Optical Sensing Research Based On Gold Nanocages As A Carrier

Gold nanocages（GNCs）have unique cage-like structures and excellent physicochemical properties.In this paper,we focus on their applications in nanocatalysis and bioassay,and constructed three biosensing platforms for the quantitative detection of glucose and bilirubin based on the properties of gold nanocages.The GNCs were synthesized by a simple one-pot method and characterized by transmission electron microscope（TEM）,UV-visible spectroscopy（UV-vis）,particle size analysis and zeta potential,respectively.The structure and properties of GNCs were characterised.Details of the work are as follows:（1）Controlled preparation of gold nanocages:GNCs were synthesised in a facile one-pot method,with higher yields obtained by optimising the preparation conditions,and the wavelength of the gold nanocage LSPR peaks could be tuned in the 650-810 nm range.The GNCs show dual localised surface plasmon resonance peaks in the visible and near infrared regions,corresponding to the resonant absorption peaks of gold nanoparticles（Au NPs）and GNCs,respectively.The stability of the GNCs was analysed and proved that they have good stability and do not damage the structural integrity over long periods of storage.（2）Biosensing studies based on the peroxide-mimetic enzymatic properties of gold nanocages:the peroxidase-like activity of GNCs was demonstrated by the reaction with hydrogen peroxide（H₂O₂）-3’,3’,5,5’-tetramethylbenzidine（TMB）colorimetric system.The absorbance at 652 nm was found to show a linear enhancement with the H₂O₂concentration in the range of 10.0～160.0μmol/L.The fitted equation can be expressed as A=0.0039C（μmol/L）+0.2749 with a minimum limit of detection（LOD）of 0.46μmol/L（S/N=3,n=3）.The tandem catalytic detection of glucose was achieved by combining GNCs as carriers with glucose oxidase（GOD）via an amide-coupling reaction.A simple and sensitive colorimetric sensing assay for glucose was constructed based on this.The linearity was observed in the concentration range of 20.0～200.0μmol/L,and the fitted equation was A=0.0014C（μmol/L）+0.2382 with a LOD of 1.28μmol/L.The recoveries of glucose in human serum samples were 94.2～104.1%using the spiked method.The color change of the solution can be observed by the human eye,and the visual assay can be easily achieved without any instrumentation or complex design.（3）A light-absorbing bilirubin sensor based on the catalytic and structural disintegration of gold nanocages:The GNCs were found to catalyse the oxidation of bilirubin,while bilirubin disrupts the dipole-dipole gravitational force between the Au NPs triggering the disintegration of the cage structure and releasing the Au NPs into solution.Thus,with the addition of bilirubin,the absorbance of Au NPs increases while that of GNCs decreases.The GNCs-bilirubin system showed a linear response over the bilirubin concentration range of 0.20 to 3.60μmol/L.The fitted equation can be expressed as A₀/A₁=0.0526C（mmol/L）-0.0033.The LOD was 39.35 nmol/L（S/N=3,n=3）.The sensing system has high selectivity and good reproducibility for bilirubin.（4）Study of bilirubin fluorescent sensors using gold nanocages as carriers:Blue fluorescent glutathione-gold nanoclusters（GSH-Au NCs）were synthesised in one step using glutathione（GSH）as a reducing and protective agent.The positively charged GNCs were used as carriers to electrostatically bind to the negatively charged GSH-Au NCs,and the spatially restricted effect of GNCs resulted in enhanced fluorescence of GSH-Au NCs aggregates.Based on the fluorescence resonance energy transfer law,a fluorescent sensor using GNCs@GSH-Au NCs as a probe was constructed for the detection of bilirubin.Bilirubin showed a linear correlation in the range of 0.40～7.00μmol/L.The fitted equation can be expressed as（F₀-F）/F₀=0.082C（mmol/L）+0.025 with an LOD of 94.16 nmol/L（S/N=3,n=3）.The sensor has a fast response,high sensitivity and a wide detection range.