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Abstract: A novel nanocomposites film of conducting polymers including single-walled carbon nanotubes (SWCNTs), polypyrrole (PPy) and gold nanoparticles (AuNPs) modified electrode has been applied in voltammetric sensors to detect epinephrine (EP) sensitively when ascorbic acids (AA) and uric acids (UA) exist. The nanocomposites film of conducting polymers which show an excellent electrocatalystic activity for the oxidation of EP and UA was characterized by scanning electron microscopy (SEM) and electrochemical methods. The catalytic peak currents obtained from differential pulse voltammetry (DPV) increased linearly with increasing EP concentrations in the range of 4.0×10−9–1.0×10−7 M with a detection limit of 2.0×10−9 M (S/N=3), respectively. The results showed that the nanocomposites of conducting polymers can selectively determine EP in the coexistence of a large amount of UA and AA. In addition, the sensor exhibited excellent sensitivity, selectivity and stability. The PPy/AuNPs/SWCNTs nanocomposites film can also be satisfactorily used for detecting EP in epinephrine hydrochloride injection when contain AA and UA, which also shows good recovery for determination of EP in some biological fluids. [Copyright &y& Elsevier]

Abstract: Multilayers film of nanostructured gold nanoparticles (AuNPs) has been fabricated based on the layer-by-layer (LBL) technique using a self-assembled monolayer of 5,15-di-[p-(6-mercaptohexyl)-phenyl]-10,20-diphenylporphyrin (trans-PPS2). AuNPs act as physical cross-link points in the multilayers. Electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM) are applied to study the formation of the organic–inorganic multilayers film and have determined the electrochemical parameters, i.e., the heterogeneous electron transfer rate constant (K et). The observed phenomena indicate that the electron transfer (ET) process is affected by material properties and the molecular structure of self-assembled monolayers (SAMs). Using the high sensitivity of ET of ferricyanide to the modification of the gold surface with multilayers film, we select this reaction as a probe to study the different modification stages at this modified electrode. ET is retarded on the trans-PPS2 alternative deposition of layers on the electrode surface and is accelerated on the AuNPs’ layers. SECM images are used to collect surface information in the course of the successive modification process. SECM images obtained from bare and different modification stages show very high resolution with different topographies. [Copyright &y& Elsevier]

A rapid and highly selective naked-eye detection of hydrochloric acid (HCl) in an aqueous medium was established using HCl-triggered redispersion of gold nanoparticle aggregates. [ABSTRACT FROM AUTHOR]

The rapid and sensitive surface-enhanced Raman scattering (SERS) detection of molecular biomarkers from real samples is still a challenge because the intrinsically trace analytes may have a low molecular affinity for metal surfaces. Herein, we develop a smart signal conversion and amplification strategy based on silver–gold–silica core-satellite structure nanoparticles (Ag@Au@SiO2 NPs) to sensitively detect low adsorptive vitamin E using SERS, which has been considered a biomarker of neuromuscular disorders when its abnormal content is measured in the serum of patients. Through the reducibility of vitamin E, Ag+ ions are rapidly reduced to Ag atoms, resulting in the epitaxial growth of Ag nanocrystals on gold nanoparticles forming satellite particle–particle gap-narrowed Ag@Au@SiO2 NPs. The generated strong plasmonic field dramatically enhances the Raman signal of the Raman reporter molecule 4-aminothiophenol (4-ATP) and the detected vitamin E molecules at an estimated level of 58.19 nmol L−1. The sensitivity of this operational SERS strategy provides tremendous prospects for the screening of neuromuscular disorders. [ABSTRACT FROM AUTHOR]

A novel Hg2+-responsive thermometer system for translating mercury detection into temperature monitoring was developed based on an aggregation-activated oxidase-like activity of gold nanoparticles. [ABSTRACT FROM AUTHOR]

Developing a rapid, low-cost, and multimode detection method for heavy metal ions remains a compelling goal for many applications, including food safety, environmental and biological analysis. This study investigated the influence of Hg2+ on the peroxidase-like activity of gold nanoparticles (GNPs) decorated on carbon dots (CDs) from lysine (denoted as GNP@CDs). A new type of Hg2+-triggered peroxidase-like activity of GNP@CDs was discovered, which could catalyze the oxidation of the colorless 3,3′,5,5′-tetramethylbenzidine (TMB) into blue TMB. Based on the regulation of the catalytically triggered activity, a sensitive colorimetric method for the detection of Hg2+ was developed, with a linear range of 7–150 nM, providing a limit of detection as low as 3.7 nM. The sensor is simple and rapid, and was successfully applied to the detection of Hg2+ enrichment in chlorella, suggesting a promising application in biological analysis. [ABSTRACT FROM AUTHOR]

Advanced oxidation processes (AOPs) have recently proposed for advancing colorimetric sensing applications, owing to their excellent performance of sensitive color readout that generated from the oxidation of chromogenic substrates like 3,3′,5,5′-tetramethylbenzidine (TMB) by reactive oxygen species (ROS) of AOPs such as ·OH and ·O 2 − radicals. However, the efficiency of ROS generation and the related H 2 O 2 decomposition in most AOPs is quite low especially at neutral pH, which greatly hampered the practical sensing applications of the AOPs. We herein communicated that β -cyclodextrin (β -CD)-capped gold nanoparticles (β -CD@AuNPs) can promote catalysis at neutral pH for AOP as an excellent co-catalyst. In this strategy, inorganic pyrophosphate (PPi) ions was first used to coordinate with Cu2+ and form Cu2+-PPi complex. In the presence of hydrogen peroxide, target inorganic pyrophosphatase (PPase) can hydrolyze PPi into inorganic phosphate (Pi) and release free Cu2+ simultaneously, resulting in a Cu2+-triggered Fenton-like AOP reaction. The introduced β -CD@AuNPs acts as a co-catalyst, analogous to mediators in the most co-catalyzed system, to enhance the rate-limiting step of Cu2+/Cu+ conversion in Cu2+/H 2 O 2 Fenton-like AOP and resulting in an efficient generation of ·OH and ·O 2 − radicals, which further producing an intense blue color by oxidizing TMB into its oxidation product (TMBox) within a short time. Finally, this reaction system was used to simply detecting target PPase with the colorimetric and photothermal readout based on the in-situ generated TMBox indicator. More significantly, we successfully demonstrated nanozyme can serve as a co-catalyst to promote the AOP catalysis at neutral pH, and inspire other strategies to overcome the pH limitation in the AOP catalysis and expand its colorimetric and photothermometric application. Image 1 • Gold nanozyme as a co-catalyst was explored for promoting H 2 O 2 decomposition in a Fenton-like AOP reaction. • The pH limitation of traditional Fenton-like oxidation was broken successfully by using the co-catalysis system. • A colorimetric and photothermal PPase activity detection based on β -CD@AuNPs co-catalytic AOP system was developed. [ABSTRACT FROM AUTHOR]

The RGO/AuNPs/CS/ZnTCPP nanocomposites were successfully prepared with reduced graphene oxide (RGO) loaded with Au nanoparticles (AuNPs) existed in chitosan (CS) and water-soluble zinc meso-tetra (4-carboxylphenyl) porphyrin (ZnTCPP) by π-π nanoassembly method and were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), 1 H NMR spectra and UV–vis absorption spectroscopy. The most important advantage of the RGO/AuNPs/CS/ZnTCPP nanocomposites was environmentally friendly. Indium tin oxide (ITO) electrode surface was modified with the RGO/AuNPs/CS/ZnTCPP nanocomposites exhibited a good photocurrent response at −0.2 V under whitelight of Xenon lamp illumination. The photocurrent response could be greatly increased by adding hydroquinone (HQ) to the solution. Electrons of ZnTCPP were excited from HOMO to LUMO by irradiating light. The photoexcited electrons injected into the RGO, and then transferred to AuNPs further to the ITO. Addition of HQ resulted in the enhanced photocurrent signal by acting as a sacrificial electron donor; Thereby scavenged the photogenerated holes of the excited ZnTCPP and oxidized to benzoquinone (BQ). Based on the above interaction, detection of HQ was developed by a novel photoelectrochemical (PEC) sensor (S/N = 3) with a linear range from 5 to 300 nmol/L (r = 0.997) and detection limit of 0.5 nmol/L. Proposed biosensor is simple, rapid and this was successfully applied for the quantification HQ in the real sample matrices. [ABSTRACT FROM AUTHOR]

An ultrasensitive and stable “dual-potential” ratiometric electrochemiluminescence (ECL) sensor is reported for specific DNA, the femtomolar detection limit (0.12 fM, S/N = 3) and high selectivity insure its potential applications in cancer biomarkers searching or monitoring. The excellent performance of the sensor comes from simultaneously fabricated layer by layer structure “target DNA + Hemin / Au-Luminol NPs / DNA* / sl DNA / TGA / QDs / MWNTs / GCE” mode which was based on the enhancing effect of luminol by G-quadruplex / hemin and Au nanoparticles and the quenching effect of CdSe/ZnS by G-quadruplex / hemin. (i) DNA-SH could combine with Au-Luminol NPs via S-Au bond to solve the problem of poor solubility and weak ECL intensity of luminol in neutral medium. (ii) Target DNA and Hemin formed the G-quadruplex / hemin peroxidase mimicking DNAzyme could enhance the ECL of luminol and quench the ECL of CdSe/ZnS simultaneously. (iii) DNA* was employed to increase a certain distance between CdSe/ZnS and Au-Luminol for enhancing the CdSe/ZnS QDs initial ECL intensity. The dual-potential ratiometric mode lower the influence of background and side reaction of the ECL sensor which were the most important factors in trace sensing. [ABSTRACT FROM AUTHOR]

Visual inspection is expected as an ideal technique, which can directly and conveniently detect heavy metal ions by observing the color change. Insensitivity of detecting weakly colored heavy transition metal ions and low adsorptivity of metal ions on nanoparticle surface are two main factors hindering the application of visual detection in heavy metal ions detection. Herein, we demonstrated an operational colorimetric sensor based on the color dependence of nanoparticles aggregation to selective and facile detect weakly colored transition heavy metal Cd 2+ ions that have been considered as the origin of the “Itai-itai” disease. Uniform colloidal 15 nm graphite-like nitride doped carbon quantum dots-capped gold nanoparticle (Au@g-CNQDs) was successfully prepared, wherein the existence of numerous heptazine, carboxyl and hydroxyl groups on the nanoparticle's surface strengthened adsorption of the Cd 2+ ions on the surface of Au@g-CNQDs through the “cooperative effect”. As a consequence, without expensive and intricate exogenous indicators or other special additives, the Cd 2+ ions could sensitively and quickly captured to detect at ultra-low concentration within 30 s by the naked-eye. Under the optimal conditions, the Cd 2+ ions sensor possesses good analytical performances with a wide linear range of 0.01–3.0 μM and a detection limit of 10 nM (S/N = 3). Moreover, the biodistribution and aggregation of Cd 2+ ions were detected effectively in mice organ tissues suggesting its great potential use for real-word applications. [ABSTRACT FROM AUTHOR]

A novel and uniform gold nanoparticles/tryptophan-functionalized graphene nanocomposite (AuNPs/Trp-GR) has been successfully fabricated by directly electrochemical depositing gold onto the surface of tryptophan-functionalized graphene (Trp-GR). The nanostructure of AuNPs/Trp-GR was characterized by using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). It was demonstrated that Au nanoparticles were well dispersed on the surface of Trp-GR which might attribute to the more binding sites provided by Trp-GR for the formation of Au nanoparticles. The electrocatalytic activity of the AuNPs/Trp-GR towards the dopamine (DA) was systematically investigated using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Under optimum conditions, a wide and valuable linear range (0.5–411 μM), a low detection limit (0.056 μM, S/N = 3), good repeatability and stability were obtained for the determination of DA. Furthermore, the modified electrode was successfully applied to real samples analysis. [ABSTRACT FROM AUTHOR]

Abstract: A novel method for glutathione (GSH) detection in real blood sample with a nickel hexacyanoferrate (NiHCF) film modified Pt ultramicroelectrode (UME) was proposed. The electrochemical properties of NiHCF film modified Pt UME were improved by introducing cetyltrimethylammonium bromide (CTAB) and Au nanoparticles (AuNPs) into NiHCF film. The novel hybrid films (NiHCF/CTAB/AuNPs) were prepared by electrodepositing NiHCF and AuNPs in the presence of CTAB on the surface of Pt UME. The results indicated that the prepared NiHCF/CTAB/AuNPs Pt UME had a sensitive respond toward the oxidation of GSH and could be used for its selective determination in the presence of other coexisting interferents in real blood samples. The calibration curve for GSH was found to be linear from 0.2–1μM, and the limit of detection (S/N=3) was 0.08μM. The strategy explored here might provide a new pathway to design NiHCF/CTAB/AuNPs film microsensor for in situ detecting GSH, which had unique characteristics and potential applications in the fields of sensor and medical diagnosis. [Copyright &y& Elsevier]

Abstract: A novel light “on–off” photoelectrochemical sensing for the sensitive determination of hydroquinone was developed based on the porphyrin-functionalized Au nanoparticles on graphene (porphyrin/AuNPs/graphene). Gold nanoparticles (AuNPs) were firstly modified onto graphene sheets using NaBH4 as reductant and the porphyrin/AuNPs/graphene nanocomposites were then synthesized by self-assembly decoration of sulfhydryl porphyrin on AuNPs modified graphene sheets by S–Au bond. The porphyrin/AuNPs/graphene nanocomposites were characterized by transmission electron microscopy, X-ray photoelectron, and ultraviolet–visible absorption spectroscopies. The nanocomposites showed good dispersion in water and on indium tin oxide (ITO) surface. The resulting porphyrin/AuNPs/graphene modified ITO electrode showed good photoelectrochemical behavior toward the oxidation of hydroquinone (HQ) at 0V under white light illumination. The proposed photoelectrochemical method could detect hydroquinone with a wide linear response ranging from 20 to 240nM (R=0.9914). The detection limit was 4.6nM for HQ (S/N=3). Thus, the nanocomposites would be expected to be a novel photoactive material for photoelectrochemical biosensing. [Copyright &y& Elsevier]

Abstract: Capacitive detection of methyl-parathion (MP) was carried out on a polyquercetin (Qu)–polyresorcinol (Re)–gold nanoparticles (AuNPs) modified electrode using a molecular imprinting technique and electropolymerization method. Cyclic voltammetry and electrochemical impedance spectroscopy (EIS) measurements were used to monitor the process of electropolymerization. Uncovered surface areas were plugged with dodecanethiol to make the layer dense, and the insulating properties of the layer were studied in the presence of [Fe(CN)6]3−/[Fe(CN)6]4− redox couples and by the use of AC impedance measurements. The template molecules and the non-bound thiol were removed from the molecularly imprinted polymer film capacitance sensor surface with an acidic solution of ethanol. The sensor''s linear response range was between 7×10−8 molL−1 and 1×10−6 molL−1, with a detection limit of 3.4×10−10 molL−1. The presented research provides a fast, sensitive and real-time method for detecting organophosphate pesticides. In water and in organic samples, the modified electrode has good anti-interference capabilities and stability (distilled water, tap water, river water, and rain water samples all have good recovery). Moreover, the MIPC sensor can detect MP on fruit surfaces within 72h after spraying pesticides. [Copyright &y& Elsevier]

Abstract: A novel electrochemical sensor based on molecularly imprinted polymer film has been developed for aspirin detection. The sensitive film was prepared by co-polymerization of p-aminothiophenol (p-ATP) and HAuCl4 on the Au electrode surface. First, p-ATP was self-assembled on the Au electrode surface by the formation of Au–S bonds. Then, the acetylsalicylic acid (ASA) template was assembled onto the monolayer of p-ATP through the hydrogen-bonding interaction between amino group (p-ATP) and oxygen (ASA). Finally, a conductive hybrid membrane was fabricated at the surface of Au electrode by the co-polymerization in the mixing solution containing additional p-ATP, HAuCl4 and ASA template. Meanwhile, the ASA was spontaneously imprinted into the poly-aminothiophenol gold nanoparticles (PATP–AuNPs) complex film. The amount of imprinted sites at the PATP–AuNPs film significantly increases due to the additional replenishment of ASA templates. With the significant increasing of imprinted sites and doped gold nanoparticles, the sensitivity of the molecular imprinted polymer (MIP) electrode gradually increased. The molecularly imprinted sensor was characterized by electrochemical impedance spectroscopy (EIS), differential pulse voltammetry (DPV), and cyclic voltammetry (CV). The linear relationships between current and logarithmic concentration were obtained in the range from 1nmolL−1 to 0.1μmolL−1 and 0.7μmolL−1 to 0.1mmolL−1. The detection limit of 0.3nmolL−1 was achieved. This molecularly imprinted sensor for the determination of ASA has high sensitivity, good selectivity and reproducibility, with the testing in some biological fluids also has good selectivity and recovery. [ABSTRACT FROM AUTHOR]

• The evolution of noble metal nanoparticles colorimetric sensors was proposed. • The origins of noble metal nanoparticles colorimetric sensors are reviewed. • The advances of noble metal nanoparticles colorimetric sensors are summarized. Noble metal nanoparticles as color labels and signal generators have been widely accepted for the fabrication of colorimetric assays and sensors due to their simplicity and practicality. In the past, organic dye probes and interparticle distance-dependent nanocolorimetric sensors have witnessed great progress in chem/biosensing and recognition events. However, they often suffer from a low color resolution due to the inherent low extinction coefficients of organic dyes probes and the monocolor change-based signal readout. Currently, target-dependent in situ growth of noble metal nanoparticles provides a general means to follow naked-eye-detectable color readouts with high resolution, further allowing great advances in the development of monocolorimetric and multicolorimetric sensors for different target analytes in various detection areas, such as modern bioanalysis, environmental monitoring, food analysis and clinical diagnosis. However, reviews exploring the color readout classifications, signal generation and amplification mechanisms, as well as providing guidance on the progress of such noble metal nanoparticle growth-based colorimetric assays have rarely been reported. To highlight the significant advances in this newly-developing noble metal nanoparticle morphology/size-dependent colorimetric assays field, we herein exclusively summarise the sensing fundamentals, development evolution and cutting-edge applications of this emerging field. Finally, we provide general guidance on how to design such assays on the basis of their current challenges and future perspectives. [ABSTRACT FROM AUTHOR]