A novel colorimetric aptasensor for detection of chloramphenicol based on lanthanum ion–assisted gold nanoparticle aggregation and smartphone imaging

A label-free, rapid response colorimetric aptasensor for sensitive detection of chloramphenicol (CAP) was proposed, which was based on the strategy of ssDNA-modified gold nanoparticle (AuNP) aggregation assisted by lanthanum (La³⁺) ions. The AuNPs generated a color change that could be monitored in the red, green, and blue and analyzed by the smartphone imaging app. La³⁺, as a trigger agent, strongly combined with the phosphate groups of the surface of ssDNA-AuNPs probe, which helps create AuNP aggregation and the color change of AuNPs from red to blue. On the contrary, when mixing with CAP, the aptamer (Apt) bound to CAP to form a rigid structure of the Apt-CAP complex, and La³⁺ attached to the phosphate groups of the complex, which prevented the aptamer from binding to the surface of the AuNPs. As a result, the color of the AuNPs changed to violet-red. Finally, UV-vis absorption spectroscopy and the smartphone imaging app were employed to determine CAP with a lower detection limit of 7.65 nM and 5.88 nM, respectively. The proposed strategy featuring high selectivity and strong anti-interference ability for detection of CAP in practical samples was achieved. It is worth mentioning that the simple and portable colorimetric aptasensor will be used for facilitating on-site detection of food samples.

     

Development of gold nanoparticle based colorimetric method for quantitatively studying the inhibitors of Cu/Zn induced β-amyloid peptide assembly

In this paper, a kind of gold nanoparticle (GNP)-based colorimetric assay has been developed for studying the reversible interaction of β-amyloid peptide (Aβ) with Cu²⁺ and Zn²⁺, and quantitatively analyzing four inhibitors (i.e., EDTA, EGTA, histidine and clioquinol) of Cu²⁺/Zn²⁺ induced Aβ assembly. The inhibition efficiencies (e.g., half maximal inhibitory concentration, IC₅₀ value) of these inhibitors could be measured in this work. As far as we know, these IC₅₀ values were reported at the first time. In this assay, the streptavidin conjugated GNPs (SA-GNPs) were employed as indicators to monitor the Cu²⁺/Zn²⁺ induced aggregating/disaggregating behaviors of biotin modified β-amyloid 1–16 peptides (Aβ_1–16(biotin)). Because of high affinity of streptavidin (SA) with biotin, the aggregating/disaggregating of Aβ_1–16(biotin) results in the significant color change of SA-GNPs. Furthermore, we demonstrate that the assay can be used as an effective tool for designing anti-dementia drugs through quantitative analysis of the interactions of four representative inhibitors with Cu²⁺/Zn²⁺ induced Aβ assembly.     

Aptasensor for adenosine triphosphate based on electrode–supported lipid bilayer membrane

We have developed an aptasensor for adenosine triphosphate (ATP) based on an electrode-supported lipid bilayer membrane. The assay is based on a conformational change that is induced after binding the target which modulates the electron transfer rate in the conductive path. The method is highly sensitive, stable, and repeatable. The detection limit for ATP is 50 nM, and the dynamic range extends to 3.2 μM, which covers the concentration range of ATP in cell lysates (from 0.1 to 1 μM). The method also holds promise in that it may be transferred to submicro- or nano-scale electrodes so to enable intracellular monitoring of ATP.

4-Aminothiophenol functionalized gold nanoparticles as colorimetric sensors for the detection of cobalt using UV–Visible spectrometry

The 4-aminothiophenol functionalized gold nanoparticles (4-ATP-Au NPs) were used as colorimetric sensors for the detection of Co²⁺ in aqueous solution by using UV–Visible spectrometry. The 4-ATP-Au NPs were characterized by UV–Visible, FT-IR, TEM and dynamic light scattering (DLS) which confirmed their higher binding affinity towards Co²⁺ through coordinate covalent interactions that can be observed with the naked eye. The absorbance ratio (A₅₇₀/A₅₂₃) was linear with Co²⁺ concentration in the range of 15 × 10^?3 to 1 × 10^?3 M with a correlation coefficient of (R ²) 0.994, and the limit of detection was 5.79 × 10^?5 M.     

Sensitive colorimetric assays for α-glucosidase activity and inhibitor screening based on unmodified gold nanoparticles

A colorimetric sensor has been developed in this work to sensitively detect α-glucosidase activity and screen α-glucosidase inhibitors (AGIs) utilizing unmodified gold nanoparticles (AuNPs). The sensing strategy is based on triple-catalytic reaction triggered by α-glucosidase. In the presence of α-glucosidase, aggregation of AuNPs is prohibited due to the oxidation of cysteine to cystine in the system. However, with addition of AGIs, cysteine induced aggregation of AuNPs occurs. Thus, a new method for α-glucosidase activity detection and AGIs screening is developed by measuring the UV–vis absorption or visually distinguishing. A well linear relation is presented in a range of 0.0025–0.05 U mL⁻¹. The detection limit is found to be 0.001 U mL⁻¹ for α-glucosidase assay, which is one order of magnitude lower than other reports. The IC₅₀ values of four kinds of inhibitors observed with this method are in accordance with other reports. The using of unmodified AuNPs in this work avoids the complicated and time-consuming modification procedure. This simple and efficient colorimetric method can also be extended to other enzymes assays.     

Laccase–gold nanoparticle assisted bioelectrocatalytic reduction of oxygen

It was found that homogeneous activity of Trametes hirsuta laccase is considerably diminished in the presence of gold nanoparticles (Au-NPs). Heterogeneous electron transfer studies revealed that Au-NPs facilitate direct electron transfer (DET) between the T1 copper site of the laccase and the surface of Au-NP modified electrodes. DET was characterized by the standard heterogeneous ET constant of 0.5 ± 0.6 s^?1 at Au-NPs with an average diameter of 50 nm. As a consequence of this a well pronounced DET based bioelectrocatalytic oxygen reduction with current densities of 5–30 µA cm^?2 has been achieved at the laccase–Au-NP modified electrodes.     

Investigations on the electrochemical preparation of gold–nanoparticle composites

The role of electrical charges in the double layers of the electrode and in particles during the electrochemical preparation of dispersion coatings was studied for the systems Au/diamond and Au/Al₂O₃. The surface charge of the electrode under the conditions of electroplating will depend on the potential of zero charge (p.z.c.). For the nanoscaled particles the sign of the surface charge was estimated from the zeta potential in dilute solutions. Successful inclusion of Al₂O₃ and diamond nanoparticles was observed when the particles and the electrode were oppositely charged. The Vickers hardness of the layers was increased by the codeposition of Al₂O₃, whereas it decreased in the case of nanodiamond.Presented at the 3rd International Symposium on Electrochemical Processing of Tailored Materials held at the 53rd Annual Meeting of the International Society of Electrochemistry, 15–20 September 2002, Düsseldorf, Germany     

A sensitive and rapid UV–vis spectrophotometry for organophosphorus pesticides detection based on Ytterbium (Yb3+) functionalized gold nanoparticle

AuNPs possess oxygen-containing functional groups and strong complexation reaction with Yb3+. While oxygen-containing thiophosphate in the OPs molecule can combine with Yb³⁺ as a cross-linking molecule to produce insoluble yetterbium phosphate, resulting in the aggregation of AuNPs and great decrease in ultraviolet absorbance strength at 520 nm by ultraviolet visible (UV-vis) spectrophotometer.     

A highly selective colorimetric and “Off-On” fluorescence sensor for CN~- based on Zn(salphenazine) complex

The development of sensors for selective detection of cyanide ion(CN~-) is an important mission to accomplish because of the versatility and toxicity of CN~-. In the present work, an "ensemble"-based colorimetric and fluorescent sensor(L2-Zn~(2+)) for CN~-ion has been developed. The addition of cyanide ions removed Zn~(2+) from the ensemble(L2-Zn~(2+)) in aqueous medium, resulting in a color change of the solution from red to buff and a "turn-on" fluorescent response. Also, the sensitivity of both the fluorescenceand colorimetric-based assay is below the maximum allowable level of cyanide ions in drinking water set by the World Health Organization. In addition, test strips, which served as convenient and efficient CN~- test kits, were fabricated based on the sensor.Notably, the selective detection of cyanide with L2-Zn~(2+) for practical application was also performed in sprouting potatoes.     

Fenugreek hydrogel–agarose composite entrapped gold nanoparticles for acetylcholinesterase based biosensor for carbamates detection

A biosensor was fabricated to detect pesticides in food samples. Acetylcholinesterase was immobilized in a novel fenugreek hydrogel–agarose matrix with gold nanoparticles. Transparent thin films with superior mechanical strength and stability were obtained with 2% fenugreek hydrogel and 2% agarose. Immobilization of acetylcholinesterase on the membrane resulted in high enzyme retention efficiency (92%) and a significantly prolonged shelf life of the enzyme (half-life, 55 days). Transmission electron microscopy revealed that, gold nanoparticles (10–20 nm in diameter) were uniformly dispersed in the fenugreek hydrogel–agarose–acetylcholinesterase membrane. This immobilized enzyme-gold nanoparticle dip-strip system detected various carbamates, including carbofuran, oxamyl, methomyl, and carbaryl, with limits of detection of 2, 21, 113, and 236 nM (S/N = 3), respectively. Furthermore, the fabricated biosensor exhibited good testing capabilities when used to detect carbamates added to various fruit and vegetable samples.     

A colorimetric assay for measuring iodide using Au@Ag core–shell nanoparticles coupled with Cu

Au@Ag core–shell nanoparticles (NPs) were synthesized and coupled with copper ion (Cu²⁺) for the colorimetric sensing of iodide ion (I⁻). This assay relies on the fact that the absorption spectra and the color of metallic core–shell NPs are sensitive to their chemical ingredient and dimensional core-to-shell ratio. When I⁻ was added to the Au@Ag core–shell NPs-Cu²⁺ system/solution, Cu²⁺ can oxidize I⁻ into iodine (I₂), which can further oxidize silver shells to form silver iodide (AgI). The generated Au@AgI core–shell NPs led to color changes from yellow to purple, which was utilized for the colorimetric sensing of I⁻. The assay only took 10 min with a lowest detectable concentration of 0.5 μM, and it exhibited excellent selectivity for I⁻ over other common anions tested. Furthermore, Au@Ag core–shell NPs-Cu²⁺ was embedded into agarose gels as inexpensive and portable “test strips”, which were successfully used for the semi-quantitation of I⁻ in dried kelps.     

Naphthalene thiourea derivative based colorimetric and fluorescent dual chemosensor for F− and Cu2+/Hg2+ ions

A structurally simple (Z)-2-(naphthalen-2-ylmethylene)-N-phenylhydrazinecarbothioamide (R1) was used as a colorimetric and fluorescent sensor for both F^?  and Cu²⁺/Hg²⁺ ions. R1 selectively recognised F^?  ions as indicated by colour change from colourless to green. Fluorescence spectral data reveal that R1 is an excellent fluorescence chemosensor for Cu²⁺ ions. Finally, R1 was successfully applied to the bioimaging of Cu²⁺ ions in RAW 264.7 macrophage cells.     

Design of sugar–oligonucleotide conjugates installed gold nanoparticle for effective delivery to hepatic parenchymal cells

A novel oligonucleotide delivery system that is based on oligonucleotide–nanoparticle conjugates has been described. Installed oligonucleotides were modified with the carbohydrate at the 3′ terminus, accordingly, constructed nanoparticles display clustered carbohydrates on their outer layer for the targeted delivery of oligonucleotides. The method for the construction of ligand-functionalized nanoparticle was simple and reproducible. The stability of the nanoparticles displaying clustered carbohydrates greatly increased in serum compared to nanoparticles without carbohydrates. In order to investigate the targetability of oligonucleotide–nanoparticle conjugates into primary hepatic parenchymal cells, freshly isolated rat hepatocytes were incubated with nanoparticles and the amount of internalized gold nanoparticles was evaluated by an inductively coupled plasma mass spectroscopy analysis. Nanoparticles displaying clustered carbohydrates internalized more efficiently than nanoparticles without carbohydrate modifications. In particular, the cellular uptakes of oligonucleotide-conjugated gold nanoparticle increased 1.7 ～2.0-fold by galactose modification. Competition assay revealed that clustered galactose enhanced the internalization of the nanoparticle into primary hepatic parenchymal cells by a receptor-mediated process.

Imageable antigen-presenting gold nanoparticle vaccines for effective cancer immunotherapy in vivo

Delivery tracking: Goldnanoparticles (AuNPs) were functionalized with a red fluorescent protein (RFP, pink shapes in picture) as model antigen and an oligonucleotide (CpG) that stimulates the immune response. These functionalized AuNPs were used as cancer vaccines in a tumor model, where they enabled efficient delivery of an antigen to target sites, tracking of the vaccines using noninvasive clinical imaging, and cancer prevention and therapy.     

An intimately bonded titanate nanotube–polyaniline–gold nanoparticle ternary composite as a scaffold for electrochemical enzyme biosensors

In this work, titanate nanotubes (TNTs), polyaniline (PANI) and gold nanoparticles (GNPs) were assembled to form a ternary composite, which was then applied on an electrode as a scaffold of an electrochemical enzyme biosensor. The scaffold was constructed by oxidatively polymerising aniline to produce an emeraldine salt of PANI on TNTs, followed by gold nanoparticle deposition. A novel aspect of this scaffold lies in the use of the emeraldine salt of PANI as a molecular wire between TNTs and GNPs. Using horseradish peroxidase (HRP) as a model enzyme, voltammetric results demonstrated that direct electron transfer of HRP was achieved at both TNT-PANI and TNT-PANI-GNP-modified electrodes. More significantly, the catalytic reduction current of H₂O₂ by HRP was ∼75% enhanced at the TNT-PANI-GNP-modified electrode, compared to that at the TNT-PANI-modified electrode. The heterogeneous electron transfer rate constant of HRP was found to be ∼3 times larger at the TNT-PANI-GNP-modified electrode than that at the TNT-PANI-modified electrode. Based on chronoamperometric detection of H₂O₂, a linear range from 1 to 1200 μM, a sensitivity of 22.7 μA mM⁻¹ and a detection limit of 0.13 μM were obtained at the TNT-PANI-GNP-modified electrode. The performance of the biosensor can be ascribed to the superior synergistic properties of the ternary composite.     

Electrochemiluminescence DNA biosensor based on the use of gold nanoparticle modified graphite-like carbon nitride

The authors describe an electrochemiluminescent (ECL) DNA biosensor that is based on the use of gold nanoparticles (AuNPs) modified with graphite-like carbon nitride nanosheets (g-C₃N₄ NSs) and carrying a DNA probe. In parallel, nanoparticles prepared from gold-platinum (Au/Pt) alloy and carbon nanotubes (CNTs) were placed on a glassy carbon electrode (GCE). Once the g-C₃N₄ NHs hybridize with DNA-modified AuNPs, they exhibit strong and stable cathodic ECL activity. The Au/Pt-CNTs were prepared by electrochemical deposition of Au/Pt on the surface of the CNTs in order to warrant good electrical conductivity. On hybridization of immobilized capture probe (S₁), target DNA (S₂) and labeled signal probe (S₃), a sandwich-type DNA complex is formed that produces a stable ECL emission at a typical applied voltage of ?1.18 V and in the presence of peroxodisulfate. Under optimized conditions, the method has a response to target DNA that is linearly related to the logarithm of its concentration in the range between 0.04 f. and 50 pM, with a 0.018 f. detection limit.

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Graphical abstract Schematic presentation of an electrochemiluminescent DNA biosensor based on two-dimensional graphite-like carbon nitride nanosheets (g-C₃N₄ NSs) hybridized with gold nanoparticles. Abbreviations: MCH: 6-mercapto-1-hexanol; S1: Capture probe; S2: target DNA. 

     

Photochromic polyoxometalate–based enzyme-free reusable sensors for real-time colorimetric detection of alcohol in sweat and saliva

This study describes a new strategy for real-time detection of alcohol in saliva and sweat. Phosphotungstic acid (PTA) is a colorless, photoelectrochromic heteropoly acid that can be reduced by ethanol under ultraviolet (UV) radiation to produce an intense blue color. This system has useful properties in the development of a new alcohol sensor: (1) the blue color can be detected by the naked eye or mobile camera, even at low ethanol concentrations; (2) color intensity is proportional to ethanol concentration; and (3) once exposed to air, reduced PTA is subsequently oxidized and returns to its colorless state offering sensor reusability. Based on these properties, we developed a simple device consisting of a PTA-impregnated non-woven material and a low-cost UV lamp that can be used to evaluate the alcohol concentration in saliva and sweat. We further enhanced the practical applicability of this sensor by demonstrating the integration of digital image analysis, multivariate analysis, and mobile camera technology with this sensor. This device can be potentially used in vehicles as a convenient, reusable alcohol sensor for drivers.     

HPLC–based methods for the determination of levetiracetam in biological and pharmaceutical samples

Levetiracetam is one of the new generation anti–epileptic agents (also known as anticonvulsants or antiseizure drugs). Following its approval for marketing in 2000, levetiracetam has been widely used in the treatment of epilepsy due to its broad spectrum effects. One of the advantages of this antiseizure drug is its rapid and complete absorption after oral administration. It has also minimal drug–drug and food interactions, and shows more than 95% bioavailability. The determination of levetiracetam in various samples is carried out using several analytical methods including HPLC–based methods. HPLC–based methods are used for different pharmaceutical analyses and play an important role in drug monitoring during patient follow–ups. This review provides a summary of the HPLC–based methods used in the determination and quantification of levetiracetam in biological fluids and pharmaceutical preparations.