The replacement of antibodies by molecularly imprinted polymers (MIPs) has been investigated for many decades. However, indirect protocols (including natural primary and secondary antibodies) are still utilized to evaluate the ability of MIP thin films to recognize target molecules. MIPs can be prepared as either a thin film or as particles, and cavities that are complementary to the template can be generated on their surfaces. We have prepared thin film MIPs and particle MIPs prepared by solvent evaporation and phase inversion, respectively, from solutions of poly(ethylene-co-vinyl alcohol) (pEVAL) in the presence of the target analytes amylase, lysozyme, and lipase. These were first adsorbed on MIP thin films and by MIP particles that contain fluorescent quantum dots. Sandwich fluoroimmunoassays were then conducted to quantify them in MIP-coated 96-well microplates. The method was applied to determine amylase in saliva, and results were compared with a commercial analytical system.
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.
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 report on an ultrasensitive fluorescence immunoassay for human chorionic gonadotrophin antigen (hCG). It is based on the use of silica nanoparticles coated with a copolymer (prepared from a fluorene, a phenylenediamine, and divinylbenzene; PF@SiO2) that acts as a fluorescent label for the secondary monoclonal antibody to β-hCG antigen. In parallel, Fe3O4 nanoparticles were coated with polyaniline, and these magnetic particles (Fe3O4@PANI) served as a solid support for the primary monoclonal antibody to β-hCG antigen. The PF@SiO2 exhibited strong fluorescence and good dispersibility in water. A fluorescence sandwich immunoassay was developed that enables hCG concentrations to be determined in the 0.01–100 ng·mL−1 concentration range, with a detection limit of 3 pg·mL−1.
Fluorescence detection of prepared immune reagent nano-composites using the fluorescence cell
Hetero-dimeric magnetic nanoparticles of the type Au-Fe3O4 have been synthesised from separately prepared, differently shaped (spheres and cubes), monodisperse nanoparticles. This synthesis was achieved by the following steps: (a) Mono-functionalising each type of nanoparticles with aldehyde functional groups through a solid support approach, where nanoparticle decorated silica nanoparticles were fabricated as an intermediate step; (b) Derivatising the functional faces with complementary functionalities (e.g. amines and carboxylic acids); (c) Dimerising the two types of particles via amide bond formation. The resulting hetero-dimers were characterised by high-resolution TEM, Fourier transform IR spectroscopy and other appropriate methods.
Nano-LEGO: Assembling two types of separately prepared nanoparticles into a hetero-dimer is the first step towards complex nano-architectures. This study shows a solid support approach to combine a gold and a magnetite nanocrystal.
A molecularly imprinted polymer (MIP) for the specific retention of neopterin has been developed. A set of 6 polymers was prepared by radical polymerization under different experimental condition using methacrylic acid as functional monomer and ethylene glycol dimethacrylate as crosslinker, with the aim to understand their influence on the efficiency of the MIP. The performance of each MIP was tested in batch experiments via their binding capacity. The MIP prepared in the presence of nickel ions in dimethylsulfoxide-acetonitrile mixture (P4) exhibited the highest binding capacity for neopterin (260 μmol per gram of polymer). A selectivity study with two other pteridines demonstrated the polymer P4 also to possess the best selectivity.
A molecularly imprinted polymer for the specific retention of neopterin was developed. A set of 6 polymers was prepared under different experimental condition. The performance of each MIP was tested through their binding capacity. The MIP P4 prepared in the presence of nickel ions exhibited the highest binding capacity
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 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.
This article describes an electrochemical sensor for the dye additive Sunset Yellow (SY). It consists of a carbon paste electrode modified with nanostructured resorcinol-formaldehyde (RF) resin. The RF resin warrants strong signal enhancement and a strongly increased oxidation peak currents of SY at 0.66 V (vs. SCE). The effects of pH value, amount of RF polymer, accumulation potential and time were optimized. The sensor has a linear response to SY in the 0.3 to 125 nM concentration range, and the limit of detection is 0.09 nM after a 2-min accumulation time. The electrode was applied to the analysis of samples of wastewater and drinks, and the results are consistent with those obtained by HPLC.
Nanostructured resorcinol-formaldehyde (RF) resin was prepared and used as a material for electrochemical determination of Sunset Yellow.
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.
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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.
We describe a near-infrared (NIR) fluorescent thrombin assay using a thrombin-binding aptamer (TBA) and Zn(II)-activated CuInS2 quantum dots (Q-dots). The fluorescence of Zn(II)-activated Q-dots is quenched by the TBA via photoinduced electron transfer, but if thrombin is added, it will bind to TBA to form G-quadruplexes and the Q-dots are released. As a result, the fluorescence intensity of the system is restored. This effect was exploited to design an assay for thrombin whose calibration plot, under optimum conditions, is linear in the 0.034 to 102 nmol L−1 concentration range, with a 12 pmol L−1 detection limit. The method is fairly simple, fast, and due to its picomolar detection limits holds great potential in the diagnosis of diseases associated with coagulation abnormalities and certain kinds of cancer.
We developed a simple near-infrared fluorescence assay using thrombin binding aptamer (TBA) and Zn(II)-activated CuInS2 quantum dots for the highly selective and sensitive detection of thrombin.
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.
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.
Gold nanoclusters (AuNCs) stabilized with bovine serum albumin were utilized as a fluorescent probe for ferrous ion. The detection scheme is based on the quenching of the fluorescence of the modified AuNCs by hydroxyl radical (•OH) that is generated in the Fenton reaction between Fe(II) and H2O2. Fe(II) can be quantified in the 0.08 to 100 μM concentration range, and the limit of detection is as low as 24 nM. The method also displays good accuracy and high sensitivity when employed to the determination of Fe(II) in rat cerebrospinal fluids (CSFs). When applied to CSFs of a rat model of Alzheimer’s disease, it revealed enhanced levels of Fe(II) compared to a control, thereby showing the important physiological role of iron(II) in this disease.
BSA-stabilized gold nanoclusters (BSA-AuNCs) were utilized for the determination of ferrous ion in rat cerebrospinal fluids. The method is based on the quenching of the fluorescence by hydroxyl radical (•OH) which is generated in the Fenton reaction between Fe(II) and H2O2.
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.
Thin-layered molybdenum disulfide (MoS2) was intercalated, via ultrasonic exfoliation, into self-doped polyaniline (SPAN). This material, when placed on a glassy carbon electrode (GCE), exhibits excellent electrical conductivity and synergistic catalytic activity with respect to the detection of bisphenol A (BPA). The electrochemical response of the modified GCE to BPA was investigated by cyclic voltammetry and differential pulse voltammetry. Under optimal conditions, the oxidation peak current (measured best at 446 mV vs. SCE) is related to the concentration of BPA in the range from 1.0 nM to 1.0 μM, and the detection limit is 0.6 nM.
Thin-layered molybdenum disulfide (MoS2) was intercalated into self-doped polyaniline (SPAN) via ultrasonic exfoliation. The special conjugated structure and functional groups of MoS2-SPAN composite help to adsorb BPA easily. MoS2-SPAN has a synergistic effect for catalyzing the oxidation of BPA. The BPA electrochemical sensor based on MoS2-SPAN has a high sensitivity and low detection limit.
A one-pot route has been developed for the preparation of bovine serum albumin-templated nickel-doped bimetallic gold-nickel nanoclusters (BSA-Au-Ni NCs) at a 10:1 M ratio of the precursor salts in a BSA matrix under alkaline conditions. The metal ions are reduced to the metal alloys by BSA. The resulting NCs display strong fluorescence and dual emission with peaks at 405 and 640 nm, respectively, under excitation at 340 nm. Fluorescence is strongly enhanced on addition of Cd(II) ions, but quenched on addition of Hg(II) ions. The findings have been exploited to design a fluorometric method for the separate determination of Cd(II) and Hg(II), respectively. The optimized analytical nanosystem displays relatively good dynamics between enhancement and quenching. Cd(II) and Hg(II) can be quantified in the 0 to 200 and 0 nM to 24 μM, respectively. The limits of detection are ~1.8 nM in both cases, which indicates the highest sensitivity to Cd(II) and Hg(II) ions for a fluorescent probe. This new kind of nanocrystal probe is hardly interfered by a range of commonly encountered metal ions. Its advantages were demonstrated by determining Cd(II) and Hg(II) ions in spiked serum samples.
Dually emitting nanoclusters composed of gold-nickel alloys are shown to act as very sensitive fluorescent probes for the detection of Cd(II) and Hg(II) ions.
We describe a nanosensor for sensitive and selective detection of cyanide anions. The Ir(III) chlorine bridge complex [Ir(C^N)2-m-Cl]2 (Irpq, where pq is C^N = 2-phenyl quinoline) was doped into silica nanoparticles (SiNPs) with a typical size of about 30 nm. The intensity of the yellow emission of the doped SiNPs (under 410 nm exCitation) was strongly enhanced on addition of cyanide ions due to the replacement of chloride by cyanide. The method can detect cyanide ions in the 12.5 to 113 μM concentration range, and the limit of detection is 1.66 μM (at an S/N ratio of 3). The method is simple, sensitive and fast, and this makes it a candidate probe for the fast optical determination of cyanide.
The nanosensor is exploiting the cyanide-induced enhancement of the fluorescence of silica nanoparticles doped with an Ir(III) complex which is the result of the replacement of chloride by cyanide.
We report on the preparation of fluorescent silica nanoparticles (SiNPs) modified with chitosan and lucigenin by using a reverse microemulsion method. The introduction of chitosan to the lucigenin doped SiNPs is shown to improve the fluorescence quantum yield. The modified SiNPs were used as fluorescent markers in an aptamer-based method for selective determination of thrombin. In this protocol, thrombin was sandwiched between streptavidin-coated magnetic beads and the fluorescent SiNPs modified with a thrombin-binding aptamer. The method was successfully applied to the determination of thrombin in human serum and showed a detection limit as low as 0.02 nM. In our perception, the protocol presented here is promising in that such SiNPs may be applied to the sensitive fluorescent detection of other analytes by changing the corresponding aptamer.
The introduction of chitosan to the lucigenin doped SiNPs is shown to improve the fluorescence quantum yield. The modified SiNPs were used as fluorescent markers in an aptamer-based method for selective determination of thrombin. The effect of chitosan concentration on fluorescence intensity of lucigenin/SiO2 nanoparticles (the volume of chitosan solution is 100 μL)