Stimuli Responsive Fluorescent Materials For Biosensing Applications

Fluorescence is one of the most versatile and extensively used techniques for bioimaging and biosensing as it investigates the biological samples in situ and provides suitable evidence at molecular level with extraordinary temporal and spatial resolution.However,low water solubility,enhanced cytotoxicity,strenuous synthesis techniques,tedious polymeric modifications and low quantum yields are still the major challenges associated with fluorescent materials used for biosensing applications.Fluorescent dyes and polymers with unconventional chromophore have been given a great emphasis by the researchers lately.Particular importance has been given to fluorescent dyes based on small organic molecules due to their sophisticated properties,such as easily modifiable structure,small size and possibility to tune their desired properties.Similarly,stimuli responsive fluorescent polymers with unconventional chromophores have also been focused recently due to their decent biocompatibility,enhanced water solubility and brilliant stability.In this thesis,the development of stimuli responsive and biocompatible fluorescent dyes and polymers for biosensing applications have been discussed.Our work can be divided into two parts.In the first and main part synthesis and characterization of polyethylene glycol(PEG)modified cystamine based multifunctional fluorescent dyes and their application for detection of F'and Cu2+have been reported.These fluorescent dyes named as CPEG-168,CPEG-1000 and CPEG-2000 were synthesized by one pot facile synthesis technique and chain length dependent quantum yields were calculated in pure aqueous medium.Due to the presence of disulfide group these probes could be the potential candidates for detection of thiols.Intramolecular hydrogen bonding(IMHB)between(NH----H)facilitates the formation of rigid cyclic structure with electron dense region for strong fluorescence emission.Sensitivity towards Cu2+ ions was obtained by exploiting the high chelating affinity of copper with-NH groups,while sensitivity towards pH and F-ions was provided by IMHB between-NH groups.Desired quantum yields can be tuned by changing the chain length or molecular weight of the PEG.In the second part optical properties of stimuli responsive fluorescent poly(amido amine)s(PAMAM)and their application for the detection of thiols in pure aqueous medium have been investigated.Three different kinds of hyperbranched PAMAM,named as MBAP(without disulfide group),CBAP and HPAP(with disulfide groups)were synthesized by Michael addition copolymerization technique.Redox sensitivity was achieved due to the presence of disulfide functionality while the amine groups made them pH sensitive.These unconventional fluorescent PAMAM were found to have enhanced water solubility,low cytotoxicity and high redox sensitivity hence applied for detection of thiols in pure aqueous medium.These stimuli responsive fluorescent materials could not only be used for biosensing applications but also to create opportunities for academic researchers to design new fluorescent materials based on unconventional chromophores.In the first chapter of this thesis different kinds of organic fluorescent materials were summarized.Those particularly designed for the detection of F-,Cu2+and thiols were discussed in the Chapter 2.In the third chapter synthesis and characterization of novel multifunctional polyethylene glycol-modified cystamine and their application for detection of Cu2+and F-have been reported.In the fourth chapter optical properties of stimuli responsive fluorescent PAMAM and their application for the detection of thiols were investigated.Finally,general conclusion and future perspectives have been discussed in chapter 5.