Fluorosurfactant-capped Gold Nanoparticles Research Articles

Single-Step Hydrolysis and Derivatization of Homocysteine Thiolactone Using Zone Fluidics: Simultaneous Analysis of Mixtures with Homocysteine Following Separation by Fluorosurfactant-Modified Gold Nanoparticles.

Herein, we report a new automated flow method based on zone fluidics for the simultaneous determination of homocysteine and homocysteine thiolactone using fluorimetric detection (λext = 370 nm/λem = 480 nm). Homocysteine thiolactone is hydrolyzed on-line in alkaline medium (1 mol L−1 NaOH) to yield homocysteine, followed by reaction with o-phthalaldehyde in a single step. Derivatization is rapid without the need of elevated temperatures and stopped-flow steps, while specificity is achieved through a unique reaction mechanism in the absence of nucleophilic compounds. Mixtures of the analytes can be analyzed quantitatively after specific separation with fluorosurfactant-capped gold nanoparticles that are selectively aggregated by homocysteine, leaving the thiolactone analogue in solution. As low as 100 nmol L−1 of the analyte(s) can be quantified in aqueous solutions, while concentrations > 2 μmol L−1 can be analyzed in artificial and real urine matrix following 20-fold dilution. The percent recoveries ranged between 87 and 119%.

A new approach for bisphenol A detection employing fluorosurfactant-capped gold nanoparticle-amplified chemiluminescence from cobalt(II) and peroxymonocarbonate

In this work, we utilized the nonionic fluorosurfactant-capped gold nanoparticles (GNPs) as a novel chemiluminescence (CL) probe for the determination of trace bisphenol A. Bisphenol A can induce a sharp decrease in CL intensity from the GNP–Co2+–peroxymonocarbonate (HCO4−) system. Under the selected experimental conditions, a linear relationship was obtained between the CL intensity and the logarithm of concentration of bisphenol A in the range of 0.05–50μM (R2=0.9936), and the detection limit at a signal-to-noise ratio of 3 for bisphenol A was 10nM. The applicability of the proposed method has been validated by determining bisphenol A in real polycarbonate samples with satisfactory results. The recoveries for bisphenol A in spiked samples were found to be between 94.4% and 105.0%. The relative standard deviation (RSD) for 12 repeated measurements of 0.5μM bisphenol A was 2.2%. The proposed method described herein was simple, selective and obviated the need of extensive sample pretreatment.

Determination of cysteine, homocysteine, cystine, and homocystine in biological fluids by HPLC using fluorosurfactant-capped gold nanoparticles as postcolumn colorimetric reagents

We have demonstrated for the first time the suitability of fluorosurfactant-capped spherical gold nanoparticles as HPLC postcolumn colorimetric reagents for the direct assay of cysteine, homocysteine, cystine, and homocystine. The success of this work was based on the use of an on-line tris(2-carboxyethyl)phosphine reduction column for cystine and homocystine. Several parameters affecting the separation efficiency and the postcolumn colorimetric detection were thoroughly investigated. Under the optimized conditions, cysteine, homocysteine, cystine, and homocystine in human urine and plasma samples were determined. Detection limits for cysteine, homocysteine, cystine, and homocystine ranged from 0.16-0.49 μM. The accuracy in terms of recoveries ranged between 94.0-102.1%. This proposed method was rapid, inexpensive, and simple.

Ligand exchange on the surface of cadmium telluride quantum dots with fluorosurfactant-capped gold nanoparticles: Synthesis, characterization and toxicity evaluation

CdTe quantum dots (QDs) can provide high-intensity and photostable luminescent signals when they are used as labeling materials for sensing trace amounts of bioanalytes. However, a major concern is whether the capping ligands of CdTe QDs cause toxic effects in living systems. In the current study, we address this problem through the complete ligand transformation of CdTe QDs from toxic thiolglycolic acid (TGA) to green citrate, which is attributed to the CdS bond breaking and the AuS bond formation. The highly efficient depletion of S atom from the surface of the CdTe QDs occurs after the addition of fluorosurfactant (FSN)-capped gold nanoparticles into TGA-capped CdTe QDs, accompanying with the rapid aggregation of FSN-capped gold nanoparticles via noncrosslinking mechanism in the presence of high salt. After the ligand transformation, negligible differences are observed on both photoluminescence spectra and luminescent quantum yield. In addition, the cytotoxicity of the original and new-born CdTe QDs is detected by measuring cell viability after the nanoparticle treatment. In comparison with the original TGA-capped QDs, the new-born CdTe QDs can induce minimal cytotoxicity against human hepatocellular liver carcinoma (HepG2) cells even at high dosages. Our study indicates that the extremely simple method herein opens up novel pathways for the synthesis of green CdTe QDs, and the as-prepared citrate-capped CdTe QDs might have great potential for biological labeling and imaging applications.

Fluorosurfactant-capped gold nanoparticles-based label-free colorimetric assay for Au3+ with tunable dynamic range via a redox strategy

Gold nanoparticles-based colorimetric assay possesses several unique advantages, and has been applied for a wide range of targets, varying from nucleic acids to different metal ions. However, due to the lack of proper coordinating ligand, gold nanoparticles-based colorimetric sensing system for Au3+ has not been developed so far. It is well-known that Au3+ could induce the oxidation transition of thiol compounds to disulfide compounds. In this article, for the first time we converted such thiol masking reaction into colorimetric sensing system for label-free detection of Au3+ via a target-controlled aggregation of nanoparticles strategy. In the new proposed sensing system, fluorosurfactant-capped gold nanoparticles were chosen as signal reporter units, while an Au3+-triggered oxidation of cysteine (Cys), which inhibited the aggregation of gold nanoparticles, acted as the recognition unit. By varying the amount of Cys, a tunable response range accompanied with different windows of color change could be obtained for Au3+, illustrating the universality of the sensing system for Au3+ samples with different sensitivity requirements. Under optimized condition, the proposed sensing system exhibits a high sensitivity towards Au3+ with a detection limit of 50nM, which is lower than previously reported spectroscopic methods. It has also been applied for detection of Au3+ in practical water samples with satisfactory result.

High-performance liquid chromatography assay of cysteine and homocysteine using fluorosurfactant-functionalized gold nanoparticles as postcolumn resonance light scattering reagents

Herein, a new postcolumn resonance light scattering (RLS) detection approach coupled with high-performance liquid chromatography (HPLC) was developed to detect cysteine and homocysteine. In the established system, the fluorosurfactant-capped gold nanoparticles (AuNPs) were first employed as postcolumn RLS reagents. The detection principle was based on the enhancement of RLS intensity of AuNPs upon the addition of cysteine/homocysteine. The RLS signals were detected by a common fluorescence detector at λEX=λEM=560nm. The linear ranges for both cysteine and homocysteine were in the range of 5.0–50μM. The detection limits were 5.9pmol for cysteine and 12pmol for homocysteine at a signal-to-noise ratio of 3. HPLC separation and RLS detection conditions were optimized in detail. The applicability of the proposed method has been validated by detecting cysteine and homocysteine in human urine samples. Recoveries from spiked urine samples were 95.0–103.0%.

Resonance light scattering technique for simultaneous determination of cysteine and homocysteine using fluorosurfactant-capped gold nanoparticles

In this paper, based on the enhancement effect on resonance light scattering (RLS) intensity of fluorosurfactant-capped gold nanoparticles (FSN-capped AuNPs), homocysteine can be discriminated from cysteine by tuning the pH values of the 14nm FSN-capped AuNP solutions. In contrast to the reported enhanced RLS of AuNPs for cysteine and homocysteine assays, the present method was improved by the following aspects: (1) cysteine and homocysteine could be determined simultaneously without separation techniques; (2) the incubation time of less than 2.0min for FSN-capped AuNP aggregation was employed in the proposed approach, which is much shorter than those reported by RLS probes (e.g., 25min and 60min). Under optimum experimental conditions, the calibration curve was found to be linear over the range of 0.08–6.0μM for cysteine and homocysteine with a detection limit of 0.04μM. The applicability of the proposed method has been validated by determining cysteine and homocysteine in human urine samples with satisfactory results. Recoveries from spiked urine samples were in the range of 96.0–113.0%.

Gold nanoparticle extraction followed by o-phthaldialdehyde derivatization for fluorescence sensing of different forms of homocysteine in plasma

This study reports a selective and sensitive method for fluorescent detection of total, protein-bound, free, and free oxidized homocysteine (HCys) using tris(2-carboxyethyl)phosphine (TCEP) as a reducing agent, fluorosurfactant-capped gold nanoparticles (FSN–AuNP) as a preconcentrating probe, and o-phthaldialdehyde (OPA) as a derivatizing agent. TCEP was used to reduce the disulfide bonds of protein-bound and free oxidized HCys. FSN–AuNPs can extract HCys from a complicated complex because the FSN capping layer stabilizes the AuNPs in a high-salt solution and inhibits non-specific adsorption. HCys was selectively derivatized with OPA in the absence of a nucleophile. By taking advantage of these features, the selectivity of the proposed system is greater than 100-fold for HCys and homocystine (HCys–HCys disulfide; diHCys) compared to any aminothiols. The limits of detection for HCys and diHCys were 4.4 and 4.6nM, respectively. Different forms of plasma HCys were determined by varying the order of disulfide reduction with TCEP.

Specific detection of cysteine and homocysteine in biological fluids by tuning the pH values of fluorosurfactant-stabilized gold colloidal solution

This study describes the use of 14 nm nonionic fluorosurfactant-capped gold nanoparticles (FSN-capped AuNPs) for the simultaneous detection of cysteine (Cys) and homocysteine (Hcy) using colorimetric method, requiring no use of separation techniques. It was found that the kinetics of Cys/Hcy-induced aggregation of the 14 nm FSN-capped AuNPs strongly depends on the pH value of gold colloidal solution. At a pH of 6.5, the Cys-induced aggregation kinetics of the FSN-capped AuNPs was almost identical to that induced by Hcy, facilitating simultaneous detection of total Cys and Hcy up to a concentration as low as 0.15 μM; while at pH 12.0, the kinetics of Cys-induced aggregation was much faster than that inducted by Hcy, leading to selective detection of Cys at concentration as low as 1.0 μM in the presence of Hcy. The applicability of the method was validated by spiking known amount of Cys and Hcy in human urine and plasma samples, obtaining a recovery of 95.4–105.5%. The present approach is simple, high selective and provides high reproducibility, and has a great potentiality in disease diagnosis.

Colorimetric Assay for S-Adenosylhomocysteine Hydrolase Activity and Inhibition Using Fluorosurfactant-Capped Gold Nanoparticles

This study reports a simple colorimetric method for the sensitive detection of S-adenosylhomocysteine hydrolase (SAHH) activity and inhibition using fluorosurfactant-capped gold nanoparticles (FSN-AuNPs). FSN stabilizes the AuNPs against conditions of high ionic strength, and FSN-AuNPs are merely aggregated in the presence of homocysteine (HCys) and cysteine. Because of this feature, FSN-AuNPs were found to be dispersed in the presence of S-adenosylhomocysteine (SAH) that lacks a free thiol group. After SAHH catalyzed the hydrolysis of SAH, the produced HCys molecules were bound to the surface of AuNPs through the formation of Au-S bonds. As a result, the nanoparticle (NP) aggregation occurred through electrostatic attraction between each HCys-attached AuNP. This approach had a minimum detectable concentration of 100 units/L (~6 nM). Additionally, because adenosine analogs are capable of inhibiting SAHH activity, the addition of adenosine analogs to a solution containing SAH and SAHH resulted in the suppression of hydrolyzed SAH-induced NP aggregation. Adenosine analogs exhibited the following trend in the half-maximal inhibitory concentrations: adenosine > adenosine monophosphate > adenosine diphosphate ~ adenosine triphosphate. We have demonstrated that the combination of SAHH inhibition and FSN-AuNPs can be utilized for the selective detection of adenosine.

Detection of captopril via fluorosurfactant-capped gold nanoparticles

In the presence of high ionic strength(50 mM NaCl) and high temperature(40 ℃),captopril may cause the aggregation of the nonionic fluorosurfactant(FSN-100)-capped 14 nm gold nanoparticles(GNPs) and led to the red-shift of the surface plasmon resonance absorption peak.Based on this phenomenon,a rapid spectrophotometry method for captopril has been developed.The typical interference species in pharmaceutical formulations,such as starch,dextrin,glucose,fructose,maltose,sucrose,gelatine,sorbitol,and lactose did not result in the aggregation of gold colloidal solution.The present approach possessed various advantages,such as simple,rapid and high selective.The calibration curve is linear over the range of 2.0?12.5 μg/mL for captopril,the detection limit(S/N=3) is 1.25 μg/mL.This method has been successfully used for detection of captopril in tablets,and the recoveries of captopril were in the range between 99% and 103%.

Colorimetric detection of cephradine in pharmaceutical formulations via fluorosurfactant-capped gold nanoparticles

The aggregation of gold nanoparticles (GNPs) capped with nonionic fluorosurfactant (FSN) could be induced rapidly and selectively by cephradine degradation products, but not by cephradine and other excipients in pharmaceutical formulations. A new detection method for cephradine has been developed based on the cephradine degradation products-induced aggregation of the GNPs. The present approach offers various advantages, such as simplicity and high selectivity. Under optimum conditions, the lowest detectable concentration of cephradine through this approach (S/N=3) is 0.8 microg mL(-1). The calibration curve was linear over the range of 2.0-10.0 microg mL(-1) for the detection of cephradine. The recoveries of cephradine were found to fall in the range between 97% and 105%. We have validated the applicability of our method through the analyses of cephradine in pharmaceutical formulations. Good agreements were obtained for the determination of cephradine between the present approach and official method.

Fluorescent sensing of homocysteine in urine: Using fluorosurfactant-capped gold nanoparticles and o-Phthaldialdehyde

This study reports the development of a simple, sensitive, and selective-detection system for homocysteine (HCys) based on the combination of fluorosurfactant-capped gold nanoparticles (FSN-AuNPs) and o-Phthaldialdehyde (OPA). The proposed assay utilizes FSN-AuNPs as extractors for HCys and cysteine (Cys), which can then be collected by centrifugation. As long as the HCys and Cys are isolated from the initial sample, they can be liberated from the NP surface by 2-mercaptoethanol (2-ME). The derivatization of released HCys with OPA/2-ME has a strong fluorescence maximum at 485 nm, whereas the derivatization of released Cys with the same reagent shows an extremely weak fluorescence maximum at 457 nm. As a result, the selectivity of this system is more than 100-fold for HCys over any aminothiols when excited at 370 nm. The extraction and derivation efficiencies are monitored as functions of the concentration of FSN-AuNPs and OPA, respectively. The proposed system has a detection limit of 180 nM at a signal-to-noise ratio of 3 for HCys. This study validates the applicability of this system by analyzing the amount of HCys in urine samples.

Sodium hydroxide as pretreatment and fluorosurfactant-capped gold nanoparticles as sensor for the highly selective detection of cysteine

A sensor for detecting cysteine (Cys) in a solution of fluorosurfactant (FSN)-capped gold nanoparticles (AuNPs) has been developed. Under acidic conditions, FSN-capped AuNPs are aggregated in the presence of homocysteine (HCys) and Cys but not in the presence of cysteinylglycine, glutathione, and γ-glutamycysteine. When adding NaOH to a solution of HCys, the five-membered ring transition state is formed through intramolecular hydrogen abstraction. By contrast, it is difficult for Cys to form a four-membered ring transition state after Cys has been pretreated with NaOH. As a result, the HCys-induced aggregation of the FSN-capped AuNPs is suppressed because the five-membered ring transition state exhibits relatively larger steric hindrance and has stronger interaction with the FSN molecules. Thus, we can discriminate between Cys and HCys on the basis of different aggregation kinetics. Under the optimum condition, the selectivity of the probe for Cys in aqueous solutions is remarkably high over the other aminthiols. Note that HCys and Cys have very similar structure and p K a value. We have validated the applicability of our method through the analyses of Cys in urine samples. It is believed that this approach has great potential for the detection of Cys in biological samples.

Specific detection of cysteine and homocysteine: recognizing one-methylene difference using fluorosurfactant-capped gold nanoparticles

Aggregation of fluorosurfactant-capped gold nanoparticles could be induced selectively by cysteine and homocysteine and, when solution ionic strength was low, the kinetics of homocysteine-induced aggregation of large size nanoparticles (approximately 40 nm) was much faster than that induced by cysteine, leading to specific detection of homocysteine in the presence of excess cysteine.

Specific Postcolumn Detection Method for HPLC Assay of Homocysteine Based on Aggregation of Fluorosurfactant-Capped Gold Nanoparticles

Gold nanoparticles (GNPs) capped with nonionic fluorosurfactant molecules (Zonyl FSN) were synthesized, and with the colloidal solution as a probe reagent, a new postcolumn colorimetric detection method for HPLC assay of homocysteine (Hcy) has been developed. The FSN-capped GNPs exhibited excellent stability in aqueous solutions, even in the presence of high salt. The aggregation of the GNPs could be induced by either Hcy or cysteine, resulting in an absorption decrease of the colloidal solution at 525 nm and an absorption increase at longer wavelengths (600-700 nm); however, the GNPs did not respond to other amino acids and biomolecules such as glutathione, cysteinylglycine, and glucose. Under optimal conditions (i.e., high salt, neutral pH, and approximately 70 degrees C), the color change of the GNP solution could almost complete ( approximately 90%) within approximately 30 s upon the addition of Hcy. The high selectivity and very fast kinetics of the reaction make it a promising system for HPLC postcolumn detection. The new technique has been employed to determine total Hcy levels in human urine and plasma samples, and the results are satisfactory.