Photoelectrochemical Bioanalysis Based On Polymer Nanoparticles

Semiconductor polymer nanoparticles(SPNs)is a new type of organic optical nanomaterials.They have excellent optical properties and good biocompatibility,such as large absorption coefficiency,adjustable optical property,controllable size,good photostability,easy surface functionalization,and the incorporation of organic and biological-inert components without toxic metals,and thus,become important materials for the bioanalysis.Semiconductor polymer nanoparticles have broad application prospects in fluorescence imaging and photodynamic therapy of tumors.As the optical properties of SPNs are mainly determined by the precursor of semiconductor polymers(SPs),they do not depend on the size of nanoparticles.This feature makes SPNs different from many metal nanoparticles whose spectral properties depend on the size of particles.In addition,sensing and functional components can be easily integrated or wrapped into the SPNs during the synthesis process,so that the optoelectronic properties of the SPNs can be adjusted to achieve fluorescence,chemiluminescence and photoacoustic imaging in living systems.Therefore,SPNs represent a multifunctional nano-platform for many in vivo studies of physiological and pathological processes.Although SPNs is widely used in in vivo molecular imaging,the application for photoelectrochemical(PEC)bioanalysis is rarely reported.In this dissertation,SPNs with many particle sizes were prepared according to different synthesis methods,which were sucesffully appied for PEC bioanalysis development.In addition,according to facile functionalization of the SPNs,upconverting ion-selective nanospheres were firstly prepared that emit the light at near-infrared region for the imaging of intracellular target ions.The main works in this dissertation are as following:1.Polymer Dots for Photoelectrochemical BioanalysisDifferent from the most extensively used inorganic quantum dots(Qdots)for the current state-of-the-art photoelectrochemical(PEC)bioanalysis,this work in Chapter 2 reports the first demonstration of polymer dots(Pdots)for novel PEC bioanalysis.The semiconducting Pdots were prepared via the reprecipitation method and then immobilized onto the transparent indium tin oxide(ITO)glass electrode for PEC biodetection of the model molecule L-cysteine.The experimental results revealed that the as-fabricated Pdots exhibited excellent and interesting PEC activity and good analytical performance of rapid response,high stability,wide linear range,and excellent selectivity.In particular,the PEC sensor could easily discriminate L-cysteine from reduced L-glutathione(L-GSH).This work manifested the great promise of Pdots in the field of PEC bioanalysis,and it is believed that our work could inspire the development of numerous functional Pdots with unique properties for innovative PEC bioanalytical purposes in the future.2.Self-assembled Peptide Nanostructures for Photoelectrochemical Bioanalysis ApplicationCurrently,one of important research directions of photoelectrochemical(PEC)bioanalysis is to exploit innovative photoactive species and their elegant implementations for selective detection and signal transduction.Different from existing candidates for the state-of-the-art photoelectrode development,this study in Chapter 3,exemplified by the cationic dipeptide NPs(CDNPs),reports the first demonstration of self-assembled peptide nanostructures(SAPN)for the novel PEC bioanalysis.Specifically,the CDNPs were prepared as representative materials and then immobilized onto ITO electrode for the PEC differentiation of several commonly involved biomolecules such as ascorbic acid(AA)and L-cysteine.Significantly,the experimental results disclosed that the CDNPs possessed unique photocathodic responses and good analytical performance toward AA detection in terms of rapid response,high stability,and excellent selectivity.This work demonstrates the great potential of the large S APN family for the future PEC bioanalysis development and has not been reported to our knowledge.3.Upconverting Ion-Selective Nanospheres for the imaging of Intracellular Calcium IonsIn Chapter 4,upconverting ion-selective nanospheres are firstly prepared that emit the light at near-infrared region for the imaging of intracellular target ions(e.g.calcium ions).The incorporated chromoionophore(P6)in the nanospheres has the adsorption peaks at 789 nm that overlaps the red emission of upconverting nanoparticles(UCNPs)at 804nm.The presence of aqueous calcium ions induces the deprotonation of P6 through ion exchange resulting in a decrease in the adsorption peak intensity at 789 nm and the resultant increase from the emission of UCNPs for the detection.More emission is observed from the cells loaded with the nanospheres after the stimulation that is consistent with the elevation of intracellular calcium ions.The successful realization of upconverting ion-selective nanospheres for cellular imaging will not only provide a new detection approach for intracellular ions,but also advance the application of these ion-selective nanospheres for the future in-vivo analysis.