A colorimetric sensing probe for chromium (III) ion based on domino like reaction

In this work, a gold nanobipyramid@Ag nanorod (AuNBP@Ag NR)-based sensor platform was developed for the quantitative, visual, and sensitive detection of Cr³⁺ ions in aqueous solutions. This assay provides quantitative detection of Cr³⁺, which relies on the absorbance change of AuNBP@Ag NRs due to morphological change of the AuNBP@Ag NRs induced by Cr³⁺. When AuNBP@Ag NRs and Cr³⁺ mix, the coordination reaction of the carboxyl groups of citrate and Cr³⁺ occurs, which leads to the collapse of Ag shell nanorods, similar to the domino effect, and obvious color changes from yellow to pink can be observed by the naked eye. When combined with UV-vis spectrophotometer-based colorimetric detection, a detection limit of 8.7 nM for Cr³⁺ in ultrapure water was achieved. With the advantages of high sensitivity, selectivity, and performance, we anticipate that the sensor will be helpful for the on-site, quantitative detection of Cr³⁺ ions in water samples.

High Performance Polymer Solar Cells Using Grating Nanostructure and Plasmonic Nanoparticles

This work introduces a high-efficiency organic solar cell with grating nanostructure in both hole and electron transport layers and plasmonic gold nanoparticles (Au NPs) distributed on the zinc oxide (ZnO) layer. The periods of the grating structure in both hole and electro transport layers were optimized using Lumerical finite difference time domain (FDTD) solution software. The optimum AuNP radius distributed on the ZnO layer was also simulated and analyzed before studying the effect of changing the temperature on the solar cell performance, fill factor, and power conversion efficiency. In addition, optical and electrical models were used to calculate the short circuit current density, fill factor, and overall efficiency of the produced polymer solar cell nanostructure. The maximum obtained short circuit current density and efficiency of the solar cell were 18.11 mA/cm² and 9.46%, respectively, which gives a high light absorption in the visible region. Furthermore, the effect of light polarization for incident light angles from θ = 0° to 70° with step angle 10° on the electrical and optical parameters were also studied. Finally, optical power, electric field, and magnetic field distribution inside the nanostructure are also illustrated.

Mimetic peroxidase based on a gold amalgam for the colorimetric sensing of trace mercury(ii) in water samples

A simple and effective AuNPs/H-rGO/CC colorimetric sensing interface was constructed for the sensitive, selective, and facile determination of Hg2+ in water samples.

Co-reactant-free self-enhanced solid-state electrochemiluminescence platform based on polyluminol-gold nanocomposite for signal-on detection of mercury ion

Development of a self-enhanced solid-state ECL platform creates a straightforward experimental design for the fabrication of point-of-care applications. Herein, we develop a promising method for self-enhanced solid-state ECL platform of polyluminol gold nanocomposite on glassy carbon electrode [(PL-Au)_nano/GCE] via simple one-step electrochemical deposition process without involving any additional co-reactants. The presence of gold nanoparticles (AuNPs) augments the electron transfer kinetics of PL (polyluminol) and enhances the solid-state ECL intensity and promotes label-free, excellent sensitivity, and selectivity to detect Hg²⁺ in physiological pH through signal-on mode. Unlike pristine PL/GCE, electrochemically co-deposited AuNPs in the (PL-Au)_nano/GCE composite, enable the co-reactant accelerator by improving the catalytic activity of PL towards oxygen reduction reaction (ORR) yielding in-situ ROS (co-reactant) generation. Further, the ECL intensity of (PL-Au)_nano/GCE composite, gradually increases with each addition of Hg²⁺ ion. This is because of the formation of an amalgamation of Au-Hg on (PL-Au)_nano/GCE composite surface which further accelerates the yield of in-situ ROS and enhances the intensity of ECL. Whereas no ECL signals changes were observed for PL/GCE composite. The proposed self-enhanced solid-state ECL platform is selectively sensing the Hg²⁺ ion in the linear range of 0.3–200 nM with a detection limit of 0.1 nM. The demonstrated (PL-Au)_nano/GCE platform might pave new avenues for further studies in the solid-state ECL platform which could be more useful in on-site monitoring of clinical bioassay and immunosensors.

Efficient Visual Chemosensor for Hexavalent Chromium via a Controlled Strategy for Signal Amplification in Water

Generally, 3,3',5,5'-tetramethylbenzidine (TMB) cannot react with hydrogen peroxide (H₂O₂) in neutral pH or in water at room temperature and pressure. Herein, we found that hexavalent chromium (Cr⁶⁺) can trigger TMB reacting with H₂O₂ (TMB-H₂O₂) in ultrapure water along with a weak signal output. Then, to implement signal amplification effectively, we designed a ternary nanohybrid material containing graphene oxide (GO) nanosheets, gold nanoparticles (Au NPs), and hyperbranched polyethylenimine (PEI) to form rGO/PEI/Au nanohybrids via chemical bonding. After addition of a trace amount of Cr⁶⁺, rGO/PEI/Au nanohybrids can effectively catalyze TMB-H₂O₂ in ultrapure water; thus, a visual chemosensor and electronic spectrum quantitative analysis method for Cr⁶⁺ based on chromium-stimulated peroxidase mimetic activity of rGO/PEI/Au nanohybrids were established. The visual chemosensor exhibits excellent selectivity and interference immunity against 34 other interfering substances with a detection limit as low as 2.14 nM. The visual chemosensor for Cr⁶⁺ with a low detection limit and high selectivity is expected to have a potential application in environmental analysis, monitoring, and human health maintenance.

Recent developments of nanoenzyme-based colorimetric sensors for heavy metal detection and the interaction mechanism

This work highlights the application and interaction mechanism of metal nanoparticles, metal oxides, metal sulfides, graphene-based nanomaterials and G-quadruplex, etc. in nanoenzyme-based colorimetric sensors.

In situ generated nanozyme-initiated cascade reaction for amplified surface plasmon resonance sensing

A novel nanozyme-amplified surface plasmon resonance (SPR) sensor was successfully developed based on target-induced in situ generation of AuNPs and a AuNP-guided cascade amplification reaction, with Hg²⁺ as the target analyte.

Simulated enzyme inhibition-based strategy for ultrasensitive colorimetric biothiol detection based on nanoperoxidases

A simulated enzyme inhibition-based strategy based on a nanoperoxidase mimic was adopted for ultrasensitive colorimetric glutathione detection.

Ultrahigh Selective Colorimetric Quantification of Chromium(VI) Ions Based on Gold Amalgam Catalyst Oxidoreductase-like Activity in Water

Hexavalent chromium ion (Cr⁶⁺) is one of the most toxic substances for plants, for animals, and is a confirmed human respiratory carcinogen. However, so far, there are few independent and efficient colorimetric methods for detection of Cr⁶⁺. Here, we introduce a convenient, label-free, catalysis-based, and efficient strategy for quantification of Cr⁶⁺ by using a colorimetric sensing probe 3,3',5,5'-tetramethylbenzidine (TMB). In the presence of a trace amount of gold amalgam nanocomposites (Au@Hg) and Cr⁶⁺, TMB can be oxidized to oxTMB and the color changed to an intense blue that was observed by naked-eye and absorption spectroscopic method. In addition, the colorimetric method shows the high selectivity against 34 other interfering substances, and it can be performed at room temperature, in water, and requires only ∼5 min. Thus, the catalysis-based colorimetric assay for accurate and ultrahigh selective identification of Cr⁶⁺ will find widespread use in the world.

A pH-Resolved Colorimetric Biosensor for Simultaneous Multiple Target Detection

Colorimetric detection has been widely applied in daily life. However, on the other hand, the further development of colorimetric biosensors has been constrained by the lack of multiple detection capabilities. In this work, we proposed a pH-resolved colorimetric biosensor for the first time for the simultaneous detection of four targets, including ochratoxin A (OTA), aflatoxins B1 (AFB1), fumonisin B1 (FB1), and microcystin-LR (MC-LR). With allochroic dyes as the signal indicators, pH value was introduced as the new dimension to control the release of dyes. The concentrations of four targets can be obtained in order by adjusting the pH of the solution. Meanwhile, tedious and high-cost chemical modification processes in the fabrications of biosensors were also avoided by the combination of DNA-directed self-assembly of graphene oxide and magnetic separation. This biosensor provided a simple, rapid, accurate, and low-cost strategy for multiple target detection.

Ultratrace and robust visual sensor of Cd2+ ions based on the size-dependent optical properties of Au@g-CNQDs nanoparticles in mice models

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 Cd²⁺ ions that have been considered as the origin of the "Itai-itai" disease. Uniform colloidal 15nm 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 Cd²⁺ 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 Cd²⁺ ions could sensitively and quickly captured to detect at ultra-low concentration within 30s by the naked-eye. Under the optimal conditions, the Cd²⁺ ions sensor possesses good analytical performances with a wide linear range of 0.01-3.0μM and a detection limit of 10nM (S/N = 3). Moreover, the biodistribution and aggregation of Cd²⁺ ions were detected effectively in mice organ tissues suggesting its great potential use for real-word applications.