The Resonant Rayleigh Scattering And Raman Scattering Characteristics Of Gold Nanoshells And Their Application In Detection

Gold nanoshells (GNSs) were often used in surface-enhanced Raman scattering (SERS)-based detection, photo-thermal therapy, and bioimaging due to a tunable surface plasmon resonance by controlling the material and size of core/shell structure. In this paper, monodispersed gold nanoshells were firstly synthesized, followed by the study of the resonant Rayleigh scattering and Raman scattering characteristics of GNSs which were both resulted from localized surface plasmon resonance. GNSs arrays with crystalline structure were then assembled by drop boundary evaporation with controlled concentration, temperature and angle with the horizontal plane. The GNSs arrays have high SERS effects and excellent reproducibility. By conjugating capture antibody to the GNSs arrays and detection antibody to free GNSs, a SERS-detected immunoassay was developed for Neuro-specific enolase (NSE) immune-sensing.The details are as follows:1. The fabrication of monodispersed gold nanoshells. Firstly,-110 nm of silica (SiO2,0.013 g/mL) was firstly dispersed in 40 mL of ethanol and amino-functionalized by APTES (1% v/v in ethanol) at 80℃. 2-3 nm of GNPs were synthesized by THPC reducing HAuCl4.Functionalized SiO2 was added to GNPs under stirring to form SiO2/GNPs composites. The growing solution was prepared by mixing 750 mL deionized water,200 mg of K2CO3, and 12 mL of 1% HAuCl4 and stirring for 30 min. SiO2/GNPs composites and H2O2 were added in turn to growing solution while stirring. The HAuCl4 was reduced by H2O2 and gold was growing based on SiO2/GNPs composites. The observation of scanning electron microscopy (SEM) showed that the shells of GNSs are -30nm thick and the fabricated GNSs are of highly consistent size which is necessary for further assembly of ordered GNSs arrays. The resonant Rayleigh scattering and Raman scattering characteristics of GNSs were also examined by the resonant Rayleigh scattering and Raman scattering platforms which was built up in lab.2. Assemble GNSs arrays with crystalline structure by drop boundary evaporation with controlled concentration, temperature and angle with the horizontal plane. From the SEM image of the dried drop, it includes two patterns of GNSs deposit, the closely ordered-stack GNSs array in boundary area and randomly-stack GNSs array in the rest area. The closely-stack GNSs arrays have better performance than randomly-stack GNSs arrays under different excitations, increasing the signal by 2 to 3 times. The closely-stack GNSs arrays also have higher reproducibility with an RSD (relative standard deviation) of 2.7% according to Raman mapping over a scan area of 60×60 μm2. The results demonstrates that the closely ordered-stack GNSs array can be used as a SERS substrate with good sensitivity and excellent reproducibility. It has potential to produce this kind of GNSs arrays in mass production since drop boundary evaporation is an easy assemble method with little consumption of raw material.3. According to the above work of controllable synthesis of GNSs and GNSs arrays, and their surface-enhanced Raman characteristics, we fabricated SERS immuno-sensor for NSE based on GNSs and GNSs arrays. A SERS-detected immunoassay was developed for NSE immune-sensing by conjugating capture antibody and detection antibody to the SERS substrates and GNSs, respectively. NBA molecules were chosen as the Raman reporter which absorbed on the GNSs.The NSE immuno-sensing was performed by two steps. First, a mixed solution containing 2 μL of sample/analyte,3 μL of buffer solution, and 5 μL of SERS probes was dropped onto the antibody-modified GNSs arrays and incubated for 40 min. The SERS probes labeling NBA molecules would be bound to the GNSs arrays in the presence of NSE. The GNSs arrays were washed by buffer solutions to remove excess reagents and dried in air. SERS spectra of GNSs arrays were then recorded. The more NSE in the circumstance, the more NBA molecules would be connected to the SERS substrate by specific binding between antibody and antigen. The GNSs arrays used for NSE immune-sensing were able to detect NSE in buffer solution with a wide linear range from O.lng to 1 μg/mL. In addition, the biosensor was capable of detecting NSE in diluted human blood plasma samples between 1 ng/mL to 160 ng/mL.