Ratiometric Luminescent Nanosensors For Detecting Cysteine And Dissolved Oxygen

Ratiometric luminescence in combination with nanoparticles and their superior properties has enable designing of improved chemosensors. With ratiometric luminescence, interferences to detecting caused by external factors including variation in sensor concentration, environment, and excitation intensity are expected to be alleviated. With nanomaterials, on the other hand, functions including sensing as well as imaging, drug delivering and photodynamic therapy can be effectively integrate together. Hence a growing number of rariocmetric luminescent nanosensors have been developed. Among them, fluorescent sensors based on upconversion nanoparticles(UCNPs) have been considered as a promising strategy to detect bio-analyte due to their advantages in deep penetration, minimum autofluorescence, and ratiometric fluorescent output. Fluorescent carbon dots(CDs) have attracted considerable attention in recent years as well for their superior properties including effective water dispersity, good biocompatibility, small size and good photostablity.In this dissertation, nanosensors with rariocmetric luminescence for detecting biological small-molecules including cysteine(Cys) and dissolved oxygen(DO) are designed. Efforts have been made in following aspects:A prototype of nanosensors combined with mesoporous silica coated UCNPs and a fluorescein-based fluorescent probe loaded in pores was established to detect Cys. The silica shell provided loading space for the probe and enabled the nanosensors to disperse in water. In the presence of Cys, the fluorescent probe was transformed into 5(6)-carboxyfluorescein with an emission band centering at 518 nm which was secondarily excited by the light at around 475 nm from NaYF4: Yb3+, Tm3+ UCNPs driven by 980 nm near-infrared(NIR) laser. The intensity ratio between green and blue luminescence(I518/I475) grew exponentially with increasing concentrations of Cys over a range of 20~200 μmol·L-1. The response of the nanosensors towards Cys was recognizable with naked eyes by luminescence color change. Evidences suggest that these nanosensors are capable of sensing Cys in aqueous solution and distinguishing Cys from homocysteine(Hcy) with kinetically-controlled selectivity. The system was further employed to detect Cys in human serum and the result was in agreement with it tested by high performance liquid chromatography with acceptable recoveryTo establish sensing systems with ratiometric luminescence based on F?rster resonance energy transfer(FRET), fluorescent probes and modified UCNPs were bound together via either coordination or covalence bonding. Under 980 nm laser excitation, both systems responded ratiometricly being treated with Cys. Although they exhibited inferior sensing performances, valuble informations about energy transfer mechanism and surface modification were revealed in this work.An optical oxygen nanosensor combined with CDs and Ru(III) complex was built. Under UV excitation, two emission bands existed in this system. One originated from Ru(III) complex centered at 624 nm whose phosphorescent intensity(I624) was sensitive towards O2, the other from CDs centered at 432 nm that hardly affected by O2. Therefore, I432 could be used as built-in standard in detection. Variation of I624/I432 of nanosensor with DO concentration in water could be described by Stern-Volmer equation in Lehrer expression. With a caliberated characteristic equation, this nanosensor was able to be used to measure DO concentration in a range of 0.72 ~ 42.14 mg/L.