Sensitive and selective colorimetric detection of cadmium(II) using gold nanoparticles modified with 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole

Establishment of a Rapid Detection Method for Cadmium Ions via a Specific Cadmium Chelator N-(2-Acetamido)-Iminodiacetic Acid Screened by a Novel Biological Method

Heavy metal ions such as cadmium, mercury, lead, and arsenic in the soil cannot be degraded naturally and are absorbed by crops, leading to accumulation in agricultural products, which poses a serious threat to human health. Therefore, establishing a rapid and efficient method for detecting heavy metal ions in agricultural products is of great significance to ensuring the health and safety. In this study, a novel optimized spectrometric method was developed for the rapid and specific colorimetric detection of cadmium ions based on N-(2-Acetamido)-iminodiacetic acid (ADA) and Victoria blue B (VBB) as the chromogenic unit. The safety evaluation of ADA showed extremely low biological toxicity in cultured cells and live animals. The standard curve is y = 0.0212x + 0.1723, R2 = 0.9978, and LOD = 0.08 μM (0.018 mg/kg). The liner concentrations detection range of cadmium is 0.1-10 μM. An inexpensive paper strip detection method was developed with a detection limit of 0.2 μM to the naked eye and a detection time of less than 1 min. The method was successfully used to assess the cadmium content of rice, soybean, milk, grape, peach, and cabbage, and the results correlated well with those determined by inductively coupled plasma-mass spectrometry (ICP-MS). Thus, our study demonstrated a novel rapid, safe, and economical method for onsite, real-time detection of cadmium ions in agricultural products.

Sustainable and reusable probe-encapsulated porous poly(AMST-co-TRIM) monolithic sensor for the selective and ultra-sensitive detection of toxic cadmium(II) from industrial/environmental wastewater

This study focuses on a new type of fast responsive solid-state visual colorimetric sensor, custom engineered with dual-entwined porous polymer imbued with chromoionophoric 4-(sec-butyl)- 2-((5-mercapto-1,3,4-thiadiazol-2-yl)diazenyl)phenol (SMDP) probe for selective and ultra-sensitive colorimetric sensing of Cd(II). The polymer monolith, i.e., poly(aminostyrene-co-trimethylolpropanetrimethacrylate) denoted as poly(AMST-co-TRIM), is designed through a stoichiometric blending of monomer, crosslinker, and porogens leading to superior surface area, pore and adsorption properties for the voluminous incorporation of SMDP probe for target specific ion sensing. The porosity, surface and structural characteristics of the poly(AMST-co-TRIM)monolith and poly(AMST-co-TRIM)SMDP sensor are investigated using p-XRD, XPS, TG-DTA, FT-IR, BET/BJH, FE-SEM, HR-TEM, EDAX, and SAED techniques. The poly(AMST-co-TRIM)SMDP sensor reveals a frozen geometrical orientation of SMDP molecules to bind selectively with Cd(II), forming stable charge-transfer complexes by exhibiting transitional visible color shifts from light yellow to dark green (λmax 608 nm). The sensor imposes a linear response from 0-200 ppb, with quantification and detection limits of 0.95 and 0.28 ppb. The fabricated sensor material is cost-effective and versatile in its solid-state naked-eye sensing, with excellent reusability. The sensor performance has been verified using various environmentally contaminated water and commercial cigarette samples, with a recovery of ≥ 99.12% and an RSD of ≤ 1.95%, thus reflecting exceptional data reproducibility/reliability.

Rapid and naked-eye colorimetric detection of ultra trace sumatriptan in drinking water, saliva, and human urine samples based on the aggregation of gold nanoparticles

In this study, the determination of sumatriptan (SUM) was performed using a simple, rapid, and precise colorimetric method based on the surface plasmon resonance (SPR) feature of gold nanoparticles (AuNPs). By adding SUM, the aggregation was observed in AuNPs with red-to-blue color shifts. The size distribution of NPs was estimated before and after adding SUM via dynamic light scattering (DLS), which was found to be 15.34 and 97.45 nm, respectively. Characterization of AuNPs, SUM, and AuNPs in combination with SUM was investigated using transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). Examining the effect of pH, the volume of buffer, the concentration of AuNPs, interaction time, and ionic strength revealed that their optimal values were 6, 100 μL, 5 μM, 14 min, and 12 μg L-1, respectively. The suggested method was able to determine the amount of SUM in a linear range of 10 to 250 μg L-1 with a limit of detection (LOD) and limit of quantification (LOQ) of 0.392 and 1.03 μg L-1, respectively. This approach was successfully applied to determine SUM in drinking water, saliva, and human urine samples with relative standard deviations (RSD) lower than 0.03%, 0.3%, and 1.0%, respectively.

Gold Nanoparticles as Exquisite Colorimetric Transducers for Water Pollutant Detection

Gold nanoparticles (AuNPs) are useful nanomaterials as transducers for colorimetric sensors because of their high extinction coefficient and ability to change color depending on aggregation status. Therefore, over the past few decades, AuNP-based colorimetric sensors have been widely applied in several environmental and biological applications, including the detection of water pollutants. According to various studies, water pollutants are classified into heavy metals or cationic metal ions, toxins, and pesticides. Notably, many researchers have been interested in AuNP that detect water pollutants with high sensitivity and selectivity, while offering no adverse environmental issues in terms of AuNP use. This review provides a representative overview of AuNP-based colorimetric sensors for detecting several water pollutants. In particular, we emphasize the advantages of AuNP as colorimetric transducers for water pollutant detection in terms of their low toxicity, high stability, facile processability, and unique optical properties. Next, we discuss the status quo and future prospects of AuNP-based colorimetric sensors for the detection of water pollutants. We believe that this review will promote research and development of AuNP as next-generation colorimetric transducers for water pollutant detection.

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.

A theoretical approach on the ability of functionalized gold nanoparticles for detection of Cd2

Cadmium (Cd) as a toxic element that is widely present in water, soil, and air has important effects on human health, therefore proposing an accurate and selective method for detection of this element is of importance. In this article, by employing full atomistic molecular dynamics (MD) simulations and density functional theory dispersion corrected (DFT-D3) calculations, the effects of 6-mercaptonicotinic acid (MNA) and L-cysteine (CYS) on the stability of gold nanoparticles (AuNPs) and their sensitivity against Cd²⁺ were investigated. The obtained results indicate that pure AuNPs are not stable in water, while functionalized AuNPs with CYS and MNA groups have considerable stability without aggregation. In other words, the functional groups on the surface of AuNPs elevate their resistance against aggregation by an increase in the repulsive interactions between the gold nanoparticles. Moreover, functionalized AuNPs have considerable ability for selective detection of Cd²⁺ in the presence of different metal ions. Based on the MD simulation results, MNA-CYS-AuNPs (functionalized AuNPs with both functional groups) have the maximum sensitivity against Cd²⁺ in comparison with MNA-AuNPs and CYS-AuNPs due to the strong electrostatic interactions. DFT-D3 calculations reveal that the most probable interactions between the metal ions and functional groups are electrostatic, and Cd²⁺ can aggregate functionalized AuNPs due to strong electrostatic interactions with MNA and CYS groups. Moreover, charge transfer and donor-acceptor analyses show that molecular orbital interactions between the functional groups and Cd²⁺ can be considered as the driving force for AuNPs aggregation. A good agreement between the theoretical results and experimental data confirms the importance of the molecular modeling methods as a fast scientific protocol for designing new functionalized nanoparticles for application in different fields.

Chemical sensing with Au and Ag nanoparticles

Noble metal nanoparticles (NPs) are ideal scaffolds for the fabrication of sensing devices because of their high surface-to-volume ratio combined with their unique optical and electrical properties which are extremely sensitive to changes in the environment. Such characteristics guarantee high sensitivity in sensing processes. Metal NPs can be decorated with ad hoc molecular building blocks which can act as receptors of specific analytes. By pursuing this strategy, and by taking full advantage of the specificity of supramolecular recognition events, highly selective sensing devices can be fabricated. Besides, noble metal NPs can also be a pivotal element for the fabrication of chemical nose/tongue sensors to target complex mixtures of analytes. This review highlights the most enlightening strategies developed during the last decade, towards the fabrication of chemical sensors with either optical or electrical readout combining high sensitivity and selectivity, along with fast response and full reversibility, with special attention to approaches that enable efficient environmental and health monitoring.

MXene-Coated Air-Permeable Pressure-Sensing Fabric for Smart Wear

Considering the fast development of wearable electronics and soft robotics, pressure sensors with high sensitivity, durability, and washability are of great importance. However, the surface modification of fabrics with high-sensitivity active materials requires that issues associated with poor interface adhesion and stability are resolved. In this study, we explored the key factors for firmly bonding MXene to fabric substrates to fabricate wearable and washable pressure sensing fabric. The interactions between MXene and various fabrics were elucidated by investigating the adsorption and binding capacities. The natural rough surface of cotton fibers also promoted the firm adsorption of MXene. As a result, MXene was difficult to detach, even with mechanical washing and ultrasonic treatment. Further, the abundant functional groups on the MXene surface were conducive to interfacial interactions with cotton fibers. An increase in the amount of fluorine-containing functional groups also improved the hydrophobicity of the fabric surface. The good force-sensitive resistance of MXene-coated cotton allowed this pressure-sensing fabric to function as a flexible pressure sensor, which showed a high gauge factor (7.67 kPa^-1), a rapid response and relaxation speed (<35 ms), excellent stability (>2000 cycles), and good washing durability. Further, the as-fabricated flexible pressure sensor was demonstrated as a wearable human-machine interface that supported multitouch interactions and exhibited a rapid response. Thus, this work provides a new approach for developing next-generation high-sensitivity wearable pressure sensors.

Enhanced Pollutant Adsorption and Regeneration of Layered Double Hydroxide-Based Photoregenerable Adsorbent

Efforts to combine photocatalysts with organic and inorganic adsorbents in engineered composite materials have been pursued extensively to harness sunlight for a green, sustainable regeneration of exhausted adsorbent. Recent advances combining benchmark photocatalyst, titanium dioxide (TiO₂), with an inorganic adsorbent, layered double hydroxides (LDHs), have shown potential for an inorganic adsorbent-photocatalyst system but faced critical limitations in realizing practical applications: low adsorption capacity and slow, inefficient photocatalytic regeneration. This study presents an enhanced TiO₂/LDH based material that demonstrates a dramatically increased efficiency for both decontamination through adsorption and subsequent solar, photocatalytic regeneration. The combination of delamination and high temperature treatment of LDH is utilized to drastically enhance the adsorption capacity toward model contaminant Methyl Orange to 1450-1459 mg/g, which is even higher than most commercial and lab-synthesized carbon-based adsorbents. Light-active plasmonic nanoparticles are employed to increase the photocatalytic regeneration performance, and experimental results show that the synthesized composite material regains above 97% of its adsorption capacity for 5 cycles of regeneration and readsorption. Overall, the results of this study demonstrate potential for the development of inorganic multifunctional adsorbents that can harness a variety of chemical reactions without the loss of adsorptivity over long-term use.

Metal Cation Detection in Drinking Water

Maintaining a clean water supply is of utmost importance for human civilization. Human activities are putting an increasing strain on Earth’s freshwater reserves and on the quality of available water on Earth. To ensure cleanliness and potability of water, sensors are required to monitor various water quality parameters in surface, ground, drinking, process, and waste water. One set of parameters with high importance is the presence of cations. Some cations can play a beneficial role in human biology, and others have detrimental effects. In this review, various lab-based and field-based methods of cation detection are discussed, and the uses of these methods for the monitoring of water are investigated for their selectivity and sensitivity. The cations chosen were barium, cadmium, chromium, copper, hardness (calcium, magnesium), lead, mercury, nickel, silver, uranium, and zinc. The methods investigated range from optical (absorbance/fluorescence) to electrical (potentiometry, voltammetry, chemiresistivity), mechanical (quartz crystal microbalance), and spectrometric (mass spectrometry). Emphasis is placed on recent developments in mobile sensing technologies, including for integration into microfluidics.

Highly selective and sensitive colorimetric determination of Cr3+ ion by 4-amino-5-methyl-4H-1,2,4-triazole-3-thiol functionalized Au nanoparticles

In this work, a rapid, selective naked eyes colorimetric chemical probe for the detection of Cr³⁺ was developed based on functionalization of gold nanoparticles. For this purpose, surface of Au NPs was functionalized using 4-amino-5-methyl-4H-1,2,4-triazole-3-thiol (AMTT). Through colorimetric studies, it was found that in the presence of Cr³⁺ ions, AMTT-Au NPs instantly aggregated and resulted in a color change of the solution from red to blue. The color change of AMTT-Au NPs due to the aggregation induced by Cr³⁺ can be seen with even naked eyes and also by UV-Vis spectroscopy with a detection limit of 1.8μM and 0.1μM, respectively. AMTT-Au NPs showed excellent selectivity toward Cr³⁺ compared to other cations tested, including K⁺, Na⁺, Cs⁺, Fe³⁺, Ni²⁺, Cu²⁺, Co²⁺, Zn²⁺, Ba²⁺, Ca²⁺, Mg²⁺, Cd²⁺, Pb²⁺, Hg²⁺ ions and especially all trivalent lanthanide ions. The absorbance ratio (A₆₅₀/A₅₂₅) was linear toward Cr³⁺ concentrations in the range of 0.6-6.1μM (R²=0.996). The best response was achieved over a pH range of 3-5. Furthermore, the proposed colorimetric method based on AMTT-Au NPs was successfully used for Cr³⁺ ion detection in plasma sample and some water samples.

Hydrogen bonding recognition and colorimetric detection of isoprenaline using 2-amino-5-mercapto-1,3,4-thiadiazol functionalized gold nanoparticles

In this paper, we describe a rapid, low-cost and highly sensitive colorimetric method for the detection of isoprenaline, based on 2-amino-5-mercapto-1,3,4-thiadiazol (AMTD) functionalized gold nanoparticles (AMTD-AuNPs) as a sensing element. Hydrogen bonding interaction between isoprenaline and AMTD resulted in the aggregation of AuNPs and a consequent color change of AuNPs from red to blue. The concentration of isoprenaline could be detected with the naked eye or a UV-visible spectrometer. Results showed that the absorbance ratio (A650/A524) was linear with isoprenaline concentrations in the range of 0.2 to 2.6μM (R=0.997). The detection limit of this method was 0.08μM. The proposed method is simple, without using complicated instruments and adding salts for enhancing sensitivity. This probe could be successfully applied to the determination of isoprenaline in human serum samples and urine samples after deproteinization.

Naked eye and spectrophotometric detection of chromogenic insecticide in aquaculture using amine functionalized gold nanoparticles in the presence of major interferents

Detection of a chromogenic insecticide, malachite green (MG) using 3,5-diamino-1,2,4-triazole capped gold nanoparticles (DAT-AuNPs) by both naked eye and spectrophotometry was described in this paper. The DAT-AuNPs were prepared by wet chemical method and show absorption maximum at 518nm. The zeta potential of DAT-AuNPs was found to be -39.9mV, suggesting that one of the amine groups of DAT adsorbed on the surface of AuNPs and the other amine group stabilizes the AuNPs from aggregation. The wine red color DAT-AuNPs changes to violet while adding 25μM MG whereas the absorption band at 518nm was increased and shifted towards longer wavelength. However, addition of 70μM MG leads to the aggregation of DAT-AuNPs. This is due to strong electrostatic interaction between ammonium ion of MG and the free amine group of DAT. Based on the color change and shift in SPR band, 25 and 5μM MG can be easily detected by naked eye and spectrophotometry. The DAT-AuNPs show high selectivity towards MG even in the presence of 5000-fold higher concentrations of common interferents. The practical application was successfully demonstrated by determining MG in fish farm water.

A coumarin–chalcone hybrid used as a selective and sensitive colorimetric and turn-on fluorometric sensor for Cd2+ detection

A chalcone-based naked-eye colorimetric chemical sensor, (E)-4-hydroxy-3-(3-(4-methoxyphenyl)acryloyl)-2H-chromen-2-one 1a, was developed for selective and sensitive recognition of Cd²⁺ in mixed aqueous–organic media.

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.

Hydrophilic silver nanoparticles with tunable optical properties: application for the detection of heavy metals in water

Due their excellent chemo-physical properties and ability to exhibit surface plasmon resonance, silver nanoparticles (AgNPs) have become a material of choice in various applications, such as nanosensors, electronic devices, nanobiotechnology and nanomedicine. In particular, from the environmental monitoring perspective, sensors based on silver nanoparticles are in great demand because of their antibacterial and inexpensive synthetic method. In the present study, we synthesized AgNPs in water phase using silver nitrate as precursor molecules, hydrophilic thiol (3-mercapto-1-propanesulfonic acid sodium salt, 3MPS) and sodium borohydride as capping and reducing agents, respectively. The AgNPs were characterized using techniques such as surface plasmon resonance (SPR) spectroscopy, dynamic light scattering (DLS), zeta potential (ζ-potential) measurements and scanning tunneling microscopy (STM). Further, to demonstrate the environmental application of our AgNPs, we also applied them for heavy metal sensing by detecting visible color modification due to SPR spectral changes. We found that these negatively charged AgNPs show good response to nickel (II) and presented good sensibility properties for the detection of low amount of ions in water in the working range of 1.0-0.1 ppm.

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.

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

Low-level cadmium ion (Cd(2+)) exposure contributes much toward the causation of chronic disease. Due to its low permissible exposure limit, overexposures may occur even in situations where trace quantities of Cd(2+) exist. So far, no effective treatment for Cd(2+) toxicity has been reported. Prevention of further exposure is the most important step in management of patients suggestive of Cd(2+) intoxication. Development of sensors for Cd(2+) is of great interest to ensure early diagnosis and improve management. We propose here a simple, low-cost (0.1$ per sample) yet very sensitive (limit of detection is 3.0 nM) and selective colorimetric assay for rapid (2 min) determination of Cd(2+) based on 5-sulfosalicylic acid functionalized silver nanoparticles (SAA-AgNPs). This method shows excellent selectivity for Cd(2+) over the other 16 metal ions. It is also precise and highly reproducible in determining Cd(2+) in real samples such as tap water, milk, serum, and urine with recoveries ranging from 93 to 110%, indicating the wide practical application to samples suspected of Cd(2+) exposure.

Phytolatex synthesized gold nanoparticles as novel agent to enhance sun protection factor of commercial sunscreens

OBJECTIVE

To study the potential of phytolatex (latex of Jatropha gossypifolia) fabricated gold nanoparticles as promising candidate in sunscreen formulations for enhancement in sun protection factor.

METHODS

In this study, plant latex was used as reducing and capping agent to synthesize gold nanoparticles. Latex fabricated gold nanoparticles were characterized by different analytical techniques such as UV-Vis spectroscopy, Fourier transforms infrared spectroscopy, dynamic light scattering, zeta potential, transmission electron microscopy and X-ray diffraction. Potential of sunscreen preparations containing gold nanoparticles to protect skin from UV radiation was investigated by in vitro sun protection factor analysis. Transmission electron microscopy and UV-Vis spectroscopy techniques were used to get insight into mechanism by which AuNPs enhance sun protection factor of sunscreen.

RESULTS

Monodisperse gold nanoparticles were synthesized using plant latex without need of hazardous chemical reducing and capping agents. Gold nanoparticles showed surface plasmon resonance peak at 550 nm in UV-Vis spectroscopic study. Gold nanoparticles were spherical and triangular in shape with size range of 30-50 nm. The zeta potential of gold nanoparticles was found to be -9.39 ± 0.19 mV. XRD analysis confirmed face-centred cubic (fcc) structure of gold nanoparticles. Incorporation of latex synthesized gold nanoparticles (2 and 4 [% w/w]) into commercial sunscreens increased the sun protection factor from 2.43 ± 0.74 to 24.11 ± 0.46% than sunscreen devoid of gold nanoparticles. From UV-Vis absorption spectroscopy and TEM analysis, it was observed that gold nanoparticles enhance the sun protection factor of commercial sunscreens due to reflection and scattering of UV radiation.

CONCLUSION

Phytolatex synthesized gold nanoparticle is novel agent to enhance sun protection factor of commercial sunscreens. Gold nanoparticles aggregation in commercial sunscreen was the main factor behind SPF enhancement. This study showed that gold nanoparticles are potent alternative to traditionally used hazardous titanium dioxide and zinc oxide nanoparticles in sunscreen.