Synthesis Of Room Temperature Phosphorescence Carbon Dots Towards The PH Sensing Mechanism And Biosensing Applications

Recently,room temperature phosphorescence(RTP)materials developed rapidly in sensing,bioimaging,optoelectronic devices and information security fields.However,the RTP matrials can be divided into organometallic complexes(metal-containing)and those focusing on pure organic compounds(metal-free).The metal-coordination based RTP materials suffer from high costs,toxicity and complex preparation methed,which greatly limited their applications.As an emerging class of metal-free luminescent nanomaterials,carbon dots(CDs)have attracted sustained attention due to their superior luminescence,low toxicity,favorate biocompatibility,and ease of manufacture.Recently,unique RTP phenomena have been reported for CDs,and there are two ways to achieve the RTP emission for CDs cantaining elements doping and embedding them into composite matrices.Nevertheless,due to the fact that phosphorescence is hampered by the spin-forbidden nature of triplet exciton transitions and by nonradiative decay processes,it is still a great challenge to synthesis room temperature carbon dots.In this study,we have successfully prepared the CDs with both RTP and fluorescence properties,in which process the nomal micromolecule such as triethanolamine and methotrexate(MTX)severd as precursors,and explored pH sensing mechanism and applications in biomarker analysis with obtained RTP carbon dots,respectively.The specific research contents are listed as follows:1.Synthsis of room temperature phodphorescence carbon dots towards pH sensing mechanismChemical doping with nitrogen,phosphorus or halogens can effectively favor the room temperature phosphorescence(RTP)appearing of carbon dots(CDs)through facilitating their intersystem crossing(ISC)process.Here we raised a facile microwave strategy to synthesize nitrogen and phosphorus co-doped carbon dots(P-CDs),while triethanolamine served as the carbon source with phosphoric acid being the dopant.Meanwhile,the P-CDs showed both the bright-blue fluorescent emission with a high fluorescent quantum yields of 22.4%and the green-RTP emission with the phosphorescent quantum yields to be 15.85%.Additionally,the filter paper functioned as the matrix to stabilize the triplet excitons of P-CDs,thus achieving their RTP emission by suppressing the non-radiative transitions.Then,the P-CDs were roundly characterized by high resolution-transmission electron microscopy(HR-TEM),fourier transform infrared(FTIR)spectra,X-ray photoelectron spectroscopy(XPS)spectra,Raman spectra,dynamic light scattering and so on.The results showed that morphology of P-CDs dispersed uniformly with the particle size from 0.96 to 3.62 nm,and P-CDs consisted of C,N,O and P elemants,which was equipped with PO₃^4-and C-N/C=N.Significantly,with the resistence to photobleaching,an innovative painting technology of employing P-CDs as RTP-ink has been developed toward the confidential information encryption.Moreover,we applied the proposed P-CDs to respectively assay pH ranging from 9.15 to 13.55 and 2.29 to 13.55 by virtue of their pH-responsible fluorescence and RTP.Again,we further explored the fluorescent and phosphorescent sensing mechanism of P-CDs.To be specific,P-CDs was stable owing to abundant P=O···H hydrogen bonds as well as protonated P-O on their surfaces.While the concentration of Na OH increased,leading to the deprotonation of P-O bonds and the dissociation of hydrogen bonds,precipitation of P-CDs decreased their concentration in solution and caused the RTP and fluorescence(FL)quenching.This work achieved FL and RTP dual channel pH sensing,and the RTP channel greatly increased the linear range and also improved the degree of accuracy.2.Designing MnO₂ Nanosheet modified room temperature phosphorescence carbon dots towards assaying cholesterol and glucoseOvercoming the quenching of dissolved oxygen to the room temperature phosphorescence(RTP)materials have received increasing attention in the fields of biological sensing,and large stokes shift along with the low background interference extended their applications in building a universal sensing platform.Herein,we prepared a kind of blue fluorescence CDs through hydrothermal method,which achieved the phosphorescence emission in aqueous environment after combining with cyanuric acid(CA),and this composite(CA-CDs)overcome the quenching effect of dissoved oxygen.Creatively,CA-CDs suspension could emit blue fluorescence and cyan phosphorescence in water conditions,and the RTP was activated by forming hydrogen-bonded interactions between the carbon dots,water molecules and cyanuric acid,which rigidified the whole system,handered the dissoved oxygen and thus achieved the RTP emission.Interestingly,the dual emissive(fluorescence and phosphorescence)signals of CA-CDs suspension could be effectively quenched by manganese dioxide(MnO₂)nanosheet through the F(?)rster resonance energy transfer(FRET)and dynamic quenching effect(DQE).Through the enzyme-catalytic generation of hydrogen peroxide from the substrate,a universal strategy has been designed for phosphorescence and fluorescence“turn on”detecting substrates such as cholesterol and glucose.For the“turn on”sensing mechanism,the hydrogen peroxide reduced MnO₂ nanosheets to the Mn(?)ions which promoted the fluorescence and phosphorescence signals restored.Therefore,a unique RTP sensing platform based on the CA-CDs and MnO₂ nanosheets is constructed originally to assay the cholesterol and glucose.To be specific,this platform was applied to examine cholesterol with a linear range of 26.25?g/m L?2.1 mg/m L and a detection limit of 29.86?g/m L for RTP detection,while a linear range of 26.25?2625?g/m L was acquired for FL assaying accompanied by a detection limit of 4.16?g/m L.In addition,the designed method was applied for gluocose dual channel sensing,which presented a linear range of 0.1?20m M with a detection limit of 0.49 m M for RTP sensing and a linear range of 0.08?20m M with the detection limit of 0.48 m M for FL assaying.Relying on their phosphorescence behavior,the RTP CA-CDs were employed for fingerprint recognition and information encryption.Overall,this strategy designed a universal room temperature phosphorescence sensing platform to detect multiple target substances in a dual-signal analysis mode,and provided a new way to assay other biomarkers and also to extend the applications of RTP materals.The above experiments have explored the methods for synthesizing RTP carbon dots,and deeply explored the luminescence mechanisms.Meanwhile,a varity of characterizations were carried out to roundly clarify the strcture and functional groups for RTP CDs.Furthermore,on the basis of diverse response to different substances,we established original dual-channel analytical methods towards pH and multiple biomarkers,which broden the applications of CDs based RTP materials.