Rapid colorimetric detection of proteins and bacteria using silver reduction/precipitation catalyzed by gold nanoparticles

A colorimetric immunoassay has been developed based on the reduction and precipitation of silver ions catalyzed by colloidal gold. This method was evaluated for a noncompetitive heterogeneous immunoassay to detect ovalbumin as a model protein and Escherichia coli as model bacterium. The influence of relevant experimental variables, including the reaction time of antigen with antibody, the dilution ratio of the colloidal gold-labeled protein, time allowed for silver reduction/precipitation reaction and other parameters were examined and optimized. This colorimetric method of detection is convenient, easy to use and economic. The presence of the target molecules or antigens can be visually inferred based on the color change that occurs in a short time without using major instrumentation. This method is widely amenable for detection of proteins, viruses and bacteria.     

A new approach to measure melamine, cyanuric acid, and melamine cyanurate using surface enhanced Raman spectroscopy coupled with gold nanosubstrates

Vibrational spectroscopic characteristics of melamine, cyanuric acid, and melamine cyanurate were measured using surface-enhanced Raman spectroscopy (SERS) coupled with gold nanosubstrates. Trace amounts of melamine and its analogues (cyanuric acid and melamine cyanurate) were characterized and quantified quickly and accurately by SERS in combination with partial least squares (PLS) analysis. Based on the relationship between the Raman intensity of the most prominent peak at around 676 cm⁻¹ and log values of melamine concentrations, the limit of detection (LOD) of SERS for melamine was estimated to be 2.6 × 10⁻⁷ mol L⁻¹ (∼33 ppb). An approximately 3 × 10⁴ fold of enhancement factor for SERS signals of melamine on gold nanosubstrates was obtained. This result was based upon the comparison of the peak at around 676 cm⁻¹ in the SERS spectra with that of normal Raman spectra of melamine in aqueous solutions. SERS spectra of cyanuric acid acquired from its solid form differ significantly from this compound in an aqueous solution, indicating a possible keto-enol isomerization reaction of cyanuric acid in water. When equal amounts of melamine and cyanuric acid were added together, spoke-like crystals of melamine cyanurate formed instantly, which could be measured and characterized by SERS. This study demonstrates that SERS could provide a fast and ultra-sensitive tool for detection and characterization of melamine and its derivative compounds in aqueous solutions.     

纳米金在食品安全检测中的应用研究进展

纳米金具有良好的生物相容性和独特的光学性质,可与生物和有机分子结合,形成功能化的纳米金。基于这些特性,纳米金在食品安全检测方面有着广泛的应用。本文综述了纳米金在食源性致病菌、生物毒素、重金属离子、药物残留、食品添加剂及非法添加物和其他食品有害因子检测中的应用实例,并对纳米金在食品安全检测方面的应用进行了展望。     

基于纳米金显色的非标记核酸适配体可视化检测重金属镉的方法研究

目的建立以特异性非标记核酸适配体为识别探针的重金属镉可视化检测方法。方法根据适配体与镉的高亲和力结合特性,利用纳米金溶液在盐诱导下凝聚后引起的颜色变化反应,通过分光光度计检测溶液的吸光度来检测镉离子浓度。通过优化适配体DNA浓度、盐离子浓度和纳米金溶液体积,确定最佳反应条件,建立样品溶液中镉离子浓度与吸光度的线性关系。结果该方法的线性范围和检测限分别是0.14~10 ng/m L和0.14 ng/m L,可以满足痕量检测要求。通过对灌溉水样的加标回收实验证明,检测体系具有很好的实用性和复杂基体适应性。结论利用核酸适配体和纳米金显色实现了镉的痕量可视化检测,该方法是一种简单、快速、灵敏的检测方法,在现场快速检测和高通量分析中都具有很好的应用前景。     

基于纳米金粒子的猪源性成分快速比色检测

目的 开发一种基于纳米金粒子快速比色的猪源性成分快速检测方法。方法 选取猪线粒体基因中特异性DNA片段为靶点, 利用互补单链DNA与纳米金粒子偶联为探针, 提取检测目标DNA后在盐溶液中进行检测。结果 探针上DNA结合检测目标后, 纳米金粒子失去单链DNA的保护, 发生聚集, 由红色变为蓝色, 实现裸眼可视检测。核酸偶联的最佳用量为0.1 mmol/L的核酸添加30 μL, 方法的检出限为5%。 结论 这种比色检测可以在不使用复杂仪器的条件下将猪肉与其牛肉类产品区分开来, 方法快捷迅速, 对肉制品掺假的防控具有重要意义。     

Two-step aggregation of gold nanoparticles based on charge neutralization for detection of melamine by colorimetric and surface-enhanced Raman spectroscopy platform

A colorimetric and surface-enhanced Raman scattering (SERS) signal amplification platform based on 2-step aggregation of gold nanoparticles (AuNP) was constructed for the sensitive detection of melamine. In this study, the positively charged SYBR Green I was used for the first step of aggregation of AuNP, via charge neutralization, to obtain small-sized AuNP aggregates. The positively charged SYBR Green I decreased the negative charges of the surface of AuNP, which was beneficial to the aggregation of AuNP. In addition, the melamine could aggregate AuNP by decreasing the negative charges of the surface of AuNP and self-assemble with each other on the surface of AuNP by hydrogen bonds. Therefore, the second efficient aggregation of small-sized AuNP aggregates could be achieved with melamine at low concentration, resulting in significant signal changes of color and SERS. The sensitivity of a colorimetric (0.60 mg/L) and SERS (0.089 mg/L) platform, based on 2-step aggregation of AuNP, was 15 and 2.2 times higher than that based on 1-step aggregation of AuNP for detecting melamine.     

金纳米粒子在食品检测领域中的研究进展

随着纳米技术的快速发展,作为纳米材料中化学性质最稳定的金纳米粒子,以其独特地光学、电学性质和良好地生物兼容性广泛的被应用于食品检测领域。文章综述了金纳米粒子在食品检测领域的最新研究进展,讨论了金纳米粒子在当前食品安全与检测领域的优势和不足,并对金纳米粒子在食品检测领域的未来发展趋势做了展望。      

Residue analysis of melamine in milk products by micellar electrokinetic capillary chromatography with amperometric detection

A high-performance micellar electrokinetic capillary chromatography with amperometric detection (MECC–AD) method for the fast determination of melamine (MM), occasionally used to increase the apparent protein content of milk products, has been developed. Method development involved optimisation of the working electrode, the running buffer system and acidity, the concentration of sodium dodecyl sulphate (SDS), the separation voltage, the applied potential and the sample injection time. Under the optimum conditions, MM can be well separated from its co-existing interferences in real-world samples within 9 min at the separation voltage of 20 kV in a 8 mmol/L SDS/20 mmol/L H₃BO₃–Na₂B₄O₇ running buffer (pH 7.4). Satisfactory recovery (83.3–105.5%), repeatability of the peak current (3.2%) and migration time (3.8%), and the limit of detection (2.1 × 10⁻⁶ g/mL) for the method were achieved. This proposed procedure has been successfully used for the determination of MM in milk products.     

基于金纳米粒子的比色法在食品安全检测中的应用

金纳米粒子(gold nanoparticle, AuNPs)是一种有着良好的光学性质,具有类似天然酶活性的纳米材料,通过改变AuNPs的尺寸、形貌,进行表面修饰,优化局部环境以及改变催化条件等手段,可以改变AuNPs聚集状态,吸收峰发生变化,从而引起溶液颜色发生改变;也可以改变AuNPs的类酶活性,促进有机底物发生颜色变化,提高方法的灵敏度。基于AuNPs的比色法以其操作简便、特异性识别能力高、可视性强、灵敏度高、检测成本低等优点在食品快速检测中有着很大的优势,尤其是近年来随着纳米技术的快速发展,此方法成为食品安全检测领域的研究热点。本文介绍了AuNPs的制备方法,总结了基于AuNPs的比色法的显色机制,重点介绍了近年来此方法在食品安全检测中的最新应用进展,主要包括金属离子、农兽药残留、真菌毒素、微生物等检测方法的最新研究成果,对两种显色机制的基于AuNPs的比色法在食品安全检测中的应用进行了对比,就目前存在的问题提出建议,对未来发展前景作了简要展望,以期将此方法更好的应用于食品快速检测及现场风险筛查,及时、快速、有效地从源头确保食品安全。     

基于静电作用诱导金铂纳米粒子聚集的比色方法检测鱼肉中组胺

目的 基于金铂纳米粒子(AuPt nanoparticles, AuPt NPs)建立一种简便、灵敏的比色方法检测鱼肉中的组胺。方法 由柠檬酸钠制备的AuPt NPs表面带负电,组胺通过静电作用能与AuPt NPs相结合,诱导AuPt NPs聚集,溶液由棕红色变为灰色;同时引起AuPt NPs表面等离子体共振发生红移,吸收峰由510 nm移至650 nm附近,将650 nm和510 nm的吸光度比值(A650/A510)作为检测组胺的参数。结果 在最优的条件下(反应时间为1 h、反应温度为25℃),A650/A510随着组胺浓度的升高而升高,A650/A510与0.5-30 μmol/L的组胺浓度呈现良好的线性关系,线性方程为A650/A510=0.019C组胺+0.3686(r2=0.9962),方法检出限为0.32 μmol/L。将方法用于鱼肉样品的检测,加标回收率为102.1%-111.7%,相对标准偏差为1.8%-3.1%。结论 本实验方法具有简便、快捷和成本低的优点,可实现鱼肉中组胺的可视化快速检测。     

On-site detection of sub-mg/kg melamine mixed in powdered infant formula and chocolate using sharp-edged gold nanostar substrates

We report a facile method for sample preparation and sensitive on-site detection of melamine in powdered infant formula and chocolate using Raman spectroscopy on sharp-edged gold nanostars (AuNSs). The aggregation of AuNSs by sodium chloride (1.2 M) facilitates the more sensitive detection of melamine in comparison with spherical gold nanoparticles (AuNPs). Density functional theory quantum mechanical calculations were performed to determine the energetic stability on gold cluster atoms. Our spectroscopic data indicated that AuNSs are an efficient platform for detecting melamine in food mixtures. The detection limits of melamine in powdered infant formula and chocolate were found to be ~0.1 mg/kg and ~1 mg/kg, respectively, on AuNPs, whereas they were observed to be ~0.01 mg/kg and ~0.1 mg/kg, respectively, on AuNSs. Using a handheld Raman spectrometer, a sub-mg/kg detection of melamine in both powdered infant formula and chocolate could be achieved within a few minutes.     

微生物法在原料奶验收中的应用

对微生物法的应用进行了研究。采用对抗生素最敏感的嗜热链球菌为实验菌，从产酸能力和凝乳时间两个因素来检测牛乳中抗生素的残留，并定量得出该嗜热链球菌对青霉素类抗生素的最低检出量为0.04单位。结果表明，该方法操作简便。     

微生物法在原料奶验收中的应用

对微生物法的应用进行了研究。采用对抗生素最敏感的嗜热链球菌,从产酸能力和凝乳时间两个因素来检测牛乳中抗生素的残留,并定量得出该嗜热链球菌的最低检出量为0．04单位。结果表明,该方法操作简便。     

Visual detection of blemishes in potatoes using minimalist boosted classifiers

This paper introduces novel methods for detecting blemishes in potatoes using machine vision. After segmentation of the potato from the background, a pixel-wise classifier is trained to detect blemishes using features extracted from the image. A very large set of candidate features, based on statistical information relating to the colour and texture of the region surrounding a given pixel, is first extracted. Then an adaptive boosting algorithm (AdaBoost) is used to automatically select the best features for discriminating between blemishes and non-blemishes. With this approach, different features can be selected for different potato varieties, while also handling the natural variation in fresh produce due to different seasons, lighting conditions, etc. The results show that the method is able to build “minimalist” classifiers that optimise detection performance at low computational cost. In experiments, blemish detectors were trained for both white and red potato varieties, achieving 89.6% and 89.5% accuracy, respectively.     

Gold nanoparticles: From synthesis,properties to their potential application as colorimetric sensors in food safety screening

BackgroundFood safety management and guarantee are the basic requirement during food processing, circulation, storage, and marketing. Elevating the ability to evaluate food quality and safety in a rapid, sensitive and reliable manner is of great importance in food industry. Recently, gold nanoparticles due to unique optical property, ease of functionalization and preparation, and high selectivity and sensitivity have received considerable attention in the field of food safety.Scope and approachGold nanoparticles exhibit distinguishable optical characteristic in different aggregated states and thus have been developed into simple colorimetric sensors for the quick detection of chemical contaminants in food samples. Herein, we reviewed the current methods for synthesis and functionalization of gold nanoparticles, strategies for fabrication of gold nanoparticle based colorimetric sensors and their applications in rapid analysis of food contaminant. Moreover, the inherent optical property of gold nanoparticles and their detecting principle have been highlighted. Finally, the main challenges and future efforts in developing such colorimetric sensors for food contaminants detection were discussed.Key findings and conclusionsGold nanoparticles as smart colorimetric sensors conform to the requirement of modern analysis, such as high selectivity, sensitivity, simplicity, celerity, and portability. Thus, they have great potential to be applied as power sensing tools for food safety screening.     

基于纳米金标记-适配体识别对鱼中磺胺二甲氧嘧啶的定量检测

纳米金因具有独特的光学效应,已成为极具应用前景的标记材料。适配体对目标分子具有较强特异识别能力,被广泛应用于分析检测领域。本文利用纳米金标记适配体,构建了一种磺胺二甲氧嘧啶的可视化检测新方法。利用该方法对磺胺二甲氧嘧啶进行定量分析,在添加水平分别为2、7 ng/m L下,测得回收率为89.86%和85.64%,日内日间相对标准偏差分别为4.00%、5.28%和5.88%、6.67%。方法的检测线性范围为1~10 ng/m L,检测限为1 ng/m L。以上结果表明该方法准确度高,精密度好,将其应用于鲈鱼、鲶鱼等实际水产样品中磺胺二甲氧嘧啶的定量分析具有可行性。      

基于纳米金光学性质检测脂肪酶活性的研究进展

脂肪酶是食品工业广泛应用的酶制剂, 其活性大小对食品品质有重要影响, 因此对其活力测定成为食品检测中不可或缺的一部分。脂肪酶常见的测定方法有滴定法、皂铜比色法、平板法等, 但这些方法往往存在操作复杂、灵敏度不足、测量误差较大的缺点, 而基于纳米金光学性质检测脂肪酶具有简单快速、灵敏度高、特异性强、操作简单等优点, 是一种良好的测定方法。本文主要从纳米金的光学性质和测定的原理、基于纳米金的光学特性检测脂肪酶的方法及未来发展3个方面对纳米金在测定脂肪酶活性方面的研究进展进行评述。目前, 使用纳米金检测脂肪酶活性仍然存在很多问题, 通过总结近年来脂肪酶活性的检测方法, 希望能对未来脂肪酶活性快速、灵敏检测起到一定的推进作用。     

高效液相色谱法分析原料乳和奶粉中三聚氰胺

建立了二极管阵列检测器-高效液相色谱测定原料乳及奶粉中三聚氰胺的方法。奶粉样品经三氯乙酸超声提取,乙酸铅沉淀蛋白,三氯甲烷除去脂肪和非极性杂质,PROELUTPXCSPE阳离子交换固相萃取小柱进一步除去样品基质干扰,氨化甲醇洗脱。实验对色谱分离条件进行了优化,三聚氰胺的质量浓度在1.0～100.0μg/mL范围内与色谱峰面积呈良好的线性关系,回归方程为y=89.763x-113.72,相关系数为R2=0.9988。加标回收率为90.5%～105.0%,相对标准偏差(RSD)小于4.0%。该方法简单、快速,结果准确可靠。     

Synthesis and stability analysis of papain-functionalized gold nanoparticles (P-AuNPs) for the colorimetric detection of mercury in milk

To detect mercury in dairy cow milk by colorimetric techniques, papain-functionalized gold nanoparticles (P-AuNPs) were synthesised. Papain-functionalized gold nanoparticles aggregated when mercury ions were introduced, causing their absorption peak to shift from 525 to 575 nm. Dynamic light scattering and transmission electron microscopy determined that aggregated P-AuNPs average sizes were 26.60 nm and 15.17–18.23 nm, respectively, with monodispersed. The detection limit of P-AuNPs for mercury in milk samples was 1.0 ppm with high recovery. This sensor showed relatively high selectivity and sensitivity towards Hg²⁺ ions in milk. This method shows utility in developing countries for monitoring the concentration of Hg²⁺ in water, milk and food items for safety purposes.     

Simultaneous determination of Sunset yellow and Tartrazine in soft drinks using gold nanoparticles carbon paste electrode

The monitoring of synthetic dyes in foods is very important due to their potential harmfulness to human beings. Herein, a carbon-paste electrode (CPE) that is chemically modified with gold nanoparticles (nAu) was fabricated and used for the determination of Sunset yellow (SY) and Tartrazine (Tz). Cyclic and differential pulse voltammetry (CV and DPV) results revealed two well-resolved anodic peaks for SY and Tz with remarkably increase in oxidation signals of these colourants. Based on this, a novel electrochemical method was developed for the simultaneous determination of SY and Tz. High sensitivity and selectivity, sub-micromolar detection limit, high reproducibility and regeneration of the electrode surface by simple polishing make the nAu-CPE electrode very suitable for the determination of SY and Tz in commercially available soft drinks. The detection limits was 3.0 × 10⁻⁸ and 2.0 × 10⁻⁹ mol l⁻¹ for SY and Tz, respectively, which are remarkably lower than those reported previously for SY and Tz using other modified electrodes.