Ultrasensitive colorimetric assay of cadmium ion based on silver nanoparticles functionalized with 5-sulfosalicylic acid for wide practical applications

Multifunctional nanomaterials and nanocomposites for sensing and monitoring of environmentally hazardous heavy metal contaminants

The applications of conventional sensors are limited by the long response time, high cost, large detection limit, low sensitivity, complicated usage and low selectivity. These sensors are nowadays replaced by Nanocomposite-based modalities and nanomaterials which are known for their high selectivity and physical and chemical properties. These nanosensors effectively detect heavy metal contaminants in the environment as the discharge of heavy metals into natural water as a result of human activity has become a global epidemic. Exposure to these toxic metals might induce many health-related complications, including kidney failure, brain injury, immune disorders, muscle paleness, cardiac damage, nervous system impairment and limb paralysis. Therefore, designing and developing novel sensing systems for the detection and recognition of these harmful metals in various environmental matrices, particularly water, is of extremely important. Emerging nanotechnological approaches in the past two decades have played a key role in overcoming environmentally-related problems. Nanomaterial-based fabrication of chemical nanosensors has widely been applied as a powerful analytical tool for sensing heavy metals. Portability, high sensitivity, on-site detection capability, better device performance and selectivity are all advantages of these nanosensors. The detection and selectivity have been improved using molecular recognition probes for selective binding on different nanostructures. This study aims to evaluate the sensing properties of various nanomaterials such as metal-organic frameworks, fluorescent materials, metal-based nanoparticles, carbon-based nanomaterials and quantum dots and graphene-based nanomaterials and quantum dots for heavy metal ions recognition. All these nano-architectures are frequently served as effective fluorescence probes to directly (or by modification with some large or small biomolecules) sense heavy metal ions for improved selectivity. However, efforts are still needed for the simultaneous designing of multiple metal ion-based detection systems, exclusively in colorimetric or optical fluorescence nanosensors for heavy metal cations.

Probing the Interaction of Heavy and Transition Metal Ions with Silver Nanoparticles Decorated on Graphene Quantum Dots by Spectroscopic and Microscopic Methods

We report a comprehensive study of the interaction of transition and heavy metal ions with graphene quantum dots-capped silver nanoparticles (AgGQDs) using different spectroscopic and microscopic techniques. High-resolution transmission electron microscopy studies show that the interaction of metal ions with AgGQDs leads to the formation of metal oxides, the formation of zerovalent metals, and the aggregation of Ag nanoparticles (AgNPs). The metal ions may interact with AgGQDs through selective coordination with -OH and -COOH functionalities, adsorption on the graphene moiety, and directly to AgNPs. For instance, the interaction of Cd²⁺ with AgGQDs altered the spherical shape of AgNPs into a chain-like structure. On the contrary, the formation of PbO is observed after the addition of Pb²⁺ to AgGQDs. Interestingly, the interaction of AgGQDs with Hg²⁺ results in the complete dissolution of Ag⁰ from the surface of GQDs and subsequent deposition of Hg⁰ on the graphene moiety of GQDs. Unlike transition metal ions, Cd²⁺, Pb²⁺, and Hg²⁺ can adsorb strongly on the graphene surface at the bridge, hollow, and top sites, respectively. This special interaction of heavy metal ions with the graphene surface would decide the mechanistic pathway in which the reaction proceeds. The transition metal ions Cu²⁺, Zn²⁺, Co³⁺, Mn²⁺, Ni²⁺, and Fe³⁺ induced the aggregation of AgNPs.

Identification of heavy metal ions from aqueous environment through gold, Silver and Copper Nanoparticles: An excellent colorimetric approach

Heavy metal pollution has become a severe threat to human health and the environment for many years. Their extensive release can severely damage the environment and promote the generation of many harmful diseases of public health concerns. These toxic heavy metals can cause many health problems such as brain damage, kidney failure, immune system disorder, muscle weakness, paralysis of the limbs, cardio complaint, nervous system. For many years, researchers focus on developing specific reliable analytical methods for the determination of heavy metal ions and preventing their acute toxicity to a significant extent. The modern researchers intended to utilize efficient and discerning materials, e.g. nanomaterials, especially the metal nanoparticles to detect heavy metal ions from different real sources rapidly. The metal nanoparticles have been broadly utilized as a sensing material for the colorimetric detection of toxic metal ions. The metal nanoparticles such as Gold (Au), Silver (Ag), and Copper (Cu) exhibited localized plasmon surface resonance (LPSR) properties which adds an outstanding contribution to the colorimetric sensing field. Though, the stability of metal nanoparticles was major issue to be exploited colorimetric sensing of heavy emtal ions, but from last decade different capping and stabilizing agents such as amino acids, vitmains, acids and ploymers were used to functionalize the metal surface of metal nanoparticles. These capping agents prevent the agglomeration of nanoparticles and make them more active for prolong period of time. This review covers a comprehensive work carried out for colorimetric detection of heavy metals based on metal nanoparticles from the year 2014 to onwards.

Application of Nanotechnology in Analysis and Removal of Heavy Metals in Food and Water Resources

Toxic heavy metal contamination in food and water from environmental pollution is a significant public health issue. Heavy metals do not biodegrade easily yet can be enriched hundreds of times by biological magnification, where toxic substances move up the food chain and eventually enter the human body. Nanotechnology as an emerging field has provided significant improvement in heavy metal analysis and removal from complex matrices. Various techniques have been adapted based on nanomaterials for heavy metal analysis, such as electrochemical, colorimetric, fluorescent, and biosensing technology. Multiple categories of nanomaterials have been utilized for heavy metal removal, such as metal oxide nanoparticles, magnetic nanoparticles, graphene and derivatives, and carbon nanotubes. Nanotechnology-based heavy metal analysis and removal from food and water resources has the advantages of wide linear range, low detection and quantification limits, high sensitivity, and good selectivity. There is a need for easy and safe field application of nanomaterial-based approaches.

A solvent sensitive coumarin derivative coupled with gold nanoparticles as selective fluorescent sensor for Pb2+ ions in real samples

A coumarin based fluorescent molecule, 3-amino-2-cynano-3-(7-diethylamino-2-oxo-2H-chromen-3-yl)-acrylic acid ethyl ester (1) has been synthesized and characterised. Photophysical studies of 1 exhibit polarity dependent shift of its emission maxima which have been explained on the basis the existence of polar excited state of the molecule. Combination of compound 1 and citrate capped AuNPs (AuNPs/1 conjugate) has been used as a sensing tool for heavy metals. AuNPs/1 conjugate has been found to detect Pb²⁺ selectively by naked-eye color change as well as fluorescence enhancement. On addition of molecule 1 to gold nanoparticles solution, the color of the solution becomes reddish followed by quenching in fluorescence intensity. With gradual addition of Pb²⁺, the solution of AuNPs/1 conjugate becomes violet accompanied by a fluorescence enhancement. Excited state lifetime measurement revealed that compound 1 exhibits very fast decay pattern in aqueous medium whereas in AuNPs medium the lifetime of 1 increases. Upon addition of Pb²⁺ ions to that AuNPs/1 solution the lifetime of 1 decreases again. Based on the experimental observations the mechanism of sensing of lead has been proposed thoroughly. Initially compound 1 gets absorbed on the surface of the spherical gold nanoparticles. When Pb²⁺ is added, probably gold nanoparticles aggregates to form bigger particles by releasing compound 1 from its surface to show fluorescence enhancement.

Selective Interactions of Al(III) with Plasmonic AgNPs by Colorimetric, Kinetic, and Thermodynamic Studies

In this paper, we report a simple, novel, and highly selective plasmonic nanoparticles (NPs)-based colorimetric nanoprobe for the detection of Al(III) ions in aqueous solution. 5-Hydroxy indole-2-carboxylic acid (5H-I2CA) was utilized as a reducing as well as capping agent for the preparation of silver nanoparticles (5H-I2CA@AgNPs). The interaction between Al(III) and AgNPs was determined by UV-vis absorption spectroscopy, high-resolution transmission electron microscopy, Fourier transform infrared, X-ray photoelectron spectroscopy, and dynamic light scattering techniques. The absorption values (A 452-410) of the 5H-I2CA@AgNPs solution exhibited a linear correlation with Al(III) ion concentrations within the linear range of 0.1-50 nM. An outstanding selectivity toward Al(III) was demonstrated by the proposed nanoprobe in the presence of interfering cations. Kinetics was used to study the selectivity of nanoprobe, which indicated second-order kinetics, and the rate constant was very high. The activation energies of Al(III) were found to be the lowest compared to those of other interfering ions. The results of kinetics and thermodynamic study of Al(III) were compared to those of four other competing ions. The thermodynamic data reveal that the interaction best suited for Al(III) ion compared to other metal ions (Al(III) > Co(II) > Hg(II) > Cr(III) ≅ Cr(VI)). The lower detection limit of the proposed nanoprobe for Al(III) is 1 nM. The present method also holds practical applicability for real water samples.

A compact prospective investigation on the colorimetric recognition of Hg2+ ion and photostimulated degradation of discharged toxic organic dyes motivated by H. mutabilis directed silver nanoparticles

A colorimetric sensing method for Hg²⁺ ion was developed using H. mutabilis motivated silver NPs. The calculated detection limit was estimated ∼48 pM. The nanoparticles also work as a good photo catalyst for degradation of TB and Rh-B.

A ratiometric nanoprobe based on silver nanoclusters and carbon dots for the fluorescent detection of biothiols

Ratiometric fluorescent probes could eliminate the influence from experimental factors and improve the detection accuracy. In this article, a ratiometric nanoprobe was constructed based on silver nanoclusters (AgNCs) with nitrogen-doped carbon dots (NCDs) and used for the detection of biothiols. The fluorescence peak of AgNCs was observed at 650nm with excitation wavelength at 370nm. In order to construct the ratiometric fluorescent probe, NCDs with the excitation and emission wavelengths at 370nm and 450nm were selected. After adding AgNCs, the fluorescence of NCDs was quenched. The mechanism of the fluorescence quenching was studied by fluorescence, UV-Vis absorption and the fluorescence lifetime spectra. The results indicated that the quenching could be ascribed to the inner filter effect (IFE). With the addition of biothiols, the fluorescence of AgNCs at 650nm decreased due to the breakdown of AgNCs, and the fluorescence of NCDs at 450nm recovered accordingly. Thus, the relationship between the ratio of the fluorescence intensities (I₄₅₀/I₆₅₀) and biothiol concentration was used to establish the determination method for biothiols. Cysteine (Cys) was taken as the model of biothiols, and the working curve for Cys was I₄₅₀/I₆₅₀=0.60C_Cys-1.86 (C_Cys: μmol/L) with the detection limit of 0.14μmol/L (S/N=3). Then, the method was used for the detection of Cys in human urine and serum samples with satisfactory accuracy and recovery ratios. Furthermore, the probe could be applied for the visual semi-quantitative determination of Cys by naked eyes.

A circular dichroism sensor for selective detection of Cd2+ and S2- based on the in-situ generation of chiral CdS quantum dots

We demonstrate an advance in the fabrication of circular dichroism (CD) sensors for detection of Cd²⁺ and S^2- based on chiral CdS quantum dots (QDs) generated by a facile in-situ reaction. The chiral quantum dots are generated in solutions composed of Cd²⁺, S^2-, cysteamine (CA) and L-penicillamine (L-PA), with the number of the generated particles limited by either the Cd²⁺ or S^2- concentration. We show that the magnitude of the CD signal produced by the QDs is linearly related to the initial concentration of Cd²⁺ and S^2-, with excellent selectivity over other ions. Our sensor functions over concentration ranges of 65-200μM and 7-125μM with detection limits of 59.7 and 1.6μM for Cd²⁺ and S^2-, respectively. The sensor is applied in real water samples with results comparing favorably with those obtained from ICP-OES (for Cd²⁺) and HPLC (for S^2-).

Perylene dye-functionalized silver nanoparticles serving as pH-dependent metal sensor systems

Lysine-functionalized perylene was used to modify nanoparticles. Due to the benefits from a synergetic effect that originated between the perylene and silver nanoparticles, color-based metal sensor systems were established.

Functionalization of silver nanoparticles with 5-sulfoanthranilic acid dithiocarbamate for selective colorimetric detection of Mn2+ and Cd2+ ions

A schematic representation of Mn²⁺ and Cd²⁺ ion-induced aggregation of SAA-DTC-Ag NPs.

Green synthesized nanospherical silver for selective and sensitive sensing of Cd2+colorimetrically

We report here a facile, green and one-pot synthesis of nano-spherical silver (NSS) usingBombax ceibaleaf extract (BCLE) as both a reducing and stabilizing agent.

Cysteine-based silver nanoparticles as dual colorimetric sensors for cations and anions

The synthesis of amide–triazole-based Ag NPs and their sensing ability towards anions and cations in aqueous solution were investigated. The importance of amide–triazole as a binding motif, in conjunction with Ag NPs, and the mode of the sensing ability of these amide–triazole Ag NPs as dual colorimetric sensors have been studied in detail.