanoprobes are based on the gold nanoclusters with outstanding optical properties.The gold nanocluster-based nanoplatform can be further applied to develop many ratiometric and long-lived luminescent sensors for specific analytes through conjugation of different responsive organic compounds.Additonally,chitosan oligosaccharide lactate functionalized gold nanoclusters exhibit emission in the green region,with enhanced quantum yield,elongated emission lifetime and remarkable photophysical stability over gold nanoclusters,showing their potential value for biological appliactions.3.Highly effective nanoaggregate photosensitizer based on D-A type organic dye for photodynamic therapyA series of donor-acceptor based fluorescent organic dyes have been designed and synthesized.The photoluminescence emission maxima of these organic dyes have been adjusted from visible light to near infrared regions by employing different eletron donors,which provides an effective regulation for rational design of novel fluorescent organic dyes.Additonally,we select organic molecule QM-3 with intense emission in solids and high reactive oxygen species production as a photosensitizer.By encapsulating QM-3 into amphiphilic molecules,water-soluble nanoaggregate,QM-3@NP,has been obtained and exhibited good reactive oxygen species generation.QM-3@NP has been further applied for intracellular photodynamic therapy.Different from the traditional photosensitizer,QM-3@NP shows the enhanced reactive oxygen species generation in aggregates,which makes it potential nanomaterials for image-guided cancer therapy.