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SYNTHESIS OF SEMICONDUCTOR NANOPARTICLES USING LIQUID PHASE LASER ABLATION FOR ELECTROCHEMILUMINESCENT ASSAY
Yu.T. Zholudov*, M.M. Rozhitskii*, M.I. Slipchenko±, C.L. Sajti+, B.N. Chichkov+
* Laboratory of Analytical Optochemotronics, Kharkiv National University of Radioelectronics
± Microelectronics Department, Kharkiv National University of Radioelectronics
+ Nanotechnology Department, Laser Zentrum Hannover e.V.
The method of electrogenerated chemiluminescence (ECL) is a promising detection tool in the analytical chemistry of liquids. ECL is the luminescence that is produced from the relaxation of electron excited molecules formed in the course of electrochemically initiated reactions. The ECL method has a number of advantages over other detection methods. It combines the advantages of electrochemical and chemiluminescent assay methods and eliminates their main drawbacks .
In order to broaden the application area of ECL assay method it is promising to replace commonly used organic luminophores with semiconductor quantum dots that have certain advantages over the former ones namely narrow fluorescence spectrum, that is dependent on their size, high photostability and fluorescence quantum yield. Preliminary studies showed that use of chemically synthesized quantum dots for ECL generation is not efficient probably due to the presence of the stabilizing layer of surface-active substance on their surface. We believe that such coatings prevent participation of quantum dots in the charge transfer reactions at the electrodes and in the solution bulk . In order to solve mentioned problems we propose the use of shell-free, colloidal semiconductor quantum dots that are produced using the liquid phase laser ablation or fragmentation methods .
The possibility of semiconductor nanoparticles synthesis using laser fragmentation method was studied in the Laser Center of Hannover. The fragmentation was performed using a Trumph TruMicro 5050 pulsed ultrashort laser system (pulse duration tp<10 ps, maximum pulse energy Ep=250 µJ, emission wavelength λ=1030 nm, maximum repetition rate fp=200 kHz.). The target for fragmentation was the suspension of CdSe powder in organic solvent that was produced by ultrasonication. There were tested several solvents among which dimethylformamide (DMF) was found to be the most suitable.
Synthesis of CdSe nanoparticles in DMF showed no visible agglomeration. The produced solution possesses well defined absorption peak typical for CdSe quantum dots (Fig.1). As the duration of laser fragmentation increases, the peak becomes more distinct. The position of absorption peak (~400nm) is characteristic for core-type CdSe quantum dots with a diameter about 1.5 nm . The half width at half maximum of the peak is about 28 nm indicating rather good monodispersity of the obtained nanoparticles. The calculated concentration of CdSe quantum dots gives the value about 0.97·10-4 M .
At the same time it was found that the absorption peak is unstable and completely disappears after 2 days of storage of the laser treated solution.
After laser treatment both pure DMF and DMF with CdSe suspension posses blue fluorescence that is visible by naked eye when excited by a 405 nm diode laser. Comparison of recorded fluorescence spectra of both solutions indicates that fluorescence signal attributed to CdSe quantum dots has maximum around 550 nm. The exact fluorescence spectra of pure CdSe nanoparticles can not be recorded well due to high background fluorescence from the solvent itself.
The conducted preliminary studies show that the method of laser fragmentation is a promising tool for fast and efficient production of semiconductor nanoparticles in the solutions.
Further work will be focused on the optimization of CdSe nanoparticles production conditions, stabilization of the produced nanoparticles, study of laser fragmentation and sample treatment parameters influence on the properties of produced nanoparticles, study of their electrochemical and electrochemiluminescent activity.
Fig.1 – Absorption spectra of synthesized CdSe quantum dots, laser fragmentation during 3 min (1); 25 min (2) and pure DMF after 25 min of laser irradiation (3)
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