Analytical Application Of Activatable D-A-D Type Benzothiadiazole-based Near-infrared Fluorescent Probes

As one of the main tools for fluorescence monitoring,organic fluorescent probes have been widely developed and used in biological analysis,such as molecular tracing,surgical navigation and bio-detection,which was reasonably due to its operation-simplicity,high sensitivity,low poisonousness and high modifiability.Compared with those common "Always on" fluorescent probes,activated fluorescent probes which shows visual signal only turned on by specific stimulus own many obvious advantages,such as low background and high information dencity reflected by imaging effects.Moreover,regulating optical properties of fluorescent probes to achieve at the near-infrared imaging window is a new development direction because it could have weak autofluorescence and little tissue damage.In recent decades,it was reported that many activation strategies and fluorophore frameworks with excellent performance have been developmented,and the monitoring platform has been extended from the first near-infrared region(NIR-I)to the second near-infrared region(NIR-II),which means the possibility for a higher signal-to-noise ratio could be reached.From the views of analytical chemistry,high signal-to-noise ratios can afford a lower detection limit and higher accuracy.Based on the above research background,we are mainly inspired from the donor-acceptor-donor(D-A-D)type near-infrared fluorescent organic skeleton,activated fluorescent probes with stronger functionality are developed on account of applications in different diseasemodels.According to special monitoring purposes and response characteristics,targeting modification and packaging materials are used to give our organic probes excellent biocompatibility,then in situ near infrared response imaging in cells and living mice are performed to monitoring bioactive small molecules like nitric oxide and methylglyoxal.This dissertation totally includes the following five chapters:Chapter 1.OverviewIn this chapter,we introduced different response strategies of activated fluorescent probes,including construction of bioluminescence,chemiluminescence,near-infrared organic fluorophore and artful activation strategies to achieve high signal-to-noise ratios.Subsequently,the molecular design of D-A-D type fluorophore which is one of fluorescence frameworks with NIR-II emission is introduced,and we described the research evolution to summarize theoretical experience and develop fluorescence properties from respects of electron acceptor,electron donor and other material modifications.Finally,an overview of our research about the the content,significance and innovation are described.Chapter 2.Nitric oxide prodrug delivery and release monitoring based on galactose-modified multifunctional nanoprobeNitric oxide(NO)-based cancer therapy has attracted much attention in a dozen years owing to its broad impact on cancer.Low concentrations of NO stimulate cancer cell progression,while its higher levels induce cell apoptosis,and thus,it has motivated the development of probes for in situ NO release monitoring.In this chapter,a galactose-modified benzothiadiazole-based fluorescent probe Gal NONP/C was synthesized as both a NO-responsive nanoprobe and NO prodrug carrier.The probe exhibited far-red emission in the range from 550 to 800 nm,and the response showed acidity preference.The galactose on the probe enabled selective targeting of hepatocellular carcinoma cells by binding to over-expressed asialoglycoprotein receptors on the cell surface.The probe also delivered lowmolecular weight NO prodrug JS-K into cells and monitored the real-time release of the generated NO.Furthermore,in vivo NO imaging with tumor targeting was demonstrated in HCC orthotopic transplantation nude mice and liver sections.Compared with the control experiment using a probe without NO prodrug loading,higher fluorescence response of NO was detected in the cell and liver slices of the HCC tumor model.This strategy presented in this chapter may pave the way to develop nanoprobes for in situ NO monitoring and therapy evaluation in NO-related cancer therapy.Chapter 3.An activatable near-infrared fluorescent probe for methylglyoxal imaging in Alzheimer’s disease miceVisual detection of the methylglyoxal(MGO)level in the brain is critical for understanding its role in the onset and progression of AD.In this chapter,we disclosed a near-infrared fluorescent probe DBTPP,for detecting MGO by utilizing o-phenylenediamine moiety derived from the acceptor benzothiadiazole as a MGO-specific sensing unit.DBTPP exhibits a series of distinct advantages,such as near-infrared emission,high selectivity and sensitivity,excellent acid-stability,and a huge off on ratio.The probe could accurately monitor both exogenous and endogenous MGO variations in human neuroblastoma cells.Besides,it was able to image the endogenous MGO in a transgenic AD mouse model successfully while nomal group presents negative results,suggesting the great potential of MGO as a biomarker for early AD diagnosis in the filed of clinical medicine.Chapter 4.An activatable NIR-II fluorescent nanoprobe improved by rational packaging for rapid detection of methylglyoxalAs one of active small molecules closely relating to multiple chronic inflammation especially Type-2 diabetes,MGO may be a potential key to visualize disease progression and treatment effect.However,lack of convenient and fast analytical methods cannot afford accurate MGO quantitative evaluation.In this chapter,an activatable NIR-II fluorescent probe TDTCD were synthesized and its reaction mechanism with MGO was discussed.A novel activatable nanoprobe MG-SLNP for MGO was then constructed based on molecular engineering and rational packaging.The solid core of nanoparticle not only successfully improved the stability and water solubility of the nanoprobe,but also greatly promoted the response rate while reacting with MGO.The comparison of MGO values between NIR-II fluorescence and the traditional HPLC method in vitro was discussed in blood samples for Type-2 diabetes.High-resolution viewing window,quick response and good biocompatibility led to satisfactory signal-to-noise ratio of MG-SLNP for real-time MGO bio-detection and imaging in vivo.Chapter 5.Summary and outlookIn this chapter,we make a systematic summary of the previous chapters,further elaborate the research significance and innovation of this dissertation.Then with the view of the current trends on activated D-A-D near-infrared fluorescent probes,we propose the difficulties and challenges which will be faced in the subsequent research.Meanwhile,our outlook will be presented at the end of this part.