Facile colorimetric detection of Hg2+ based on anti-aggregation of silver nanoparticles

High-Performance Colorimetric Detection of Thiosulfate by Using Silver Nanoparticles for Smartphone-Based Analysis

Developing thiosulfate (S₂O₃^2-) sensors with silver nanoparticles (AgNPs) for analysis of aqueous solutions with the interference of other anions remains challenging. In this study, we propose a new strategy for excellent selective colorimetric detection of S₂O₃^2-. The nonmorphological transition of AgNPs leading to a color change from yellow to brown is verified by UV-vis, TEM, DLS, SEM, and XPS analyses. The sensor exhibits high sensitivity with detection limits of 1.0 μM by naked-eye determination and 0.2 μM by UV-vis spectroscopy analysis. The linear relationship (R² = 0.998) between the (A₀ - A)/A₀ values and S₂O₃^2- concentrations from 0.2 μM to 2.0 μM indicates that the fabricated AgNPs-based colorimetric sensor can be employed for quantitative assay of S₂O₃^2-. Colorimetric responses are also monitored using the built-in camera of a smartphone. The sensor shows a linear response to S₂O₃^2- in 0-20.0 μM solutions under the optimized conditions and is thus more suitable for rapid on-site tests than other detection methods. A smartphone application (app) is downloaded under Android or IOS platforms to measure the RGB (red, green, blue) values of the colorimetric sensor after exposure to the analyte. Following data processing, the RGB values are converted into concentration values by using preloaded calibration curves. Confirmatory analysis indicates that the proposed S₂O₃^2- colorimetric sensor exhibits feasibility and sensitivity for S₂O₃^2- detection in real environmental samples.

Noble metal nanoparticles in biosensors: recent studies and applications

The aim of this review is to cover advances in noble metal nanoparticle (MNP)-based biosensors and to outline the principles and main functions of MNPs in different classes of biosensors according to the transduction methods employed. The important biorecognition elements are enzymes, antibodies, aptamers, DNA sequences, and whole cells. The main readouts are electrochemical (amperometric and voltametric), optical (surface plasmon resonance, colorimetric, chemiluminescence, photoelectrochemical, etc.) and piezoelectric. MNPs have received attention for applications in biosensing due to their fascinating properties. These properties include a large surface area that enhances biorecognizers and receptor immobilization, good ability for reaction catalysis and electron transfer, and good biocompatibility. MNPs can be used alone and in combination with other classes of nanostructures. MNP-based sensors can lead to significant signal amplification, higher sensitivity, and great improvements in the detection and quantification of biomolecules and different ions. Some recent examples of biomolecular sensors using MNPs are given, and the effects of structure, shape, and other physical properties of noble MNPs and nanohybrids in biosensor performance are discussed.

Green synthesis of silver nanoparticle for the selective and sensitive colorimetric detection of mercury (II) ion

An ecofriendly and zero cost approach has been developed for the photoinduced synthesis of more stable AgNPs using an aqueous extract of Murraya koenigii (AEM) as a reducing and stabilizing agent. The exposed reaction mixture of AEM and AgNO₃ to sunlight turned dark brown which primarily confirmed the biosynthesis of AgNPs. The biosynthesis was monitored by UV-vis spectroscopy which exhibited a sharp SPR band at 430nm after 30min of sunlight exposure. The optimum conditions for biosynthesis of AgNPs were 30min of sunlight exposure, 2.0% (v/v) of AEM inoculuam dose and 4.0mM AgNO₃ concentration. TEM analysis confirmed the presence of spherical AgNPs with average size 8.6nm. The crystalline nature of the AgNPs was confirmed by XRD analysis where the Bragg's diffraction pattern at (111), (200), (220) and (311) corresponded to face centered cubic crystal lattice of metallic silver. The surface texture was analyzed by AFM analysis where the average roughness of the synthesized AgNPs was found 1.8nm. FTIR analysis was recorded between 4000 and 400cm^-1 which confirmed the involvement of various functional groups in the synthesis of AgNPs. On the basis of the linear relationship between SPR band intensity and different concentration of Hg²⁺, the synthesized AgNPs can be used for colorimetric detection of Hg²⁺ with a linear range from 50nm to 500μM. Based on experimental findings, an oxidation-reduction mechanism between AgNPs and Hg²⁺ was also proposed.

Photo-mediated optimized synthesis of silver nanoparticles for the selective detection of Iron(III), antibacterial and antioxidant activity

The AgNPs synthesized by green method have shown great potential in several applications such as biosensing, biomedical, catalysis, electronic etc. The present study deals with the selective colorimetric detection of Fe³⁺ using photoinduced green synthesized AgNPs. For the synthesis purpose, an aqueous extract of Croton bonplandianum (AEC) was used as a reducing and stabilizing agent. The biosynthesis was confirmed by UV-visible spectroscopy where an SPR band at λ_max 436nm after 40s and 428nm after 30min corresponded to the existence of AgNPs. The optimum conditions for biosynthesis of AgNPs were 30min sunlight exposure time, 5.0% (v/v) AEC inoculum dose and 4mM AgNO₃ concentration. The stability of synthesized AgNPs was monitored up to 9months. The size and shape of AgNPs with average size 19.4nm were determined by Field Emission Scanning Electron Microscope (FE-SEM) and High-Resolution Transmission Electron Microscope (HR-TEM). The crystallinity was determined by High-Resolution X-ray Diffractometer (HR-XRD) and Selected Area Electron Diffraction (SAED) pattern. The chemical and elemental compositions were determined by Fourier Transformed Infrared Spectroscopy (FTIR) and Energy Dispersive X-ray Spectroscopy (EDX) respectively. The Atomic Force Microscopy (AFM) images represented the lateral and 3D topological characteristics of AgNPs. The XPS analysis confirmed the presence of two individual peaks which attributed to the Ag 3d3/2 and Ag 3d5/2 binding energies corresponding to the presence of metallic silver. The biosynthesized AgNPs showed potent antibacterial activity against both gram-positive and gram-negative bacterial strains as well as antioxidant activity. On the basis of results and facts, a probable mechanism was also proposed to explore the possible route of AgNPs synthesis, colorimetric detection of Fe³⁺, antibacterial and antioxidant activity.

Mechanism of adsorption of single and double stranded DNA on gold and silver nanoparticles: Investigating some important parameters in bio-sensing applications

The mechanism of adsorption of single and double stranded DNAs on colloidal gold and silver nanoparticles has been studied by measuring the resistance of the nanoparticles, surrounded by various oligonucleotides, against salt induced aggregation. It is shown that both single and double stranded DNAs can be adsorbed on the metal nanoparticles and the adsorption strength is determined by the interaction between various bases of DNA and the nanoparticles. By changing the salt concentration, the difference between adsorption of various DNA strands on the nanoparticles can be specified. The results indicate that a key parameter in success of a sensing assay of DNA hybridization is the salt concentration which should be greater than a minimum threshold depending on the nanoparticles characteristics. We have also investigated the interaction mechanism between various DNA bases with the metal nanoparticles. For both gold and silver nanoparticles, adenine has the highest and thymine has the lowest attachment to the nanoparticles. From surface enhanced Raman spectroscopy (SERS) data of various bases in the presence of gold nanoparticles, the probable interaction points in the bases with the nanoparticles have been determined, which are mainly the nitrogen sites of these oligonucleotides.

Recent Progresses in Nanobiosensing for Food Safety Analysis

With increasing adulteration, food safety analysis has become an important research field. Nanomaterials-based biosensing holds great potential in designing highly sensitive and selective detection strategies necessary for food safety analysis. This review summarizes various function types of nanomaterials, the methods of functionalization of nanomaterials, and recent (2014-present) progress in the design and development of nanobiosensing for the detection of food contaminants including pathogens, toxins, pesticides, antibiotics, metal contaminants, and other analytes, which are sub-classified according to various recognition methods of each analyte. The existing shortcomings and future perspectives of the rapidly growing field of nanobiosensing addressing food safety issues are also discussed briefly.

Sensitive and selective colorimetric detection of Hg2+ by a Hg2+ induced dual signal amplification strategy based on cascade-type catalytic reactions

A simple and fast colorimetric method is developed for the sensitive and selective detection of Hg²⁺ based on a dual signal amplification strategy.

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.

Colorimetric determination of o-phenylenediamine in water samples based on the formation of silver nanoparticles as a colorimetric probe

A simple, rapid and cost-effective method for visual colorimetric detection of o-phenylenediamine (OPD) based on the formation of silver nanoparticles (AgNPs) has been developed in this paper. Silver ions can be reduced to AgNPs by OPD in a few minutes, causing changes in absorption spectra and color of the reaction system. Therefore, colorimetric detection of OPD could be realized by a UV-vis spectrophotometer or even the naked eye. Results showed that the absorption intensity of AgNPs at 416 nm exhibited a good linear correlation (R2=0.998) with OPD concentration in the range from 10(-6) to 8×10(-5) mol L(-1) and the detection limit (3σ/S) was calculated to be 1.61×10(-7) mol L(-1). Furthermore, as low as 4×10(-6) mol L(-1)OPD can be visualized by the naked eye without the requirement of any complicated or expensive instruments. This proposed method has been successfully applied to determine OPD in water samples, and may provide an innovative platform in the development of sensors for guiding environmental monitoring in the future.

Colorimetric detection of iron ions (III) based on the highly sensitive plasmonic response of the N-acetyl-L-cysteine-stabilized silver nanoparticles

We report here a facile colorimetric sensor based on the N-acetyl-L-cysteine (NALC)-stabilized Ag nanoparticles (NALC-Ag NPs) for detection of Fe(3+) ions in aqueous solution. The Ag NPs with an average diameter of 6.55±1.0 nm are successfully synthesized through a simple method using sodium borohydride as reducing agent and N-acetyl-L-cysteine as protecting ligand. The synthesized silver nanoparticles show a strong surface plasmon resonance (SPR) around 400 nm and the SPR intensity decreases with the increasing of Fe(3+) concentration in aqueous solution. Based on the linear relationship between SPR intensity and concentration of Fe(3+) ions, the as-synthesized water-soluble silver nanoparticles can be used for the sensitive and selective detection of Fe(3+) ions in water with a linear range from 80 nM to 80 μM and a detection limit of 80 nM. On the basis of the experimental results, a new detection mechanism of oxidation-reduction reaction between Ag NPs and Fe(3+) ions is proposed, which is different from previously reported mechanisms. Moreover, the NALC-Ag NPs could be applied to the detection of Fe(3+) ions in real environmental water samples.

An exonuclease-assisted amplification electrochemical aptasensor for Hg(2+) detection based on hybridization chain reaction

In this work, a novel electrochemical aptasensor was developed for Hg(2+) detection based on exonuclease-assisted target recycling and hybridization chain reaction (HCR) dual signal amplification strategy. The presence of Hg(2+) induced the T-rich DNA partly folded into duplex-like structure via the Hg(2+) mediated T-Hg(2+)-T base pairs, which triggered the activity of exonuclease III (Exo III). Exo III selectively digested the double-strand DNA containing multiple T-Hg(2+)-T base pairs from its 3'-end, the released Hg(2+) participated analyte recycle. With each digestion cycle, a digestion product named as help DNA was obtained, which acted as a linkage between the capture DNA and auxiliary DNA. The presence of help DNA and two auxiliary DNA collectively facilitated successful HCR process and formed long double-stranded DNA. [Ru(NH3)6](3+) was used as redox indicator, which electrostatically bound to the double strands and produced an electrochemical signal. Exo III-assisted target recycling and HCR dual amplification significantly improved the sensitivity for Hg(2+) with a detection limit of 0.12 pM (S/N=3). Furthermore, the proposed aptasensor had a promising potential for the application of Hg(2+) detection in real aquatic sample analysis.

Guanine chemiluminescent biosensor capable of rapidly sensing mercury in a sample

Using DNA aptamer (T–Hg²⁺–T hairpin-DNA) and guanine chemiluminescene detection, a highly sensitive biosensor was developed for the rapid quantification and monitoring of Hg²⁺ in drinking water.

Optical sensor: a promising strategy for environmental and biomedical monitoring of ionic species

In this review, we cover the recent developments in fluorogenic and chromogenic sensors for Cu²⁺, Fe²⁺/Fe³⁺, Zn²⁺and Hg²⁺.

Formation of plasmonic silver nanoparticles by flavonoid reduction: A comparative study and application for determination of these substances

Formation of plasmonic silver nanoparticles by flavonoid reduction was studied. Effects of the nature and the concentration of a flavonoid and a stabilizer, composition of the solution and the interaction time were revealed. It was found that quercetin, dihydroquercetin, rutin and morin produced an intense surface plasmon resonance band of silver nanoparticles at 415 nm which was linearly related to the concentration of a flavonoid, while chrysin, naringenin and naringin did not produce any remarkable changes. It was used for the spectrophotometric determination of the former four flavonoids with the detection limits of 0.03; 0.06; 0.09 and 0.1 μg mL(-1), respectively. The developed method was applied for the determination of flavonoids in biologically active food additives.

Preparation and characterization of a novel tetrakis(4-hydroxyphenyl)porphyrin–graphene oxide nanocomposite and application in an optical sensor and determination of mercury ions

Optical chemical sensor for determination of mercury ions.

An ultrasensitive colorimetric sensor for efficient detection of Hg2+ at physiological pH

The estimation of Hg²⁺ in a buffer system (Tris buffer; pH 7.4) has been performed using a novel, enzyme-based, indirect detection method with the aid of non-functionalized AgNPs.

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.