Fluorescent microspheres are a category of functional microspheres which have attracted wide attention in materials research in recent years.It usually refers to some spherical solid particles in nanoscale or microscale,which can emit visible fluorescence when excited by external light due to the attached fluorescent materials.Fluorescent microspheres exhibit great potentials for many science and technological researches,such as bio-medical and bio-technology science,etc.So far,fluorescent microspheres are commercially available in different sizes and colors.Among them,the most common and typical type of fluorescent microspheres are polymeric microspheres attached with fluorescent dyes.Those commercial available microspheres prepared by conventional methods always have some disadvantages,for example,fluorescent leakage and photobleaching problem.Additionally,another serious problem is that most fluorescent materials are high toxic for living things,unsuited to be used in biomedical science.An ideal tracer should be with inherently fluorescence without the need for conjugating an external fluorochrome.In this study,we have incidentally found that polystyrene(PS)microspheres could emit obvious fluorescence without attaching any external fluorochrome if modified through Friedel-Crafts reaction.So,the fluorescent microspheres prepared in this research displayed neither toxicity for living things nor fluorescent leaking nor photo bleaching problems.This study includes three parts.The first part is the discovery of fluorescent phenomenon of PS-based microspheres and the exploration of their fluorescent mechanism.It is assumed that the fluorescence phenomenon is probably caused byπ-πor p-πconjugated system between benzene of PS microspheres and functional groups introduced by Friedel-Crafts reaction.Two kinds of typical fluorescent microspheres,ACPS and CMPS microspheres originated from PS microspheres,have been selected to analyze their chemical constitution and optical performance.In addition,p-ethylacetophenone and p-ethylbenzyl chloride that has similar functional structure with ACPS and CMPS microspheres respectively,have been synthesized to compare their fluorescent properties with fluorescent microspheres.ACPS microspheres have been successfully transformed into PS-NH2 microspheres through two steps of chemical reactions in the second part.PS-NH2 microspheres showed obvious response to mercury ions in solution as a linear relationship of((F0–F)/F0)to the negative logarithm of Hg2+concentration.It is fortunate that the quenched fluorescence signal of PS-NH2 microspheres can recover up to 90%of the original value after washed by ethanol,saturated EDTA solution and deionized water in turn.And the fluorescence of the microspheres can keep a long period of stability either in solution or at dry powder state without fluorescence leakage or photo-bleaching problem.In the third part,water-dispersible CMPS-PEG microspheres are prepared from CMPS microspheres by grafting poly(ethylene glycol)(PEG)on the microspheres.The water-dispensability and biocompatibility of fluorescent microspheres was improved significantly after PEGylation without decrease of fluorescent signal.Additionally,MTT assay suggests that the microspheres have very low cytotoxicity,which bestows the CMPS-PEG microspheres great advantage to be applied as a Fe3+sensitive cellular imaging agent.The particles exhibit bright blue fluorescence under the irradiation of UV light and show excellent stability under severe conditions,including long-term soaking in water,continuous irradiation in daylight,and dried in air as a thin film.This work should provide fresh insight into the development of new strategies to build stable fluorescent microspheres for coating,sensing and imaging applications. |