| In recent years, with the rise of nanotechnology, gold nanoparticles (AuNPs) with its unique optical and electrical properties, good stability, small size, surface effects and unique biological affinity, show the potential value in the biochemical colorimetric analysis and other areas.So far, it has been developed a variety of methods for preparing AuNPs. The main methods can be divided into chemical synthesis and physical synthesis. Chemical synthesis method is reducing reaction of the gold particles by the material of gold compounds, such as a chemical reduction method. Physical synthesis method is for massive solid gold dispersed as gold particles by various techniques.In this study, AuNPs prepared by different methods, using different aptamer to modify AuNPs with special functions, and applied to the detection of melamine,the detection of H2+ and the study of pH response behavior, in order to be widely applied in the field of biochemical analysis. The experimental results are as follows:1-. We have successfully prepared the chitosan-stabilized AuNPs. The results showed that:The plasmon absorption of chitosan-stabilized AuNPs varies with the concentration of chitosan. When the concentration of chitosan is increased, the intensity of the absorption increases and then decreases with a further increase of the concentration. This result indicates that the size of chitosan-stabilized AuNPs formed varies with the concentration of chitosan, which acts as a controller of nucleation as well as a stabilizer.2^ A selective and simple colorimetric assay was proposed to detect melamine during the formation of chitosan-stabilized AuNPs in this study. The prepared chitosan-stabilized AuNPs probes were then applied to detection of melamine in liquid milk. To investigate this simple assay for the direct colorimetric visualization of melamine, quantitative analysis was performed by adding different concentration of melamine into the growth solution and monitoring the absorption peak and the color changes of the system. The absorption ratio (A650/A520) of the assay exhibited a linear correlation to melamine concentration in milk in the range from 10-5 g/L to 10-2 g/L (R=0.996). The limit of detection (LOD) is taken to be three times the standard derivation in blank solution is found to be 6 × 10-6 g/L, which is much lower than the safety limit. Some commonly found metal ions and food additives in dairy products were chosen for interference investigations, including Ca2+, Mg2+, Zn2+, K+, Fe3+ and Na+, as well as urea, glucose and sucrose. The results indicated that only melamine could introduce the aggregation of AuNPs. Therefore, a highly selective strategy was attained with an impressive specificity for melamine.3、With HAuCl4 and NaBH4 as reactants, monodisperse gold nanoparticles with different diameters were successfully synthesized by one-step process at room temperature. X-ray diffraction, transmission electronmicroscopy, laser particle size analyzer, and UV-V spectroscopy were used to characterize the samples. The results indicate that the as-prepared gold nanoparticles are spherical and their structure is face centercubic (FCC). Sodium citrate not only improves monodispersity and stability of gold nanoparticles, but also restrains the crystal growth, making the particles have narrow size distribut ion with controllable size. The peak positions of UV-V was absorption spectra exhibited a blue-shift as the crystal size decreases.4、A colorimetric method was developed for the detection of Hg2+ based on the specific thymine T-Hg2+-T structure and gold nanoparticles. A tweezers-like duplex DNA, containing T-T mismatches in the end, was designed. The mismatched thymines in the tweezers like dsDNA could not form helix structure, which could attach to AuNPs and effectively prevent AuNPs from salt induced aggregation. While in the presence of Hg2+ ions, the T- Hg2+-T coordinations would lead these thymines to form the structures of helix. The AuNPs were less well-protected thus aggregated at the same salt concentration, accompanied by color changing from red to blue. The results of fluorescence spectroscopy showed that when the mercury ions in the system, the gold nanoparticles to agglomerate based on the role of the aptamer, accompanied by the increase of the concentration of mercury ions, a strong agglomeration, so that in the 432 nm fluorescence intensity increased. With eight kinds of the composite ion system, the colorimetric results are not changed, indicating that colorimetric detection system has high detection selectivity and immunity.5、CTAB-capped AuNPs are modified by polymethyl glutamate (PGA).Then PGA-AuNPs are characterized by TEM, UV-visible spectrophotometer and FT-IR infrared spectrum. The results showed that:the particles of PGA-AuNPs dispersion liquid exhibit a star-like shape with a mean diameter of 60-70 nm. These results of FT-IR measurements suggested that the surface of AuNPs was successfully coated using PGA.6、We demonstrate a facile, sensitive and selective colorimetric probe for detection of Hg2+ based on the PGA functionalized AuNPs. The absorption ratio (A750/A580) of the assay exhibited a linear correlation to Hg2+concentration in the range from 0.01 to 10 μM and from 50 to 300 μM, with the correlation coefficients of 0.998 and 0.991, respectively. To test the selectivity, the colorimetric responses in the presence of various metal ions including Cd+, Ag+, Cu2+,Co2+, Zn2+, Ca2+, Fe3+ and Mn2+(at a concentration of 1000 pM) were performed under the same experimental conditions in case of Hg2+(50 μM).The results show the absorbance ratio A750/A580 caused by Hg2+. This means that our probe responds selectively towards Hg2+ The average recoveries of Hg2+ from tap water and mineral water were 97.13%(varying from 90% to 103%) and 108.76 (varying from 103.53% to 113%), respectively. The average coefficients of variation (CV) of Hg2+ from tap water and mineral water were 7.0% (varying from 4.6% to 9.5%) and 6.9 (varying from 2.7% to 11.1%), respectively. The results reveal the practicality of the developed method for the determination of Hg2+ in environmental water samples.7、We propose a methods of AuNPs green synthesis, using that citrus fruit juices rich in ascorbic acid prepared AuNPs, and test its stability and catalytic activity. The results showed that:1×,5× and 10× AuNPs prepared juices appear absorption peak at about 530 nm; liquor, 15x and 20x AuNPs appear absorption peak at 570 nm. The measure of AuNPs prepared by 1 x oranges, tangerine and lemon juice by laser particle analyzer shows AuNPs was normal distributed, and the average particle size was 7.8 ± 0.4 nm,11.8 ± 0.5 nm and 6.8 ± 0.3 nm respectively. In temperature conditions(25 ℃), the activity of AuNPs prepared by oranges, tangerine and lemon juice were 76%,47% and 69% respectively after 120h. Using a probe reaction catalyzed hydrogenation of p-nitrophenol as the evaluation of different fruit juices prepared AuNPs catalytic activity. the AuNPs prepared by three fruit juices have all catalytically active and the catalytically active of AuNPs prepared by oranges and lemons longer than continuous preparation of tangerine juice.8、A rapid and simple real-time visualization of colorimetric method for pH-sensitive was development based upon the aggregation of poly-(y-glutamic acid)-stabilized gold nanoparticles (PGA-AuNPs). It is observed that,the main color of the colloidal solution is pink red when the pH reaches 6.0. Lowering the solution pH by adding HCl solution leads to visible changes in the color of the solution from pink red (pH 6) to light red (pH 2). A further decrease in pH to 1 leads to the color changed to purple blue. It is also observed that the color changes from red to blue when the PGA-AuNPs solution reaches high pH (7-9). The designed pH probe is being extensively applied in biological and medical applications such as colorimetric biosensors, drug delivery, cancer imaging, and cancer therapies. |
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