The Construction Of Fluorescent Silicon Nanomaterials-Based PH Sensors And Their Quantitative Investigations For Intracellular PH In Live Cells

Up to now,with the rapid development of fluorescent sensors,many fluorescent pH sensors featuring excellent properties(e.g.,feeble cytotoxicity,wide-pH range response,and strong fluorescence coupled with good photostability)have been well developed.During past decades,organic dyes and fluorescent nanomaterials have been employed for constructing a number of fluorescent pH sensors,and have further been applied for quantitative pH measurement in vitro and in vivo.In recent years,owing to many attractive merits of silicon nanomaterials,such as favorable biocompatibility,unique electronic,optical,and/or mechanical properties,they have been extensively used for various applications in a variety of fields,including energy,catalysis,optoelectronics,and biology.Importantly,unique properties(e.g.,low cytotoxicity,strong fluorescence and good photostability)of fluorescent silicon nanomaterials are considered ascritical factors for creating fluorescent pH sensors.Therefore,taking advantage of above merits of silicon nanomaterials,the construction of fluorescent silicon nanomaterials-based pH sensors has aroused many researchers' interests.In this dissertation,we will focus on utilizing zero-dimensional fluorescent silicon nanoparticles and one-dimensional fluorescent silicon nanorods to construct fluorescent pH sensors and their quantitative investigations for intracellular pH in live cells.The main research results are as follows:Chapter 1:In this chapter,we give an introduction to the importance of intracellular pH for controlling the balance of the micro-environment in live cells,and the development history of fluorescent pH sensors.Next,we introduce the synthetic methods of fluorescent silicon nanomaterials and their research progress in bioimaging and biosensing field.Finally,we discuss the basis,objectives,and methods of the study in this dissertation.Chapter 2:In this chapter,we systematically investigate the construction of zero-dimensional fluorescent silicon nanoparticles(SiNPs)-based pH sensors and their quantitative investigations for intracellular pH in live cells.In detail,by simultaneously functionalizing zero-dimensional fluorescent SiNPs with dopamine(DA)and rhodamine B isothiocyanate(RBITC),we successfully fabricate the zero-dimensional fluorescent SiNPs-based pH sensors.Interestingly,the red fluorescence of RBITC is pH insensitive,as thus their red fluorescence can be used as internal standard for zero-dimensional fluorescent SiNPs-based pH sensors.Our results demonstrate that the resultant zero-dimensional fluorescent SiNPs-based pH sensors have good selectivity(the sensors only show response to changes of pH,but don't response to other different ions and molecules),minimal cytotoxicity(cell viability of treated cells remains above 95%during 24-h treatment),sensitive fluorescent response(a broad pH ranges from 4 to 10),and bright fluorescence coupled with robust photostability.Further investigations reveal that the zero-dimensional fluorescent SiNPs-based pH sensors can be used for long-term and real-time tracking of lysosomal pH change mediated by nigericin in live cells.On the basis of which,we further reveal that the whole dynamic process of lysosomal pH change mediated by nigericin can be divided into two consecutive stages:the first stage of stationary phase,in which the lysosomal pH changes slowly and fluctuates up and down;the second stage of exponential growth phase,in which the lysosomal pH changes rapidly and appears rising trend.These results are helpful for understanding the whole dynamic progress of intracellular pH in live cells.Chapter 3:In this chapter,we investigate the construction of one-dimensional fluorescent silicon nanorods(SiNRs)-based pH sensors and their quantitative investigations for intracellular pH in live cells.In detail,by using europium(Eu)-doped one-dimensional fluorescent SiNRs,we successfully establish the one-dimensionalfluorescent SiNRs-based pH sensors.Of note,the Eu under the influence of silicon is able to generate strong red fluorescence and their red fluorescence is pH insensitive.Therefore,the red fluorescence coming from Eu can be used as internal standard for the one-dimensional fluorescent SiNRs-based pH sensors.Our results demonstrate that the resultant one-dimensional fluorescent SiNRs-based pH sensors also have good selectivity,good repetition utilization,minimal cytotoxicity,broad pH response range,and bright fluorescence coupled with robust photostability.More importantly,compared to the fluorescent SiNPs-based pH sensors mentioned above,the as-prepared one-dimensional fluorescent SiNRs-based pH sensors show two specific peaks of their fluorescence spectrum under the irradiation of 405 nm UV laser.Those are blue fluorescence with emission wavelength ranging from 450 to 520 nm and the maximum emission wavelength of 470 nm,and red fluorescence with emission wavelength ranging from 580 to 650 nm and the maximum emission wavelength of 620 nm.We further demonstrate that the one-dimensional fluorescent SiNRs-based pH sensors can be used for cytoplasmic pH quantitative investigations in live cells,capable of tracing cytoplasmic pH change mediated by nigericin in long-term and real-time manners.Two consecutive stages,i.e.,stationary phase and exponential growth phase,are observed during the whole dynamic process of lysosomal pH change,similar to those observed by the SiNPs-based pH sensors,as mentioned in the Chapter 2.In summary,this thesis demonstrates a relatively comprehensive investigation of the construction of fluorescent silicon nanomaterials(including zero-dimensional fluorescent SiNPs and one-dimensional fluorescent SiNRs)-based pH sensors and their quantitative investigations for intracellular pH in live cells.Our results are useful for developing novel fluorescent pH sensors featuring excellent properties,including feeble cytotoxicity,wide-pH range response,strong fluorescence,and robust photostability.