Highly selective and sensitive gold nanoparticle-based colorimetric assay for PO43− in aqueous solution

A Chromogenic Probe for Detection of Biologically Important Anions and its Implications for Designing Molecular Logic Gates

Detection of fluoride (F-), acetate (AcO-), and cyanide (CN-) anions is vital from the biological and environmental aspects. In the present contributions, we have introduced a simple Salen-type chromogenic sensor, BEN, to detect these biologically important anions. Changes in UV-visible absorption spectra and color of BEN solution from very pale yellow to pink color are similar for each of these anions and found to be reversible only in the case of F- ions in attendance of HSO4- ions. The estimated limit of detection of BEN solution for detecting F-, AcO-, and CN- anions is found to be below the micromolar (μM) concentration level. Our fabricated handy paper test kit is suitable for qualitatively naked-eye detection of the anions. An immediate quantitative estimation of these important anions is possible using our BEN employing a smartphone, avoiding any costly experimental setup.

Portable Colorimetric Hydrogel Test Kits and On-Mobile Digital Image Colorimetry for On-Site Determination of Nutrients in Water

Portable colorimetric hydrogel test kits are newly developed for the on-site detection of nitrite, nitrate, and phosphate in water. Griess-doped hydrogel was prepared at the bottom of a 1.5 mL plastic tube for nitrite detection, a nitrate reduction film based on zinc powder was placed on the inner lid of a second 1.5 mL plastic tube for use in conjunction with the Griess-doped hydrogel for nitrate detection, and a molybdenum blue-based reagent was entrapped within a poly(vinyl alcohol) hydrogel matrix placed at the bottom of a third 1.5 mL plastic tube to detect phosphate. These test kits are usable with on-mobile digital image colorimetry (DIC) for the on-site determination of nutrients with good analytical performance. The detection limits were 0.02, 0.04, and 0.14 mg L−1 for nitrite, nitrate, and phosphate, respectively, with good accuracy (<4.8% relative error) and precision (<1.85% relative standard deviation). These test kits and on-mobile DIC were used for the on-site determination of nutrients in the Pak Bang and Bang Yai canals, the main canals in Phuket, Thailand. The concentrations of nitrite, nitrate, and phosphate were undetectable to 0.60 mg L−1, undetectable to 2.98 mg L−1, and undetectable to 0.52 mg L−1, respectively.

Photoactive ultrathin molecular nanosheets with reversible lanthanide binding terpyridine centers

In recent years, functional molecular nanosheets have attracted much attention in the fields of sensors and energy storage. Here, we present an approach for the synthesis of photoactive metal-organic nanosheets with ultimate molecular thickness. To this end, we apply low-energy electron irradiation induced cross-linking of 4'-(2,2':6',2''-terpyridine-4'-yl)-1,1'-biphenyl-4-thiol self-assembled monolayers on gold to convert them into functional ∼1 nm thick carbon nanomembranes possessing the ability to reversibly complex lanthanide ions (Ln-CNMs). The obtained Ln-CNMs can be prepared on a large-scale (>10 cm²) and inherit the photoactivity of the pristine terpyridine lanthanide complex (Ln(III)-tpy). Moreover, they possess mechanical stability as free-standing sheets over micrometer sized openings. The presented methodology paves a simple and robust way for the preparation of ultrathin nanosheets with tailored photoactive properties for application in photocatalytic and energy conversion devices.

A sensitive colorimetric probe for detection of the phosphate ion

In the present article, we report a novel colorimetric probe (TNT@MB) for the detection of the phosphate ion, which is based on the strong binding affinity between the phosphate ion and titanium dioxide nanotubes (TNTs). TNTs were synthesized from TiO₂ nanoparticles by hydrothermal treatment. The obtained TNTs had an average length of 200 ± 50 nm and an average width of 12 ± 5 nm. TNT@MB was prepared by adsorbing methyl blue onto TNTs in acidic condition. The optimal synthesis conditions for TNT@MB consisted in having 0.05 g of TNTs react with 1 μmole of methyl blue at pH 2 for 90 min. TNTs and TNT@MB were characterized by UV–vis diffuse reflection spectroscopy, TEM, FTIR, and XPS. The phosphate-ion sensing behavior of TNT@MB was investigated by UV–visible spectroscopy. The phosphate-ion concentration linear range and detection limit of this method based on TNT@MB were 1–40 μM and 0.59 μM, respectively. A sample of lake water was used as a real sample, and analyte recovery rates were measured in the 102.5–103.6% range, with relative standard deviations below 5.6% (n = 3). We also found that this probe could be reused after regeneration in alkaline solution. These results indicate that as a colorimetric probe, TNT@MB has the advantages of being environmentally friendly, inexpensive, and simple to use, as well as giving rise to an easily observable color change.

Detection of cyanide ions in aqueous solutions using cost effective colorimetric sensor

Cyanide (CN̄) is one of the most toxic material to the human and environment. It is very important to develop the diagnostic tools for the detection of CN̄ ions. Moreover, detection of the ions in an aqueous medium is a challenging task as water molecules interfere with the sensing mechanism. In this context, we prepared chemical sensor, S1, having anthraquinone as a signaling unit and thiourea as a binding site. This sensor exhibited distinct visual color and spectral changes in response to CN̄ ion over other testing anions in 50% aq. DMSO solution. However, in 20% aq. DMSO solution, S1 exhibited obvious spectral and color changes in response to CN̄, fluoride (F̄), acetate (Ac̄) and benzoate (Bz̄). Another sensor, S2, having a same signaling unit with that of S1, but a different binding site of urea group. In contrast to S1, S2 exhibited obvious spectral and color changes to F̄ in 2.5% aq. DMSO solution. NMR titration results suggested that the spectral and colorimetric responses were due to the formation of host-guest complex and deprotonation events. Finally, economically viable paper-based colorimetric "test stripes" of S1 were fabricated to detect the CN̄ ions in 100% aqueous solution.

Label-free selective detection of ampicillin drug in human urine samples using silver nanoparticles as a colorimetric sensing probe

Stable citrate-capped silver nanoparticles (AgNPs) were developed as a colorimetric sensing probe for selective detection of ampicillin in urine samples.

Detection of phosphate based on phosphorescence of Mn doped ZnS quantum dots combined with cerium(iii)

A simple and rapid room-temperature phosphorescence (RTP) sensor for phosphate detection was developed on the basis of Ce³⁺ modulated mercaptopropionic acid (MPA)-capped Mn-doped ZnS quantum dots (QDs).

Gold nanocomposite assemblies using functionalized Ru(ii)-polypyridyl complexes

Ru(ii)-polypyridyl complexes with various surface anchoring functional groups were prepared and utilized as capping and engineering agents to attain surface functionalized gold nanocomposites (Au NCs) with unique morphologies.

Enhancement of plasmonic resonance through an exchange reaction on the surface of silver nanoparticles: application to the highly selective detection of triazophos pesticide in food and vegetable samples

The proposed method is based on the aggregation of AgNPs due to the exchange of citrate ions from the surface of NPs with triazophos pesticide and causes the color change and red shift in LSPR of AgNPs in the UV-visible region used as sensing probe.

Reversible catalysis for the reaction between methyl orange and NaBH4 by silver nanoparticles

The reaction between MO and NaBH4 catalyzed by Ag NPs has been studied. Ag NPs catalyzed the reduction of MO rapidly, while adding CTAB into the solution caused the regeneration of MO. Thus, reversible catalysis for the reaction between MO and NaBH4 by Ag NPs was discovered for the first time.

Selective binding and extraction of aqueous dihydrogen phosphate solutions via three-armed thiourea receptors

A three-armed thiourea host that strongly and selectively binds H₂PO₄⁻and extracts HPO₄²⁻from water into chloroform.

New Gold Nanostructures for Sensor Applications: A Review

Gold based structures such as nanoparticles (NPs) and nanowires (NWs) have widely been used as building blocks for sensing devices in chemistry and biochemistry fields because of their unusual optical, electrical and mechanical properties. This article gives a detailed review of the new properties and fabrication methods for gold nanostructures, especially gold nanowires (GNWs), and recent developments for their use in optical and electrochemical sensing tools, such as surface enhanced Raman spectroscopy (SERS).

A single colorimetric sensor for multiple target ions: the simultaneous detection of Fe2+ and Cu2+ in aqueous media

The receptor 1 provides a novel approach for the simultaneous colorimetric recognition of two metal ions Fe²⁺ and Cu²⁺.

A reversible competition colorimetric assay for the detection of biothiols based on ruthenium-containing complex

A novel reversible colorimetric sensor, which based on a competitive ligation of Hg(2+) by thiols, cysteine (Cys) or glutathione (GSH), and thiocyanate (SCN) on the N3 dye (bis(4,4'-dicarboxy-2,2'-bipyridine) dithiocyanato ruthenium (II)), was developed for the detection of biothiols. First, Hg(2+) ions coordinate to the sulfur atom of the dyes' SCN groups, and this interaction induces a change in color from red to yellow, owing to the formation of a complex of Hg(2+)-N3. Then, in the presence of biothiols, the red color of N3 is recovered concomitantly with the dissociation of the Hg(2+)-N3 complex, due to the extraction of Hg(2+) by biothiols. Thus the corresponding color variation in the process of the dissociation of the Hg(2+)-N3 complex can be employed for the quantitative detection of thiols using UV-vis spectroscopy. In particular, the transformation can be readily viewed with the naked eye. A good linear relationship between the change in absorbance (ΔAbs) of Hg(2+)-N3 at 461 nm and the thiol concentration was obtained in the range of 0.5-25 μM, and the detection limits are then calculated to be 57 and 52 nM for Cys and GSH, respectively. The proposed colorimetric assay displays a high selectivity for Cys over various other amino acids and GSSG (oxidized glutathione).