Fluorescence Sensing Based On Small-size Conjugated Polymer Nanoprobes Containing Pyridyl Groups

Conjugated polymer nanoparticles(CPNPs)have become a research hotspot in chemical biosensing and cell imaging technology due to their unique physical and chemical properties,such as easy chemical modification,excellent spectroscopic characteristics,good stability and low toxicity.Reducing the size of CPNPs can minimize non-specific interactions and increase sensitivity in complex environments.In recent years,conjugated polymer nanoparticles with a particle size of?10 nm or smaller have gradually attracted particular attention.Therefore,a series of pyridyl-containing conjugated polymers(P1,P2,P3)were synthesized.Furthermore,the small-sized conjugated polymer nanoparticles were synthesized by reprecipitation or microemulsion method to construct highly sensitive biochemical sensing systems for heparin(Hep),protamine(Pro)and palladium ion(Pd²⁺).The specific research content includes the following three parts:(1)Ultra-small size(?1.2 nm)conjugated polymer nanoparticles(P1NPs)were synthesized by reprecipitation using a pyridyl-containing cationic conjugated polyelectrolyte P1 for the detection of heparin(Hep)and protamine(Pro).Cationic conjugated polymer nanoparticles can electrostatically interact with highly negatively charged heparin to form agglomerate of P1NPs,thereby causing fluorescence quenching of P1NPs at 420 nm.Protamine can specifically bind to heparin.Therefore,when protamine was added to P1NPs/Hep system,Hep and Pro form a stable ion-pair complex to release P1NPs,resulting in fluorescence recovery of P1NPs.These results can lead to highly sensitive and selective detection of heparin and protamine.Under the optimized conditions,the detection limits for heparin and protamine were as low as 2.0 ng/m L and 0.8 ng/m L,respectively.In addition,the P1NPs system has low cytotoxicity and can be used for imaging of live MCF-7 cell.(2)A novel hydrophobic pyridyl-containing conjugated polymer P2was converted into small-sized(about 8.1 nm in diameter)hydrophilic conjugated polymer nanorods(P2NRs)by a modified microemulsion method.The nitrogen atoms of the pyridyl groups in the P2NRs may coordinate with palladium ion to induce aggregation of the nanorods and fluorescence quenching at 413 nm.At the same time,a new absorption peak in the UV spectra is formed at 358 nm.Under the optimized conditions,the detection limits of Pd²⁺by fluorescence sensing or colorimetric assay were 0.065 and 2.36?M(S/N=3),respectively.Significantly,the system can detect Pd²⁺in liquid samples and He La cell lysates.(3)Dye-doped small-sized conjugated polymer nanoparticles(P3NPs/5%coumarin 6,?2 nm)were synthesized by a modified reprecipitation method using coumarin 6 and pyridine-containing conjugated polyelectrolyte P3 to achieve ultrasensitive detection of palladium ions.When Pd²⁺was added to the P3NPs/5%coumarin 6system,it can coordinated with the nitrogen and sulfur atoms in coumarin6 and the nitrogen atoms of pyridyl groups in P3 to form nanoparticles of slightly larger size(?4.5 nm).Therefore,the fluorescence at 450 nm was quenched accompanying a slight blue shift,thereby establishing a more sensitive detection system for palladium ion with the detection limit as low as 5.0 n M.