Counterion Enrichment Performance Of Spherical Polyelectrolyte Brush And Its Application In Protein Adsorption And Metal Detection

Spherical Polyelectrolyte Brushes(SPB)are a class of core-shell nanoparticles with unique properties,which are prepared by densely grafting polyelectrolyte chains onto polymer cores.By selecting appropriate monomers,various SPB with environmental response behavior(pH,ionic strength,temperature,light,etc.)can be prepared.SPB have shown great application potential in the fields of selective adsorption of metal ions,protein immobilization,nanocatalyst preparation and controlled drug release.In this paper,both anionic and cationic spherical polyelectrolyte brushes were synthesized.The outstanding counterion enrichment performance of nano-spherical polyelectrolyte brushes has been confirmed by small angle X-ray scattering(SAXS).And the application research of SPB in protein controllable immobilization,protein selective adsorption,and ratiometric fluorescence probe construction were systematically carried out.The main work is as follows:(1)Poly(sodium styrene sulfonate)spherical polyelectrolyte brush(PS@PSS SPB)was prepared by densely grafting poly(sodium styrene sulfonate)(PSS)chains from the surface of polystyrene(PS)core through photo-emulsion polymerization.The distribution of various counterions(Li+,NH4+,(CH3)4N+,Na+,Rb+,Cs+)within PS@PSS SPB was comprehensively studied by combining SAXS,dynamic light scattering(DLS)and Zeta potential.Results show that the SAXS intensity of PS@PSS SPB seemed to be "insensitive" to the concentration of Na+.Introducing salt ions with an electron cloud density lower than sodium(Li+,NH4+ and(CH3)4N+)into the SPB layer led to a decrease in the scattering intensity while introducing those with a higher electron cloud density than sodium(Rb+and Cs+)the opposite result was obtained.The SAXS fitting results show that the distribution of counterions in the brush layer was consistent with the distribution of the charge density of the brush chain,that is,the radial attenuation distribution.The density of counterions was highest near the PS core and decreased rapidly as the brush chain extended outward.(2)The controllable immobilization of lysozyme(Lys,p? 11)onto poly(sodium styrene sulfonate)spherical polyelectrolyte brush(PS@PSS SPB)was systematically studied by a combination of SAXS,steady-state/time resolved fluorescence spectroscopy,DLS and turbidimetric titration.Time-resolved fluorescence spectroscopy confirmed that the capture of Lys by SPB is a dynamic process,composed of a quick agglomeration process and a slow rearrangement process.Meanwhile,the SAXS and steady-state fluorescence measurements indicate that Lys molecule inclined to immobilize in the inner layer of the brush,and saturation of Lys adsorption onto the SPB was gradually reached as the protein concentration increased,proceeding from the inside to the outside of the brush layers.As the pH and ionic strength increased,the previously adsorbed Lys was partially released into the solution and migrated from the inner to the outer layer of SPB.Competitive adsorption experiments between Lys and bovine serum albumin(BSA)or ?-glucosidase(?-G)show that besides electrostatic interaction counterion release force also plays an important role in the immobilization of protein onto SPB.Under the contribution of the counterion release force,the adsorption of larger-sized proteins(BSA or ?-G)could cause the previously adsorbed smaller-sized proteins(Lys)to be replaced.(3)Two cationic spherical polyelectrolyte brushes(annealed PS@PAEMH SPB and quenched PS@PMAETA SPB)were prepared by grafting poly(2-aminoethyl methacrylate hydrochloride)(PAEMH)or poly[2-(methacryloyloxy)ethyl]trimethylammonium chloride(PMAETA)chains from the surface of PS core through photo-emulsion polymerization.By combining DLS,turbidimetric titration and SAXS,the difference between annealed brush(PS@PAEMH SPB)and quenched brush(PS@PMAETA SPB)in the selective adsorption of BSA and ?-G was systematically compared.Results indicate that by changing external conditions(such as pH and ionic strength),the adsorption and desorption of proteins on SPB can be easily controlled.For these two SPB,there was a significant difference in the adsorption selectivity of the brush for BSA and ?-G,and this difference was highly dependent on ionic strength.At low ionic strength,quenched PS@PMAETA SPB showed higher selectivity for BSA and ?-G,while annealed PS@PAEMH SPB performed better at high ionic strength.SAXS analysis shows that the volume exclusion effect played an important role in the adsorption of proteins by both SPB,and larger-sized proteins were more likely to be adsorbed on the outer layer of the brush.(4)Due to the outstanding ability of SPB to enrich counterions and immobilize charged nanoparticles,here a high-quality dual-emission ratiometric fluorescent probe for the determination of trace amount of Cu2+ was fabricated with poly(sodium styrene sulfonate)spherical polyelectrolyte brush(PS@PSS SPB)as the template.The fluorescent SPB with europium complex Eu(TTA)3Phen embedded in the PS core was prepared by mini-emulsion and photo-emulsion polymerization,and the desired ratiometric fluorescent probe was obtained after immobilizing the water-soluble GSH-CdTe QDs in the grafted PSS brush shell.For the ratiometric probe,the red fluorescence emitted by Eu(TTA)3Phen was used as the reference signal and the green fluorescence emitted by GSH-CdTe QDs was used as the sensing signal.Results show that the sensitivity and selectivity of this probe for Cu2+ were much higher over other metal ions,the addition of Cu2+could greatly quench the probe's fluorescence at 550 nm while the fluorescence signal at 614 nm remained unchanged.As the compound mass ratio between the fluorescent brush and the QDs(SPB:QDs)decreased,the probe became more sensitive and the detection limit also became lower,which may be because more concentrated QDs and Cu2+were accommodated in a single SPB.When the mass ratio of SPB to QDs was at 9:1,the intensity ratio of the two fluorescence emissions showed a great linear response to Cu2+ in the concentration range from 0 to 1000 nM,and the limit of detection(LOD)of Cu2+can be as low as 1.45 nM.In addition,the detection results of Cu2+ in real water samples indicate that the ratiometric fluorescent probe fabricated by this method has excellent reliability and applicability.