A Novel Sensing Platform Based On Nanoplasmonics And Mxenes

Noble metal nanoparticles are widely used in the construction of colorimetric sensors because of their unique localized surface plasmon resonance（LSPR）extinction under the visible-light irradiation.Furthermore,metal nanoparticles exhibit the ability to adjust the optical properties of local fluorophores,and further dramatically enhance fluorescence intensity which is known as plasmonic enhanced fluorescence（PEF）.PEF-based methods have been applied to biosensors for improving the detecting sensitivity of low abundance molecular.H owever,the synthesis of metal nanoparticles or the modification of fluorescence probes is needed in either colorimetric or fluorescent assays,which is time-consuming and needs strict operating procedures.Therefore,it is important to develop label-free analysis methods without labeling steps,and which can achieve direct chemical reactions and model conductions between the sensor unit and the target analytes.As one of typical MXenes,titanium carbide nanosheets（Ti ₃C₂NSs）have attracted great attentions in biosensing and environmental monitoring due to their unique physics and chemical properities.Ti₃C₂NSs with Ti surfaces covered with hydroxyl and fluorine exhibit unique adsorption behaviors towards heavy metal ions.Furthermore,Ti₃C₂MXenes quantum dots（Ti₃C₂QDs）have unique properties such as tunable size,photoluminescence,excellent photostability and solubility.They have been served as the fluorescent probes to achieve fluorescence response to the targets.In addition,the terminations（-OH,-F）of Ti₃C₂MXenes gift an excellent reducibility and strong adsorption capacity for heavy metal ions.These properties have not yet received attention and applications in t he field of nanosensing.In this thesis,on the basics of the LSPR of precious metal nanoparticles,combined with the adsorption and reduction properties of Ti₃C₂NSs and Ti₃C₂ QDs on Ag⁺,a series of new sensors for Ag⁺detection was constructed.The main research contents areas follows:1.We synthesized and characterized Ti₃C₂ NSs,corroborated the feasibility of the Ag⁺sensing platform based on Ti₃C₂NSs and further explored the sensing mechanism.First,Ti₃C₂ NSs functionalized with polyacrylic acid（PAA）reduced Ag⁺to Ag NPs,which caused changes in solution color and plasmonic optical signal and further proved the feasibility of sensing Ag⁺with Ti₃C₂NSs.Based on the conversion of Ag⁺to Ag NPs with Ti₃C₂NS,a series of novel nanosensing platform s can be developed,and it is expected to realize the enrichment and recovery of Ag⁺in real samples.2.We demonstrate a proof-of-principle concept of a label-free and visualized nanoplasmonic strategy for silver ions sensing,where only Ti ₃C₂ MXenes are employed by exploring their excellent adsorption affinity and reductive property toward metal ions.Ag⁺was reduced to silver nanoparticles（Ag NPs）in situ without adding any extra stabilizing or reducing agent.The localized surface plasmon resonances provide Ag NPs the capability for colorimetric assay.With the assistance of a smartphone,RGB analysis exhibited visualized results consistent with the results measured on a UV-Vis spectrometer.Therefore,based on the combination of the plasmon optical properties of Ag NPs and the reducibility of Ti ₃C₂ MXenes gifts sensing assay the capabilities of sensing Ag⁺without the preparation of nanoprobe.3.We demonstrated a fluorescence/colorimetry dual-mode assay based on plasmon-enhanced fluorescence（PEF）and Ti₃C₂ QDs.In this paper,the reducibility of Ti₃C₂ QDs obtained by hydrothermal treatment induces the conversion of Ag⁺to Ag NPs.Under laser irradiation,the effect of PEF induced the fluorescence enhancement of Ti₃C₂ QDs.At the same time,the generati on of Ag NPs causes color changes which correspond to the results measured on a UV-vis spectrometer.This work constructed a dual-modal sensor for Ag⁺detection with excellent selectivity based on PEF and Ti ₃C₂QDs.