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Assays for detecting tetanus toxoid are of great significance to be applied in the research of the safety testing of tetanus vaccine. Currently, guinea pigs or mice are usually used to evaluate the toxicity in these assays. Herein, a facile and quick biomineralization process was carried out to generate tetanus human immunoglobulin G (Tet-IgG)-functionalized Au nanoclusters (Tet-IgG-AuNCs). The obtained Tet-IgG-AuNCs exhibited strong red emission with a photoluminescence quantum yield of 13%. Based on surface plasmon resonance measurements, the apparent dissociation constant of the Tet-IgG-AuNC-tetanus toxoid complexes was measured to be 2.27 × 10 -8  M. A facile detection approach was developed using a fluorescent Tet-IgG-AuNC-based immunochromatography test strip. By utilizing the high-brightness fluorescent Tet-IgG-AuNCs, this immunosensor showed favorable sensitivity with a detection limit at the level of 0.03 μg/mL. Further results demonstrated that this assay can reliably detect tetanus toxoid and therefore might provide a novel method to replace animal tests for the quantification of tetanus toxicity. Moreover, the antibody-AuNC-based immunochromatography test strip platform serves as a promising candidate to develop new approaches for detecting targeted antigens and biological events of interest., (Copyright © 2021 Elsevier B.V. All rights reserved.)

This report outlines a highly sensitive and facile electrochemiluminescence (ECL) sensing platform based on a novel high-quantum-yield Au-nanocluster (AuNC) probe for glutathione (GSH) detection. Owing to the prominent quenching effect of GSH on the ECL of the AuNCs, the proposed ECL nanosensor showed a wide response to GSH in the ranges of 1.0 × 10 -9 -1.0 × 10 -5 M and 1.0 × 10 -5 -1.0 × 10 -1 M and a low detection limit of 3.2 × 10 -10 M. In addition, the proposed system exhibited good selectivity for GSH in the presence of other chemical/biological interferences. Moreover, since no further functionalization of AuNC-based sensor interface was necessary, together with the stability, high sensitivity and selectivity of the proposed nanosensor, this convenient approach was able to successfully detect GSH in both of human urine samples and blood samples with excellent recoveries, which indicated its promising application under physiological conditions. Of significant importance is that this study not only helps in gaining a better understanding of the applicability of the ECL properties of AuNCs, but also provides a new avenue for the design and development of ECL sensors based on the novel high-quantum-yield AuNC-based probe and other functional-metal-based NC probes., (Copyright © 2018 Elsevier B.V. All rights reserved.)

It is desirable but challenging to assemble various biomimetic properties into a functional catalytic cascade system. In this work, cupric oxide nanoparticles were investigated as oxidase mimics for the aerobic oxidation of cysteine to cystine with the generation of hydrogen peroxide. Coupling this property with the peroxidase-like activity of CuO nanoparticles, we constructed a self-organized cascade reaction system based on a single-component nanozyme, which includes the oxidation of cysteine to yield cystine and hydrogen peroxide and the hydrogen peroxide-mediated oxidation of terephthalic acid to produce a fluorescence change. Based on this artificial enzymatic cascade reaction system, a fluorometric assay method with a low detection limit of 6.6nM was established for cysteine determination. This platform was then applied for the detection of cysteine in pharmaceutical products and human plasma, which yielded satisfactory results. Our investigations open up a new route and holds promise for the development and applications of multifunctional nanomaterials as enzyme mimics., (Copyright © 2017 Elsevier B.V. All rights reserved.)

This paper reports a new and facile method for the synthesis of water-soluble thiolate-protected AuNCs via protein-ligand interaction. Using 3-mercaptopropionic acid (MPA) as a model ligand and bovine serum albumin (BSA) as a model protein, water-soluble AuNCs (BSA/MPA-AuNCs) with intense orange-yellow fluorescent emission (quantum yield=16%) are obtained. Results show that AuNCs produced with this method have hydrophobic interactions with BSA. The synthetic strategy is then successfully extended to produce water-soluble AuNCs protected by other thiolates. Moreover, a sensitive and eco-friendly sensing system is established for detection of the activity of inorganic pyrophosphatase (PPase), which relies on the selective coordination of Fe(3+)with BSA/MPA-AuNCs, the higher affinity between pyrophosphate (PPi) and Fe(3+), and the hydrolysis of PPi by PPase. A good linearity between the fluorescence intensity and PPase activity within the range from 0.1 to 3U/L is found, with a detection limit down to 0.07U/L. Additionally, the fluorescent assay developed here is utilized to assay the PPase activity in real biological samples and as well as to evaluate PPase inhibitor, illustrating the great potential for biological analysis., (Copyright © 2016 Elsevier B.V. All rights reserved.)

This work investigates the effect of reduction degree on graphene oxide (GO)-DNA interaction and the fluorescence quenching mechanism. Partial reduced graphene oxide (pRGO), which maintains well water-dispersibility, is synthesized using a mild reduction method by incubating GO suspension under alkaline condition at room temperature. The fluorescence quenching enhances with the restoration degree of sp(2) carbon bonds and follows the static quenching mechanism. The binding constant values imply that pRGO has much stronger affinity with ssDNA than GO. Utilizing this highly efficient nanoprobe, a universal sensing strategy is proposed for homogeneous detection of DNA. Compared with the reported GO-based DNA, this present strategy has obvious advantages such as requirement of low nanoprobe dosage, significantly reduced background, fast fluorescence quenching, and improved sensitivity. Even without any amplification process, the limit of detection can reach as low as 50 pM., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Taking advantage of "Y" junction structure and restriction endonuclease assisted cyclic enzymatic amplification, a dual-probe electrochemical DNA (DE-DNA) biosensor was designed to detect double-stranded DNA (dsDNA) of acute promyelocytic leukemia (APL) related gene. Two groups of detection probes were designed, and each group was composed of a biotinylated capture probe and an assisted probe. They were separately complementary with two strands of target dsDNA in order to prevent the reannealing of the two separate strands from target dsDNA. First, thiol functionalized capture probes (C1 and C2) were severally assembled onto two different gold electrodes, followed by hybridizing with target dsDNA (S1a-S1b) and assistant probes to form two Y-junction-structure ternary complexes. Subsequently, restriction sites on the ternary complexes were digested by Rsa I, which can release S1a, S1b and biotins from the electrode surfaces. Meanwhile, the released S1a and S1b can further hybridize with the unhybridized corresponding detection probes and then initiate another new hybridization-cleavage-separation cycle. Finally, the current signals were produced by the enzyme-catalyzed reaction of streptavidin-horse reddish peroxidase (streptavidin-HRP). The distinct difference in current signals between different sequences allowed detection of target dsDNA down to a low detection limit of 47 fM and presented excellent specificity with discriminating only a single-base mismatched dsDNA sequence. Moreover, this biosensor was also used for assay of polymerase chain reaction (PCR) samples with satisfactory results. According to the results, the power of the DE-DNA biosensor as a promising tool for the detection of APL and other diseases., (Copyright © 2015 Elsevier B.V. All rights reserved.)

In this study, a novel biomolecule immobilization approach has been proposed to the synthesis of multi-functional core-shell glucose oxidase-Au-polydopamine-Fe₃O₄ magnetic bionanoparticles (GOx-Au-PDA-Fe₃O₄ MBNPs) using the one-pot chemical polymerization method. Then, a high performance biosensor has been constructed by effectively attaching the proposed GOx-Au-PDA-Fe₃O₄ MBNPs to the surface of the magnetic glassy carbon electrode. Scanning electron microscope, energy dispersive x-ray spectrometer, UV-vis spectroscopy, and electrochemical methods were used to characterize the GOx-Au-PDA-Fe₃O₄ MBNPs. The resultant GOx-Au-PDA-Fe₃O₄ MBNPs not only have the magnetism of Fe₃O₄ nanoparticles which makes them easily manipulated by an external magnetic field, but also have the excellent biocompatibility of PDA to maintain the native structure of the GOx, and good conductivity of Au nanoparticles which can facilitate the direct electrochemistry of GOx in the biofilm. Hence, the present GOx-Au-PDA-Fe₃O₄ biofilm displays good linear amperometric response to glucose concentration ranging from 0.02 to 1.875 mM. This efficient biomolecule immobilization platform is recommended for the preparation of many other MBNPs with interesting properties and application potentials in many fields, such as biosensing, biocatalysis, biofuel cells, and bioaffinity separation., (Copyright © 2012 Elsevier B.V. All rights reserved.)

In this study, magnetic core-shell Fe(3)O(4)@Al(2)O(3) nanoparticles (NPs) attached to the surface of a magnetic glassy carbon electrode (MGCE) were used as a functional interface to immobilize several heme proteins including hemoglobin (Hb), myoglobin (Mb) and horseradish peroxidase (HRP) for fabricating protein/Fe(3)O(4)@Al(2)O(3) film. Transmission electron microscope, UV-vis spectroscopy, electrochemical impedance spectroscopy, and cyclic voltammetry were used to characterize the films. With the advantages of the magnetism and the excellent biocompatibility of the Fe(3)O(4)@Al(2)O(3) NPs, the protein/Fe(3)O(4)@Al(2)O(3) film could be easily fabricated in the present of external magnetic field, and well retained the bioactivity of the immobilized proteins, hence dramatically facilitated direct electron transfer of heme proteins and excellent electrocatalytic behaviors towards H(2)O(2) were demonstrated. The presented system avoids the complex synthesis for protecting Fe(3)O(4) NPs, supplies a facile, low cost and universal way to immobilize proteins, and is promising for construction of third-generation biosensors and other bio-magnetic induction devices., (Copyright © 2010 Elsevier B.V. All rights reserved.)

In this work, the magnetic core-shell Fe(3)O(4)@Au nanoparticles attached to the surface of a magnetic glassy carbon electrode (MGCE) were applied to the immobilization/adsorption of myoglobin (Mb) for fabricating Mb/Fe(3)O(4)@Au biofilm. The morphology, structure, and electrochemistry of the nanocomposite were characterized by transmission electron microscope, UV-vis spectroscopy, electrochemical impedance spectroscopy, and cyclic voltammetry, respectively. The resultant Fe(3)O(4)@Au NPs not only have the magnetism of Fe(3)O(4) NPs that make them easily manipulated by an external magnetic field, but also have the good conductivity and excellent biocompatibility of Au layer which can maintain the bioactivity and facilitate the direct electrochemistry of Mb in the biofilm. The modified electrode based on this Mb/Fe(3)O(4)@Au biofilm displayed good electrocatalytic activity to the reduction of H(2)O(2) with a linear range from 1.28 to 283 microM. The proposed method simplified the immobilization methodology of proteins and showed potential application for fabricating novel biosensors and bioelectronic devices., (Copyright 2009 Elsevier B.V. All rights reserved.)

A novel dopamine sensor was fabricated by forming the 6-ferrocenylhexanethiol (HS(CH(2))(6)Fc) functionalized Fe(3)O(4)@Au nanoparticles (NPs) films on the surface of a carbon paste electrode with the aid of a permanent magnet. HS(CH(2))(6)Fc, which acted as the redox mediator, was self-assembled to Fe(3)O(4)@Au NPs via Au-S bond. Transmission electron microscopy, UV-visible absorption spectroscopy, Fourier transform infrared spectra, and cyclic voltammetry were used to characterize the properties of the Fe(3)O(4)@Au NPs/HS(CH(2))(6)Fc nanocomposite. It is shown that the prepared ferrocene-functionalized Fe(3)O(4)@Au NPs composite shuttled electrons between analyte and electrode, increased the mediator loading, and more importantly prevented the leakage of the mediator during measurements, which resulted in the substantially enhanced stability and reproducibility of the modified electrode. The electrooxidation of dopamine could be catalyzed by Fc/Fc(+) couple as a mediator and had a higher electrochemical response due to the unique performance of Fe(3)O(4)@Au NPs. The nanocomposite modified electrode exhibited fast response (3 s) and the linear range was from 2.0x10(-6) to 9.2x10(-4) M with a detection limit of 0.64 microM. This immobilization approach effectively improved the stability of the electron transfer mediator and is promising for construction of other sensors and bioelectronic devices.