Controllable Preparation And Application Of Thiolactic Acid Capped Gold Nanoclusters

Gold nanoclusters（Au NCs）are a new type of luminescent nanomaterials.They have been widely used in biological imaging,analytical detection and other fields due to their unique physicochemical properties,such as large Stokes shift,tunable emission range,good biocompatibility,strong photostability and so on,Especially,near-infrared emitted Au NCs have higher potential for biological applications because they have good tissue penetration,low tissue absorption,anti-interference of tissue auto-luminescence and high signal-to-noise ratio.However,there are few types of near-infrared emitted Au NCs reported at present,and the low fluorescence quantum yields greatly limit their application.Therefore,we have employed a new ligand,thiolactic acid（TLA）,to prepare a novel of Au NCs with near-infrared luminescence.By further improving the photoluminescence properties of the nanoclusters,it is found that the near-infrared emitted Au NCs also have assembly-induced luminescence enhancement（AIEE）properties.Moreover,the Au NCs are applied to detect metal ion,it is found that only silver ions can induce a new red emission peak,while other metal ions can only affect the intensity of the near infrared emission of the Au NCs.And the results show that the ratio response can be used to sensitively and quantitatively determine silver ions.Firstly,the thiolactic acid（TLA）protected gold nanoclusters（Au NCs@TLA）were prepared by following the hydrothermal method and adjusting the reaction time,temperature,raw material ratio,and so on,Surprisingly,the obtained Au NCs@TLA showed strong near-infrared emission centered at 800 nm.Typical TEM images show that the average particle size is about 1.75±0.38 nm,and electrospray ionization mass spectrometry（ESI-MS）illustrated the nanoclusters mainly contains Au₃₈TLA₄₈ and Au₄₂TLA₄₁.When bovine serum albumin（BSA）was introduced into the system,it could greatly improve the emission intensity and quantum yield（from 0.45%to 1.35%）.The mechanism study show that Au NCs@TLA was mainly assembled with the positively charged region of BSA through electrostatic interaction,and the luminescence enhancement was mainly attributed to the assembly-induced luminescence enhancement（AIEE）property of Au NCs.Besides,such AIEE effect was also adaptable to other available proteins,indicating the excellent generalizability of the proposed strategy.Therefore,the present work not only provided a method to prepare near-infrared emitted Au NCs,but also paves a general strategy of AIEE to improve the emission property of near-infrared emitted Au NCsSecondly,the Au NCs@TLA was applied to detect metal ions.It found that only silver ion can induce new red emission peaks,while other metal ions only affect the near-infrared emission in different degree.The ratiometric response showed very high selectivity and strong anti-interference toward silver ion.In the presence of silver ion,there were two new emission peaks around 610 and 670 nm produced in turn,meanwhile,the original emission（800 nm）was simultaneous quenched.These two-steps responses had different linear determination ranges at 0.10-4.0μM and 10-50μM,respectively.And the limit of detection（LOD）was calculated to be 40 n M.Besides,when introduce BSA as a signal amplifier,it significantly improved the detection performance（LOD at 10 n M）.The proposed method was also applied to the detect silver ion in serum,which showed a very good recovery rate（95.26-103.67%）,indicating good practical application potential.The present study supplies a novel ratiometric probe of silver ion with two-step responses,and employ BSA as a signal amplifier to improve the detection performance,which expand the application range of near-infrared emitted Au NCs.