Magnetic Fe3O4@SiO2 core shell nanoparticles containing diphenylcarbazide in the shell were utilized for solid phase extraction of Hg(II) from aqueous solutions. The Hg(II) loaded nanoparticles were then separated by applying an external magnetic field. Adsorbed Hg(II) was desorbed and its concentration determined with a rhodamine-based fluorescent probe. The calibration graph for Hg(II) is linear in the 60 nM to 7.0 μM concentration range, and the detection limit is at 23 nM. The method was applied, with satisfying results, to the determination of Hg(II) in industrial waste water.
Platinum nanoparticles (Pt-NPs) with sizes in the range from 10 to 30 nm were synthesized using protein-directed one-pot reduction. The model globular protein bovine serum albumin (BSA) was exploited as the template, and the resulting BSA/Pt-NPs were studied by transmission electron microscopy, energy dispersive X-ray spectroscopy, and resonance Rayleigh scattering spectroscopy. The modified nanoparticles display a peroxidase-like activity that was exploited in a rapid method for the colorimetric determination of hydrogen peroxide which can be detected in the 50 μM to 3 mM concentration range. The limit of detection is 7.9 μM, and the lowest concentration that can be visually detected is 200 μM.
Pt-NPs were synthesized using BSA-directed one-pot reduction and BSA/Pt-NPs composite can effectively catalyze the oxidation of TMB producing blue solution in the presence of H2O2.
We report on the first application of terahertz metamaterials acting as transducers for chemical sensors based on conducting polymers. In our feasibility study aimed at sensing of gaseous hydrochloric and ammonia, a two-dimensional sensor metamaterial consisting of an array of split-ring resonators on the surface of undoped silicon wafer was prepared. The surface of the resonator was coated with a 150-μm layer of polyaniline. Binding of hydrogen chloride to polyaniline leads to distinct changes in the resonance frequency of the metamaterial. Measurements can be performed both in the reflection and transmission mode. A numerical simulation of the response revealed an increase of both the real and the imaginary components of the dielectric function of the polyaniline film. These changes are attributed to the transition from emaraldine base to emeraldine salt. The results demonstrate a new approach for formation of highly sensitive transducers for chemical sensors.
ᅟ
Acetylcholinesterase (AChE) from Electrophorus electricus was immobilized on the surface of amino-modified magnetic beads (AChE-MB), and its activity evaluated by the quantification of acetylcholine hydrolysis. A reference mixture composed of AChE binders (galanthamine and a probe coumarin, K i = 0.031 ± 0.010 μM) and non-binders (ketamine and propranolol) was used to probe the fishing assay. The performance of the bioconjugation assay was demonstrated with a library of 12 reference coumarins from which two ligands were directly identified by LC-MS/MS in a single assay, demonstrating the usefulness of this approach.
A bioconjugate-screening assay with AChE-modified magnetic beads was developed to direct identification of AChE binders, in mixtures, by LC-MS/MS. A reference mixture of twelve coumarins was used and, the two ligands were identified.
We describe a reversible fluorescent DNA–based INHIBIT logic gate for the determination of silver(I) and iodide ions using graphene oxide (GO) as a signal transducer and Ag(I) and iodide as mechanical activators. The basic performance, optimized conditions, sensitivity and selectivity of the logic gate were investigated and revealed that the method is highly sensitive and selective over potentially interfering ions. The limits of detection for Ag(I) and iodide are 10 nM and 50 nM, respectively. This logic gate was successfully applied to the determination of Ag(I) and iodide in (spiked) tap water and river water. It was also used for the determination of iodide in human urine samples with satisfactory results. Compared to other methods, this INHIBIT logic gate is simple in design and has small background interference.
A simple and reversible fluorescent DNA-based INHIBIT logic gate is designed by using graphene oxide as a signal transducer and silver ions and iodide as mechanical activators.
A label-free and single-step method is reported for rapid and highly sensitive detection of bisphenol A (BPA) in aqueous samples. It utilizes an aptamer acting as a probe molecule immobilized on a commercially available array of interdigitated aluminum microelectrodes. BPA was quantified by measuring the interfacial capacitance change rate caused by the specific binding between bisphenol A and the immobilized aptamer. The AC signal also induces an AC electrokinetic effect to generate microfluidic motion for enhanced binding. The capacitive aptasensor achieves a limit of detection as low as 10 fM(2.8 fg ⋅ mL − 1) with a 20 s response time. The method is inexpensive, highly sensitive, rapid and therefore provides a promising technology for on-site detection of BPA in food and water samples.
A. AC electrokinetics effect plays a vital role in BPA detection by introducing microfluidic movement to accelerate the molecular transport to the electrode surface.
B. The ACEK capacitive aptasensor has a limit of detection as low as 10 fM (2.8 fg ⋅ mL − 1) with a 20-s response time.
We have developed a crown ether based selective colorimetric sensing scheme for the determination of Pb(II) ion by using gold nanoparticles modified with dithiocarbamate derivative of 4′-aminobenzo-18-crown-6 that acts as a colorimetric probe. Monodisperse Au-NPs were prepared by reacting 4′-aminobenzo-18-crown-6 with carbon disulfide to generate the dithiocarbamate ligand which was then added to the Au-NPs to form a supramolecular assembly on their surface. The Au-NPs modified in this way undergo aggregation in the presence of Pb(II) ions, and this causes the color to change from red to blue. The Pb(II)-induced aggregation can be monitored by using UV-visible spectrometry and even with the bare eye. The absorbance ratio (A650nm/A520nm) is linearly related to the concentration of Pb(II) in the 0.1 to 75 μM range (with a correlation coefficient of 0.9957), and the detection limit is 50 nM which is lower than the allowable level (75 nM) as defined by the US EPA. The method was successfully applied to the determination of Pb(II) in spiked water samples.
Schematic representation of Pb2+ ion-induced DTC-CE-Au NPs aggregation via sandwich complex formation.
We are presenting an electrochemical method for the determination of pyrophosphate ions (PPi) that is based on the competitive coordination of Cu(II) ion to a nanofilm of cysteine (Cys) and dissolved PPi. Cys was immobilized on the surface of a gold electrode by self-assembly. The Cys-modified gold electrode was loaded with Cu(II) ion which is released from the surface on addition of a sample containing PPi. The sensor shows an unprecedented electrochemical response to PPi, and the reduction peak currents is linearly related to the logarithm of the concentration of PPi in the 100 nM to 10 mM range (with an R2 or 0.982). The limit of detection is ~10 nM which is lower than the detection limits hitherto reported for PPi. Adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP) and common anions give a much weaker response. The method demonstrated here is simple, effective, highly sensitive, hardly interfered, and does not require the addition of a reagent. The method was applied to the determination of PPi in (spiked) serum samples.
Schematic illustration of the pyrophosphate sensing process.
We describe a sensitive method for the immunochromatographic determination of aflatoxin B1. It is based on the following steps: 1) Competitive interaction between non-labeled specific primary antibodies and target antigens in a sample and in the test zone of a membrane; 2) detection of the immune complexes on the membrane by using a secondary antibodies labeled with gold nanoparticles. The method enables precise adjustment of the required quantities of specific antibodies and the colloidal (gold) marker. It was applied in a lateral flow format to the detection of aflatoxin B1 and exhibits a limit of detection (LOD) of 160 pg · mL−1 if detected visually, and of 30 pg · mL−1 via instrumental detection. This is significantly lower than the LOD of 2 ng · mL−1 achieved by conventional lateral flow analysis using the same reagents.
Immunochromatography with secondary labeled antibodies caused 10-fold decrease of detection limit
This article describes a fluorescent molecularly imprinted polymer (MIP) capable of selective fluorescent turn-on recognition of the tumor biomarker α-fetoprotein. The technique is making use of amino-modified Mn-doped ZnS quantum dots (QDs) as solid supports, 4-vinylphenylboronic acid and methyl methacrylate as the functional monomers, γ-methacryloxypropyl trimethoxysilane as the grafting agent, and α-fetoprotein as a template. A graft imprint is created on the surface of the QDs. The functional monomers are shown to play an important role in the formation of the binding sites and in preventing nonspecific protein binding. The resulting MIP-QDs display a good linear response to α-fetoprotein in the 50 ng · L−1 to 10 μg · L−1 concentration range, and the limit of detection is 48 ng · L−1. In our perception, the method has a wide scope in that it may be adapted to various other glycoproteins.
Schematic illustration of the synthesis of the MIP-QDs composites
We describe a new chemiluminescence (CL) system based on the oxidation of rhodamine B (RhoB) with alkaline potassium permanganate in the presence of gold nanoparticles (Au-NPs) and anionic detergent sodium dodecyl sulfate. Free RhoB is weakly chemiluminescent when oxidized with permanganate at alkaline pH values. However, a remarkably strong enhancement of CL is observed in the presence of Au-NPs, probably due to a strong interaction between RhoB and the NPs. The possible mechanism was studied via recording the CL emission. It is also found that the intensity of CL gradually decreases in the presence of cyanide due to its interaction with the Au-NPs. The relation between the decreased CL intensity and cyanide concentration was exploited to develop a method for the determination of cyanide in the 0.01–0.5 μM concentration range, with a detection limit of 2.8 nM. The method was used to determine cyanide in spiked water, urine, and serum.
Alkaline permanganate-rhodamine B-SDS CL reaction is dramatically enhanced by gold nanoparticles. Based on the inhibiting effect of cyanide on this system, a sensitive CL method was developed for its determination
This review (with 129 refs.) gives an overview on how the integration of silica nanowires (NWs) into micro-scale devices has resulted, in recent years, in simple yet robust nano-instrumentation with improved performance in targeted application areas such as sensing. This has been achieved by the use of appropriate techniques such as di-electrophoresis and direct vapor-liquid-growth phenomena, to restrict the growth of NWs to site-specific locations. This also has eliminated the need for post-growth processing and enables nanostructures to be placed on pre-patterned substrates. Various kinds of NWs have been investigated to determine how their physical and chemical properties can be tuned for integration into sensing structures. NWs integrated onto interdigitated micro-electrodes have been applied to the determination of gases and biomarkers. The technique of directly growing NWs eliminates the need for their physical transfer and thus preserves their structure and performance, and further reduces the costs of fabrication. The biocompatibility of NWs also has been studied with respect to possible biological applications. This review addresses the challenges in growth and integration of NWs to understand related mechanism on biological contact or gas exposure and sensing performance for personalized health and environmental monitoring.
Silica nanowires decorated micro-electrodes for sensing application
We have prepared a surface imprinted polymer (SIP) film for label-free recognition of immunoglobulin G (IgG). The IgG-SIPs were obtained by covalent immobilization of IgG via a cleavable covalent bond and a suitable spacer unit to a gold electrode, followed by electrodepostion of a nm-thin film of polydopamine (PDA). The IgG was then removed by destruction of the cleavable bond so that complementary binding sites were created on the surface of the film. IgG-SIPs with various thicknesses of the PDA films were compared with respect to their affinity to IgG using a quartz crystal microbalance combined with flow injection analysis. The films were also characterized by cyclic voltammetry and scanning electron microscopy. The IgG-SIPs with a film thickness of around 17 nm showed the most pronounced imprinting effect (IF 1.66) and a binding constant of 296 nM.
A strategy for preparation of the IgG-Surface Imprinted Polymeric (IgG-SIP) thin films was developed. IgG was covalently immobilized via a cleavable cross-linker to a gold electrode surface followed by electrochemical deposition of a nanometer thin PDA film. After cleaving S-S bond in the linker the IgG was removed leaving behind the complementary binding sites confined in the surface of the polymer film. The prepared IgG-SIPs were applied for IgG recognition.
We have prepared a hydrophilic molecularly imprinted polymer (MIP) for the hydrophobic compound bisphenol A (BPA) in aqueous solution using 3-acrylamido-N,N,N-trimethylpropan-1-aminium chloride (AMTC) as the functional monomer. Under redox-polymerization conditions, BPA forms an ion-pair with AMTC, which was confirmed by 1H-NMR titration. The imprinting effect in aqueous solution was evaluated by comparison of this material with the corresponding non-imprinted polymer (NIP) and with a control polymer (CP) bearing no AMTC. The MIP showed the highest activity among the three polymers, and the imprinting factors as calculated from the amount of BPA bound to the MIP divided by the amounts bound to NIP and CP, respectively, are 1.8 and 6.0. The MIP was selective for BPA in aqueous solution, while structurally related compounds are not recognized. Such a selectivity for a hydrophobic compound is rarely observed in aqueous medium because non-specific binding of BPA inevitably leads to hydrophobic interaction.
We describe a simple and homogenous fluorimetric method for sensitive determination of DNA. It is based on target-triggered isothermal cycling and a cascade exponential amplification reaction that generates a large amount of a G-quadruplex. This results in strong fluorescence signal when using thioflavin T as a G-quadruplex-specific light-up fluorescent probe. Tedious handling after amplification is widely eliminated by the addition of thioflavin T. No other exogenous reagent is required. This detection platform is inexpensive and rapid, and displays high sensitivity for target DNA, with a detection limit as low as 91 pM.
The addition of target DNA can trigger the isothermal exponential amplification reaction to generate a large amount of G-quadruplex sequence oligonucleotides and then employ thioflavin T (Th T) (a G-quadruplex-specific light-up dye) as signal output for sensitive DNA detection.
Novel nanocomposites were prepared from graphene oxide (GO) and octahedral tin dioxide (SnO2) through a facile process that included synthesis of octahedral SnO2 and the reduction of GO with ascorbic acid. The morphology and structure of the nanocomposites were characterized by UV–vis spectroscopy, transmission electron microscopy, and Raman spectroscopy. The nanocomposites were placed on a glassy carbon electrode where they displayed excellent performance in terms of differential pulse voltammetric determination of dopamine (DA). This is attributed to (a) the synergetic interactions between reduced graphene oxide (r-GO) and octahedral SnO2, and (b) the presence of a large number of active sites on the nanocomposites surface. The sensor responds to DA in the concentration range of 0.08 to 30 μM, with a 6 nM detection limit if operated at 0.24 V (vs. Ag/AgCl). The modified electrode also widely suppresses the background current resulting from excess ascorbic acid and uric acids. The method was applied to the determination of DA in spiked human urine and gave satisfactory results, with recoveries in the range from 96.4 to 98.2 %.
Green and facile synthesis of reduced graphene oxide-octahedral SnO2 (r-GO-SnO2) nanocomposites for the sensitive and selective electrochemical detection of dopamine.
We present hybrid films consisting of a composite prepared from polystyrene (PS) and titanium dioxide (titania; TiO2) and molecularly imprinted with 1-pyrenebutyric acid (PBA). The interaction of PBA with the polymer is shown to occur via binding of the carboxylic group to TiO2 and hydrophobic interaction of the pyrene moiety with the PS network. We investigated the effects of the PS fraction on morphology, imprinting properties, and guest binding. The template could be completely removed by incubating the films in an acetonitrile solution of pyrene, which is due to the stronger π–π interaction between PBA and pyrene than the interaction between PBA and its binding site. A guest binding study with pyrene, 1-aminopyrene, pyrenemethanol, and anthracene-9-carboxylic acid showed that the hybrid films possessed selectivity and much higher binding capacity for PBA. This study demonstrates the first case of clear PS-assisted imprinting, where the π–π interaction of the template with a linear (non-crosslinked) polymer creates selective binding sites and enhances the binding capacity. This is a driving force for guest binding in addition to the interaction of the template/analyte with TiO2. All molecularly imprinted films displayed better binding, repeatability and reversibility compared to the respective non-imprinted films.
Illustration of the fabricated polystyrene/titania hybrids imprinted with 1-pyrenebutyric acid providing the interaction between the organic and inorganic components through the pyrene and carboxylic moieties
We describe an electrochemical sensor for nitric oxide that was obtained by modifying the surface of a nanofiber carbon paste microelectrode with a film composed of hexadecyl trimethylammonium bromide and nafion. The modified microelectrode displays excellent catalytic activity in the electrochemical oxidation of nitric oxide. The mechanism was studied by scanning electron microscopy and cyclic voltammetry. Under optimal conditions, the oxidation peak current at a working voltage of 0.75 V (vs. SCE) is related to the concentration of nitric oxide in the 2 nM to 0.2 mM range, and the detection limit is as low as 2 nM (at an S/N ratio of 3). The sensor was successfully applied to the determination of nitric oxide released from mouse hepatocytes.
NO electrochemical sensor based on CTAB-Nafion/CNFPME was fabricated through a simple method and applied to detect NO released from mouse hepatocytes successfully.
Alloy nanoparticles of the type PtxFe (where x is 1, 2 or 3) were synthesized by coreduction with sodium borohydride in the presence of carbon acting as a chemical support. The resulting nanocomposites were characterized by scanning electron microscopy and X-ray diffraction. The nanocomposite was placed on a glassy carbon electrode, and electrochemical measurements indicated an excellent catalytic activity for the oxidation of glucose even a near-neutral pH values and at a working voltage as low as 50 mV (vs. SCE). Under optimized conditions, the sensor responds to glucose in the 10.0 μM to 18.9 mM concentration range and with a 3.0 μM detection limit (at an S/N ratio of 3). Interferences by ascorbic acid, uric acid, fructose, acetamidophenol and chloride ions are negligible.
Nonenzymatic sensing of glucose is demonstrated at neutral pH values and low working potential using a glassy carbon electrode modified with platinum-iron alloy nanoparticles on a carbon support.
Magnetic nanoparticles (MNPs), prepared via thiol-ene click chemistry and containing both diol and octadecyl groups, are shown to possess both hydrophobic and hydrophilic functionalities. They display excellent dispersibility in water and also are capable of extracting non-steroidal anti-inflammatory drugs (NSAIDs) from water samples. The MNPs can be magnetically separated, and the NSAIDs eluted with acetonitrile-water (9:1, v:v) and submitted to high performance liquid chromatographic analysis. Extraction variables, such as the kind of ion-pairing reagents, amount of MNPs, pH of sample solution, extraction and desorption time, volume of desorption solvent and salt addition, were optimized. Under optimum conditions, the method has a wide analytical range (from 5 to 800 ng∙mL‾1), good reproducibility with intra-day and inter-day relative standard deviations of <19.2 % (for n = 6), and low detection limits of 0.32 to 1.44 ng∙mL‾1 for water samples. The results demonstrate that the material possesses good water compatibility, thus warranting ease of operation and good reproducibility.
The water-dispersible C18/diol-Fe3O4 MNPs were prepared via “Thiol-ene” click reaction. The material can be used as MSPE sorbent to extract non-steroidal anti-inflammatory drugs from river water. Satisfactory results were obtained with convenient operation and good reproducibility.