| Metal nanoclusters (NCs), composed of a few to roughly a hundred atoms, are anew type of luminescent nanomaterials that recently have attracted a great deal ofinterest. Metal nanoclusters typically have diameters below2nm and properties thatplace them between isolated atoms and larger nanoparticles or even bulk noble metals.For nanoclusters dimensions approaching the Fermi wavelength of electrons, thecontinuous density of states breaks up into discrete energy levels leading to theobservation of dramatically different optical, electrical and chemical properties ascompared to nanoparticles. Compared with these luminescent nanoprobes,conventional fluorescent emission substance exhibit much shortcomings: Thefluorescence emission of organic dye molecules have a short duration, unstableperformance, bad monochromatic beam; Although the semiconductor quantum dotfluorescent dyes can overcome physical shortcomings, generally their precursors havehigh toxicity, and the preparation process is carried out at high temperatures, so thecost is relatively high. Gold nanoclusters have unique optical and physical-chemicalproperties, such as having a strong fluorescence emission, ultraviolet absorptioncharacteristics, two-photon absorption, solvent effects and so on. Protein-protectedgold nanoclusters possess good biocompatible and non-toxic, so they could be used asfluorescent probes for metal ions, small biological molecules, proteins and othersubstance, simultaneously they have a wide application in biomarkers and biologicalimaging.Based on the property of the gold nanoclusters, we studied the performanceoptimization, application in the detection of small molecule drugs and interaction withinorganic small molecule systems about protein-protected gold nanoclusters. Themain contents and conclusions are as follows:1. We investigated the pH-induced fluorescence changes of BSA-protected goldnanoclusters, AuNCs@BSA, and the corresponding conformational changes of ligand protein by fluorescence, CD and IR spectral measurements. And the mechanism offluorescence change and conformational changes of ligand protein was analysed bythe second derivative and curve fitting. The results of CD and IR interpreted thesignificant change of second structures at extreme acidity and alkaline, where moreunordered structures were gained. In addition there was a big difference from ligandBSA and native BSA about the fluorescence intensity of tryptophan, it might transferefficient energy between the BSA and AuNCs. The studies presented heredemonstrated that BSA in AuNCs@BSA underwent identifiable conformationalchanges on both the secondary and the tertiary structure levels.2. In the present study, the biomolecule-stabilized Au nanoclusters weredemonstrated as a novel fluorescence probe for sensitive and selective detection ofpazufloxacin mesilate. The linear decrease of the fluorescence intensity of Aunanoclusters induced by pazufloxacin allowed the quantitative detection ofpazufloxacin in the range of0.2μg/mL to1mg/mL, and the detection limit forpazufloxacin was0.2μg/mL. Interference experiment indicated that our sensingsystem had highly selective towards pazufloxacin over other potentially interferingsubstances. In addition, the practical application of the present approach was alsodemonstrated for real samples. The circular dichroism spectroscopy and fluorescencedecay studies were then performed to discuss the quenching mechanism. These resultsprovided an evidence for a strong interaction occurring between pazufloxacin andAuNCs@BSA. Herein, we presumed that the quenching of the system emission mightbe attributed to the microenvironment change of AuNCs@BSA.3. A highly simple method for the detection of trace amount of clenbuterol based onBSA-protected gold nanoclusters (AuNCs@BSA) with dual-wavelength responsivefluorescence method was studied. Clenbuterol was converted to its diazobenzyl formby treatment with a solution containing HCl and NaNO2, and then couple withAuNCs@BSA. The linear decrease of the fluorescence intensity of AuNCs@BSinduced by diazotized clenbuterol allowed the quantitative detection of clenbuterol inthe range of3nM to300μM, and the detection limit for clenbuterol was3nM uponexcitation at280nm and1.6nM upon excitation at500nm. In addition, the proposed method was successfully applied to the determination of clenbuterol in pork samples.Therefore, the described methods could be used as a reliable, rapid, and cost-effectivetechnique for the determination of clenbuterol residues in real samples. At last thequenching mechanism was discussed. We speculated that the binding position ofclenbuterol to BSA may locate within this hydrophobic pocket, the addition ofdiazotized clenbuterol changed the polarity of this hydrophobic microenvironmentand thus resulting in the conformational changes of BSA.4. We investigated the spectrum of Au NCs@BSA with inorganic small moleculeKI-I2. The results showed that KI-I2could cause fluorescence quenching by addingdifferent concentrations of KI-I2. The emission peak intensity of gold nanoclustersdecreased more obvious, and accompanied by a clear blue shift. The thermodynamiccalculations were calculated with the result of variable temperature test, and thendiscussed the mechanism of KI-I2and Au NCs@BSA. The following conclusions:(1)the fluorescence quenching rate constants calculated results showed that the intrinsicfluorescence of Au NCs@BSA via a dynamic quenching procedure;(2)thermodynamic parameters implied that hydrophobic interaction played a major rolein stabilizing the complex;(3) the strong interaction between KI-I2and AuNCs@BSAmight be due to the redox reaction.In conclusion, based on the property of small protein protected gold nanoclustersAu16NCs@BSA, we studied the performance optimization, application in thedetection of small molecule drugs and interaction with inorganic small moleculesystems about protein-protected gold nanoclusters. Meanwhile, we have alsoperformed substantially studying of the mechanism in the process of quenching forthe wider application of gold nanoclusters. |
PDF Full Text Request