Citrate-capped Gold Nanoparticles Research Articles

Gold nanoparticle decorated pH-sensitive polymeric nanocontainers as a potential theranostic agent

A pH-sensitive system of hollow P(MAA-co-MBA-co-AA) nanocontainers (NCs) modified with gold nanoparticles (GNCs) has been developed for theranostic applications, drug delivery and real time monitoring through imaging. The GNCs were synthesised by the distillation precipitation copolymerization procedure followed by in situ synthesis and embodiment of gold nanoparticles on the polymeric matrix (CSNs). Separately, citrate capped gold nanoparticles (GNPs) were also synthesized and compared with the GNCs for their fluorescence and cellular localization ability. The GNCs were tested for their drug loading and release behavior in response to the anticancer drug doxorubicin (DOX) at different pH values. Sustained drug release was observed at acidic pH. The viability of MCF-7 breast cancer cells and HEK-293 human embryonic kidney cells in relation to the GNCs, GNPs, GNC@DOX and DOX was also evaluated. GNCs and GNPs at the tested concentrations did not inhibit proliferation at either cell lines, whereas the GNCs@DOX presented comparable results. Cellular migration of MCF-7 cells treated with GNCs or GNPs was evaluated through the scratch-wound healing assay but no significant inhibition was detected. GNCs’ and GNPs’ fluorescence ability was exploited for assessing cellular localization through confocal laser scanning microscopy. GNCs after only 1 h of treatment were found in the cytoplasm of MCF7 cells, whereas GNCs@DOX were localized in the nucleus; the desirable site of action of DOX.

Gold nanoparticles regulate tight junctions and improve cetuximab effect in colon cancer cells.

Aim: Colon cancer (CC) is the second cause of cancer death worldwide. The use of nanoparticles for drug delivery has been increasing in cancer clinical trials over recent years. Materials & methods: We evaluated cytotoxicity of citrate-capped gold nanoparticles (GNPs) and the role they play on cell-cell adhesion. We also used GNP for delivery of cetuximab into different CC cell lines. Results: CC cells with well-formed tight junctions impair GNP uptake. Noncytotoxic concentration of GNP increases paracellular permeability in Caco-2 cells in a reversible way, concomitantly to tight junctions proteins CLDN1 and ZO-1 redistribution. GNP functionalized with cetuximab increases death of invasive HCT-116 CC cells. Conclusion: GNP can be used for drug delivery and can improve efficiency of CC therapy.

A polyamidoamine-mediated competitive colorimetric assay based on gold nanoparticles for determining acid values in edible sunflower seed, corn and extra virgin olive oils

We synthesized polyamidoamine (PAMAM) dendrimers and citrate-capped gold nanoparticles (AuNPs), and explored the applicability of the PAMAM/AuNP assay in determining total free fatty acid (FFA) contents in edible oils based on a competitive colorimetry, in which the PAMAM-triggered AuNP aggregation was suppressed by FFAs. The generation and concentration of PAMAMs, the chain lengths of FFAs as well as the concentration and pH of the background electrolytes of the assay were optimized. The average acid values of the sunflower seed, corn and extra virgin olive oils determined by PAMAM/AuNP assay were 1.31 ± 0.07, 0.33 ± 0.02 and 1.49 ± 0.07, respectively, which were not significantly different from the corresponding 1.27 ± 0.08, 0.32 ± 0.01 and 1.61 ± 0.06 by the standard nonaqueous titration. Our results suggest that the method is promising in detecting FFAs in edible oils, and implementation of the method expands the technological scope for FFA analysis.

Electrophoretic analysis of polyamines in exhaled breath condensate based on gold-nanoparticles microextraction coupled with field-amplified sample stacking

In this work, citrate-capped gold-nanoparticles (citrate-AuNPs) have been firstly used for selective extraction of trace polyamines, putrescine (Put) and cadaverine (Cad), followed by field-amplified sample stacking (FASS) coupled with capillary electrophoresis and capacitively coupled contactless conductivity detection (FASS-CE-C4D). Put and Cad were extracted by electrostatic attractions between the amine group of the polyamines and the citrate ligands adsorbed on the surfaces of AuNPs. AuNPs microextraction (AuNPs-ME) effectively shortened preparation time (50 min) by introducing ultrasound, and the required sample extraction volume was only 1 mL. Furthermore, a synergistic enrichment strategy based on off-line AuNPs-ME and on-line FASS significantly improved the detection sensitivity, making the enrichment factors up to 1726–1887 times. Under the optimum conditions, Put and Cad could be well separated from the potential coexisting substances and then directly determined by CE-C4D without derivatization. Due to its low sample consumption, high sensitivity (LODs: 0.070–0.17 ng mL−1), and acceptable recoveries (90–105%), this AuNPs-ME/FASS-CE-C4D method provides a rapid, economical and eco-friendly approach for direct determination of polyamines in human exhaled breath condensate, and has potential application prospects in preliminary noninvasive diagnosis of oral and respiratory inflammation.

Combined in silico and in vitro study of an aptasensor based on citrate-capped AuNPs for naked-eye detection of a critical biomarker of oxidative stress.

An elevated level of 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxo-dG) in biosamples has been found to correlate to oxidative stress, and it has been assigned as a critical biomarker of various diseases. Herein, insights into the mechanisms of an aptasensor, based on citrate-capped gold nanoparticles (AuNPs), for 8-oxo-dG detection were elucidated using molecular dynamics (MD) simulations and validated experimentally. We found that the binding mechanism for binding between the anti-8-oxo-dG aptamer and 8-oxo-dG has the following characteristic stages: (i) adsorption stage, (ii) binding stage, and (iii) complex stabilization stage. Our simulations also reveal the binding sites between the anti-8-oxo-dG aptamer and 8-oxo-dG formed through hydrogen bonding during complex formation. A shortened anti-8-oxo-dG-aptamer was also engineered using in silico design, which was expected to improve the analytical performance of the colorimetric aptasensor. The mechanisms of the colorimetric aptasensor in the presence and absence of 8-oxo-dG were also investigated, and found to be in good agreement with the experiments. Complete understanding of the mechanism of the colorimetric aptasensor would open the door for development of novel naked-eye aptasensors.

Colorimetric Sensor Array Based on Amino Acid-Modified Gold Nanoparticles for Toxic Metal Ion Detection in Water.

Several chromatographic and spectroscopic methods are available for the detection of toxic mercury (Hg2+) in water; however simple, rapid, inexpensive, and sensitive methods are still needed. In this chapter, we describe a facile, very sensitive, and rapid method for the colorimetric detection of Hg2+ in water with the detection limit of 2.9nM. This simple procedure is based on the lysine-induced aggregation of citrate-capped gold nanoparticles (AuNPs) in the presence of Hg2+ ions.

Fabrication of prime number checkers based on colorimetric responses of gold nanoparticles

In this work, we demonstrated the fabrication of molecular prime number checkers based on the concentration- and sequence-dependent colorimetric responses of citrate-capped gold nanoparticles (Au NPs) to two simple model chemicals, i.e. cysteine (Cys) and Hg2+ ions.

Molecular Dynamics Simulation of Polarizable Gold Nanoparticles Interacting with Sodium Citrate.

To study the structure of a citrate-capped gold nanoparticle and forces involved in citrate-gold interactions, we performed a molecular dynamics simulation of a truncated-octahedron nanoparticle containing Au(111) and Au(100) surfaces with sodium citrate. In this paper, we employed an approach to the modeling of interactions of a gold nanoparticle with citrate molecules taking into account the image charge effect in the metal. First, we built models of 6 and 14 nm nanoparticles, which can reproduce the polarization effects, based on a rigid-rod gold model and the GolP-CHARMM force field. To verify the simulation results, we analyzed density plots, radial distributions, distributions perpendicular to Au(111) and Au(100) surfaces, the electric potential of the system, and the dynamics of citrate crown formation. We observed formation of a stable citrate crown around the nanoparticle and detected nonuniform surface distribution of citrate ions with the preference for Au(111) facets over Au(100) ones. Testing of the model of the citrate-capped gold nanoparticle in a simulation at high concentrations of Na+ and Cl- ions (0.8 M) showed incorporation of chloride anions into the citrate crown. We compared the results of citrate crown formation between polarizable and nonpolarizable gold models and noticed a difference in the citrate distribution on the surface of the gold nanoparticle. We found that polarization effects in the metal are involved in the mechanism of interaction of the gold nanoparticle and citrate ions. The obtained results are in good agreement with experimental data and computer simulations from a number of other studies, which prove the validity of the proposed model.

Study of the Stability of Functionalized Gold Nanoparticles for the Colorimetric Detection of Dipeptidyl Peptidase IV

In this report, we investigated three stabilization strategies of gold nanoparticles and their practical application for the visual detection of dipeptidyl peptidase IV (DPP-IV). Citrate-capped gold nanoparticles (Au NPs) are generally unstable in high-ionic-strength samples. Au NPs are easily tagged with various proteins and biomolecules rich in amino acids, leading to important biomedical applications including targeted drug delivery, cellular imaging, and biosensing. The investigated assays were based on different modes of stabilization, such as the incorporation of polyethylene glycol (PEG) groups, stabilizer peptide, and bifunctionalization. Although all approaches provided highly stable Au NP platforms demonstrated by zeta potential measurements and resistance to aggregation in a high-ionic-strength saline solution, we found that the Au NPs modified with a separate stabilizer ligand provided the highest stability and was the only platform that demonstrated sensitivity to the addition of DPP-IV, whilst PEGylated and peptide-stabilized Au NPs showed no significant response.

Elucidating the interaction of Spathodea campanulata leaf extracts mediated potential bactericidal gold nanoparticles with human serum albumin: spectroscopic analysis

Nanomaterials in different form have been thoroughly used in the area of pharmaceutics and medicine for drug delivery. The large scale of nanoparticles (NPs) synthesis from plant extract is much safe, cheap and eco-friendly. Here, we demonstrated a new, one-step, ultra-fast biosynthesis of gold nanoparticles (sc-AuNPs, 19.54 nm) by using aqueous Spathodea campanulata leaf extracts as a reducing and capping agent. And also, we presented the synthesis of citrate capped gold nanoparticles (cit-AuNPs) of approximately same size (19.66 nm). These two NPs were characterized by UV-Visible, dynamic light scattering, transmission electron microscope and energy dispersive X-ray spectroscopy. Fourier transform infrared spectroscopy confirmed that the functional groups like OH, NH, OH of COOH and CO were contributed in the sc-AuNPs formation. The negative zeta potential (−20.5, −22.8 mV) established the stability and dispersion of the sc- and cit-AuNPs. The anti-bacterial activity of the sc- and cit-AuNPs were checked against Escherichia coli (DH5-Alpha). Minimum inhibitory concentration was 2.4 and 3.0 nM, respectively for sc- and cit-AuNPs. The interaction study of the sc-AuNPs/cit-AuNPs-human serum albumin (HSA) system was done by UV-Visible absorbance, fluorescence, circular dichroism, time resolved fluorescence spectroscopy and the measurement of zeta potential. Absorbance, three dimensional fluorescence, synchronous fluorescence and circular dichroism spectroscopy showed a minor conformational change of HSA upon interaction with the sc-AuNPs compared to cit-AuNPs. The present comparative study will advance our knowledge about the binding mode, mechanism and conformational change of the protein upon interaction with green synthesized sc-AuNPs and cit-AuNPs.Communicated by Ramaswamy H. Sarma

Inhibition of catalytic activity of fibrinogen-stabilized gold nanoparticles via thrombin-induced inclusion of nanoparticle into fibrin: Application for thrombin sensing with more than 104-fold selectivity.

Citrate-capped gold nanoparticles (AuNPs) modified with thrombin-binding aptamer are often implemented for colorimetric, fluorescent, and electrochemical detection of thrombin in an aqueous solution. However, researchers have rarely explored the application of fibrinogen-modified AuNPs (F-AuNPs) for thrombin sensing. We present a simple, inexpensive, sensitive, and selective probe for colorimetric assay of thrombin through combining thrombin-induced inclusion of F-AuNPs into Fibrin and F-AuNPs-catalyzed reduction of 4-nitrophenol with an excess amount of NaBH4. Considering that fibrinogen stabilized citrate-capped AuNPs against a high-ionic-strength buffer, F-AuNPs efficiently catalyzed the NaBH4-mediated decrease of yellow 4-nitrophenol to colorless 4-aminophenol. The presence of thrombin converted fibrinogen into fibrin on the nanoparticle surface, leading to the inclusion of nanoparticles into fibrin. The formation of fibrin inhibited that the AuNPs catalyzed the NaBH4-mediated reduction of 4-nitrophenol. Consequently, the color of the solution gradually varied from colorless to yellow with increasing thrombin concentration. The proposed system was shown to be accurate in the quantification of small differences in the concentration of human thrombin over the range of 4-60 pM. The lowest detectable concentration of human thrombin by the naked eye was as low as 16 pM. We demonstrated the practical application of the proposed system in quantifying 1-15 nM human thrombin in human plasma.

Facile Electrostatic Immobilization of Glucose Oxidase onto Citrate Capped Gold Nanoparticles for Surface-enhanced (Bio)-Catalysis

Facile Electrostatic Immobilization of Glucose Oxidase onto Citrate Capped Gold Nanoparticles for Surface-enhanced (Bio)-Catalysis

Protein A- and Protein G-gold nanoparticle bioconjugates as nano-immunoaffinity platform for human IgG depletion in plasma and antibody extraction from cell culture supernatant

Detection of disease-related biomarkers in plasma provides a possibility for early clinical diagnosis. However, highly abundant proteins in plasma, such as human immunoglobulin (hIgG) are a main impediment to biomarker discovery and analysis. Therefore, rapid and easy depletion of hIgG in the plasma is beneficial for biomarker discovery. In this work, citrate-capped gold nanoparticles (GNPs) were synthesized and conjugated with cysteine-tagged recombinant Protein A (rProtA) and Protein G (ProtG), respectively. The resultant protein-GNP bioconjugates were thoroughly characterized by surface plasmon resonance spectroscopy, hydrodynamic light scattering (DLS), electrophoretic light scattering (ELS) and rotary metal shadowing transmission electron microscopy (TEM) measurements. In order to quantitatively control the amount of the rProt A and ProtG on the GNP surface, binding studies and isotherm measurements have been performed. rProtA-GNP conjugate exhibited better binding capacities towards hIgG. Its surface coverage with rProtA molecules was determined by protein quantification after hydrolysis of the rProtA-GNP conjugate, GNP removal and subsequent amino acid assay by HPLC with fluorescence detection. Binding isotherms acquired with hIgG revealed their maximal capacity for depletion experiments. Depletion efficiency of around 90% could be achieved in a standard solution. With optimized amount of rProtA-GNP and ProtG-GNP, respectively, hIgG could be efficiently extracted from real samples (human plasma and hIgG-spiked cell culture supernatant). A benchmarking study with ProteinA-modified magnetic particles (Dynabeads) was performed as well. The results document that these rProtA-GNP and ProtG-GNP affinity nanoparticles could be a promising alternative to magnetic bead based immunoaffinity trapping and constitutes a flexible platform for both depletion of hIgG from human plasma and antibody affinity capture from cell culture supernatants in process control of biopharmaceuticals by simple solution handling (via pipetting) and centrifugation steps.

Synthesis and in vitro photobiological studies of porphyrin capped gold nanoparticles $$^{\S }$$ §

We describe the synthesis and characterization of a thiol-functionalized porphyrin derivative 2 and its gold nanoparticle conjugates. The porphyrin 2 exhibited its characteristic intense Soret absorption at 420 nm with a molar extinction coefficient value of $$3.6\times 10^{5}\, \hbox {M}^{-1}\, \hbox {cm}^{-1}$$ and good fluorescence in the region of 650–660 nm. The porphyrin-capped gold nanoparticles (POPNPs) were synthesized from the citrate-capped gold nanoparticles by the ligand exchange method and characterized by spectroscopic and morphological analyses (UV–Vis, DLS and TEM). The broadening of the absorption spectrum and quenching of the fluorescence intensity for the porphyrin gold nanoconjugates suggest efficient incorporation of the porphyrin moiety onto the gold surface. The results of DLS and TEM analyses indicate that the nanoconjugate POPNPs are uniformly spherical in shape with a size of ca. $$25 \pm 5\, \hbox {nm}$$ and exhibits a negative zeta potential value of $$-\,16.0 \pm 2\, \hbox {mV}$$ . The singlet oxygen generation efficiency of the porphyrin 2 and POPNPs was calculated and are found to be ca. $$0.53 \pm 0.02$$ and $$0.43 \pm 0.03$$ , respectively. The in vitro photobiological studies revealed that POPNPs exhibited enhanced photodynamic activity compared to their parent porphyrin derivative 2 with an $$\hbox {IC}_{50}$$ value of $$5\, \upmu \hbox {M}$$ in MDA MB 231 cell lines. The mechanism of the cell destruction was studied by Annexin-FITC and confirmed through TMRM assay. We observed the increase in the percentage of cell population corresponding to the late apoptotic stage ca. 37.7% and 51.2% for 5 and $$10\, \upmu \hbox {M}$$ of POPNPs, respectively, thereby demonstrating their apoptotic-mediated cell destruction and use in PDT applications. Synopsis We synthesized a thiol-functionalized porphyrin-based sensitizer 2 and its gold nanoparticles (POPNPs) and have investigated their photophysical properties, singlet oxygen generation and in vitro photobiological efficacy. Our results demonstrate that the incorporation of the sensitizer onto the surface of nanoparticles not only improved its solubility in the aqueous medium, photophysical and photobiological properties but also its potential as a novel sensitizer for photodynamic therapeutical applications.

Colorimetric determination of the pesticide chlorothalonil based on the aggregation of gold nanoparticles.

A method is described for the determination of the pesticide chlorothalonil (CLT). It is based on the finding that citrate-capped gold nanoparticles (AuNPs) undergo aggregation on exposure to chlorothalonil. This is accompanied by a visually detectable color change from wine red to blue. The effect is due to the interaction of the cyano group of chlorothalonil with gold nanoparticles. The assay may also be performed by using a spectrometer. The ratio of absorbances at 700nm and 520nm (A700/A520) linearly drops in the 5 to 100ng·mL-1 CLT concentration range, with a 3.6ng·mL-1 detection limit. This is below the Chinese guideline value for cucumber. The method is rather simple and does not require any modification of the AuNPs or the utilization of antibody. It was successfully applied to the determination of CLT in (spiked) cucumber samples. Recoveries ranged from 80.4 to 97.4%, and the analytical results compared well with those obtained by HPLC. Graphical abstract Schematic of the assay.The strong interaction of thecyano group of acetamiprid with gold nanoparticles (AuNPs) via Au-N bond induces the aggregation of gold nanoparticles, and this isaccompanied by a color change from red to purple.

PHRM-02. DELIVERY OF CHEMOTHERAPEUTICS TO PEDIATRIC BRAIN TUMORS USING CITRATE-CAPPED GOLD NANOPARTICLES

Medulloblastomas and gliomas account for nearly 28% of primary tumors and about 80% of malignant tumors in children. Many of the chemo-drugs that are found effective in killing tumor cells perform well in laboratory settings but fail to cross the blood-brain barrier in humans in direct clinical applications. This problem is overcome by using carriers which could deliver the drugs across the blood-brain barrier. To increase the efficacy of drugs in targeting different tumors, different nanoparticles have been used as carriers in the recent past. Some drugs, including AZD-1775 and Gemcitabine, have been shown by researchers to be effective in multiple brain tumors but have not been adequately utilized alone and/or in combination in pediatric brain tumor patients. In our study, we have conjugated AZD-1775 and Gemcitabine to citrate-capped gold nanoparticles (AuNPs). Cells have been treated with a drug alone, or AuNP alone and AuNP conjugated with drugs for 72 hours. Cell viability assays, cell cycle analysis and western blotting have been used to evaluate the delivery of drug to cells. Both the drugs and their AuNP-conjugates inhibited the growth of cells tested. AuNPs conjugated with the drugs showed more effective delivery of the drugs to cells than drugs alone at the same concentrations, as measured by tumor cell growth. Also, our initial in vivo study shows prolonged survival of mice bearing brain tumors treated with AuNP-conjugated AZD-1775 than those treated with AZD-1775 alone. These results confirm that AuNPs are a suitable platform to deliver chemotherapeutics to brain tumors.

Continuous flow synthesis of ultrasmall gold nanoparticles in a microreactor using trisodium citrate and their SERS performance

Ultrasmall gold nanoparticles were synthesized without strong capping agents by using a capillary-based continuous flow system. A mixture of gold(III) chloride trihydrate and trisodium citrate flowed through capillaries at elevated temperature. The effect of capillary material (polytetrafluoroethylene, fluorinated ethylene propylene, polyetheretherketone, fused silica), surface-to-volume ratio (capillary internal diameter 0.3–1 mm), average residence time (1.5–30 min) and temperature (70–100 °C) were investigated. At a flow rate of 0.006 ml/min (residence time 30 min), 100 °C, 275 kPa back pressure, citrate/gold molar ratio 3.15 and using PTFE capillary tubing with an inner diameter of 0.3 mm, very small (1.9 ± 0.2 nm) nanoparticles were obtained. For comparison, experiments were also performed under the same experimental conditions, but in slug flow using octane as segmenting fluid, thus isolating the reactants from the tubing wall. The synthesized particles were 17.4 ± 1.4 nm for segmented flow, demonstrating the important effect of the capillary wall surface. The performance of these citrate-capped gold nanoparticles was tested for Surface-Enhanced Raman Scattering (SERS). The average enhancement factor (AEF) of 2 nm gold nanoparticles capped by citrate from our work (AEF = 1.54 × 108) was nearly double when compared to 2 nm phosphate-capped commercial gold nanoparticles (AEF = 7.34 × 107). The adsorption of analyte molecules onto citrate-capped gold surface was easier due to the weaker binding strength of the carboxylate ligand and more hotspots formed with narrower gaps between neighbouring particles, giving rise to improved enhancement.This work has been selected by the Editors as a Featured Cover Article for this issue.

Interactions between citrate-capped gold nanoparticles and polymersomes

Polymersomes are vesicles formed by self-assembled amphiphilic block copolymers. Polymersomes generally have better stability than liposomes and they have been widely used in making drug delivery vehicles. In this work, the interaction between two types of polymersomes and citrate-capped gold nanoparticles (AuNPs) was studied. The following two polymers: poly(2-methyloxazoline-b-dimethylsiloxane-b-2-methyloxazoline) (called P1) and poly(butadiene-b-ethylene oxide) (called P2) were respectively used to form polymersomes. While P1 only formed spherical vesicle structures, worm-like structures were also observed with P2 as indicated by cryo-TEM. Both polymersomes adsorbed AuNPs leading to their subsequent aggregation. A lower polymersome concentration produced more obvious aggregation of AuNPs as judged from the color change. Capping AuNPs with glutathione inhibited adsorption of AuNPs. Considering the surface property of the polymers, the interaction with AuNPs was likely due to van der Waals forces. P1 polymersomes encapsulated calcein stably and AuNPs did not induce leakage. The P1/AuNP complex was more efficiently internalized by HeLa cells compared to free P1 polymersomes, further indicating a stable adsorption under cell culture conditions. In summary, this work indicates citrate-capped AuNPs form stable adsorption complexes with these polymersomes and their interactions have been explored.

Anti-aggregation of gold nanoparticles for metal ion discrimination: A promising strategy to design colorimetric sensor arrays

The first report of anti-aggregation-based sensor arrays is presented. The strategy is based on the competitive interaction of citrate-capped gold nanoparticles (AuNPs) and heavy metal ions (i.e., Hg(II), Ag(I), Fe(III), and Pb(II)) with three aggregation reagents (i.e., cysteine, melamine, and arginine). In the presence of aggregation reagent, the color and UV–vis spectra of AuNPs are changed indicating the aggregation of AuNPs. Addition of the aggregation reagents which are firstly treated with the ions, causes AuNPs turn from the aggregation to the dispersion state. The anti-aggregation capability of ions towards various aggregation reagents is different because of distinct stability constants of ion-aggregation reagent complexes. The combinatorial colorimetric response of all sensor elements enables discrimination among the ions in various concentrations, as well as mixtures of them by linear discriminant analysis (LDA). Moreover, heavy metal ions are well-distinguished in river and fish samples with an accuracy of 100%.

The mechanism of the adsorption of dsDNA on citrate-stabilized gold nanoparticles and a colorimetric and visual method for detecting the V600E point mutation of the BRAF gene.

A study is presented on the binding kinetics and mechanism of the adsorption of dsDNA on citrate-capped gold nanoparticles (AuNPs). Methods include fluorescence titration, isothermal calorimetry (ITC) titration, dynamic light scattering and gel electrophoresis. It is found that the fluorescence of probe DNA (labeled with Rhodamine Green and measured at excitation/emission peaks of 498/531nm) is quenched by addition of AuNPs. The Stern-Volmer quenching constant (Ksv) is 1.67 × 10^9 L·mol-1 at 308K and drops with increasing temperature. The quenching mechanism is mainly static. The results of both fluorescence titrations and ITC show negative values for ΔH and ΔS values. This shows ion-induced dipole-dipole interaction to be the main attractive forces between dsDNA and AuNPs, while electrostatic interactions result in repulsion. The repulsive forces lead to a lower affinity between dsDNA and AuNPs (compared to single-strand DNA). It is also found that dsDNA can prevent the aggregation of AuNPs which is accompanied by a color change from red into blue. The visual detection limit with bare eyes for dsDNA1 is 36 pM. Based on these findings, a colorimetric method was developed to detect the proto-oncogene of serine/threonine-protein kinase B-Raf V600E point mutation in HT29, Ec109, A549, Huh-7 and SW480 cell lines. Graphical abstract Schematic of the salt-induced aggregation of uncapped gold nanoparticles (AuNPs) which leads to a color change from red to blue. If the AuNPs are coated with dsDNA, aggregation is suppressed.