Citrate-capped Gold Nanoparticles Research Articles

Factors that control the gold nanoparticles' aggregation induced by adenine molecules: New insights through a combined experimental and theoretical study

The adsorption of adenine molecules and its derivatives on citrate capped gold nanoparticles (AuNPs) is quantified by a colorimetric method. The strength of the interaction is reflected in the aggregation grade of the colloids, that is detected though the changes in the absorption spectra of the samples, which allow for the determination of apparent binding constants. The positive charge of adenine molecules facilitates the approach to the colloid surface, a fact that is reflected in the measured binding free energies being more negative than those of neutral molecules. In the case of nucleosides and nucleotides, the aggregated structures are smaller or simply do not appear. Theoretical calculations based on density functional theory (DFT) were performed in order to compare the interaction of adenine, adenosine and AMP with gold nanoparticles. Our results indicate the relevance of the N atom of the amino group of adenine, adenosine and AMP in the stabilization with the nanoparticle surface. Thus, in this stabilization the amino group adopts a pyramidal disposition typical of a sp3 hybridization, being found the gold-adenine interaction more stable than that of adenosine and AMP.

AR-ESIHE and ARS-ESIHE-based image enhancement methods on 9oba pure and nano dispersed liquid crystalline compound

Systematic studies have been carried out on pure p-n-nonyloxy benzoic acid and dispersed citrate capped gold nanoparticles in low molar concentration. The phase transition temperatures are acquired from polarizing thermal microscope and differential scanning calorimeter, which are found to reduce with the increase in concentration of nanoparticles. Low contrast images from POM are enhanced with proposed methods of advanced recursive separated exposure-based sub-image histogram equalization (ARS-ESIHE) and advanced recursive exposure-based sub-image histogram Equalization (AR-ESIHE). The image enhancement performance characteristics are analyzed using statistical parameters like mean square error (MSE), peak signal-to-noise ratio (PSNR), standard deviation (SD) and entropy.

Multicomponent Layer-By-Layer Films of Chitosan/Phthalocyanine/AuNPs As Biosensing Platforms

The search of new biosensing platforms is crucial to improve the performance of electrochemical biosensors. In this work, Layer by Layer films containing combinations of materials with different functionalities were used to design electrochemical biosensor platforms for phenols detection [1-3]. Catechol and hydroquinone biosensors were obtained by depositing tyrosinase (Tyr) or laccase (Lac) on the surface of LbL films formed by alternating layers of chitosan (CHI), a cationic species which acted as enzyme linker, and layers of two anionic electrocatalytic materials (sulfonated copper phthalocyanine, CuPcS and citrate capped gold nanoparticles, AuNPs). Films with different sequences [(CHI)-(AuNPs)]2, [(CHI)-(CuPc)]2, [(CHI)-(CuPc)-(CHI)-(AuNPs)]2 [(CHI)-(AuNPs)-(CHI)-(CuPc)]2, and [(CHI)-(AuNPs/CuPc)]2 (with CuPcS and AuNP mixed in the same layer) were characterized by UV–visible, FTIR spectroscopy and AFM.It was demonstrated that the resulting films provided an efficient immobilization surface for phenol oxidases. At the same time, the LbL platform improved the electron transfer between the enzymes and the electrode surface. Although all the biosensors obtained exhibited excellent performances, the sequence of the anionic and cationic layers strongly influenced the electron transfer process. The best results were obtained when CuPcS was present in the last layer which caused a 2-fold increase in the intensity over the response of the biosensor without the LbL platform. The [CHI-AuNP-CHI-CuPcS]2-Tyr bioelectrode showed an LOD of 8.7∙10-4 mM (S/N=3) for catechol and of 7.77∙10-4 mM (S/N=3) for hydroquinone. The LbL platform was not so efficient for laccase and the [CHI-AuNP-CHI-CuPcS]-Lac biosensor showed a LOD of 1.84∙10-2 mM (S/N=3) for catechol and of 1.27∙10-3 mM (S/N=3) for hydroquinone.

Investigation of the synergistic effect with chiral D-penicillamine functionalized gold nanoparticle as an additive for enantiomeric separation in capillary electrophoresis.

The authors describe a synergistic system for nanoparticle based chiral separation. It is based on the use of a conventional chiral selector hydroxyproyl-β-cyclodextrin and a kind of gold nanoparticle functionalized with D-penicillamine as an additive. This nanomaterial displays a synergistic effect on the efficiency of the enantioseparation of the chiral drugs amlodipine, tropicamide, and ofloxacin. A comparative study on the enantioseparation capability of three separation systems, viz. (a) single hydroxyproyl-β-cyclodextrin system, (b) achiral citrate capped gold nanoparticle/ hydroxyproyl-β-cyclodextrin system, and (c) chiral D-penicillamine functionalized gold nanoparticle/ hydroxyproyl-β-cyclodextrin system was performed. The results show that the D-penicillamine functionalized gold nanoparticle/hydroxyproyl-β-cyclodextrin synergistic system has remarkable superiority. The effects of concentrations of D-penicillamine functionalized gold nanoparticle and hydroxyproyl-β-cyclodextrin, of buffer pH value and concentration, and of applied voltage on the performance of enantioseparation were investigated.

Label-Free Colorimetric Detection of Prothioconazole Using Gold Nanoparticles Based on One-Step Reaction.

One simple, sensitive detection method for pesticide prothioconazole based on citrate-capped gold nanoparticles (AuNPs) in one step at room temperature was presented in this study. Prothioconazole could be easily linked onto the AuNPs through a Au-S covalent bond, and AuNPs undergo aggregation via hydrogen bonds formed among prothioconazole molecules. As a result, the color of AuNP solution changes from wine red to royal purple, which could be monitored by naked eyes and UV-vis spectra. This label-free visual detection method could determine prothioconazole with concentrations ranging from 1.33 to 19.99 μg/L with a detection limit of 0.38 μg/L (S/N = 3). This method was convenient and free of complex equipment and successfully applied to prothioconazole determination in rice field water where it gave satisfactory recoveries.

Study on the Assembly Structure Variation of Cetyltrimethylammonium Bromide on the Surface of Gold Nanoparticles.

In this work, the self-assembly behavior of cetyltrimethylammonium bromide (CTAB) on the surface of citrate-capped gold nanoparticles (AuNPs) in solution has been studied by UV–vis absorption spectroscopy, fluorescence probe techniques, ζ potentiometric methods, transmission electron microscopy, etc. The UV–vis spectra show that the color with the increase of CTAB for the mixture containing CTAB and a given amount of AuNPs changes from red to blue and then to red. The absolute value of ζ potential corresponding to this color change decreases initially and then increases. Specially, the reversible color change, from red to blue and then to red, could be observed only in the case of a gradual addition of a AuNP solution to a CTAB solution; however, this reversible change is not suitable for the mixture formed in a reverse order of mixing. The results from pyrene used as the fluorescence probe indicate that the features in the fluorescence spectrum (including fluorescence quenching, I1/I3, and the excimer) well correspond to those from the UV–vis spectrum mentioned above. Based on the experimental results, the mechanism of the assembly structure variation of CTAB on the surface of negatively charged AuNPs was proposed. For a given amount of AuNPs, the assembly structure of CTAB on the surface of AuNPs undergoes the transformation from a monolayer to a bilayer with the increase of CTAB. In the case of the concentration of CTAB far beyond its critical micelle concentration (CMC) and the higher ratio of CTAB and AuNPs, there is a possibility of the formation of an extra micellar structure only after the formation of a double-layer structure.

A simple aptamer-based colorimetric assay for rapid detection of C-reactive protein using gold nanoparticles

C-reactive protein (CRP) is a clinical biomarker for inflammatory diseases. In this work, we present a simple and fast colorimetric method for CRP detection that employs citrate–capped gold nanoparticles (AuNPs) and a CRP-binding aptamer as sensing elements. The aptamer consisted in a guanine rich single-stranded DNA (ssDNA) that adsorbs onto the surface of the AuNPs. In the presence of the CRP, the ssDNA releases from the AuNPs surface to interact preferentially with the protein to form guanine-quadruplexes. The exposure of the unprotected AuNPs to buffer salts leads to aggregation and subsequent color change from red-wine to blue-purple that was readily seen by the naked eye. The AuNPs aggregation was monitored using UV–Vis spectroscopy and the CRP concentration in the samples could be correlated with the aggregation ratio (A670nm/A520nm). A linear sensing range of 0.889–20.7 μg/mL was found. The detection limit (LOD) was 1.2 μg/mL which is comparable to the typical clinical cutoff concentration in high-sensitivity CRP assays (1 μg/mL) and lower than the detection limit of nephelometric methods used in clinical practice. This method can provide a fast (5 min analysis time), simple, and sensitive way for CRP detection, with negligible interference of bovine serum albumin (BSA) up to concentrations of 100 nM.

Study of the intestinal uptake and permeability of gold nanoparticles using both in vitro and in vivo approaches

Gold nanoparticles (AuNPs) are highly attractive to biomedical applications. Here, we investigated the effects of (i) ca. 15 nm spherical AuNPs capped with citrate or 11-mercaptoundecanoic acid (MUA) and (ii) ca. 60 nm spherical citrate-capped AuNPs, and ca. 60 nm MUA-capped star-shaped AuNPs on the cytotoxicity, cellular uptake and permeability, using media supplemented or not with 1% fetal bovine serum (FBS) on caucasian colon adenocarcinoma Caco-2 cells. In addition, the colloidal stability of the nanoparticles in media (supplemented or not) was assessed after 24 h-incubations at 60 μM. The 60 nm gold nanospheres and stars were administrated orally to Wistar rats in order to evaluate their systemic absorption and biodistribution after 24 h. At non-supplemented media settings, citrate-capped gold nanoparticles seem to be more toxic than their MUA-capped counterparts. Also, smaller nanoparticles show higher toxicity than larger ones. The use of cell culture media with 1% FBS not only increased the stability of all AuNPs, as also significantly reduced their cytotoxicity. In the uptake studies, higher AuNPs incorporation was noticed in serum supplemented media, this effect being particularly significant for the 60 nm nanoparticles. Cellular incorporation depended also on the capping agent and size. None of the tested samples crossed the in vitro intestinal barrier. Confirming the in vitro results, the in vivo biodistribution study of the 60 nm AuNPs orally given to rats showed that their systemic absorption is low and that they are mainly eliminated through the faeces. Altogether, these preliminary results suggest that our novel AuNPs have high potential to be considered promising candidates for application in diagnostics or drug delivery at the intestinal level, showing high biocompatibility. However, unless it is desired that these nanomaterials avoid systemic absorption upon oral administration, additional functionalization should be sought to increase their low bioavailability.

Restriction of microwave-induced amyloid fibrillar growth by gold nanoparticles

Microwave radiations from various electronic devices are of serious health concern. In this article, using spectroscopic measurements, we show that the microwave radiation of strength 22 dBm and frequency 10 GHz facilitates protein fibrillation. However, this adverse effect of low-field radiation can be restricted by the presence of biocompatible citrate-capped gold nanoparticles. The dissipative field by metallic particles is able to disrupt the fibrillar network. We believe that the obtained results paved a way to find a therapeutic measure to combat fibrillation related diseases.

Good's buffers have various affinities to gold nanoparticles regulating fluorescent and colorimetric DNA sensing.

Citrate-capped gold nanoparticles (AuNPs) are highly important for sensing, drug delivery, and materials design. Many of their reactions take place in various buffers such as phosphate and Good's buffers. The effect of buffer on the surface properties of AuNPs is critical, yet this topic has not been systematically explored. Herein, we used halides such as fluoride, chloride, and bromide as probes to measure the relative adsorption strength of six common buffers. Among them, HEPES had the highest adsorption affinity, while MES, citrate and phosphate were weakly adsorbed with an overall ranking of HEPES > PIPES > MOPS > MES > citrate, phosphate. The adsorption strength was reflected from the inhibited adsorption of DNA and from the displacement of pre-adsorbed DNA. This conclusion is also supported by surface enhanced Raman spectroscopy. Furthermore, some buffer molecules did not get adsorbed instantaneously, and the MOPS buffer took up to 1 h to reach equilibrium. Finally, a classic label-free AuNP-based colorimetric sensor was tested. Its sensitivity increased by 15.7-fold when performed in a MES buffer compared to a HEPES buffer. This study has articulated the importance of buffer for AuNP-based studies and how it can improve sensors and yield more reproducible experimental systems.

Development and characterization of functionalized glyco thiolate capped gold nanoparticles for biological applications.

Glyco-gold nanoparticles (AuNPs) in aqueous dispersions were prepared by two approaches, namely direct reduction and ligand substitution methods. In the direct method, potassium salts of glyco thiols, with the general formula (C6H11O6)NH(CH2) n CH2SK (where L1, n = 1; L2, n = 2; L3, n = 3, L4, n = 4; L5, n = 5), were used as reducing and capping agents to give the glyco thiolate capped gold nanoparticles (AuNPs G1-G5); meanwhile in the ligand exchange experiments, L1-L5 and their acetylated forms (L6-L8) replaced citrate ions in citrate-capped gold nanoparticles to give additional AuNPs G6-G11. UV-visible spectroscopy, surface charge (ζ-potential,) measurements and transmission electron microscopy (TEM) were used for physical and chemical characterization of all the resultant AuNPs. The ζ-potential studies of AuNPs prepared through the direct method revealed that the surface charge is dependent on the length of the alkyl unit of (C6H11O6)NH(CH2) n CH2S- ligands. TEM images of the acetylated and non-acetylated glyco thiolate capped gold nanoparticles (AuNPs G6-G11) prepared via the ligand exchange method indicate that the size and shape of the gold nanoparticles remained the same as those of the citrate-capped gold nanoparticles used to prepare them. Selected AuNPs were tested on peripheral blood mononuclear cells (PBMCs) and the A549 cancer cell line to investigate their respective toxicity and cytotoxicity profiles. All AuNPs showed indiscriminate activity against both PBMCs and A4549 cells, although the gold nanoparticles having an acetylated glyco moiety with an amino propyl thiol linker as the ligand (G10) prepared via the citrate exchange method had better selectivity (PBMCs >59 mg mL-1 and for A549 ∼7 μg mL-1).

Polyvinylalcohol-citrate-stabilized gold nanoparticles supported congo red indicator as an optical sensor for selective colorimetric determination of Cr(III) ion

A selective and sensitive chemical optical sensor was prepared based on citrate capped gold nanoparticles growth in polyvinyl-alcohol (PVA) holding matrix and congo red (CR)-functionalized (PVA-Au-Citrate-NPs-CR), while consequently applied for the determination of trace amount of Cr(III) ion in aqueous media. Polyvinyl alcohol and trisodium citrate as a processor of Gold nanoparticles have the safest NFPA 704 so there is not any toxicity for using them in any condition including biological samples. The PVA-Au-Citrate-NPs-CR sensor was characterized via UV–Vis, SEM, DLS, XRD, FTIR, and EDS. At best operational conditions, an understudy sensor applied for monitoring the Cr(III) ion over 8.06 × 10−6–5.26 × 10−5 mol L−1 with a detection limit of 2.418 × 10−6 mol L−1. The present sensor has an acceptable response time as fast as 60 s with high stability over 1 month. The PVA-Au-Citrate-NPs-CR sensor is highly selective for Cr(III) ion in the presence of Cu2+, Pb2+, Co2+, Ag+, etc with good repeatability and reproducibility and satisfactory relative standard deviation (R.S.D) (less than 4.044% and 3.535%, respectively). Finally, the developed PVA-Au-Citrate-NPs-CR sensor is used for Cr(III) ion in different real water and green tee samples and in all situations, their accuracy was checked using recovery and RSD.

Spectroscopic studies on liquid crystalline n-hexyloxy-cyanobiphenyl with dispersed citrate-capped gold nanoparticles in visible region

ABSTRACTIn the present manuscript, the characterisation was done on liquid crystalline n-hexyloxycyanobiphenyl (6ocb) compound with dispersed citrate-capped gold nanoparticles (Au NPs) at different concentrations. It is observed that the birefringence enhances with increase in concentration of Au NPs. Also, strong Vander Waal’s interaction takes place due to well capping between the Au NPs and 6ocb molecules. The refractive indices are determined by using modified spectrometer at different wavelengths. The orientational order parameter has been determined from various theoretical molecular internal field models namely, Kuczynski, Effective geometry, Haller’s extrapolation and Vuks. The dispersive power ω is estimated for two consecutive wavelengths for the case of <n>, ne and no at different wavelengths found to be constant with temperature. The values of cross-over temperature, TCO determined from the temperature gradients of ne and no. Further, the refractive indices measured are fitted with two and three coefficient Cauchy model. Three coefficient Cauchy model is favourable than two coefficient Cauchy model for high birefringence liquid crystals. The results obtained are compared and discussed. Further, the phase transitions can be easily identified by GMSD Image processing method with Matlab tool to reduce the costly equipment’s usage in finding the heat flow with respect to temperature.

Technical Note: Film-based measurement of gold nanoparticle dose enhancement for 192 Ir.

The purpose of this work is to introduce a simple yet accurate technique to measure the dose enhancement factor (DEF) of a citrate-capped gold nanoparticle (GNP) solution using EBT3 film in an 192 Ir setup. Dose enhancement factor is the ratio of absorbed dose in a solution compared to absorbed dose in water, assuming identical irradiation parameters. Citrate-capped GNPs were synthesized. An acrylic apparatus was constructed such that the EBT3 film was placed in charged particle equilibrium within the GNP solution with 0.28%, 0.56%, and 0.77% gold by mass. Sets of 12 dose measurements were collected for each GNP concentration as well as for water. The expected value of DEF was also calculated with the effective mass absorption coefficient of the GNP solution and water for an 192 Ir spectrum. Furthermore, Burlin cavity correction factors were calculated and experimentally verified. Experimental verification of the cavity correction was performed by measuring DEF using stacks of 1, 3, and 5 sheets of film and extrapolating the DEF to 0 sheets of film. Experimental cavity corrections agreed with those calculated with the Burlin cavity formalism. The calculated DEF was 1.013, 1.027, and 1.037 for the 0.28%, 0.56%, and 0.77% gold by mass GNP solutions, respectively. The corresponding uncorrected DEF measurement values were 1.013±0.006, 1.024±0.010, and 1.032±0.006, respectively. When applying the Burlin cavity formalism, the final corrected DEF measurement values were 1.016±0.006, 1.029±0.010, and 1.039±0.006, respectively. The experimental cavity correction results agreed with the theoretical Burlin calculations, which allowed for the Burlin corrections to be performed for all GNP concentrations and measured DEF values. The adjusted DEF values agreed with the theoretical calculations. Thus, these results indicate that a Burlin cavity calculation can be applied to correct film-based DEF measurements for 192 Ir.

Development of a gold nanomaterial enabled colorimetric sensor method for the analysis of sodium chloride in seawater

In this study, a simple and practical gold nanoparticle enabled colorimetric sensor technique was developed for the detection of sodium chloride. The synthesis of gold nanoparticles was based on the chemical reduction of gold (III) chloride trihydrate using tri-sodium citrate that also served as a capping agent thus, protecting the particles against aggregation. UV–vis spectra and transmission electron microscopy were used to characterise the synthesized citrate capped gold nanoparticles. The colorimetric response of sodium chloride was performed by the gold nanoparticle sensor, based on the property of localized surface plasmon resonance. The interaction between sodium ions, chloride and tri-sodium citrate causes rapid aggregation of the gold nanoparticles conjugates, resulting in color conversion from wine red to blue which is clearly visible by the naked eye. Thereby, we propose the use of gold nanoparticles as colorimetric sensors, as they cause a color change when interacting with sodium chloride which is recognized easily by naked eye with high selectivity. The detection limit of the sensor calculated by the linear relationship of localised surface plasmon resonance for sodium chloride was found to be 1.18 parts per thousand and the lowest quantified amount was 3.57 parts per thousand, making the developed sensor to be highly sensitive. The practical applicability of the gold nanoparticles was also verified by the detection of sodium chloride in estuary and seawater samples.

Voltammetric immunosensing platform based on dual signal amplification using gold nanoparticle labels

An electrochemical immunosensing platform based on dual signal amplification strategy has been developed using gold nanoparticles. Human Immunoglobulin G was used as a model analyte in order to establish the immunosensing platform. The platform was fabricated using of 1,6-hexanedithiol self assembled on a gold disc electrode and was further modified by citrate capped gold nanoparticles. The direct immobilization of antibody was achieved through electrostatic interaction between negatively charged citrate capped gold nanoparticles and positively charged amino group of antibody. Each step of modification was analyzed using electroanalytical techniques like cyclic voltammetry and electrochemical impedance spectroscopy. The horseradish peroxidase (HRP)-labeled secondary antibodies conjugated on gold nanoparticles (AuNP-Ab2) acted as nanolabels. Thus the sandwich immunocomplex formed on the electrode surface produced an electrocatalytic response through the reduction of hydrogen peroxide by HRP in the presence of thionine. Electrochemical studies were carried out to understand the role of citrate capped AuNP and AuNP-Ab2 in dual signal amplification. The fabricated sensing platform can be used for the sensitive determination of various protein biomarkers by immobilizing specific antibody.

A Facile Colorimetric and Spectrophotometric Method for Sensitive Determination of Metformin in Human Serum Based on Citrate-Capped Gold Nanoparticles: Central Composite Design Optimization.

For the determination of Metformin in human serum, a facile colorimetric and spectrophotometric sensor was designed based on citrate-capped gold nanoparticles (citrate-GNPs). In this probe, the addition of Metformin to GNP solution generates a naked-eye color change resulting from the aggregation of GNPs. Study of this color conversion and quantity analysis of analyte is operated by spectrophotometric instruments. The three factors pH, time, and GNP ratio were selected to examine their effects on sensing results and their values optimization. The optimization of parameters was done by means of central composite design and one-at-a-time methods. The sensing results proved the highly selective and sensitive performance of the sensor for Metformin in a linear range of 6.25–133.3 ppm with a detection limit of 1.79 ppm. The relative standard deviation (RSD) of the reported method is 2.53%.

Citrate stabilized gold nanoparticles on graphenic carbon spheres for the selective detection of hydrazine

We have studied the electrocatalytic properties of hydrazine in the alkaline environment by using the stable sensor matrix. Thereby, we have selected the citrate-capped gold nanoparticles (AuNPs) decorated graphenic carbon spheres (GCS). The hydrothermal carbonization method is utilized to prepare the GCS by using reduced graphene oxide (rGO) and glucose. In hydrothermal treatment, the glucose undergoes polycondensation and simultaneously reduced the rGO which results in spherical morphology. These spheres consist of a carbonized nucleus and a hydrophilic surface that facilitates the formation of citrate-capped AuNPs on its surface. This novel composite provides the stable platform to determine the hydrazine in pH 13. Various physicochemical techniques confirm the formation of GCS-AuNPs and also characterized by electrochemical techniques. This GCS-AuNPs modified GCE has showed the good electrochemical performance to the hydrazine oxidation. Also, it revealed the acceptable analytical performance to the determination of hydrazine. The estimated linear concentration range, limit of detection and sensitivity are 0.02 to 530.1 μM, 6 nM and 4.45 μA μM−1 cm−2. Moreover, GCS-AuNPs/GCE shows good reproducibility and good recovery in real sample analysis.

Citrate-capped gold nanoparticles as a sensing probe for determination of cetyltrimethylammonium surfactant using FTIR spectroscopy and colorimetry

A novel, facile, and low-cost method was developed for determination of cetyltrimethylammonium (CTA+) cationic surfactant in water samples using diffuse reflectance Fourier transform IR (FTIR) spectroscopy and colorimetry. Cetyltrimethylammonium bromide was chosen as a model compound to demonstrate the optimization of the method for determination of CTA+ in water samples. The absorption peak at 3015.96 cm-1 (for CTA+) was enhanced when gold nanoparticles were used as a chemical sensor in diffuse reflectance FTIR spectroscopy, and this absorption peak was used for determination of CTA+. Alternatively, the color change from wine red (525 nm) to blue (740 nm) and the redshift of the localized surface plasmon resonance band in the visible region were used as a sensing probe for determination of CTA+. A linear calibration curve for determination in water samples was obtained in the range from 10 to 100 ng mL-1 with a limit of detection of 3 ng mL-1 by diffuse reflectance FTIR spectroscopy and in the range from 20 to 400 ng mL-1 with a limit of detection of 7 ng mL-1 by colorimetry. The advantageous features of the methods are their simplicity, rapidity, and sensitivity for the determination of CTA+ in water samples. Graphical abstract.

Gold nanoparticle-based detection of dopamine based on fluorescence resonance energy transfer between a 4-(4-dialkylaminostyryl)pyridinium derived fluorophore and citrate-capped gold nanoparticles.

A colorimetric/fluorometric dual-signal assay is described for the determination of dopamine (DA). A nanoprobe was obtained by linking a 4-(4-dialkylaminostyryl)pyridinium derived fluorophore to citrate-capped gold nanoparticles (AuNPs). The fluorescence of the fluorophore is quenched by the AuNPs via fluorescence resonance energy transfe. In the presence of DA, the catechol group of DA can absorb on the surface of AuNPs to induce aggregation, which is accompanied by a color change from red to blue. The yellow fluorescence of the fluorophore with excitation/emission maximum at 365/570nm is recovered. The dual-signal detection allows the quantitative analysis of DA within 300μM by the colorimetric method and 80μM by the fluorometric method. The detection limits for the colorimetric/fluorometric methods are 1.85μM and 0.29μM, respectively. Quantitative determination of DA in spiked urine samples was successfully demonstrated, with recoveries ranging from 98.2 to 106.0%. Graphical abstract A colorimetric/fluorometric dual-signal assay is described for the determination of dopamine by linking a fluorophore to gold nanoparticles. The dopamine causes aggregation of the nanoparticles to induce color change, which is followed by the recovery of the fluorescence.