The Synthesis Of Functionalized Silica And Polymer Nanoparticles And Their Application In Fluorescence Signal Amplification And Analysis

Fluorescence analysis has been extensively used in analytical detection field because of its super comprehensive performance such as simple equipment,high sensitivity and in-situ detection.In recent years,the as-designed fluorescence analysis methods present higher sensitivity based on the nanomaterials,especially,those of functionalized with eminent signal amplification performance.Therefore,fluorescent nanoanalysis has been attracted much attention.Among various kinds of nanomaterials,functionalized fluorescent silica nanoparticles(SiO2 NPs)are extraordinary concerned in the field of the signal amplified detection.In general,grafting or pre-organization of dye molecules on the surface of SiO2 NPs is a facile strategy,based on the cooperative and collective sensing effect,to achieve fluorescence signal amplification.However,due to the steric hindrance effect,the number of dye molecules on the surface of the nanoparticles is limited,so that the signal amplification capability of the designed stratergies is restricted.House numerous dye molecules,carbon dots(CDs)or other fluorescenct materials inside a SiO2 NP can increase the loading fraction of the fluorophores significantly.Thus,it is a promising pathway to obtaine the stronger signal amplification based on the cooperative and collective sensing effect of fluorophores inside of the nanoparticles.In addition,according to previous literatures,conjugated polymers are widely used in fluorescence signal amplification analysis because of their light-harvesting ability and "molecular wire" effect.However,their preparation processes are complicated.In contrast,fluorescent non-conjugated polymer nanoparticles can overcome the above-mentioned shortcoming with low synthesis cost,which have attracted much attention in the field of fluorescence analysis and sensing,but few of works were focused on their signal amplification ability.In this study,three kinds of amplified fluorescence analysis methods were proposed based on the close communication of the fluorophores inside of functionalized fluorescent SiO2 NPs and the sub-fluorophores of the polymer nanoparticles.The details are summarized as follows:1.A signal amplification strategy based on the cooperative and collective effect of the dyes inside of the nano-core of the silica nanoparticles.Firstly,polyethyleneimine/silica NPs with core-shell structure(PEI@SiO2 NPs)were prepared by a reverse microemulsion method.Fluorescent FITC/PEI@SiO2 NPs were synthesized by covalent grafting FITC into the PEI core of the etched PEI@SiO2 NPs.Herein,copper ion quenching of the fluorescence intensity of FTIC was selected as a model to confirm the signal amplification of the densely grafted fluorescent receptor units inside the core of these particles.With respect to Stern-Volmer constant(Ksv)of Cu2+ quenching fluorescence,it revealed that,Ksv value of the FITC/PEI@SiO2 NPs was 10 and 5.6 times higher than that of the FITC in solution and on the surface of silica NPs,respectively.Thus,compared with traditional signal amplification strategy,as-prepared fluorescent receptor units can significant enhance the signal amplification with higher sensitivity.2.A kind of fluorescence signal amplification sensing method was designed based on the CDs inside of the CDs/PEI/silica nanoparticles(CDs/PEI/SiO2 NPs).CDs/PEI/SiO2 NPs were prepared by doping of CDs together with PEI inside SiO2 NPs via a reverse microemulsion route.According to the investigation,the as-prepared CDs/PEI/SiO2 NPs presented the higher fluorescence quantum yield(QY)and stronger signal amplification ability than that of free-state CDs.The QY of the CDs/PEI/SiO2 NPs was 38.6%,2.8 times higher than that of free CDs(13.7%).Here,the possible fluorescence enhancing mechanism of CDs inside CDs/PEI/SiO2 NPs was investigated by UV-vis absorption spectra,fluorescence spectra,IR spectra,transmission electron microscope and zeta potential technique,and the possible mechanism was also proposed.More importantly,the signal amplification performance of the CDs/PEI/SiO2 NPs was revealed by choosing Cu2+ as model.In our system,Ksv value of the CDs/PEI/SiO2 NPs was 2.3 times as much as that of free-state CDs.Meanwhile,the as-prepared CDs/PEI/SiO2 NPs exhibited 100-times sensitivity increasing for sensing Cu2+compared with free-state CDs sensing scheme reported by the previous literature.This work plays an important role in the study of the close communication effect between the nanodots and the fluorescence behavior of aggregated carbon quantum dots for amplified sensing.3.A novel "turn-on" amplified fluorescence sensing strategy was put forward based on the polymer nanoparticles(PNPs).They were prepared by the reaction of PEI with ascorbic acid at room temperature.Herein,a "turn-on" fluorescent sensing platform for amplified detection of formaldehyde is designed based on the as-prepared PNPs.As the PNPs possess an aggregated PEI structure,the sub-fluorophores at PNPs are densely concentrated.Concerning the supra-molecular or bond crosslink-enhanced emission(CEE)effect of formaldehyde to the PNPs,the formaldehyde can trigger a"turn-on" response for the fluorescence of the PNPs.Furthermore,the spatial proximity between the sub-fluorophores at PNPs led to an amplified detection of formaldehyde due the cooperative and collective sensing process.The results showed that signal amplification capability of as-prepared PNPs is closely related to the concentration of PEI during the reaction.When the concentration of PEI up to 50 mg mL-1,corresponding PNPs show superb signal amplification properties:the limit of detection is as low as 0.37 ?g mL-1 and the response constant is increased 9 times than that of low concentration of PEI(1 mg mL-1).The excellent performance can be responsible for the synergistic sensing effect between higher density sub-fluorophores and formaldehyde.