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A dual-mode sensing platform for Pb 2+ was constructed based on the dual optical channels of Au NPs system with the amplification of DNAzyme, and it was successfully applied for Pb 2+ determination in preserved egg with satisfactory results. The presence of Pb 2+ activated the DNAzyme and induced the dispersion change of Au NPs in high salt concentration. The sequent absorption change of Au NPs was translated to the fluorescence change of carbon dots through FRET, and the scattering change was transferred to grey value of images involving the Tyndall effect. Thus, a sensing platform based on fluorescence and colorimetric dual-technique was achieved for Pb 2+ detection, under the optimized conditions. With the assistance of DNAzyme, the linear range of fluorometric and colorimetric method were 2.0 × 10 -14  ∼ 8.0 × 10 -10 mol/L and 2.4 × 10 -13  ∼ 9.5 × 10 -9 mol/L, respectively. The dual-mode sensing platform demonstrated its promising application in the environmental monitoring and food safety field., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Herein, a novel ternary nanocomposite (AuNPs/CdS QDs/CeO 2 ) with excellent photoelectrochemical (PEC) performance was synthesized as signal probe to construct a near-zero background biosensor for sensitive miRNA-182-5p detection, by integrating with a scrollable three-dimensional (3D) DNA walker mediated cleavage cycling amplification. Impressively, the formation and rolling of scrollable 3D DNA walker triggered by target could realize dynamic, rapid and specific digestion of hairpin DNA on electrode with the aid of Exonuclease III (Exo III), which thus exposed abundant binding sites for assembling stable DNA labeled AuNPs/CdS QDs/CeO 2 nanoprobes. Thanks to the formation of type-II heterojunction (between CeO 2 and CdS QDs) and Schottky junction (generated by CeO 2 and AuNPs), an ideal photoelectric conversion efficiency accompanied with stunningly improved photocurrent was thus acquired for significantly improving the detection sensitivity. It turned out that the detection limit (LOD) of biosensor was ultralow (31 aM). Significantly, the proposed PEC biosensor would exhibit great potential for the composite as a splendid indicator and provide an avenue for constructing the sensing platform with excellent sensitivity and ultralow background., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

The poly-L-cysteine modified Au nanoparticles (Au@p-L-Cys) were constructed on electrode surface as a highly efficient chiral interface for tryptophan (Trp) enantiomers recognition via one step electropolymerization. With the aid of Cu 2+ , L-Cys residues and D-Trp target formed a sandwich complex D-Trp-Cu 2+ -L-Cys, while L-Trp was unable to form such complex due to the steric hindrance provided by the chiral interface, which was confirmed by the electrochemical and SEM results. With the introduction of ferricyanide probe, D-Trp produced significant current decrease while L-Trp produced a slight current increase, which implied the successful enantioselective recognition of Trp enantiomers (specifically D-Trp) in the true sense. This novel sensor showed a surprisingly wide linear range toward D-Trp of 6 × 10 -7  M to 1 × 10 -2  M, with a detection limit as low as 75 nM (S/N = 3). Moreover, the exclusive enantioselectivity toward D-Trp was discovered since other amino acids showed negligible interference to detection of D-Trp. The recovery of D-Trp in human serum was between 91.30 and 109.3%, which further verified the satisfying specificity and practicality of the proposed strategy. The coordination thermodynamics by UV-Vis spectroscopy and DFT simulation were also used to investigate the enantioselective mechanism. These results highlight the great potential of using Au@p-L-Cys to construct chiral interface for enantiomers recognition and hold the promise of practical application of electrochemical chiral sensors in fields like pharmaceutics and bioanalysis., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

This work initially reports a new nanosening method for simple, sensitive, specific, visual detection of mercury (II) (Hg 2+ ) and glutathione (GSH) using the Tyndall Effect (TE) of the same colloidal gold nanoparticle (GNP) probes for efficient colorimetric signaling amplification. For the TE-inspired assay (TEA) method, arginine (Arg) molecules are pre-modified on the GNPs' surfaces (Arg-GNPs). Upon the Hg 2+ introduction, it can be specifically coordinated with the terminal -NH 2 and -COOH groups of the Arg molecules to make the Arg-GNPs aggregate, producing a significantly-enhanced TE signal in the reaction solution after its irradiation by a 635-nm red laser pointer pen. On the other hand, the introduction of the GSH results in the production of the original Arg-GNPs' weak TE response, as it is able to bind such metal ion via mercury-thiol reactions to inhibit the above aggregation. Under the optimal conditions, the utility of the new TEA method is well demonstrated to quantitatively detect the Hg 2+ and GSH with the aid of a smartphone as a portable TE reader during the linear concentration ranges of 50-3000 and 10-3000 nM, respectively. The detection limits for the Hg 2+ and GSH are estimated to be as low as ∼3.5 and ∼0.3 nM, respectively. The recovery results obtained from the detection of Hg 2+ in the complex tap and pond water samples and the assay of GSH in real human serum and urine samples are also satisfactory., (Copyright © 2021 Elsevier B.V. All rights reserved.)

In this work, a "signal-off" electrochemical biosensor was established for sensitive detection of adenosine triphosphate (ATP) based on Fe 3 O 4 @covalent organic framework-immobilized gold nanoparticles (Fe 3 O 4 @COF-Au NPs) porous composite material as a nanocarrier. The proposed Fe 3 O 4 @COF-Au NPs could effectively confine Au NPs in the uniform channels of the Fe 3 O 4 @COF, which successfully avoided Au NPs aggregation to a certain extent and provided a comparatively independent and stable micro-environment via its hydrophobic porous nanochannels, thereby owning excellent electro-catalytic performance for the reduction of 4-nitrophenol. Moreover, the Fe 3 O 4 @COF-Au NPs nanomaterials were served as functional platform for immobilizing DNA substrate (S0), which was used to bind with the conversion product (S1) of the target ATP for subsequent branched hybridization chain reaction (b-HCR) to form dendritic DNA strands to hinder electron transfer between Fe 3 O 4 @COF-Au NPs and 4-nitrophenol, finally achieving sensitive detection of ATP with a wide linear range of 5 pM-50 μM and a low detection limit of 1.6 pM. Such strategy provides a multifunctional immobilized platform for the sensitive detection of ATP and a versatile strategy for monitoring other biomolecules., (Copyright © 2021 Elsevier B.V. All rights reserved.)

This work reports a new methodology for naked-eye nanosensing of Hg 2+ where the Tyndall effect of gold nanoparticles (GNPs) acts as a light scattering signalling readout. Its utility is demonstrated with ultrasensitive detection of the target with a limit down to 0.13 nM (∼5461-fold sensitivity improvement over conventional GNP-based methods with surface plasmon resonance signalling).

Herein, a novel electrochemical biosensor was constructed for the highly efficient detection of silver ions. A porous platform constructed with functionalized gold nanoparticles (AuPP) was electropolymerized on the gold electrode surface. The obtained polymer, analogous to a metal-organic framework, was used as the sensing platform together with cytosine-Ag + -cytosine interaction for dual signal amplification. The scanning electron microscopy (SEM) image of the AuPP platform exhibited a porous structure and considerable binding sites for C-riched single stranded DNA, leading to predictable silver ion preconcentration. Based on this strategy, the biosensor showed that the peak current in differential pulse voltammetry rose linearly as the concentration of silver ion increased from 0.005 to 3 μM with a detection limit of 1.3 nM. In addition, in the presence of other metal ions, such as Pb 2+ , Mn 2+ , Ni 2+ , Co 2+ , Cu 2+ , Zn 2+ , Na + , Ca 2+ , and Cd 2+ , at the same concentration, the current signal remained almost unchanged, manifesting high selectivity for Ag + . This proposed sensor might exhibit a novel fabrication method for metal ion detection with the aid of multiple AuPP materials by designing ligands with different functional groups.

A superior electrochemical biosensor was designed for the determination of UO 2 2+ in aqueous solution by integration of DNAzyme and DNA-modified gold nanoparticle (DNA-AuNP) network structure. Key features of this method include UO 2 2+ inducing the cleavage of the DNAzyme and signal amplification of DNA-AuNP network structure. In this electrochemical method, the DNA-AuNP network structure can be effectively modified on the surface of gold electrode and then employed as an ideal signal amplification unit to generate amplified electrochemical response by inserting a large amount of electrochemically active indicator methylene blue (MB). In the presence of UO 2 2+ , the specific sites on DNA-AuNP network structure can be cleaved by UO 2 2+ , releasing the DNA-AuNP network structure with detectable reduction of electrochemical response intensity. The electrochemical response intensity is related to the concentration of UO 2 2+ . The logarithm of electrochemical response intensity and UO 2 2+ concentration showed a wide linear range of 10~100 pM, and the detection limit reached 8.1 pM (S/N = 3). This method is successfully used for determination of UO 2 2+ in water samples. Graphical abstract Fabricated DNAzyme network structure for enhanced electrical signal. Numerical experiments show that the current signal decreases as the concentration of UO 2 2+ increases. It can be seen that the biosensors could be used to detect UO 2 2+ in aqueous solution effectively.

Herein, gold nanoparticles (Au NPs) in solution protected by various concentration of DNA at different aggregation states were found to have different quenching effect to the fluorescence of carbon dots (CDs). Au NPs wrapped up in more amount of DNA were able to quench the fluorescence of CDs more effectively, and vice versa. Based on this phenomenon, a facile and novel fluorescence sensing platform without labeling was constructed by designing the sequence of DNA as the aptamer of the detection target. With the addition of specific molecule, taking acetamiprid as representative, DNA was prior to bind with target and the Au NPs became less protected, leading to the fluorescence recovery of the CDs. Experimental results showed that the fluorescence of CDs was linearly recovered by acetamiprid in the concentration range of 7.8 × 10 -9 -1.4 × 10 -6  mol/L, with the detection limit of 1.5 × 10 -9  mol/L. This promising sensor might provide a new aspect for exploring the versatile application of CDs in various fields., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Herein, a novel signal-off photoelectrochemical (PEC) aptasensor was proposed for sensitive detection of thrombin on the basis of C 60 @C 3 N 4 nanocomposites as quencher and Au nanoparticles (depAu) decorated perylene tetracarboxylic acid (PTCA) as sensing platform. Owing to the excellent membrane-forming of PTCA and superior conductivity of depAu, the PTCA between two depAu layers can simply and effectively produce an extremely high initial photocurrent to afford a precondition for sensitive biodetection. Thereafter, the assembly of C 60 @C 3 N 4 nanocomposites on electrode via typical sandwich reaction enabled the generation of a significantly decreased photocurrent. Here, the C 3 N 4 with high surface area not only provided massive binding sites for C 60 immobilization, but also partly competed with PTCA in light absorption for producing a significantly smaller photocurrent in the presence of electron donor ascorbic acid (AA). Additionally, both the C 3 N 4 and C 60 have the poor conductivity, which could inhibit the electron transfer to achieve a further decreased photocurrent, effectively improving the sensitivity of proposed biosensor. As a result, the PEC biosensor in a "signal-off" mode showed an extremely low detection limit down to 1.5 fM, providing a sensitive and universal strategy for protein detection., (Copyright © 2019 Elsevier B.V. All rights reserved.)

In this work, a new label-free biosensor based on highly effective decomposition of a branched DNA polymer and target-transition recycling amplification was designed for ultrasensitive electrochemical determination of lead ion (Pb 2+ ). The branched DNA polymer formed by hybridization chain reaction (HCR) was first immobilized on electrode and served as the carrier for loading abundant silver nanoparticle (AgNPs) to generate an extremely high initial current signal output. Then, the molecular triggers T 1 and T 2 , which were produced through a target-transition recycling amplification, could respectively disassemble the backbone and side chain of the branched DNA polymer with remarkably decreased current for sensitive detection of Pb 2+ . Compared with traditional one-trigger induced disassembly strategy, the proposed approach exhibited higher decomposition efficiency. The experimental data showed that this developed biosensor had a superior performance for Pb 2+ detection with a low detection limit down to 0.24 pM. Furthermore, the established strategy set up a new way to achieve the ultrasensitive detection of other metal ions., (Copyright © 2018 Elsevier B.V. All rights reserved.)

In this work, a label-free electrochemical biosensor was developed for sensitive and selective detection of mercury (II) ions (Hg(2+)) based on in-situ deposition of silver nanoparticles (AgNPs) on terminal deoxynucleotidyl transferase (TdT) extended ssDNA for signal output and nicking endonuclease for cycling amplification. In the presence of target Hg(2+), the T-rich DNA (HP1) could partly fold into duplex-like structure (termed as output DNA) via T-Hg(2+)-T base pairs and thus exposed its sticky end. The sticky end of output DNA could then hybridize with 3'-PO4 terminated capture DNA (HP2) on electrode surface to form output DNA-HP2 hybridization complex with the sequence 5'-CCTCAGC-3'/3'-GGAGTCG-5' (the sequence could be recognized by nicking endonuclease Nt. BbvCI). With the introduction of Nt. BbvCI, output DNA existed in hybridization complex was released from electrode and participated in the next hybridization process, accompanying with the cleave of HP2 to expose substantial 3'-OH group, which could be extended into a long ssDNA nanotail with the aid of TdT and deoxyadenosine triphosphate (dATP). Since the long negatively charged ssDNA nanotail absorbed the positively charged silver ions on the DNA skeleton, the metallic silver could be in-situ deposited on electrode surface for electrochemical signal output upon addition of reduction regent sodium borohydride. Under optimal conditions, the developed electrochemical biosensor presented a good response to Hg(2+) with a detection limit of 3 pM (S/N=3). Furthermore, the biosensor exhibited good reproducibility and high selectivity towards other interfering ions. The proposed sensing system also showed a promising potential application in real sample analysis., (Copyright © 2016 Elsevier B.V. All rights reserved.)

In this work, N-(aminobutyl)-N-(ethylisoluminol) (ABEI), an analogue of luminol, is served as both the reductant and luminescence reagent to synthesize ABEI capped Pd@Au core-shell nanoparticles (ABEI-Pd@AuNPs). The nanoparticles not only exhibit inherent electrochemiluminescence (ECL) property, but also possess advantages of noble-metal nanomaterials such as outstanding electronic property, high specific surface area and good biocompatibility. In order to enhance the luminescence efficiency, ferrocene monocarboxylic acid (Fc) as catalyzer is grafted on the surface of ABEI-Pd@AuNPs with the aid of l-cysteine (l-Cys). When the Fc is electrochemically oxidized to ferricinium cation species (Fc(+)), the decomposition of H2O2 which existed in detection solution can be catalyzed by Fc(+) to generate oxygen-related free radicals, resulting effective signal amplification for ABEI-H2O2 system. For potential applications, the Pd@Au core-shell nanoparticles bifunctionalized by ABEI and catalyzer are employed as nano-carriers to immobilize detection antibody (Ab2). Based on sandwiched immunoreactions, a "signal-on" ECL immunosensor is developed for detection of human collagen type IV (Col IV), a potential biomarker associated with diabetic nephropathy. Consequently, the proposed immunosensor provides a wide linear detection ranging from 1pgmL(-1) to 10ngmL(-1) with a relatively low detection limit of 0.3pgmL(-1) (S/N=3)., (Copyright © 2016 Elsevier B.V. All rights reserved.)

We successfully applied the novel l-cysteine (RSH) induced manganese porphyrin (MnTPP) electrocatalytic amplification in electrochemical aptasensor for detection of thrombin (TB) with the 3D DNA-Au@Pt nanoparticles (DNA-Au@Pt NPs) as nanocarrier. A further discussion for the suggested mechanism of the reaction involved the MnTPP-catalyzed oxidation of thiols (RSH) to disulfides l-cystine (RSSR) was also discussed in detail in this work. In comparison with traditional H2O2 mediated MnTPP electrocatalytic amplification, the novel reaction with more stable catalytic substrate RSH possessed high catalytic amplification efficiency. In addition, the 3D DNA-Au@Pt NPs could provide abundant binding sites for immobilizing signal tags and enzymes. As a result, the electrochemical signal can be greatly enhanced by the RSH mediated MnTPP electrocatalytic reaction and 3D DNA-Au@Pt NPs. Under optimal conditions, the proposed aptasensor exhibited a wider linear range of 0.1 pM-100 nM with a more sensitive detection limit of 29 fM for TB detection., (Copyright © 2015 Elsevier B.V. All rights reserved.)

A new type of multifunctional metal-organic framework (MOF) has been synthesized by encapsulating hemin into the nano-sized Fe-MIL-88 MOFs (hemin@MOFs) and first applied in an electrochemical aptasensor to detect thrombin (TB) with the aid of an enzyme for signal amplification. The gold nanoparticle functionalized hemin@MOFs (Au/hemin@MOFs) have not only simultaneously served as redox mediators and solid electrocatalysts, but have also been utilized as an ideal loading platform to immobilize a large number of biomolecules. In this aptasensor, Au/hemin@MOFs conjugated with glucose oxidase (GOD) and thrombin binding aptamer (TBA II) were used as the secondary aptamer bioconjugates (Au/hemin@MOF-TBA II-GOD bioconjugates), and TB was sandwiched between Au/hemin@MOF-TBA II-GOD bioconjugates and the amino-terminated TBA I which was self-assembled on the gold nanoparticle (AuNP) modified electrode. The GOD could oxidize glucose into gluconic acid accompanied by the generation of H2O2. The generated H2O2 on the electrode surface was further electrocatalyzed by hemin@MOFs to amplify the electrochemical signal of hemin contained in hemin@MOFs. Therefore, the synthesized hemin@MOFs represented a new paradigm for multifunctional materials since it combined three different functions including serving as catalysts, redox mediators and loading platforms within a single material. With such an ingenious design, a wide linear range of 0.0001 nM to 30 nM was acquired with a relatively low detection limit of 0.068 pM for TB detection.

In this work, a new "signal-on" electrochemical biosensor for sensitive detection of prostate-specific antigen (PSA) was developed on the basis of target protein induced cleavage of a specific peptide with positively charged gold nanoparticles (AuNPs) as signal enhancer.

In this work, a sensitive electrochemical aptasensor for thrombin (TB) based on synergetic catalysis of enzyme and porous Au@Pd core-shell nanostructure has been constructed. With the advantages of large surface area and outstanding catalytic performance, porous Au@Pd core-shell nanostructures were firstly employed as the nanocarrier for the immobilization of electroactive toluidine blue (Tb), hemin/G-quadruplex formed by intercalating hemin into the TB aptamer (TBA) and glucose oxidase (GOx). As a certain amount of glucose was added into the detection cell, GOx rapidly catalyzed the oxidation of glucose, coupling with the local generation of H2O2 in the presence of dissolved O2. Then, porous Au@Pd nanoparticles and hemin/G-quadruplex as the peroxidase mimics efficiently catalyzed the reduction of H2O2, amplifying the electrochemical signal and improving the sensitivity. Finally, a detection limit of 0.037pM for TB was achieved. The excellent performance of the aptasensor indicated its promising prospect as a valuable tool in simple and cost-effective TB detection in clinical application., (Copyright © 2014 Elsevier B.V. All rights reserved.)

This work described a pseudobienzyme electrocatalytically amplified immunosensor for sensing the spore wall protein of Nosema bombycis by adopting L-cysteine as the electrocatalytic substance to generate H2O2in situ with the aid of hemin/G-quadruplex concatemers loaded onto C60@Pt-Pd. The hemin/G-quadruplex here is also acting as the probe for electrochemical signal output.

In this work, we present a new strategy to construct an electrochemical aptasensor for sensitive detection of platelet-derived growth factor BB (PDGF-BB) based on the synergetic amplification of a three-dimensional (3D) nanoscale catalase (CAT) enzyme-functional DNA-platinum nanoparticles (PtNPs) dendrimer through autonomous layer-by-layer assembly. Firstly, polyamidoaminedendrimer (PAMAM) with a hyper-branched and three-dimensional structure was served as nanocarriers to coimmobilize a large number of PDGF-BB binding aptamer (PBA II) and ssDNA 1 (S1) to form PBA II-PAMAM-S1 bioconjugate. In the presence of PDGF-BB, the bioconjugate was self-assembled on the electrode by sandwich assay. Following that, the carried S1 propagated a chain reaction of hybridization events between CAT-PtNPs-S1 and CAT-PtNPs-ssDNA 2 (S2) to form a 3D nanoscale CAT-functional PtNPs-DNA dendrimer, which successfully immobilized substantial CAT enzyme and PtNPs with superior catalysis activity. In this process, the formed negatively charged double-helix DNA could cause the intercalation of hexaammineruthenium(III) chloride (RuHex) into the groove via electrostatic interactions. Thus, numerous RuHex redox probes and CAT were decorated inside/outside of the dendrimer. In the presence of H2O2 in electrolytic cell, the synergistic reaction of CAT and PtNPs towards electrocatalysis could further amplify electrochemical signal. Under optimal condition, the CAT-PtNPs-DNA dendrimer-based sensing system presented a linear dependence between the reduction peak currents and logarithm of PDGF-BB concentrations in the range of 0.00005-35 nM with a relatively low detection limit of 0.02 pM., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Copper nanoclusters (Cu NCs) are found to possess intrinsic peroxidase-like activity for the first time. Similar to nature peroxidase, they can catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine by H(2)O(2) to produce a nice blue color reaction. Compared with horseradish peroxidase, Cu NCs exhibits higher activity near neutral pH, which is beneficial for biological applications. The increase in absorbance caused by the Cu NCs catalytic reaction allows the detection of H(2)O(2) in the range of 10 μM to 1 mM with a detection limit of 10 μM. A colorimetric method for glucose detection was also developed by combining the Cu NCs catalytic reaction and the enzymatic oxidation of glucose with glucose oxidase. Taking into account the advantages of ultra-small size, good stability, and high biocompatibility in aqueous solutions, Cu NCs are expected to have potential applications in biotechnology and clinical diagnosis as enzymatic mimics., (Copyright © 2012 Elsevier B.V. All rights reserved.)

In this work, an advanced sandwich-type electrochemical aptasensor for thrombin was proposed by integrating hemin/G-quadruplex with functionalized graphene-Pd nanoparticles composites (PdNPs-RGs). The hemin/G-quadruplex formed by intercalating hemin into thrombin binding aptamer (TBA), firstly acted as a NADH oxidase, assisting the oxidation of NADH to NAD(+) accompanying with the generation of H(2)O(2) in the presence of dissolved O(2). Subsequently, the hemin/G-quadruplex acted as HRP-mimicking DNAzyme that rapidly bioelectrocatalyze the reduction of the produced H(2)O(2). At the same time, the Pd nanoparticles supported on p-iodoaniline functionalized graphene were also adopted to catalyze the reduction of H(2)O(2). Thus, with the dual catalysis, a dramatically amplified electrochemical signal could be obtained. Besides, the avidin-biotin system for binding aptamer sequences on electrodes not only improved the sensitivity of thrombin analysis but also obtained an acceptable repeatability of the aptasensor. With several factors mentioned above, a wide linear ranged from 0.1 pM to 50 nM was acquired with a relatively low detection limit of 0.03 pM (defined as S/N=3). These excellent performances provided our approach a promising way for ultrasensitive assay in electrochemical aptasensors., (Copyright © 2012 Elsevier B.V. All rights reserved.)

In the present study, toluidine blue-graphene (Tb-Gra) nanocomposites were prepared to design a Lable-free electrochemical aptasensor for highly sensitive detection of thrombin based on layer-by-layer (LBL) technology. The nanocomposites with excellent redox electrochemical activities were first immobilized on the gold nanoparticles (nano-Au) modified glassy carbon electrodes (GCE). Then, the LBL structure was performed by electrostatic adsorption between the positively charged Tb-Gra and negatively charged nano-Au, which formed {Tb-Gra/nano-Au}(n) multilayer films for electroactive species enrichment and biomolecule immobilization. Subsequently, the thiolated thrombin binding aptamer (TBA) was assembled on the nano-Au surface through Au-S bond. In the presence of target thrombin (TB), the TBA on the multilayer could catch the thrombin onto the electrode surface, which resulted in a barrier for electro-transfer, leading to the decrease of the electrochemical signal of Tb-Gra nanocomposites. Under the optimal conditions, a wide detection range from 0.001 nM to 80 nM and a low detection limit of 0.33 pM (defined as S/N=3) for thrombin were obtained. In addition, the sensor exhibited excellent selectivity against other proteins., (Copyright © 2012 Elsevier B.V. All rights reserved.)

A novel tracer, platinum-gold alloy nanoparticles (Pt-AuNPs) and horseradish peroxidase (HRP) functionalized single-walled carbon nanotubes (SWCNTs) composite, is employed to label the secondary thrombin aptamer for constructing an ultrasensitive electrochemical aptasensor. Thionine, immobilized on functionalized SWCNTs, provides a pair of distinguished redox peak for electrochemical detection. Both the high-content Pt-AuNPs and HRP on SWCNTs amplify the electrochemical signal of thionine through electrocatalytic reduction of H(2)O(2). Differential pulse voltammetry (DPV) is employed to detect thrombin with different concentrations. The reduction peak current is logarithmically related to the concentration of thrombin in an extremely wide range from 10 fM to 5 nM with a detection limit of 3.6 fM. The dual signal amplification of Pt-AuNPs and HRP functionalized nanocomposite provides a promising way for ultrasensitive assay in electrochemical aptasensors., (Copyright © 2011 Elsevier B.V. All rights reserved.)

In this work, a new signal amplification strategy based on hollow PtCo nanochains (HPtCoNCs) functionalized by bi-enzyme-horseradish peroxidase mimicking DNAzyme (HRP-DNAzyme) and glucose oxidase (GOD), as well as ferrocene-labeled secondary thrombin aptamer (Fc-TBA 2), is developed to construct a highly sensitive electrochemical aptasensor. The HRP-DNAzyme contains a special G-quadruplex structure with an intercalated hemin. With the surface area enlarged by HPtCoNCs, the amount of immobilized Fc-TBA 2, hemin and GOD can be enhanced. Under the enzyme catalysis of GOD, d-glucose is rapidly oxidized into gluconic acid accompanying with the generation of H₂O₂, which is further electrocatalyzed by Pt nanoparticles and HPR-DNAzyme to improve the electrochemical signal of Fc. With several amplification factors mentioned above, a wide linear ranged from 0.001 to 30 nM is acquired with a relatively low detection limit of 0.39 pM for thrombin. The present work demonstrates that using HPtCoNCs as labels is a promising way to amplify the analysis signal and improve the sensitivity of aptasensors., (Copyright © 2011 Elsevier B.V. All rights reserved.)

In this work, a label-free electrochemical aptamer-based sensor (aptasensor) was constructed on account of the direct immobilization of redox probes on an electrode surface. For this proposed aptasensor, a gold nanoparticles (AuNPs)-coated electrode was firstly modified with redox probes-nickel hexacyanoferrates nanoparticles (NiHCFNPs) through chemisorption and electrostatic adsorption. Then, platinum-gold alloy nanoparticles (Pt-AuNPs) and horseradish peroxidase (HRP) were respectively assembled onto the modified electrode surface, which formed the multilayer films for amplifying the electrochemical signal of NiHCFNPs and immobilizing thiolated thrombin aptamers (TBAs). In the presence of target thrombin, the TBA on the multilayer could catch the thrombin onto the electrode surface, which resulted in a barrier for electro-transfer, leading to the decrease of the electrochemical signal of NiHCFNPs amplified by the Pt-AuNPs and HRP toward H(2)O(2). The proposed method avoided the redox probes labeling process, increased the amount of redox probes, and further amplified the electrochemical signal. Thus, the approach showed a high sensitivity and a wider linearity to thrombin in the range between 0.01 nM and 50 nM with a detection limit of 6.3 pM.

A simple and sensitive sandwich-type electrochemiluminescence immunosensor for alpha-1-fetoprotein (AFP) on a gold nanoparticles (nano-Au) modified glassy carbon electrode (GCE) was developed by using Ru-silica (Ru(bpy)(3)(2+)-doped silica) doped Au (Ru-silica@Au) composite as labels. The primary antibody, anti-AFP was first immobilized on the gold nanoparticles modified electrode due to the covalent conjugation, then the antigen and the Ru-silica@Au composite nanoparticles labeled secondary antibody was conjugated successively to form a sandwich-type immunocomplex through the specific interaction. The surfaces of Ru-silica nanoparticles were modified via the assemble of Au nanoparticles. The prepared Ru-silica@Au composite nanoparticles own the large surface area, good biocompatibility and highly effective electrochemiluminescence properties. The morphologies of the Ru-silica@Au composite nanoparticles were investigated by using transmission electronic microscope (TEM). The Ru-silica@Au composite nanoparticles labeled anti-AFP/AFP/bovine serum albumin (BSA)/anti-AFP/nano-Au modified GCE electrode was evaluated by means of cyclic voltammetry (CV) and electrogenerated chemiluminescence (ECL). The immunosensor performed high sensitivity and wide liner for detection AFP in the range of 0.05-50 ng/mL and the limit detection was 0.03 ng/mL (defined as S/N=3)., (Copyright (c) 2010 Elsevier B.V. All rights reserved.)

We have prepared a series of TiO2 nanoparticles for antibacterial applications. These TiO2 nanoparticles were prepared by the hydrolysis precipitation method with Ti(OBu)4, silver nitrate and ammonia. Crystal structure, particle size, interfacial structure and UV-visible light response of the prepared nanoparticles were characterized by X-ray diffraction measurements (XRD), Transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR) and UV-Vis diffuse reflectance spectroscopy (UV-Vis-DRs). The XRD spectra showed that all samples were anatase structure calcined at 450 degrees C for 3 hours. The Ag doping made the peak of diffraction wider. The results of TEM showed that the nanoparticles of TiO2, N-TiO2 and 1% Ag-N-TiO2 were all spherical in shape and well distributed with a mean size of 19.8 nm, 39.2 nm and 20.7 nm, respectively. N doping caused the nanoparticle size to increase, while, when the doped amount of Ag+ increased, the TiO2 particle size decreased. The FTIR revealed that Ag and N doping of TiO2 appeared to have strong absorption by -OH group and showed the characteristic absorption band of NH4+ and Ag. The UV-Vis-DRs indicated that the absorption band of Ag-N co-doped TiO2 had red shift and that the optical absorption response (between 400 nm and 700 nm) had obvious enhancement. The antibacterial properties of nanoparticles were investigated by agar diffusion method toward Escherichia coli and Bacillus subtilis. The results indicated that both Ag- and N-doped TiO2 could increase the antibacterial properties of TiO2 nanoparticles under fluorescent light irradiation. A 1% Ag-N-TiO2 had the highest antibacterial activity with a clear antibacterial circle of 33.0 mm toward Escherichia coli and 22.8 mm toward Bacillus subtilis after cultivation for 24 hours.

[Display omitted] • A new class of colorimetric pesticide nanosensor was initially developed. • The glyphosate (model analyte) triggers anti-aggregation/anti-autocatalysis of Au and Cu nanoparticles leading to a regulatable Tyndall-effect (TE) signal. • A detection limit down to 117 nM was achieved via portable smartphone readout. • This is the first report of TE-based sensor with two sorts of colloidal nanoparticles. This work initially describes a new class of pesticide nanosensor for highly sensitive, equipment-free detection of glyphosate as a model analyte by using Tyndall effect (TE) for colorimetric signaling. In the absence of analyte, o -phenylenediamine (OPD) can be oxidized by bivalent copper (Cu2+) ions into 2, 3-diaminophenazine (OPDox), from which copper nanoparticles (CuNPs) are also formed to further act as nanocatalysts for catalyzing the above redox reactions. The resultant large number of positively-charged OPDox products can make citrate-capped gold NPs (AuNPs) aggregate via N–Au chemistry and electrostatic forces. With a 635-nm laser pointer pen, both the CuNPs and aggregated AuNPs can efficiently scatter its red light beam, leading to a significantly-enhanced TE response (compared with the dispersed AuNPs). For the glyphosate sample, however, only a weak TE signal can be recorded, because the analyte can chelate with the Cu2+ ions to inhibit the OPDox production, the generation/antocatalysis of CuNPs, and the OPDox-induced AuNPs' aggregation. The glyphosate level is inversely proportional to the TE signal which can be measured by a smartphone for quantitative analysis. The results show that the developed nanosensor enables instrument-free detection of glyphosate with a limit down to 117 nM. To the best of our knowledge, this may be the first report of designing enhanced TE-based colorimetric nanosensors with two types of colloidal nanoparticles for potential on-site detection of pesticide residue in various fields like food safety and environmental monitoring. [ABSTRACT FROM AUTHOR]