Cysteamine-modified Gold Nanoparticles Research Articles

The dual-mode platform based on cysteamine-stabilized gold nanoparticles for the high throughput and on-site detection of bongkrekic acid

This article describes the visual detection of bongkrekic acid (BA) by cysteamine modified gold nanoparticles (CS-AuNPs) as colorimetric probes. Polycarboxyl structured BA induces the aggregation of CS-AuNPs through electrostatic interaction, which results in the color change of CS-AuNPs from wine-red to blue-violet. The ratio of absorbance at 650 nm and 524 nm (A650/A524) increases linearly in the 0.18–1.64 μM BA concentration range, and the detection limit is 3.43 nM. Moreover, when combined with solid phase extraction (SPE), the method can also be used for specific detection of BA in complex food matrix (tremella). The recoveries in urine, serum, and tremella ranged from 89.31% to 109.63%. Interestingly, a smartphone application (APP) was applied to identify the R, G, and B values of the solution, and the quantitative curve was established by calculating the gray value. This approach was then used to quantify the BA in the sample solution. The linear range of APP detecting is 0.10 μM–1.44 μM and the detection limit is 12.33 nM. This method can be used not only for food safety monitoring, but also for preliminary clinical screening of BA poisoning.

Disposable electrochemical immunosensor for prostate cancer detection

Prostate cancer (PCa) is the second most common cancer amongst men worldwide; hence its early and accurate diagnosis is crucial. Due to the lacking current diagnostic approaches, an urgent need arises for an alternating analytical platform targeting selective PCa biomarkers while testing in body fluids, such as urine and serum. With this motivation, we established a disposable and label-free electrochemical immunosensor for sensitive detection of the selective PCa biomarker, prostate-specific membrane antigen (PSMA). A screen-printed gold electrode (SPGE), with its working electrode functionalized by cysteamine-modified gold nanoparticles (Cys-AuNPs), served as the sensor platform. The PSMA was detected by introducing PSMA protein/PSMA-expressing PCa cells with various concentrations and performing differential pulse voltammetry (DPV) measurements. The established biosensor has detection limits of 0.47 ng/mL for PSMA proteins (0–5 ng/mL range) and 5 cells/mL (0–100 cells/mL range) for PSMA-expressing PCa cells. The corresponding limit of quantification (LOQ) and detection sensitivities were calculated as 2.20 ng/mL and 4 cells/mL; 1.71 μA·mL/ng and 0.15 μA·mL/cell, respectively. The selectivity studies confirmed that the DPV signals exerted by PSMA (+) cells were statistically significant in comparison to the PSMA (-) groups (p = 0.012, p * < 0.05). The developed immunosensor platform offers a feasible alternative to facilitate PCa diagnosis. Also, to the best of our knowledge, it displayed the highest analytical performance for PSMA-expressing PCa cells detection amongst its peers. Therefore, it can be adapted for different proteins, particularly for cell detection, to facilitate other types of cancerous cells’ diagnosis soon.

Lactic Acid Biosensor Based on Lactate Dehydrogenase Immobilized on Au Nanoparticle Modified Microwire Electrode

Lactate, a key metabolite of the anerobic metabolic pathway serves as a biomarker for lactic acidosis in clinical diagnostics. A variety of electrochemical biosensors have been exploited for the determination of lactate. Here we describe an improved electrochemical lactic acid biosensor that utilizes self-assembled monolayers (SAMs) of cysteamine-modified gold nanoparticles (AuNPs) on flexible tungsten microwire electrode to immobilize lactate dehydrogenase (LDH) to the microwire electrode. The fabricated AuNP-cysteamine-LDH electrode showed excellent behavior towards lactic acid at pH 6 and at 35 °C at an applied potential of +0.4 V (vs Ag/AgCl reference electrode). The biosensor exhibited a linear dynamic range of $500~\mu \text{M}$ to 7 mM with a very high sensitivity of $31.40~\mu \text{A}$ /mM cm2. The biosensor demonstrated good selectivity towards lactic acid, wherein a nafion layer was utilized to screen out interfering species. The AuNP-cysteamine-LDH electrode remained stable up to 18 days. The practicality of the AuNP-cysteamine-LDH electrode was assessed by determining lactic acid concentrations in sera and a sensitivity of $73.16~\mu \text{A}$ / mM cm2 was observed up to 5 mM.

In situ colorimetric detection of glyphosate on plant tissues using cysteamine-modified gold nanoparticles.

Monitoring the levels of pesticides on plant tissues is important for achieving effective protection of crops after application, as well as ensuring low levels of residues during harvest. In this study, a simple, rapid, and fieldable colorimetric method for detecting the pesticide glyphosate (Gly) on the plant tissues in situ using cysteamine-modified gold nanoparticles (AuNPs-Cys) has been developed. The aggregation of AuNPs-Cys in the presence of Gly results in a consequent color change from red to blue (or purple), which could be observed visually on the surface of plant tissues. With the naked eye, we successfully detected Gly spiked on the surface of spinach, apple, and corn leaves in situ. Further verification and quantification were achieved using surface-enhanced Raman spectroscopy (SERS) which uses AuNPs-Cys as the substrate. Moreover, application of this method was demonstrated through the evaluation of the Gly distribution on plant tissues which could greatly facilitate the development of precision agriculture technology.

Cysteamine-Modified Gold Nanoparticles as a Colorimetric Sensor for the Rapid Detection of Gentamicin.

This study demonstrates that cysteamine-modified gold nanoparticles could be used as a rapid and efficient tool for gentamicin detection. This technique is cheaper, simpler, and more effective than many other methods that are currently used for detecting the antibiotic in industrial and commercial applications. It has a great potential to be practically applied as a rapid screening method for gentamicin and gentamicin-like compounds in food and environmental samples.

Surface-enhanced Raman scattering substrate based on cysteamine-modified gold nanoparticle aggregation for highly sensitive pentachlorophenol detection

A new surface-enhanced Raman scattering (SERS) substrate based on cysteamine-modified gold nanoparticles (AuNPs) on the glass surface has been developed for the monitoring of pentachlorophenol (PCP) in water samples.

A label-free colorimetric sensor for sulfate based on the inhibition of peroxidase-like activity of cysteamine-modified gold nanoparticles

A simple label-free colorimetric sensor for sulfate has been devised based on the analyte-induced shielding of peroxidase-like activity of cysteamine-capped gold nanoparticles (cyst-AuNPs). Aggregation triggered by sulfate through hydrogen bond and electrostatic interaction gave rise to a remarkable decrease of the catalytic activity of AuNPs. By coupling with 3,3′,5,5′-tetramethylbenzidine (TMB)–H2O2 chromogenic reaction, a novel colorimetric sensor for detection of sulfate was established. Based on the signal amplification effect of the catalytic reaction, a detection limit as low as 0.16μM was obtained by virtue of UV–vis spectroscopy or 4μM with the naked-eye observation. The as-proposed sensor exhibited an excellent selectivity over other common anions and metallic ions. In view of these characteristics, such sensing probe features simplicity, cost-effectiveness, and naked-eye screening. These advantages make this sensor a powerful protocol for the quantitative detection of sulfate in water samples with satisfactory results.

A highly sensitive dual-readout assay based on gold nanoclusters for folic acid detection

We describe a sensitive fluorometric and colorimetric dual-readout probe for folic acid (FA). It is based on the use of the gold nanoclusters (AuNCs) and cysteamine–modified gold nanoparticles (cyst-AuNPs). The bovine serum albumin stabilized AuNCs exhibit strong fluorescence emission at 652 nm. Upon addition of cyst-AuNPs, the fluorescence intensity of the AuNCs showed dramatic decrease due to the surface plasmon enhanced energy transfer process. This is due to an FA-induced aggregation of the cyst-AuNPs which shifts the absorption peaks from 530 to 670 nm. Thus, the surface plasmon enhanced energy transfer between cyst-AuNPs and AuNCs is weakened and the fluorescence intensity of AuNCs is recovered. The fluorescence intensity of the AuNCs/cyst-AuNPs system is proportional to the concentration of FA in the range from 0.11 to 2.27 μmol L−1. The dual-readout probe reported here was successfully applied to the determination of FA in spiked serum samples and folic acid tablets.

Reduction of silver ions in gold nanoparticle suspension for detection of dihydroxybenzene isomers

We have investigated the reduction of silver ions in a gold nanoparticle suspension by dihydroxybenzene isomers: hydroquinone (1,4-dihydroxybenzene), catechol (1,2-dihydroxybenzene), and resorcinol (1,3-dihydroxybenzene). We found that using these isomers as reducing agents resulted in distinctive color changes of suspensions. When hydroquinone was added to suspensions containing cysteamine-modified gold nanoparticles and silver nitrate, the suspension changed from red to yellow because a silver shell formed on the gold nanoparticles. With catechol, the suspension initially turned yellow from formation of core–shell nanoparticles, and then it became black following the polymerization of catechol on the nanoparticle surfaces. This caused charge reversal followed by aggregation of core–shell nanoparticles. The addition of resorcinol, however, did not produce core–shell nanoparticles because its high oxidation peak potential prevented the reduction of silver ions, keeping the suspension color unchanged. Based on the color changes, we could detect the concentration of hydroquinone and catechol with high sensitivity. Moreover, the addition of Fe(III) ions enabled selective detection of hydroquinone in a mixture of dihydroxybenzene isomers by forming a chelate complex with catechol.

Functionalized gold nanoparticles for the detection of nitrates in water

A rapid and sensitive colorimetric assay was developed using cysteamine modified gold nanoparticles for the direct detection of nitrates in water samples. Gold nanoparticles stabilized with citrate were modified with cysteamine that has excellent affinity for nitrates, and its capacity to capture nitrates was evaluated, in comparison with other anions. The presence of nitrates in water samples could be tracked by naked eye with a color variation of the colloidal suspension from red to gray, and these results were confirmed through ultraviolet–visible measurements within a nitrate concentration of 35 ppm. In field analysis was performed in underground water extracted from wells during the year 2012 in Arborea area (Italy), a nitrate vulnerable zone, and information of nitrate concentration in the range of the recommended nitrate level in water was studied. This simple assay can be used for onsite detection of nitrates in water without the need for skilled personnel, sample pretreatment or expensive instrumentation.

Near Infrared Fluorescent Trypsin Stabilized Gold Nanoclusters as Surface Plasmon Enhanced Energy Transfer Biosensor and in Vivo Cancer Imaging Bioprobe

The simplicity of the green-synthesized routine and the availability of surface modification of diverse bioactive molecules make noble metal nanostructures highly suitable as multifunctional biomaterials for biological and biomedical application. Here, we report the preparation of trypsin stabilized gold nanoclusters (try-AuNCs) with near-infrared fluorescence for biosensing heparin based on surface plasmon enhanced energy transfer (SPEET) and folic acid (FA) modified try-AuNCs for in vivo cancer bioimaging. The SPEET/try-AuNCs fluorescence biosensor was designed via heparin mediated energy transfer between try-AuNCs and cysteamine modified gold nanoparticles (cyst-AuNPs). The developed SPEET/try-AuNCs fluorescence biosensor allowed sensitive and selective detection of heparin with a linear range of 0.1-4.0 μg mL(-1) and a detection limit (3s) of 0.05 μg mL(-1). The relative standard deviation for eleven replicate detections of 2.5 μg mL(-1) heparin was 1.1%, and the recoveries of the spiked heparin in human serum samples ranged from 97% to 100%. In addition, folic acid was immobilized on the surface of try-AuNCs to ameliorate the specific affinity of AuNCs for tumors, and the near-infrared fluorescent FA-try-AuNCs were applied for in vivo cancer imaging of high folate receptor (FR) expressing Hela tumor. In vivo study of the dynamic behavior and targeting ability of FA-try-AuNCs probe to Hela tumor bearing mice and normal nude mice validated the high specific affinity of FA-try-AuNCs probe to FR positive tumors. The results show that the prepared try-AuNCs have great potential as multifunctional biomaterials for biosensing biomolecules with SPEET mode and in vivo cancer imaging with high targeting ability.

Colorimetric sensing strategy for mercury(ii) and melamine utilizing cysteamine-modified gold nanoparticles

A quantitative colorimetric sensing strategy utilizing cysteamine modified gold nanoparticles (CA-AuNPs) as reporters for Hg(2+) and melamine was demonstrated. Cysteamine is a cheap and commercially available aminothiol and is also the most important chelating ligand in coordination chemistry possessing the ability to coordinate to Hg(2+) and melamine. The terminal thiol group in cysteamine is used to bind to AuNPs and another terminal amine group is used as a colorimetric probe either for Hg(2+) or melamine. By adjusting the pH, protonation of cysteamine's terminal amine groups allows for tuning of the surface charge on the cysteamine-modified gold nanoparticles. At acidic pH, the CA-AuNPs are positively charged due to the protonated amine groups, which may electrostatically bind melamine resulting in aggregation of CA-AuNPs, while at alkaline pH, the amine groups are deprotonated, and if Hg(2+) is present, they may form an N-Hg(2+)-N structure to induce the aggregation of CA-AuNPs. The detection limits (S/N = 3) of Hg(2+) and melamine were 30 nM and 80 nM respectively, which were comparable with or even lower than those of other single analyte methods. The proposed sensing mechanisms, which are based on electrostatic attraction for melamine and the N-Hg(2+)-N structure for Hg(2+), were validated by zeta potential measurements. The facile one-step surface modification strategy for AuNPs is suitable for the effective analysis of large numbers of samples, which would open new opportunities for development of miniaturized Hg(2+) and melamine sensors.

A facile assay for direct colorimetric visualization of lipopolysaccharides at low nanomolar level

We report a facile assay for the rapid visual detection of lipopolysaccharide (LPS) molecules down to the low nanomolar level by taking advantage of the electrostatic interaction between LPS molecules and cysteamine-modified gold nanoparticles (CSH-Au NPs). The large amount of negatively charged groups on the LPS molecules make LPS highly negatively charged. Thus, when modified with cysteamine, the positively charged gold nanoparticles can aggregate in the presence of trace amounts of LPS. The probe is simple, does not require any advanced instrumentation, and the limit of detection (LOD) was determined to be as low as 3.3 × 10−10 mol/L. To the best of our knowledge, it is the most sensitive synthetic LPS sensor reported so far. Open image in new window

Ultrasensitive electrochemiluminescence detection of mercury ions based on DNA oligonucleotides and cysteamine modified gold nanoparticles probes

Abstract A simple and ultrasensitive biosensor for the determination of mercuric ions was developed based on an electrochemiluminescence (ECL) nanoprobe combined with DNA oligonucleotides and cysteamine-gold nanoparticle (AuNP) conjugates. In this work, we designed a rapid and simple assay by using a magnetic platform and avoiding a long and complicated electrode-modifying procedure. Moreover, we greatly improved the assay sensitivity by the employment of AuNPs labelled with a high concentration of ECL signal probes carried by cysteamine. Two types of thymine-enriched single-strand DNA (ssDNA) probes were labelled onto magnetic bead (MB) and AuNP, respectively. Upon addition of mercury ions, the thymine–Hg 2+ –thymine (T–Hg 2+ –T) interaction between two ssDNA probes directed the coordination between the AuNPs and MBs and yielded the MB–ECL nanoprobe complexes. These complexes were then captured on an unmodified electrode by magnetic separation and enrichment. Via our custom-built ECL system, a detection limit of 50 pM was achieved. This novel ECL biosensor also exhibited excellent selectivity over a series of interference metal ions, even for an ion concentration 1000 times higher than that of the mercury ions. Given the excellent sensitivity and selectivity of our biosensor, it provides great potential for future applications of mercury ion monitoring.

Target-Specific Gene Silencing of Layer-by-Layer Assembled Gold–Cysteamine/siRNA/PEI/HA Nanocomplex

Target-specific intracellular delivery of small interfering RNA (siRNA) is regarded as one of the most important technologies for the development of siRNA therapeutics. In this work, a cysteamine modified gold nanoparticles (AuCM)/siRNA/polyethyleneimine (PEI)/hyaluronic acid (HA) complex was successfully developed using a layer-by-layer method for target-specific intracellular delivery of siRNA by HA receptor mediated endocytosis. Atomic force microscopic and zeta potential analyses confirmed the formation of a AuCM/siRNA/PEI/HA complex having a particle size of ca. 37.3 nm and a negative surface charge of ca. -12 mV. With a negligible cytotoxicity, AuCM/siRNA/PEI/HA complex showed an excellent target-specific gene silencing efficiency of ca. 70% in the presence of 50 vol % serum, which was statistically much higher than that of siRNA/Lipofectamine 2000 complex. In the competitive binding tests with free HA, dark-field bioimaging and inductively coupled plasma-atomic emission spectroscopy confirmed the target-specific intracellular delivery of AuCM/siRNA/PEI/HA complex to B16F1 cells with HA receptors. Moreover, the systemic delivery of AuCM/siRNA/PEI/HA complex using apolipoprotein B (ApoB) siRNA as a model drug resulted in a significantly reduced ApoB mRNA level in the liver tissue. Taken together, AuCM/siRNA/PEI/HA complex was thought to be developed as target-specific siRNA therapeutics for the systemic treatment of various liver diseases.

Colorimetric detection of melamine in complex matrices based on cysteamine-modified gold nanoparticles

A sensitive assay for melamine in complex matrices is built using cysteamine-modified gold nanoparticles (AuNPs) and an effective sample pretreatment protocol. Citrate-stabilized AuNPs were modified by cysteamine in order to weaken the electrostatic repulsion force between the gold nanoparticles. Detection sensitivity gained through this modification increased about 100 fold compared with the result using the unmodified AuNPs. Direct colorimetric visualizations of melamine in milk products, eggs and feeds was successfully demonstrated within the linear ranges of 1-200 mg L(-1) and detection limits below 1 mg L(-1). The proposed scheme could be an alternative means for onsite detection of melamine without costly instruments.