Development Of Novel Fluorescent Sensors Based On Functional Nucleic Acids And Aggregation-induce Emission Fluorophores

The development of fluorescent sensors for ions, small molecules, biologicalmolecules and pathogens have attracted great attention since fluorescent sesorsshowed advantages of ease in operation, high sensitivity, good selectivity, and hightime and spatial resolution. Ideal fluorescent sensors require both high specificrecognition unit and excellent fluorophores as signal response unit. Hence, the aim ofthis dissertation is to design and develop novel fluorescent sensors based onfunctional nucleic acids (FNAs) and aggregation-induced emission (AIE)fluorophores.Firstly, new label-free catalytic and molecular beacon (CAMB) sensors weredeveloped for sensitive fluorescent detection of small inorganic and organicmolecules. The sensor design had the advantages of both the label-free methods,which were low cost and could preserve the activity of the FNAs, and the CAMBmethods, which exhibited signal amplification via multiple-turnover catalyticreactions and ease for the rational design of aptazymes. By using the8-17DNAzyme,the new label-free CAMB sensor showed an approximately linear relationship withPb2+concentration in the range of0-2μM and a detection limit of3.8nM. By usingthe aptazyme for adenosine based on the10-23DNAzyme, our method could alsodetect adenosine successfully with a detection limit of1.4μM. In addition, applicationof this method in biologically relevant sample analysis was successfully achieved.Secondly, by the advantages of AIE fluorophores, two novel fluorescent sensorswere developed for monitoring pH fluctuations in live cells and building test paper forCu2+determination in this dissertation, respectively. In the former case, a ratiometricfluorescent pH sensor,4-carboxylaniline-5-chlorosalicylaldehyde Schiff base, wassynthesized via a facile reaction. The integration of hydroxyl and carboxyl groupsprovided the sensor with a significant fluorescence color change from orange to greenand an intensity ratio (I516nm/I559nm) enhancement when the pH increased from5.0to7.0in aqueous solution. Confocal fluorescence imaging of intracellular pH throughratiometric response was successfully achieved by using this sensor in live HepG2cells. In the later case, a novel fluorescent sensor bis (pyridin-2-ylmethylene)terephthalohydrazide for Cu2+determination was developed. The sensor molecule showed high sensitivity and selectivity to Cu2+by forming a1:2metal-to-ligandcomplex in aqueous solution. The fluorescence decrease at516nm was linearlyrelated to the concentration of Cu2+in the range of0.2-8.0μM. In addition, thedevelopment of test paper for Cu2+determination was successfully achieved. Both ofthese sensors showed advantages of ease in preparation, high selectivity and largeStokes shift.Thirdly, highly emissive fluorescent silica nanoparticles (FSNPs) encapsulatedby AIE fluorophores were developed by a simple sol-gel reaction in this dissertation.The emission efficiencies and particle diameters of the FSNPs were manipulated bychanging the fluorophore loadings and the reaction conditions. To combine the meritproperties of FNAs and AIE fluorophores, FSNPs were functionalized with NCL-aptamer, which facilitated the nanoparticles for potential applications in targetingnucleolin-overexpressed MCF-7cells.