Stimuli-responsive fluorescent hyperbranched poly(amido amine)s for biosensing applications

Hyperbranched Poly(amido amine)s (PAMAM) especially those containing disulfide groups have been highly investigated for DNA condensation, drugs and genes delivery. However, the detailed optical properties of PAMAM, intrinsic fluorescence characteristics and their applications for detection of thiols in pure aqueous medium have not been explored yet. Here we report for the first time the detailed investigation of optical properties of PAMAM and their biosensing application in pure aqueous medium. Three PAMAM named as MBAP (without disulfide group), CRAP and HPAP (with disulfide) groups were chosen, synthesized and characterized. Quantum yields of these PAMAM at different pH value were calculated in pure aqueous medium and all the PAMAM were found to be pH sensitive due to presence of tertiary amine and have shown increase in quantum yields in acidic medium. MBAP was not found to be redox sensitive due to the absence of disulfide group while CBAP has shown low redox sensitivity in aqueous medium because of low water solubility. HPAP has shown high redox sensitivity and high quantum yields hence applied for detection of thiols with the limit of detection of 5.29 mM in pure aqueous medium under physiological conditions. These investigations have not only shown the detailed optical properties of extremely important PAMAM but also broadens their application for bioimaging and biosensing.