Catechin mediated green synthesis of Au nanoparticles: Experimental and theoretical approaches to the determination HOMO-LUMO energy gap and reactivity indexes for the (+)-epicatechin (2S, 3S)

This work suggests a green method for synthesizing Au nanoparticles (AuNPs) using the aqueous extract of Salix aegyptiaca extract. The mechanism of green synthesized AuNPs was examined by molecular electrostatic potential (MEP) calculations. AuNPs were characterized with different techniques such as Ultraviolet–visible spectroscopy (UV–vis), Fourier-transform infrared spectroscopy (FT-IR) spectroscopy, X-ray diffraction (XRD), and Transmission electron microscopy (TEM). Electrochemical investigation of modified glassy carbon electrode using AuNPs (AuNPs/GCE) shows that the electronic transmission rate between the modified electrode and [Fe (CN)₆]^3?/4? increased. Process of oxidation, energy gap, and chemical reactivity indexes of the (+)-epicatechin (2S,3S) were investigated using electrochemical techniques (cyclic voltammetry (CV) and differential pulse voltammetry (DPV) as well as UV–Visible spectroscopy and compared with quantum mechanical calculations. DPV and CV were used to obtain HOMO energies of the (+)-epicatechin (2S,3S), an optical energy gap was obtained from the UV–Vis spectroscopy. Frontier molecular orbitals analysis (FMO) and reactivity indexes such as chemical hardness (?), electrophilicity (?), electronic chemical potential (μ), electron acceptor power (?⁺), electron donor power (?^?) were determined with functional theory (DFT) calculations. In summary, the HOMO energy obtained from the experimental analyses (E_HOMO (from DPV) = -5.24 eV, and E_HOMO (from CV) = -5.28 eV) has a relative agreement with the HOMO energy calculated by B3LYP/6–31 g (d, p) including the solvent effect (water) (E_HOMO (from B3LYP) = -5.75 eV). Also, UV–Vis spectroscopy gives the bandgap energy equal to 4.31 eV, while the 4.13 eV is calculated by TD-DFT-b3lyp/6–31 + g(d).     

碳纤维微电极负载金纳米粒子用于绿茶中儿茶素的检测

本文开发了基于纳米金修饰的碳纤维超微电极(CFME)用于儿茶素的定量检测。通过使用柠檬酸三钠还原氯金酸制得纳米金粒子(AuNPs),采用恒电位电沉积法将纳米金修饰在CFME表面。在pH 2.00的Tris-HCl缓冲溶液中,采用差分脉冲法和循环伏安法考察了修饰前后电极对儿茶素的电催化性能。结果表明,纳米金修饰电极对儿茶素具有明显的电催化效果。在优化实验条件下,纳米金修饰的碳纤维超微电极(AuNPs/CFME)与儿茶素浓度在1.00×10^-3~10.0μmol/L范围内呈良好的线性关系,且AuNPs/CFME的电化学性能非常稳定,具有良好的重现性。该方法操作简单,准确性高,可用于对儿茶素进行定量检测。     

氧化石墨烯在辣根过氧化物酶传感器中的应用研究

本文研究氧化石墨烯的合成方法及其在生物传感器中的应用.通过Hummer法氧化天然石墨粉制得氧化石墨,在蒸馏水中利用超声分散将氧化石墨剥片,从而合成了氧化石墨烯(GO).通过透射电镜图表征了氧化石墨烯的形貌并通过红外光谱证实氧化石墨烯的形成.将所合成的氧化石墨烯与三角形貌的金纳米颗粒(prism AuNPs)、辣根过氧化...     

A Hairpin Electrochemical Aptasensor for Sensitive and Specific Detection of Thrombin Based on Homogenous Target Recognition

An electrochemical aptasensor was developed for sensitive and specific detection of thrombin by combining homogenous recognition strategy and gold nanoparticles (AuNPs) amplification. Streptavidin‐alkaline phosphatase was used as reporter molecule. Compared with the traditional hairpin aptasensor monitoring the distance of the redox molecule from the electrode surface, the proposed aptasensor successfully overcome the limitations of distance and improved the stability and high affinity of the aptamer hairpin through homogenous recognition, which enhanced the sensitivity and selectivity of the sensors effectively. Additionally, AuNPs were employed to increase the active area and conductivity of the electrode, thus, improving the sensitivity of the aptasensor. As a result, the designed thrombin detection sensor obtained a lower detection limit of 0.52 pM in buffer and 6.9 pM in blood serum.     

A simple visual method for DNA detection based on the formation of gold nanoparticles

A simple visual method for DNA detection during the formation of gold nanoparticles (AuNPs) was developed based on different electrostatic properties of single strand DNA (ssDNA) and double strand DNA (dsDNA). Since the ssDNA is easy to bind to AuNPs due to its exposed bases which could prevent salt-induced aggregation of AuNPs. The dsDNA always present negative charge because its negatively charged phosphate backbone is exposed. In this case, the dsDNA could disturb the adsorption between dsDNA and AuNPs and result in non-aggregation of AuNPs. After hybridization, chloroauric acid and ascorbic acid were added to the mixture solution, and the solution changed to red immediately and turned to purple in 10 min in the present of target DNA. TEM results confirmed that the change of color stemed from aggregation of AuNPs. In order to obtain accurate results by naked eye, the DNA detection assay should be conducted under pH 7.0.     

The Competitive Dynamic Binding of Some Blood Proteins Adsorbed on Gold Nanoparticles

Nanoparticle (NP) surfaces are modified immediately by the adsorption of proteins when injected into human blood, leading to the formation of a protein corona. The protein‐coated NPs may be recognized by living cells. Furthermore, the adsorption of serum proteins is a continuous competitive dynamic process that is the key to exploring the bioapplication and biosafety of NPs. In this study, the competitive dynamic adsorption of some serum proteins on gold nanoparticles (AuNPs) is investigated by fluorescence emission, dynamic light scattering, and sodium dodecyl sulfate‐polyacrylamide gel electrophoresis. Serum proteins with different AuNPs binding affinities are used to address the competitive dynamic process of protein‐AuNP interactions in vitro. The results show that more abundant serum proteins, such as human serum albumin, adsorb on AuNPs first, and then the higher binding affinity and lower concentration serum proteins, such as fibrinogen (FIB), replace the abundant and lower binding affinity serum proteins. However, the lower binding affinity serum proteins, such as hemoglobin, do not replace the higher binding affinity proteins from the protein‐AuNP conjugates. During the dynamic exchange process, the larger the binding affinities difference between two proteins, the faster the exchange rate. This dynamic exchange process usually takes longer in inner protein‐AuNP conjugates (hard corona) than the external surface of protein‐AuNP conjugates (soft corona).     

Growth kinetic study of ionic liquid mediated synthesis of gold nanoparticles using Elaeis guineensis (oil palm) kernels extract under microwave irradiation

Gold nanoparticles (AuNPs) are the most studied nanomaterials due to their promising applications. However, surface capping of AuNPs is essential to protect aggregation for enhanced colloidal stability. In this study, a single step method was established to synthesize stable AuNPs using oil palm kernel (OPK) extract prepared in IL[EMIM][OAc] (1-ethyl-3-methylimidazolium acetate). Ionic liquids were used for phytochemicals extraction along with capping and stabilizing of AuNPs after their synthesis. The OPK extract reduced the gold precursor, and UV–vis spectroscopy revealed a sharp surface plasmon (SPR) peaks in the region of 524–529 nm, which confirmed the formation of AuNPs. UV–vis and TEM analysis indicated that microwave assisted synthesis was rapid to synthesize well dispersed and small sized AuNPs in comparison with conventional heating. FTIR analysis of kernels extract before and after its reaction with gold precursor identified the involvement of CH aromatic groups, polyphenolic OH groups, and carbonyl amide groups that are responsible for reduction of trivalent gold ions to AuNPs. EDAX and XPS analysis were performed to identify the elemental gold and its surface interaction with ILs and other organic moieties. Colloidal AuNPs kept at room temperature for periods of six months were remained stable. The change of pristine nanostructure arises due to involvement of different driving forces during growth of nanoparticles. Thermodynamically instability of nanomaterials may leads to Ostwald Repining (OR) or adopt complex pattern of growth and undergo coalesce and orientation attachment (OA). These models were fitted to compare the theoretically growth of particles along with actual increase of particles size. Experimental results suggested that OA growth was originated in early phase, however, it substituted and mainly controlled by OR growth pattern over time.     

纳米金催化Luminol-H_2O_2化学发光体系对异烟肼的测定

碱性条件下,纳米金对Luminol-H2O2化学发光体系有增敏作用,而异烟肼对该化学反应具有强烈的抑制作用。基于此,在优化化学发光反应条件的基础上,提出了一种测定异烟肼的新方法,并对其可能的化学发光机理进行了探讨。该方法测定异烟肼的线性范围为0.005~9.0 mg/L,检出限(3σ)为3.0μg/L,相对标准偏差为3.5%(n=11,ρ=0.2 mg/L)。该法已成功用于药物制剂中异烟肼含量的测定。     

多孔硅-Au/Ag枝晶复合材料研究进展

基于金属包裹的多孔硅衬底具有制备成本低、检测能力强的优点。自20世纪表面增强拉曼散射(SERS)现象被发现以来,多孔硅-Au/Ag复合材料逐渐展现出作为SERS衬底的优势,被广泛应用于生物、化学、医疗等领域。本文综述了近些年来基于多孔硅复合Au/Ag纳米颗粒混合平台的研究,重点讨论了将贵金属Ag/Au复合于多孔硅衬底上的制备方法,介绍了它们在不同制备条件下枝晶结构的生长形貌和检测性能,并对多孔硅-Ag/Au枝晶复合结构作为SERS衬底的未来发展进行简要分析。     

免标记比色核酸适配体传感器同步快速检测孔雀石绿和无色孔雀石绿

研究以双特异性核酸适配体A3作为传感探针、纳米金（AuNPs）为指示剂、NaCl溶液为聚集诱导剂,构建了一种新型的免标记AuNPs比色生物传感器,可实现水产品中孔雀石绿（MG）和无色孔雀石绿（LMG）的同步、快速、可视化检测。该方法的检测原理是核酸适配体A3对MG和LMG有双特异性识别能力,可作为MG和LMG理想的识别受体。它可通过静电作用吸附到AuNPs表面,保护AuNPs并抑制高盐溶液诱导的聚集,AuNPs溶液颜色不变,即为红色;当加入靶标MG或LMG后,该核酸适配体能够与靶标特异性结合,并从AuNPs表面上解离,AuNPs失去保护作用而在高盐溶液诱导下发生聚集,溶液颜色由红变蓝。根据颜色变化,可通过肉眼定性或通过光谱仪定量分析MG和LMG的残留量。该方法首先将50 μL的核酸适配体A3（终浓度150 nmol/L）与150 μL的AuNPs（终浓度1.25 nmol/L）混合,室温孵育6 min。随后加入50 μL待测液,室温孵育30 min。最后加入50 μL NaCl（终浓度150 mmol/L）,4 min后观察溶液颜色变化,并分别测定MG和LMG在520 nm和650 nm下的吸光度值。结果表明,在最佳反应条件下,该方法能够特异性检测MG和LMG,而对磺胺嘧啶（SDZ）和硝基呋喃妥因（NFT）无交叉反应;当MG、LMG的浓度为0~17.5 μmol/L时,吸光度比值与靶标浓度呈现良好的线性关系,相关系数（R ² ）分别为0.9938和0.9715。MG和LMG的检出限分别为6.93 nmol/L和6.38 nmol/L,加标回收率分别为88.60%~93.30%和101.80%~107.00%,相对标准偏差（RSD）分别为2.27%~3.55%和2.62%~3.75%。该方法操作简单,快速和灵敏,可为水产品中MG和LMG的同步快速检测提供一种新方法。