Portable smartphone-assisted highly sensitive detection of mercury ions based on gold nanoparticle-modified NH2-UiO-66 metal-organic framework

A novel portable smartphone-assisted colorimetric method was reported for the determination of Hg2+ with good analytical performance. A Zr(IV)-based metal-organic framework functionalized with amino groups (NH2-UiO-66) has been adopted as a supporting platform to anchor gold nanoparticles (AuNPs), avoiding the migration and aggregation of AuNPs. With the addition of Hg2+, the formation of gold amalgam proved possible to enhance peroxidase-like activity of the composite (AuNPs/NH2-UiO-66), accelerating the oxidization of zymolyte 3,3',5,5'-tetramethylbenzidine (TMB). In the meantime, the color of the reaction solution turned a vivid blue, and the red, green, and blue (RGB) values of the solution color changed accordingly. On account of this strategy, the quantitative detection of Hg2+ could be achieved. After the optimization of the experiment conditions, the average color intensity (Ic) resulting from RGB values was linear related to the concentration of Hg2+ from 10 to 100 nM, accompanied with a detection limit (LOD) down to 5.4 nM calculated by 3σ/S. The successful application of the designed method has been promoted to detect Hg2+ in some water samples, displaying a great potential in practical application. Furthermore, the use of a smartphone made our proposed method simple and accurate, and thus puts forward a possible way for in situ and real-time monitoring.

A colorimetric detection of Hg2+ based on gold nanoparticles synthesized oxidized N-methylpyrrolidone as a reducing agent

In this study, a gold nanoparticles colorimetric probe (AuNPs) with direct response to mercury ions (Hg2+) were developed using treated N-methylpyrrolidone (NMP) and chloroauric acid (HAuCl4) as precursors. NMP showed good reducibility after high temperature hydrolysis and could be used as reducing and stabilizing agent to synthesize AuNPs. The prepared AuNPs have obvious characteristic absorption peaks and appear wine-red. At the same time, it was found that the presence of Hg2+ can cause the aggregation of AuNPs, increased the absorbance at 700 nm, and changed the color of the solution into blue-gray. This method is capable of sensitive and specific determination of Hg2+ ranging from 1 to 30 μM, with the limit of detection (LOD) at 0.3 μM. The method showed good specificity for the determination of Hg2+ and has the potential to be applied to Hg2+ detection in sewage samples in the environment.

A dual colorimetric probe for rapid environmental monitoring of Hg2+ and As3+ using gold nanoparticles functionalized with d-penicillamine

A highly sensitive and selective colorimetric assay for the dual detection of Hg2+ and As3+ using gold nanoparticles (AuNPs) conjugated with d-penicillamine (DPL) was developed. When Hg2+ and As3+ ions coordinate with AuNP-bound DPLs, the interparticle distance decreases, inducing aggregation; this results in a significant color change from wine red to dark midnight blue. The Hg4f and As3d signals in the X-ray photoelectron spectra of Hg2+ (As3+)-DPL-AuNPs presented binding energies indicative of Hg2+-N(O) and As3+-N(O) bonds, and the molecular fragment observed in time-of-flight secondary ion mass spectra confirmed that Hg2+ and As3+ coordinated with two oxygen and two nitrogen atoms in DPL. The detection of Hg2+ and As3+ can be accomplished by observing the color change with the naked eye or by photometric methods, and this was optimized to provide optimal probe sensitivity. The assay method can be applied for environmental monitoring by first selectively quantifying Hg2+ in water samples at pH 6, then estimating the As3+ concentration at pH 4.5. The efficiency of the DPL-AuNP probe was evaluated for the sequential quantification of Hg2+ and As3+ in tap, pond, waste, and river water samples, and absorbance ratios (A 730/A 525) were correlated with Hg2+ and As3+ concentrations in the linear range of 0-1.4 μM. The limits of detection in water samples were found to be 0.5 and 0.7 nM for Hg2+ and As3+, respectively. This novel probe can be utilized for the dual determination of Hg2+ and As3+, even in the presence of interfering substances in environmental samples.

Detection of Ag+ ions via an anti-aggregation mechanism using unmodified gold nanoparticles in the presence of thiamazole

The present study proposed a novel and highly selective and sensitive method for Ag⁺ ion detection based on gold nanoparticles (AuNPs) anti-aggregation. Thiamazole can induce AuNPs aggregation due to electrostatic interactions, which result in color transitions in the AuNPs solution from red to blue. However, the presence of Ag⁺ ions results in the preferential combination of the pyridinic nitrogen of thiamazole with the Ag⁺ ions. In addition, the Ag⁺ ions oxidize the sulfhydryl groups(-SH), which inhibit AuNPs aggregation and prompt a color change from blue to red. As a result, the present study established a method for Ag⁺ ion determination by AuNPs-thiamazole colorimetric probe based on the aforementioned anti-aggregation mechanism. The probe dynamic range was easily tuned via adjustments of the thiamazole amount. The relationship between the Ag⁺ concentration and AuNPs aggregation was monitored by ultraviolet-visible light (UV-Vis) spectroscopy at a dynamic range of 0.1 nM-9 μM and at a detection limit of 0.042 nM. The river water and tap water recovery analysis validated the successful operation of this colorimetric sensor in environmental monitoring.

Ultrasensitive colorimetric detection of Hg2+ ions based on enhanced catalytic performance of gold amalgam dispersed in channels of rose petals

We herein present a simple, low-cost, and ultrasensitive colorimetric sensing strategy for the detection of mercury ions (Hg²⁺) that takes advantage of the natural pore structure in rose petals to encapsulate gold nanoparticles (AuNPs).

In situ growth of gold nanoparticles on Hg2+-binding M13 phages for mercury sensing

Mercury poses a serious threat to human health and the ecosystem. Its pollution is still prevalent in developing areas, which calls for the development of a simple on-site method for Hg²⁺ detection. Plasmonic nanosensors for mercury, especially those based on gold nanoparticles (AuNPs), have been increasingly developed due to the flourish of nanotechnology in the last decade. However, the limitation on either selectivity or stability hindered their practical applications. Herein, by taking advantage of the unique optical properties of AuNPs and the versatility of M13 phages, a novel Hg²⁺ sensing strategy is proposed. AuNPs grew in situ on the surface of Hg²⁺-binding M13 phages at room temperature and the resulting AuNP-phage networks were directly used for mercury sensing. Hg²⁺ was selectively captured by M13 phages indwelling in the networks and gathered around AuNPs, followed by the reduction into Hg(0) and deposition on the AuNP surfaces, wherein it resulted in a blue shift of the SPR band of AuNPs and an increase in the absorbance. An LOD of 8 × 10^-8 mol L^-1 was achieved based on the quantification of the absorption ratio of AuNPs at 525 and 650 nm. As the Hg²⁺ recognition was double guaranteed by the capture of Hg²⁺-binding phages as well as the unique affinity between mercury and gold, the sensing system showed a high selectivity and a superior interference tolerance capability, facilitating its practical applications in environmental water bodies without deterioration of the sensing performance.

Valence States Modulation Strategy for Picomole Level Assay of Hg2+ in Drinking and Environmental Water by Directional Self-Assembly of Gold Nanorods

In this study, we present a valence states modulation strategy for picomole level assay of Hg²⁺ using directional self-assembly of gold nanorods (AuNRs) as signal readout. Hg²⁺ ions are first controllably reduced to Hg⁺ ions by appropriate ascorbic acid, and the reduced Hg⁺ ions react with the tips of the preadded AuNRs and form gold amalgam. Such Hg⁺ decorated AuNRs then end-to-end self-assemble into one-dimensional architectures by the bridging effects of lysine based on the high affinity of NH₂-Hg⁺ interactions. Correspondingly, the AuNRs' longitudinal surface plasmon resonance is gradually reduced and a new broad band appears at 900-1100 nm region simultaneously. The resulting distinctly ratiometric signal output is not only favorable for Hg²⁺ ions detection but competent for their quantification. Under optimal conditions, the linear range is 22.8 pM to 11.4 nM, and the detection limit is as low as 8.7 pM. Various transition/heavy metal ions, such as Pb²⁺, Ti²⁺, Co²⁺, Fe³⁺, Mn²⁺, Ba²⁺, Fe²⁺, Ni²⁺, Al³⁺, Cu²⁺, Ag⁺, and Au³⁺, do not interfere with the assay. Because of ultrahigh sensitivity and excellent selectivity, the proposed system can be employed for assaying ultratrace of Hg²⁺ containing in drinking and commonly environmental water samples, which is difficult to be achieved by conventional colorimetric systems. These results indicate that the present platform possesses specific advantages and potential applications in the assay of ultratrace amounts of Hg²⁺ ions.

Gold nanoparticle-based nanosystems for the colorimetric detection of Hg2+ ion contamination in the environment

This review highlights the impact of Hg²⁺ contamination on the human population and the need for its detection.

A sensitive electrochemical Hg2+ ions sensor based on polypyrrole coated nanospherical platinum

We report the synthesis and characterization of polypyrrole coated on nanospherical platinum (Pt/PPy NSs) composites for the detection of mercury ions.

New Chitosan-Thiomer: An Efficient Colorimetric Sensor and Effective Sorbent for Mercury at Ultralow Concentration

This paper describes an innovative procedure for the fabrication of a facile colorimetric sensor in one step with thiol functional group for Hg(2+) detection at trace level. The sensor was successfully synthesized via chitosan isothiouronium salt intermediate with innocuous low cost thiourea reagent under microwave irradiation. It is an innovative green approach to achieve thiol functionalization with a high degree of substitution. Thiomer was characterized by titrimetry, FTIR, (1)H NMR, elemental analysis (CHNS), and EDX for extent of modification with detail structure. The synthesized and well characterized thiomer was screened for sensor application. The sensing solution of thiomer resulted in an instantaneous sharp color change from colorless, yellow, to brown with increase in Hg(2+) concentration. Chitosan thiomer also exhibited high sensitivity and selectivity for Hg(2+) over other possible interfering ions in aqueous media. The sensing responses were visualized quantitatively with quick response, good selectivity, high sensitivity, and a low detection limit of ∼0.465 ppb by the naked eye. The same was tested with a paper strip method for technological applications. Furthermore, the as-prepared sensors also exhibited exceptional sorption potential for Hg(2+) even from ultralow concentration aqueous solution and reduced the Hg(2+) concentration from 10 ppb to the extremely low level of ∼0.04 ppb as studied by cyclic voltammetry. Thus, the proposed method is simple, promising, and rapid without any complicated modifying step and is an economical alternative to traditional Hg(2+) sensors for rapid sensor application in environmental water samples at ppb levels.

Layered MnO₂ nanosheet as a label-free nanoplatform for rapid detection of mercury(II)

A layered MnO2 nanosheet was established as a label-free fluorescent sensing platform for a rapid, sensitive and low-cost detection of mercury(II) ion in aqueous solution based on the target-induced conformational change of mercury-specific oligonucleotide (MSO) and the interactions between the fluorogenic MSO probe and MnO2 nanosheet.

Monolayer protected gold nanoparticles with metal-ion binding sites: functional systems for chemosensing applications

Au NPs containing binding sites for metal ions in the monolayer are attractive components of sensing assays.

Fluorescent and colorimetric sensors for environmental mercury detection

The development of fluorescent and colorimetric sensing strategies for environmental mercury is described.

High-value utilization of lignin to synthesize Ag nanoparticles with detection capacity for Hg²⁺

This study reports the rapid preparation of silver nanoparticles (AgNPs) from Tollens' reagent under microwave irradiation. In the synthesis, lignin with reducing groups and spatial three-dimensional structure was used as reducing and stabilizing agents without other chemical reagents, and the effects of the ratio of lignin to Ag(+), reaction temperature, and heating time on the synthesis of AgNPs were investigated. The obtained AgNPs were further characterized by UV-vis, Malvern particle size, TEM, XRD, and XPS analyses. The structural changes of lignin before and after reaction were also studied by FT-IR, (1)H NMR, (13)C NMR, and GC-MS. The results revealed that the obtained AgNPs were mostly spherical with diameters of around 24 nm. The optimum reaction conditions were a ratio 50 mg of lignin to 0.3 mM of Ag(+), a microwave irradiation temperature of 60 °C, and a heating time of 10 min. Moreover, AgNPs redispersed well in water and ethanol after centrifugation for the removal of lignin. During the formation of AgNPs, lignin was oxidized, and the side chains of lignin were partly disrupted into small molecules, such as hydrocarbon and alcohol. The resultant lignin-AgNPs showed highly selective sensing detection for Hg(2+), and the color of the lignin-AgNP solution containing Hg(2+) decreased gradually with increasing amounts of Hg(2+) within seconds, but the other 19 metal ions had little effect on the color and surface plasmon absorption band of the lignin-AgNPs. Also, there was a linear relationship between the absorbance and Hg(2+) concentration, with a limit of detection concentration of 23 nM. This study provides not only a new way to take advantage of agricultural and forestry residues, but also a green and rapid method for the synthesis of AgNPs to detect the toxic ion Hg(2+) selectively and sensitively.

Optical reading of contaminants in aqueous media based on gold nanoparticles

With increasing trends of global population growth, urbanization, pollution over-exploitation, and climate change, the safe water supply has become a global issue and is threatening our society in terms of sustainable development. Therefore, there is a growing need for a water-monitoring platform with the capability of rapidness, specificity, low-cost, and robustness. This review summarizes the recent developments in the design and application of gold nanoparticles (AuNPs) based optical assays to detect contaminants in aqueous media with a high performance. First, a brief discussion on the correlation between the optical reading strategy and the optical properties of AuNPs is presented. Then, we summarize the principle behind AuNP-based optical assays to detect different contaminants, such as toxic metal ion, anion, and pesticides, according to different optical reading strategies: colorimetry, scattering, and fluorescence. Finally, the comparison of these assays and the outlook of AuNP-based optical detection are discussed.

A functional graphene oxide-ionic liquid composites-gold nanoparticle sensing platform for ultrasensitive electrochemical detection of Hg2+

A simple and sensitive electrochemical assay strategy of stripping voltammetry for mercury ions (Hg(2+)) detection is described based on the synergistic effect between ionic liquid functionalized graphene oxide (GO-IL) and gold nanoparticles (AuNPs). The AuNPs-GO-IL modified onto glassy carbon electrode (GCE) resulted in highly enhanced electron conductive nanostructured membrane and large electroactive surface area, which was excellently examined by scanning electron microscopy and cyclic voltammetry. After accumulating Hg(2+), anodic stripping voltammetry (ASV) was performed, and differential pulse voltammetry (DPV) was employed for signal recording of Hg(2+). Several main experimental parameters were optimized, i.e., deposition potential and time of AuNPs were -0.2 V and 180 s, respectively, and accumulation potential and time of Hg(2+) were -0.3 V and 660 s, respectively. Under the optimal conditions, this AuNPs-GO-IL-GCE sensor attained a good linearity in a wide range of 0.1-100 nM (R = 0.9808) between the concentration of the Hg(2+) standard and peak current. The limit of detection was estimated to be 0.03 nM at a signal-to-noise ratio of 3σ. A variety of common coexistent ions in water samples were investigated, showing no obvious interferences on the Hg(2+) detection. The practical application of the proposed sensor has been carried out and demonstrated as feasible for determination of trace levels of Hg(2+) in drinking and environmental water samples.

Colorimetric detection of mercury ions based on plasmonic nanoparticles

The development of rapid, specific, cost-effective, and robust tools in monitoring Hg(2+) levels in both environmental and biological samples is of utmost importance due to the severe mercury toxicity to humans. A number of techniques exist, but the colorimetric assay, which is reviewed herein, is shown to be a possible tool in monitoring the level of mercury. These assays allow transforming target sensing events into color changes, which have applicable potential for in-the-field application through naked-eye detection. Specifically, plasmonic nanoparticle-based colorimetric assay exhibits a much better propensity for identifying various targets in terms of sensitivity, solubility, and stability compared to commonly used organic chromophores. In this review, recent progress in the development of gold nanoparticle-based colorimetric assays for Hg(2+) is summarized, with a particular emphasis on examples of functionalized gold nanoparticle systems with oligonucleotides, oligopeptides, and functional molecules. Besides highlighting the current design principle for plasmonic nanoparticle-based colorimetric probes, the discussions on challenges and the prospect of next-generation probes for in-the-field applications are also presented.

A gold nanoparticles-based colorimetric assay for alkaline phosphatase detection with tunable dynamic range

In this report, a simple and label-free colorimetric assay was developed for detecting alkaline phosphatase (ALP). Based on the conjugated gold nanoparticle/adenosine triphosphate (AuNP/ATP) sensing system, this assay is highly sensitive and selective. In this system, ATP induces the aggregation of cetyltrimethylammonium bromide (CTAB)-capped AuNPs and ALP stimulates the disaggregation of AuNPs by converting ATP into adenosine through an enzymatic dephosphorylation reaction. Hence, the presence of ALP can be visually observed (gray-to-red color change) and monitored by the shift of the surface plasmon resonance (SPR) absorption band of AuNPs. Furthermore, the dynamic range of the method can be varied by addition of different metal ions (e.g. 100-600unit/L to 5.0-100unit/L and 0.2-20unit/L in the presence of Ca(2+) and Pb(2+), respectively). The feasibility of this sensitive and specific assay with a tunable dynamic range was demonstrated to be consistent even in human serum samples.

A colorimetric selective sensing probe for calcium ions with tunable dynamic ranges using cytidine triphosphate stabilized gold nanoparticles

Cytidine triphosphate (CTP) stabilized-Au nanoparticles (CTP-AuNPs) allow a quantitative assay of Ca(2+) down to a concentration of 10(-4) M with high selectivity towards Ca(2+) ions over various metal ions including Mg(2+) and the detection range of this probe also can be easily tuned by changing the concentration of CTP.