Preparation,characterization And Application Of Colorimetric Sensors Based On Gold Nanoparticles Stabilized By Hyperbranched Polymer

In this dissertation,thermoresponsive HPEI-IBAm with terminal isobutyramide(IBAm)groups was prepared using a simple amidation reaction between the amino groups of hyperbranched polyethylenimine(HPEI)and isobutyric anhydride.HPEI-IBAm having a large amount of amino groups as reductant can not only reduce HAuCl4 to prepare gold nanoparticles(Au NPs)but also stabilize the AuNPs.The green preparation of stabilized AuNPs by in situ reduction of HPEI derivatives and HAuCl4 solution without the additional step of introducing a toxic reducing reagent is significant.AuNPs stabilized by thermoresponsive HPEI-IBAm can not only detect Ag+ but also achieve the separation of AuNPs/Ag composites.The sensing mechanism of the colorimetric assay can be explained as follows: Ag(0)reduced by HPEI-IBAm is directly deposited onto the AuNPs surface through the formation of Au-Ag core-shell NPs with a red to brown color change.The HPEI-IBAm with a high steric hindrance effect can not only stabilize the AuNPs,but also provide better stability for Au-Ag core-shell nanoparticles,which is convenient to record and observation.The color change of AuNPs sensor from red to brown is more selective than that from red to purple or blue.Because the color change from red to brown is unique.However,AuNPs prepared by traditional small-molecule reduction methods easily aggregate with a color change from red to purple or blue in an acid medium,solid state or excess ion concentrations,which can interfere with Ag+ detection.Moreover,the state of the aggregation is unstable resulting the shortened observing time.The sensing process occurred very quickly,only 0.5-1 minutes.Meanwhile,the limit of detection for Ag+ using this sensor was estimated to be 5.73 M by naked eyes,and 5.73 nM by the UV-vis spectra(which was significantly below the maximum level(0.1 mg/L?920 nM)of Ag+ in drinking water defined by the United States Environmental Protection Agency).Comparing with AuNPs prepared by classical small-molecule reduction as colorimetric sensors of Ag+,this strategy had several advantages:(1)Thermoresponsive HPEI-IBAm not only serves as a green reductant and excellent stabilizer to prepare AuNPs via in situ formation,but also serves as a trigger agent to induce an obvious color change due to the reduction of Ag+ to Ag0 deposited onto the surface of AuNPs,as well as serves as separating agent to enrich and separate sensor/Ag composites.(2)HPEI-IBAm/AuNPs can realize the integration of preparation,detection and separation,which serves aims of energy saving,environment protection and sustainable development and provides a basis to further develop multifunctional nano-composites;(3)In situ formation of HPEI-IBAm/AuNPs can greatly improve the stability of AuNPs(even under the conditions of high temperature,acid medium,solid state and excess ion concentrations)due to the existence of a large number of amino groups and high steric hindrances,which can avoid interference from an acid medium,excess ion concentrations and so on to improve the selectivity of Ag+ detection;(4)The color change of AuNPs sensor from red to brown is more sensitive and selective than that from red to purple or blue(the color change from red to brown is unique and can easily be observed by naked eyes),and therefore this colorimetric sensor exhibits high sensitivity and excellent selectivity toward Ag+;(5)The thermoresponsive HPEI-IBAm can separate AuNPs/Ag after the detection application by a simple precipitation or centrifugation process,which can avoid secondary pollutions.