Sensitive and selective detection of trivalent chromium using Hyper Rayleigh Scattering with 5,5'-dithio-bis-(2-nitrobenzoic acid)-modified gold nanoparticles

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.

Chemistry, Structures, and Advanced Applications of Nanocomposites from Biorenewable Resources

Researchers have recently focused on the advancement of new materials from biorenewable and sustainable sources because of great concerns about the environment, waste accumulation and destruction, and the inevitable depletion of fossil resources. Biorenewable materials have been extensively used as a matrix or reinforcement in many applications. In the development of innovative methods and materials, composites offer important advantages because of their excellent properties such as ease of fabrication, higher mechanical properties, high thermal stability, and many more. Especially, nanocomposites (obtained by using biorenewable sources) have significant advantages when compared to conventional composites. Nanocomposites have been utilized in many applications including food, biomedical, electroanalysis, energy storage, wastewater treatment, automotive, etc. This comprehensive review provides chemistry, structures, advanced applications, and recent developments about nanocomposites obtained from biorenewable sources.

Metal oxide QD based ultrasensitive microsphere fluorescent sensor for copper, chromium and iron ions in water

Herein we developed a rapid, cheap, and water-soluble ultra-sensitive ZnO quantum dot (QD) based metal sensor for detecting different hazardous metal ions up to the picomolar range in water. Various spectroscopic and microscopic techniques confirmed the formation of 2.15 ± 0.46 μm of ZnO QD conjugated CMC microspheres (ZCM microspheres) which contain 5.5 ± 0.5 nm fluorescent zinc oxide (ZnO) QDs. Our system, as a promising sensor, exhibited excellent photostability and affinity towards various heavy metal ions. The detection limits were calculated to be 16 pM for Cu²⁺ and 0.18 nM for Cr⁶⁺ ions which are better than previously reported values. The simple fluorescence 'turn off' property of our ZCM microsphere sensor system can serve a two-in-one purpose by not only detecting the heavy metals but also quantifying them. Nonetheless, pattern recognition for different heavy metals helped us to detect and identify multiple heavy metal ions. Finally, their practical applications on real samples also demonstrated that the ZCM sensor can be effectively utilized for detection of Cr⁶⁺, Fe³⁺, Cu²⁺ present in the real water samples. This study may inspire future research and design of target fluorescent metal oxide QDs with specific functions.

Counter-Ion Effect on the Thermodynamics of Cr(III) Exchange by Macroporous Amberlyst-15

In the present study, we have investigated the counter-ion effect on the thermodynamics of Cr(III) sorption by macroporous resin Amberlyst-15. The exchange reaction was studied as a function of concentration of Cr(III) and nature of counter-ions at different temperatures. It was observed that nature of counter-ions have a profound effect on the exchange of Cr(III) ions. The selectivity of Amberlyst-15 towards metal ion sorption follows the order univalent>divalent> trivalent forms. This trend can be associated to the electrostatic interaction of ions with the functional sites of the resin. The equilibrium pH values (pH

Gold nanoparticle-based nano-probe for the colorimetric sensing of Cr3+ and Cr2O72- by the coordination strategy

In this work, an N-T/gold nanoparticle system was assembled for the convenient and colorimetric identification of Cr based on its coordination chemistry with the thymine derivative (N-T). In addition to the visible colorimetric changes for the qualitative Cr identification, the A_{630 nm/520 nm} values changed linearly with Cr concentration over a range of 0.5-2.5 μM and the detection limits reached 0.03 μM and 0.07 μM for Cr³⁺ and Cr₂O₇^2-, respectively, both of which satisfied the Cr water quality standards of the U.S. EPA, WHO and China. Furthermore, a more convenient method was developed for quantitative determination of Cr concentrations in practical samples based on the Eyedropper function in Microsoft's PowerPoint software, wherein the RGB (red, green and blue) value of the sample could be easily screened in the colorimetric card for a more accurate result with good recovery, avoiding complicated instrumentation.

Visual Chronometric Assay for Chromium(III) Ions Based on the Cu2O Nanocube-Mediated Clock Reaction

We report a visual chronometric assay for Cr³⁺ based on the Cu₂O nanocube-mediated clock reaction of methylene blue (MB) and N₂H₄. MB with a blue color can be easily reduced by excess N₂H₄ to form colorless leuco-MB in the presence of Cu₂O nanocubes as a catalyst in a short time. However, the addition of Cr³⁺ decreases the catalytic activity of Cu₂O nanocubes owing to the coordination interactions between them, leading to an increase in the reaction time. The reaction time change was employed for selective detection of Cr³⁺. This assay has a wide dynamic range from 0.03 to 600 μM with a limit of detection of 2.7 nM. Remarkably, different concentrations of Cr³⁺ can be directly detected with the naked eye by observing the color-fading speed. Additionally, this assay was successfully used to determine Cr³⁺ in real water samples.

Alizarin Dye based ultrasensitive plasmonic SERS probe for trace level Cadmium detection in drinking water

Alizarin functionalized on plasmonic gold nanoparticle displays strong surface enhanced Raman scattering from the various Raman modes of Alizarin, which can be exploited in multiple ways for heavy metal sensing purposes. The present article reports a surface enhanced Raman spectroscopy (SERS) probe for trace level Cadmium in water samples. Alizarin, a highly Raman active dye was functionalized on plasmonic gold surface as a Raman reporter, and then 3-mercaptopropionic acid, 2,6-Pyridinedicarboxylic acid at pH 8.5 was immobilized on the surface of the nanoparticle for the selective coordination of the Cd (II). Upon addition of Cadmium, gold nanoparticle provide an excellent hotspot for Alizarin dye and Raman signal enhancement. This plasmonic SERS assay provided an excellent sensitivity for Cadmium detection from the drinking water samples. We achieved as low as 10 ppt sensitivity from various drinking water sources against other Alkali and heavy metal ions. The developed SERS probe is quite simple and rapid with excellent repeatability and has great potential for prototype scale up for field application.

Silver Nanoparticle-Enhanced Resonance Raman Sensor of Chromium(III) in Seawater Samples

Tris(hydroxymethyl)aminomethane ethylenediaminetetraacetic acid (Tris-EDTA), upon binding Cr(III) in aqueous solutions at pH 8.0 on silver nanoparticles (AgNPs), was found to provide a sensitive and selective Raman marker band at ~563 cm-1, which can be ascribed to the metal-N band. UV-Vis absorption spectra also supported the aggregation and structural change of EDTA upon binding Cr(III). Only for Cr(III) concentrations above 500 nM, the band at ~563 cm-1 become strongly intensified in the surface-enhanced Raman scattering spectra. This band, due to the metal-EDTA complex, was not observed in the case of 50 mM of K+, Cd2+, Mg2+, Ca2+, Mn2+, Co2+, Na+, Cu2+, NH4+, Hg2+, Ni2+, Fe3+, Pb2+, Fe2+, and Zn2+ ions. Seawater samples containing K, Mg, Ca, and Na ion concentrations higher than 8 mM also showed the characteristic Raman band at ~563 cm-1 above 500 nM, validating our method. Our approach may be useful in detecting real water samples by means of AgNPs and Raman spectroscopy.

Antimicrobial Activity of Gold Nanoparticles and Ionic Gold

Gold, in both nanoparticle (AuNPs) and ionic forms, has been studied for antibiotic activities. Some of the organic complexes of Au (I & III) ions are antibacterial. AuNPs are antifungal, but with conflicting results on their antibacterial activity. We summarized these publications and found that AuNPs are generally not bactericidal, or only weakly at high concentrations. However, the reason AuNPs appear to be bactericidal is possibly due to the bactericidal activity of co-existing chemicals not completely removed from AuNPs: gold ions, surface coating agents, and chemicals involved in the synthesis. AuNPs can also act as carriers or delivery vehicles of antibiotics, thus enhancing the bactericidal effect of the antibiotics.

Smart gold nanosensor for easy sensing of lead and copper ions in solution and using paper strips

A smart gold nanosensor, Au–TA–DNS is designed that can rapidly detect very low concentrations of Pb²⁺ and Cu²⁺ ions.

Highly sensitive detection of chromium (III) ions by resonance Rayleigh scattering enhanced by gold nanoparticles

Simple and sensitive determination of chromium (III) ions (Cr(3+)) has potential applications for detecting trace contamination in environment. Here, the assay is based on the enhancement of resonance Rayleigh scattering (RRS) by Cr(3+)-induced aggregation of citrate-capped gold nanoparticles (AuNPs). Transmission electron microscopy (TEM) and UV-vis absorption spectroscopy were employed to characterize the nanostructures and spectroscopic properties of the Cr(3+)-AuNP system. The experiment conditions, such as reaction time, pH value, salt concentration and interfering ions, were investigated. The combination of signal amplification of Cr(3+)-citrate chelation with high sensitivity of RRS technique allow a selective assay of Cr(3+) ions with a detection limit of up to 1.0 pM. The overall assay can be carried out at room temperature within only twenty minutes, making it suitable for high-throughput routine applications in environment and food samples.

Simple fluorescence-based detection of Cr(iii) and Cr(vi) using unmodified gold nanoparticles

A fluorescence-based method for the determination of both Cr(iii) and Cr(vi) using unmodified gold nanoparticles.

Production of a monoclonal antibody and development of an immunoassay for detection of Cr(III) in water samples

In this study we report the production of a monoclonal antibody (Mab) specific for Cr(III)-chelate and the development of a competitive immunoassay for detection of Cr(III) in water samples. In the assay, the complete antigen (Cr(III)-ITCBE-BSA) was used as coating antigen, and Cr(III)-ITCBE as competitor competes with coating antigen to bind with Mab. Using this approach, the spiked water samples with Cr(III) were detected. The linear range of the detection was 0.7-12.4 ng mL(-1). The limit of the detection (LOD) was 0.51 ng mL(-1). The spiked results were also confirmed by ICP-MS, which showed a good correlation (R(2)=0.997) between the two methods. The results indicated that the developed assay was reliable and suitable for the detection of Cr(III) in water samples.