Colloidal Gold Surface Research Articles

Study of the Electrochemical Impedance Immunosensor

Colloidal gold has been extensively studied for its unique properties in various fields, including diagnostics and therapeutics. The colloidal gold electrochemical impedance immunosensor is a promising tool in antigen detection. It has high sensitivity, specificity, and rapid results. However, it also faces certain challenges, such as the stability of colloidal gold particles and optimization of assay conditions. To address these challenges, this paper suggests several recommendations. First, advancements in colloidal gold synthesis and surface modification techniques can enhance the stability and reproducibility of the particles. Second, optimizing assay conditions, including sample pre-treatment and antigen binding conditions, can improve the overall performance of the electrochemical impedance immunosensor. Furthermore, research is needed to develop the full potential of this technique in different fields and expand its practical applications. In conclusion, the colloidal gold electrochemical impedance immunosensor shows great promise in antigen detection. By comparing it with other methods and proposing solutions to its limitations, this review paper aims to contribute to the advancement of this technique and its applications in various industries. Continued research and development in this field will undoubtedly lead to further improvements and broaden the scope of this powerful tool.

An enhanced immunochromatography assay based on colloidal gold-decorated polydopamine for rapid and sensitive determination of gentamicin in animal-derived food

In this study, an enhancing immunochromatography assay (ICA) based on colloidal gold-decorated polydopamine (CG@PDA) was firstly developed for gentamicin in milk, muscle, liver and kidney simultaneously. CG@PDA was synthesized by one-pot method with better signal intensity, colloidal stability, and antibody coupling efficiency than traditional colloidal gold. The detection limit of the developed ICA was about 1.50 μg/kg for the four animal-derived food, which was up to 92-fold more sensitive than the reported ICA based on colloidal gold. The recovery rates were ranged from 86.0% to 114.0% with coefficient of variation between 1.6% and 13.1%. Parallel analysis of 40 samples by commercial ELISA kits was confirmed the reliability. Our research indicated that polydopamine decorated can chemically modify the surface of colloidal gold and can thus remarkably improve the detection performances of ICA.

Light scattering intensity as signal transducer to enhance the performance of immunoassay for Cronobacter detection in powdered infant formula

Herein, we propose the light scattering intensity of silver and gold alloy as signal transducer to enhance the sensitivity and dynamic linearity of immunoassay for quantitative detection of Cronobacter muytjensii (C. muytjensii) in powered infant formula (PIF). Silver and gold alloy, namely, silver-coated gold nanocomposite (AuNF@Ag), was obtained by growing silver on the surface of multi-dendritic colloidal gold. The silver growth was triggered by the hydrolysis of urease to urea in the presence of silver nitrate and glucose. Owing to integrating the advantages of light scattering of AuNF@Ag and enzyme-catalyzed mediated signal amplification, the developed light scattering based immunoassay shows high sensitivity for detection of C. muytjensii, with a detection limit of 51 CFU/mL, which is three orders of magnitude lower than that of conventional enzyme-linked immunosorbent assay (ELISA, 6.39 × 104 CFU/mL). In addition, the proposed method also exhibits wide dynamic curve from 3.4 × 102 CFU/mL to 3.4 × 109 CFU/mL for quantitative detection of C. muytjensii, and is significantly superior conventional ELISA (3.4 × 105 CFU/mL to 3.4 × 109 CFU/mL). The accuracy and precision of the proposed immunoassy were evaluated by analysis of C. muytjensii-fortified PIF samples. The average recoveries of the intra- and inter-assays are within 87.90 %–107.91 %, and the coefficient of variation ranges from 2.72 %–9.32 %. This finding indicates an acceptable accuracy for quantitative detection of C. muytjensii in real PIF samples.

Origin of Laser-Induced Colloidal Gold Surface Oxidation and Charge Density, and Its Role in Oxidation Catalysis

Laser fragmentation in liquids (LFL) allows the synthesis of fully inorganic, ultrasmall gold nanoparticles, usAu NPs (<3 nm). Although the general method is well established, there is a lack of un...

Staining Traditional Colloidal Gold Test Strips with Pt Nanoshell Enables Quantitative Point-of-Care Testing with Simple and Portable Pressure Meter Readout.

Traditional immunochromatographic test strips based on colloidal gold are effective devices for portable and low-cost point-of-care (POC) testing. Nevertheless, they still suffer from the limitation of qualitative or semiquantitative tests via naked-eye detection. Replacement of gold with other signal entities, such as magnetic particles or fluorescent particles, requires professional instrumentation to obtain quantitative results. A pressure-based assay with platinum nanoparticles (PtNPs) can provide quantitative results using a portable pressure meter but is also hampered by the long-term instability of PtNPs. Consequently, we developed a Pt-staining method based on test strips to create platinum nanoshells on the surface of colloidal gold. This method not only preserves the original advantages of colloidal gold with easy synthesis and decoration but also introduces PtNPs with excellent catalytic activity as signal labels to achieve sensitive quantitative detection. Myoglobin was tested as a model target, and the limit of detection was 5.47 ng/mL in 20% diluted serum samples, which satisfies the requirements for clinical monitoring of acute myocardial infarction. In addition, the two most common colloidal gold strips available in the marketplace were applied to demonstrate the compatibility of Pt-staining. Taking advantage of low cost, user-friendliness, compatibility, simplicity, and stability, colloidal gold test strips with Pt-staining are expected to satisfy the need for quantitative POC testing of biomarkers, especially in resource-limited regions.

Near-Infrared Photothermal Release of siRNA from the Surface of Colloidal Gold-Silver-Gold Core-Shell-Shell Nanoparticles Studied with Second-Harmonic Generation.

Photothermal release of oligonucleotides from the surface of plasmonic nanoparticles represents a promising platform for spatiotemporal controlled drug delivery. Here we demonstrate the use of novel gold-silver-gold core-shell-shell (CSS) nanoparticles to study the photothermal cleaving and release of micro-RNA (miRNA) mimics or small interfering RNA (siRNA) under nearinfrared (NIR) irradiation. The furan-maleimide-based Diels-Alder adduct cleaves thermally above 60 °C and is used to bind siRNA to the colloidal nanoparticle surface in water. We investigate the photothermal cleaving kinetics of siRNA under different NIR laser powers using surface-sensitive time-dependent second-harmonic generation (SHG) spectroscopy. The photothermal release of siRNA from the surface of CSS nanoparticles is significantly higher than that from the surface of gold nanoparticles (GNPs) under similar experimental conditions. These results demonstrate that plasmonic CSS nanoparticles with photothermal cleaving linkers have important potential applications for nanoparticle-based NIR-mediated drug-delivery systems.

SERS characterization of neuropeptide Y and its C-terminal fragments deposited onto colloidal gold nanoparticle surface

It has been suggested that the family of neuropeptide Y (NPY) peptides is a promising target for the neuroprotective therapy; therefore, knowledge of the structure of these biologically active compounds and their behavior at solid/liquid interface is important in order to design new analogues. Because there is still a lack of detailed information on the behavior of NPY and its mutated analogues at the solid/liquid interfaces, in this work surface-enhanced Raman spectroscopy (SERS) analysis was used to investigate NPY and its native NPY3–36, NPY13–36, and NPY22–36 and mutated acetyl-(Leu28,31)-NPY24–36C-terminal fragments, acting on Y2 receptors (Y2R), in order to determine their possible metal surface/molecule interactions. In these studies, colloidal gold nanoparticle surface served as a solid surface, whereas an aqueous solution was used as a liquid medium. The observed differences in the band intensities, wavenumbers, and widths allowed us to draw conclusions on an adsorption mode of NPY and on changes in this mode upon the shortening of the peptide chain and increase in solution pH (from pH 3 to pH 11). Briefly, three different species of Tyr were identified onto the colloidal gold surface depending upon the length of the peptide chain and solution pH. Tyrosine (TyrOH) is present in a basic medium. Tyrosinate (TyrO−) is present in an acidic solution, whereas phenoxyl radical (Tyr*) appears at neutral pH for peptides having relatively short peptide chain (acetyl-(Leu28,31)-NPY24–36). The elongation of the peptide chain partially (NPY13–36 and NPY22–36) or completely (NPY3–36 and NPY) protects the Tyr residue against conversion to the radical form.

Merging colloidal nanoplasmonics and surface plasmon resonance spectroscopy for enhanced profiling of multiple myeloma-derived exosomes.

A novel approach for sorting exosomes from multiple myeloma (MM), monoclonal gammopathy of undetermined significance (MGUS) and healthy individuals is presented. The method is based on the combination of colloidal gold nanoplasmonics and surface plasmon resonance (SPR) biosensing and probes distinctive colloidal properties of MM-derived exosomes, such as molar concentration and cell membrane binding preferences. It allowed to discover that MM patients produce about four folds more exosomes than MGUS and healthy individuals. In addition, it showed that among the analyzed exosomes, only the MM-derived ones bind heparin - a structural analog of heparan sulfate proteoglycans known to mediate exosome endocytosis - with an apparent dissociation constant (Kd) equal to about 1 nM, indicating a high affinity binding. This plasmonic method complements the classical biochemical profiling approach to exosomes, expanding the MM biomarker panel and adding biosensors to the toolbox to diagnose MM. It may find applications for other diseases and has wider interest for fundamental and translational research involving exosomes.

Interaction of N‐benzylamino(boronphenyl)methylphosphonic acid analogs with the gold colloidal surface under different concentration and pH conditions

In this study, we present surface‐enhanced Raman spectroscopy (SERS) investigations of five analogs of a novel group of N‐benzylamino(boronphenyl)methylphosphonic acids: N‐benzylamino‐(3‐boronphenyl)‐S‐methylphosphonic acid (m‐PhS), N‐benzylamino‐(4‐boronphenyl)‐S‐methylphosphonic acid (p‐PhS), N‐benzylamino‐(2‐boronphenyl)‐R‐methylphosphonic acid (o‐PhR), N‐benzylamino‐(3‐boronphenyl)‐R‐methylphosphonic acid (m‐PhR), and N‐benzylamino‐(4‐boronphenyl)‐R‐methylphosphonic acid (p‐PhR) deposited onto 10‐nm gold nanoparticles in an aqueous solution at physiological pH (pH = 7). In addition, for the p‐PhR molecule, the SERS spectra in the various conditions of pH levels of the solutions (from pH = 3 to 11) and phosphonic acid concentration (10−3–10−5 M) were measured. In general, the SERS spectral profiles indicate that at pH = 7, all of the aforementioned molecules interact with the colloidal gold surface via a boronphenyl ring. However, the orientation of the boronphenyl ring onto the substrate surface is different for each of the studied molecules. The boronic acid group of p‐PhS and p‐PhR binds to the gold nanoparticles, whereas the phosphonic acid group assists in the interaction with the substrate for p‐PhR only. For all the molecules, the –CLCα(P)N– fragment distinctly influences the molecule/gold interactions, especially in the case of o‐PhR. The previous differences in the compound behavior at the gold/liquid interface underline the role of an absolute configuration (–R and –S) and a type of isomer (orto‐, meta‐, and para‐) on the SERS signals, which means their influence on the adsorbate geometry. Additionally, based on the SERS results for p‐PhR in various environmental conditions, we draw conclusions about spectral changes (adsorbate geometry changes) as a result of the pH of solution and molecule concentration alternations. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Exploring the Isomer Dependent SERS Spectra of (diphenylphosphoryl)(pyridin-2, -3, and -4-yl)methanol Adsorbed on Gold Nanocolloids

The surface-enhanced Raman scattering (SERS) spectra of three aminophosphonate derivatives of pyridine: (diphenylphosphoryl)(pyridin-2-yl)methanol (α-Pyr), (diphenylphosphoryl)(pyridin-3-yl)methanol (β-Pyr), and (diphenylphosphoryl)(pyridin-4-yl)methanol (γ-Pyr) were measured after immobilization onto colloidal gold surface. Changes in the wavenumber, broadness, and enhancement between the corresponding Raman and SERS bands allowed to deduce orientation of theα-,β-, andγ-isomers (α-,β-, andγ-refer to the position of the substituent relative to the ring nitrogen atom) of aminophosphonate derivatives of pyridine on the gold surface. Briefly, it was demonstrated that theα-Pyr andβ-Pyr show the same mode of adsorption, whereas the adsorption process of theγ-Pyr isomer differs in this regard that pyridine assists in the interaction with the gold surface.

Carbohydrate immobilized on a dendrimer-coated colloidal gold surface for fabrication of a lectin-sensing device based on localized surface plasmon resonance spectroscopy

Carbohydrate-mediated functions in biological systems have generated considerable interest in recent years. We have developed a device bearing immobilized carbohydrates on a colloidal gold surface and applied this device to the detection of carbohydrate-binding molecules by using localized surface plasmon resonance (LSPR) spectroscopy. The sensing device was constructed by using cyanuric chloride as an amine-linker between an amino residue of a polyamidoamine (PAMAM) dendrimer-coated colloidal gold surface and the amino residue of a 12-aminododecyl glycoside. After optimizing the construction of the device, we characterized its LSPR-based sensing capability. Binding specificity with lectins and linear range responses were obtained with the device. Our LSPR-based sensing device thus provides a label-free, low-cost detection method for use as a laboratory research tool or in medical glycan arrays.

A competitive immunochromatographic strip assay for 17-α-hydroxy progesterone using colloidal gold nanoparticles

BackgroundA rapid and competitive immunochromatographic strip (ICS) test has been developed using colloidal gold as nanoprobe for measuring 17-α-hydroxy progesterone in serum which is a marker for congenital adrenal hyperplasia, an inborn error of metabolism. MethodsColloidal gold nanoparticles (NPs) were prepared by reducing chloroauric acid with sodium citrate. The corresponding protein conjugate was prepared by passive adsorption of 17-α-hydroxy progesterone-3-carboxymethyl-bovine serum albumin (17-OHP-3-CMO-BSA) immunogen on the colloidal gold surface. Both colloidal gold and its protein conjugates were characterized using standard techniques like transmission electron microscopy (TEM) and atomic force microscopy (AFM) in addition to the optical characterization. The test line antibody was raised against 17-α-hydroxy progesterone-BSA immunogen and control line antibody was raised against BSA in New Zealand white rabbits. ResultsThis test antibody showed high immunoreactivity and specificity when characterized by ELISA for 17-α-hydroxy progesterone on microtiter plate. The primary antibody was coated on the nitrocellulose membrane as test line and anti-BSA antibody was coated as control line. The ICS test was developed in competitive assay format. The sensitivity of the present immunochromatographic strip assay was reported to be 2.5μg/l by visual observation. The signal at the test line was easily readable to the naked eye even at higher concentrations of 17-α-hydroxy progesterone normally associated with congenital adrenal hyperplasia. ConclusionThe present immunoassay takes 15min for completion. There has not been any other lateral flow immunoassay for 17-α-hydroxy progesterone reported.

Electrochemical Investigations of 3-(3-Thienyl) Acrylic Acid Protected Nanoclusters and Planar Gold Surfaces

Formation of self assembled monolayers on gold surface by thiols and disulphides is a well known phenomenon and extensive research work has been carried out in this area with envisaged applications in the area of sensors, molecular electronics, lithography, device fabrication using bottom-up approach, etc. Recently, it has been established that thiophene molecules can self assemble on gold surface due to Au-S interactions. 3-(3-thienyl) acrylic acid, a bifunctional ligand is used in this work to form self-assembled monolayers on planar gold surfaces (two dimensional assemblies) and to prepare monolayer protected gold nano clusters (three-dimensional assemblies). The electron transfer blocking properties of the two-dimensional monolayers were evaluated by using standard redox probes like ferrocyanide anions and Ruthenium hexamine cations. The functionalisation of the two-dimensional and three-dimensional assemblies has been carried out with ferrocene carboxylic acid and the functionalised monolayers were characterized by Cyclic voltammetry. The formation of thienyl acrylic acid protected nanoclusters has been verified by TEM and surface plasmon resonance absorption. It has been observed that when thiophene based ligands are used as stabilizers for the formation of metal nanoparticles, they tend to aggregate as a result of pi-pi interactions between adjacent thiophene ligands. In this case it is found that aggregation is prevented. The substituent at the thiophene ring hinders pi-pi interactions. The quantised nature of electrochemical charging of these nanoparticles has been demonstrated by differential pulse voltammetry (DPV), which exhibit peak like features (coulomb's staircase). This work also explores the possibility of using 3-(3-thienyl) acrylic acid as building blocks or spacers on planar and colloidal gold surfaces for potential applications in the field of sensors and devices.

Detection of antinuclear antibodies by a colloidal gold modified optical fiber: comparison with ELISA

A fiberoptic evanescent-wave sensor has been developed for the measurement of antinuclear antibodies in sera from patients and healthy individuals. The sensor was constructed on the basis of modification of the unclad portion of an optical fiber with self-assembled gold colloids, where the colloidal gold surface was further functionalized with extractable nuclear antigens. Results show that detection of antinuclear antibodies by this sensor agrees quantitatively with the clinically accepted enzyme-linked immunosorbent assay (ELISA) method. This sensing platform has the following advantages: label-free and real-time detection capability, simple to construct and use, highly sensitive, and does not require a secondary antibody. The sensitivity of this platform is at least an order of magnitude higher than that of the ELISA method and thus may lead to a new direction in recognition of immune response.

A chemiluminescent metalloimmunoassay based on silver deposition on colloidal gold labels

A sensitive chemiluminescent (CL) immunoassay of human immunoglobulin (IgG) which combined the inherent high sensitivity of CL analysis with the dramatic signal amplification of silver precipitation on colloidal gold tags was developed. First, the sandwich-type complex was formed in this protocol by the primary antibody immobilized on the polystyrene wells, the analyte in the sample, and the secondary antibody labeled with colloidal gold. Second, the colloidal gold was treated by an Ag + reduction solution, which resulted in the catalytic precipitation of silver on the surface of colloidal gold. Third, a large number of Ag + were oxidatively released in HNO 3 solution from the silver metal anchored on the sandwich-type complexes and then the human IgG was indirectly determined by a sensitive combined CL reaction of Ag +–K 2S 2O 8–Mn 2+– H 3PO 4–luminol. The chemiluminescence intensity depends linearly on the logarithm of the concentration of human IgG over the range of 0.02–50 ng ml −1 and detection limit (3 σ) is 0.005 ng ml −1 (i.e., ∼3 × 10 −14 M, 3 amol in 100-μl sample). This assay has been successfully applied to the determination of human IgG in human serum samples and showed great potential for numerous applications in immunoassay.

Interface characteristics between colloidal gold and kaolinite surface by XPS

The distribution of gold colloids in kaolinite and the interaction between gold and kaolinite surface were investigated by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). There is strong interaction between the gold particles and the edge surfaces of kaolinite, in low pH solution, the edge surface of kaolinite is positively charged and electrostatic attractive force between colloide gold particles and the positive edge surface of kaolinite would facilitate the adsorption of colloidal gold particles onto the suface. TEM observation shows that the aggregate morphology of gold particles was dominated by particle-particle interaction and gold particles were adsorbed on the edge surface of kaolinite crystals, resulting from the electrostatic attractive force between colloidal gold particles and the positive surfaces of kaolinite. XPS data show that in Au4f electron spectra there are four energy peaks related to gold, 83.8 eV, 85.7 eV, 87.5 eV, and 89.4 eV, respectively, which suggests that in chemical states there are metallic gold and Au bonded to O, similar to the form of Au2O3, and composite Au2O3 is formed between the edge surface of kaolinite and colloidal gold surface.

Fiber-optic biochemical sensing with a colloidal gold-modified long period fiber grating

A novel class of fiber-optic evanescent-wave sensor, which is simple to construct and easy to use, is presented and analyzed. This fiber-optic sensor is based on the modification of the grating portion of a long-period fiber grating with self-assembled gold colloids. The transmission spectra and optical properties of gold colloids change with the different refractive index of the environment near the surface of gold colloids. The sensor response of gold colloids increases linearly with solvents of increasing refractive index. When the colloidal gold surface was modified with a dinitrophenyl compound (DNP), experimental results show that the signal increase linearly with increasing concentration of the analyte, and the detection limit of the sensor for anti-DNP is 1.4 × 10 −7 g/mL or 9.5 × 10 −10 M.

FT‐Raman and NIR‐SERS characterization of the antimalarial drugs chloroquine and mefloquine and their interaction with hematin

AbstractRaman and surface‐enhanced Raman scattering (SERS) spectroscopies were employed to probe the interaction of the antimalarial drugs chloroquine (CQ) and mefloquine (MQ) with hematin. NIR‐SERS spectra of both quinoline derivatives were obtained from a colloidal gold surface. Strong chemical interactions of each drug with the Au particles are observed and the similarities of the two NIR‐SERS spectra allowed to predict a similar orientation geometry for both of the drugs on the colloidal surface, namely through the quinoline skeletal part of each molecular structure.Separately, the adsorption behavior of hematin on the Au colloid was studied under nonresonant conditions. In addition, both hematin–antimalarial drug systems (CQ and MQ) were prepared and investigated by NIR‐SERS. Copyright © 2006 John Wiley &amp; Sons, Ltd.

Part III: Surface-Enhanced Raman Scattering of Amino Acids and Their Homodipeptide Monolayers Deposited onto Colloidal Gold Surface

Surface-enhanced Raman scattering (SERS) spectra were measured for monolayers of various amino acids: L-methionine (Met), L-cysteine (Cys), L-glycine (Gly), L-leucine (Leu), L-phenylalanine (Phe), and L-proline (Pro) and their homodipeptides (Met-Met, Cys-Cys, Gly-Gly, Leu-Leu, Phe-Phe, and Pro-Pro) deposited onto a colloidal gold surface. Orientation of amino acids and their homodipeptides, as well as specific-competitive interactions of their functional groups with the gold surface, were predicted by detailed spectral analysis of the obtained SERS spectra. The analysis performed allowed us to propose a particular surface geometry for each amino acid and homodipeptide on the gold surface. In addition, we compared the structures of these molecules adsorbed on colloidal gold and silver surfaces.

Gold and colloidal gold surface influence on dna conformational change

DNA conformational changes caused by gold and colloidal gold surface have been studied by surface enhanced infrared spectroscopy (SEIRA), spectroscopy of plasmon reso- nance (SPR), atomic force microscopy (AFM) and principal component analysis. Experimen- tal data have shown that DNA conformation is slightly influenced by gold surface, while it is strongly altered by colloidal gold. Spectroscopic features of DNA-colloidal gold system have shown that the intensity of the asymmetric PO2 n band at 1240 cm n1 decreases by two times, and that of symmetric band at 1090 cm n1 decreases by 2.4 times whereas the halfwidth of phosphate bands increases by 35n40 cm n1 ; a frequency shift of asymmetric band position from 1240 to 1246 cm n1 and a symmetric band from 1090 to 1106 cm n1 has been observed. It was shown that intensity variation and shift of DNA base vibrations together with the broaden- ing of OH, NH, and CH stretching vibrations occur due to DNA conformational changes and the redistribution of the H-bonding network. A supposition about DNA condensation by colloidal gold was made. SEIRA and AFM data have showed major DNA structural changes occurred on gold colloidal particles. It was found that all the spectral features are more prominent for DNAncolloidal gold system deposited on gold substrate than on CaF2 substrate.