A simple yet highly selective colorimetric sensor for cyanide anion in an aqueous environment

The nucleophilic nature of cyanide is used to create a simple, sensitive, and highly effective sensor, 2-(trifluoroacetylamino)anthraquinone (2-TFAQ), for the easy "naked-eye" detection of very low concentrations of cyanide in an aqueous environment.     

Highly selective silver nanoparticles based label free colorimetric sensor for nitrite anions

Highly selective label free colorimetric sensor based on AgNPs stabilized by phenolic chelating ligand, N,N′-bis(2-hydroxybenzyl)-1,2-diaminobenzene (1), for NO₂⁻ anions has been developed. Addition of NO₂⁻ showed selective decolourisation of brownish yellow colour of 1-AgNPs with the detection limit of 10⁻⁷ M. Absorption studies showed the complete disappearance of 1-AgNPs peak at 426 nm due to the conversion of AgNPs to silver ions. The presence silver ions were confirmed by white precipitates of AgCl formation with NaCl. The interference studies confirmed the high selectivity of NO₂⁻ sensing in presence of anions as well as cations by 1-AgNPs. A linear relationship was observed between the change of absorption and concentration of NO₂⁻. The present approach could be performed at room temperature and ambient conditions. The practical applications of 1-AgNPs for selective sensing of NO₂⁻ in different water samples such as ground, river, pond and tap water have also been demonstrated.     

Oligonucleotide‐mediated aggregation of a cationic conjugated polymer for fluorescent detection of mercury ions in an aqueous medium

A cationically charged conjugated polymer ( P2 ) functionalized with quaternary ammonium salt was newly synthesized via Suzuki cross‐coupling polymerization. The functionalized P2 features different fluorescence colors according to its phases (blue emission in solution and green emission as asolid) which is caused by intramolecular and intermolecular exciton migration, respectively. The use of P2 as a novel fluorescent sensing platform is demonstrated for mercury ion detection. The detection of mercury ions is accomplished in two steps: (1) the cationic, blue‐emitting P2 absorbs an anionic oligonucleotide, polythymidine ( PT ) via electrostatic interaction to form a complex with green emission due to aggregation between the two species; (2) the addition of mercury ions to the complex produces a new complex of PT ‐Hg²⁺ via more favorable specific interaction, resulting in the isolation of P2 and the consequent recovery of blue fluorescence of P2 . It suggests that this detection system has high selectivity and sensitivity down to the ～10^?7 M level, even in mixtures of metal ions. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2393–2400     

Azobenzene-based colorimetric chemosensors for rapid naked-eye detection of mercury(II)

Two new highly selective colorimetric chemosensors for Hg²⁺, based on azobenzene and highly selective Hg²⁺‐promoted deprotection of a dithioacetal have been designed and synthesized. In the presence of as little as 20 μM Hg²⁺, the sensors change their color from light yellow to deep red, which can easily be observed by the naked eye. The underlying signaling mechanism is intramolecular charge transfer (ICT). The sensors have good selectivity for Hg²⁺ with respect to several common alkali, alkaline earth, and transition metal ions. Furthermore, they can be used for in‐the‐field measurements by virtue of a dipstick approach without any additional equipment.     

A highly selective colorimetric sensor to Fe3+ and Co2+ in aqueous solutions

Five aromatic azo dyes with hydroxyl groups (1–5) were designed and synthesized by coupling reactions. The relationships between structures of the compounds and the spectroscopic properties were investigated. The absorption spectra of these compounds upon titration with K⁺, Ca²⁺, Al³⁺, Mg²⁺, Ni²⁺, Mn²⁺, Cd²⁺, Cr³⁺, Fe³⁺, Cu²⁺, Zn²⁺, Co²⁺, Hg²⁺, and Pb²⁺ ions in neutral aqueous solutions were reported. The results are coincident with the calculation results using the density functional theory method. The high selectivity, excellent water solubility and simple synthetic process make 1-[(2-Hydroxyl)phenylazo]-2-naphthol (5) a potential sensor for sensing Fe³⁺ and Mn²⁺ with the naked eye. 1-[(2-hydroxyl)phenylazo]-2-naphthol-6-sulfonic acid (3) shows high selectivity for the colorimetric detection of Fe³⁺ and Co²⁺ among the tested metal ions. The detection limitations of 3 for determining Co²⁺ and Fe³⁺ were calculated to be 2.8 × 10^?7 and 5.6 × 10^?7 mol/L, respectively.     

基于铜纳米线放大的汞离子高灵敏比色检测法

将滚环扩增技术与铜纳米线相结合进行信号放大,建立高选择性、高灵敏的汞离子比色检测新方法。以链霉亲和素修饰的磁珠为探针捕获和分离基质,将生物素修饰的引物链固定到其表面。汞离子存在时,模板链将通过T-Hg^2+-T作用与引物链结合。加入T4连接酶及DNA聚合酶引发滚环扩增反应形成超长单链DNA。与短单链DNA互补形成的长双链DNA可作为铜纳米线沉积模板,加入盐酸释放出大量铜离子催化底物氧化显色。在0.005~1.0 nmol/L范围,汞离子浓度与吸收信号呈良好线性关系,检出限低至3.7 pmol/L。     

A highly selective turn-on colorimetric and luminescence sensor based on a triphenylamine-appended ruthenium(Ⅱ) dye for detecting mercury ion

A dual colorimetric and luminescent sensor based on a heteroleptic ruthenium dye[Ru(Hipdpa)(Hdcbpy)(NCS)_2]~-·0.5H~+ 0.5[N(C_4H_9)_4]~+ Ru(Hipdpa) {where Hdcbpy = monodeprotonted-4,4'-dicarboxy-2.2'-bipyridineand Hipdpa = 4-(1H-imidazo[4,5-f][l,10]phenanthroIin-2-yl)-N,N-diphenylaniIine} for selective detection of Hg~(2+) is presented.The results of spectrophotometric titrations revealed an evident luminescence intensity enhancement(I/I_0 =11) and a considerable blue shift in visible absorption and luminescence maxima with the addition of Hg~(2+).The sensitive response of the optical sensor on Hg~(2+) was attributed to the binding of the electron-deficient Hg~(2+) to the electron-rich sulfur atom of the thiocyanate(NCS) ligand in the Ru(Hipdpa).which led to an increase in the energy gap between the highest occupied molecular orbital(HOMO) and the lowest unoccupied molecular orbital(LUMO).Accordingly,the blue shift in the absorption spectrum of Ru(Hipdpa) due to the binding of Hg~(2+) was obtained.Ru(Hipdpa) was found to have decreased Hg~(2+) detection limit and improved linear region as compared to di(tetrabutylammonium) ris-bis(isothiocyanato)bis(2,2'-bipyridine-4-carboxylic acid-4'-carboxylate)ruthenium(Ⅱ) N719.Moreover,a dramatic color change from pink to yellow was observed,which allowed simple monitoring of Hg~(2+) by either naked eyes or a simple colorimetric reader.Therefore,the proposed sensor can provide potential applications for Hg~(2+) detection.     

A highly selective colorimetric and fluorescent chemosensor for Cr2+ in aqueous solutions

A new rhodamine-based chemosensor was synthetized through a modified copper-catalyzed [3+2]-cycloaddition of an azidocoumarin with an alkynyl-rhodamine. Its sensing properties toward various metal cations in aqueous solutions were investigated by colorimetric changes, UV–vis and fluorescence spectroscopies. The sensor exhibited a high selectivity for Cr²⁺ over Cr³⁺ and other divalent cations such as Cu²⁺, Mg²⁺, Zn²⁺, Ca²⁺, Cd²⁺, Co²⁺, Hg²⁺ and Ni²⁺. The linear range of detection by fluorescence spectroscopy is 0.07–3.5 mM, with a detection limit of ca. 64 μM. The binding mode of Cr²⁺ with the sensor was rationalized through experimental evidences.     

A high selective anion colorimetric sensor based on salicylaldehyde for fluoride in aqueous media

A new and simple salicylaldehyde-based sensor 1 designed for fluoride sensing has been investigated in DMSO and even in the 9/1 DMSO/H₂O (v/v) mixtures. The affinity constants of receptor 1 for anionic species in the 9/1 DMSO/H₂O (v/v) reveal that it is sensitive to F. Also, the color changes induced by anions can provide a way of detection by ‘naked-eye’. These result can be substantiated by the spectrum changes upon the addition of 25 equiv. anions to 1 in the 9/1 DMSO/H₂O solution. The further insights to the nature of interactions between the sensor 1 and F⁻ were investigated by ¹H NMR titration experiments in 9/1 DMSO-d₆/H₂O (v/v). In addition, the proposed binding mode between 1 and F⁻ was suggested.     

A Dihomooxacalix[4]arene-gold nanohybrid based colorimetric sensor for sensitive and selective detection of iodide

Bidentate ureido-dihomooxacalix[4]arene based supramolecular hosts (n-propyl 1 and tert-butyl 2) were processed into organic nanoparticles via a bottom up approach in which a single step of re-precipitation was employed. These organic nanoparticles were then coupled with gold nanoparticles on the surface, resulting in an organic – inorganic hybrid framework (n-propyl H1 and tert-butyl H2). Photophysical studies of the organic nanoparticles and of the hybrid material were performed. The size and morphology were determined by TEM and DLS analysis. Moreover, the prepared hybrid frameworks were screened against various anions using UV-Visible absorption and fluorescence spectrophotometry. H1 exhibited ratiometric response towards iodide ion in aqueous medium, and colour change of the solution from pink to light blue was observed. This hybrid material selectively and sensitively detected iodide ion with detection limit of 8.3 nM and with almost no interference from other anions. H1 sensor ability was also tested with artificial and real urine samples. H2 showed different responses and no selectivity to any anion.     

A highly selective turn-on ATP fluorescence sensor based on unmodified cysteamine capped CdS quantum dots

Unmodified cysteamine capped nanocrystalline cadmium sulfide quantum dots (Cys-CdS QDs) were demonstrated as a selective turn-on fluorescence sensor for sensing adenosine-5′-triphosphate (ATP) in aqueous solution for the first time. The fluorescence intensity of the Cys-CdS QDs was significantly enhanced in the presence of ATP. In addition, the fluorescence intensity of the Cys-CdS QDs increased when increasing ATP concentrations. On the other hand, other phosphate metabolites and other tested common anions did not significantly alter the fluorescence intensity of the Cys-CdS QDs. In addition, this sensor showed excellent discrimination of pyrophosphate (PPi) from ATP detection. The proposed sensor could efficiently be used for ATP sensing at very low concentration with LOD of 17 μM with the linear working concentration range of 20–80 μM. The feasibility of the proposed sensor for determining ATP in urine samples was also studied, and satisfactory results were obtained.     

A simple naphthalene-based colorimetric sensor selective for acetate

A new naphthalene based receptor (L) has been designed and synthesized which shows a remarkable color change from colorless to pink on selective binding with acetate. The anion recognition property of the receptor via hydrogen bonding interactions is monitored by UV-vis, fluorescence, and ¹H NMR titrations. It is observed that in each case, the receptor shows a specific selectivity toward the acetate ion over other interfering anions. Thus, a significant bathochromic shift in UV-vis spectrum with a sharp pink color in ‘naked-eye’ makes the receptor suitable for the detection of the acetate ion.     

Sensitive and selective detection of glutathione based on anti-catalytical growth of gold nanoparticles colorimetric sensor

Gold nanoparticles (AuNps) are often employed in different detection paths based on the catalytic growth mechanism; AuNps could act as catalyst for the reduction of AuCl₄^? and result in the enlargement of the original AuNps. However, there are few probes based on the anti-catalytical growth of AuNps in previous studies. In this article, we proposed a simple colorimetric sensor for the detection of glutathione (GSH) based on the anti-catalytical growth of AuNps, the strong affinity of GSH make it readily combine with AuNps or metal ions (AuCl₄^?), and thus inhibit the catalytical growth of AuNps through the specific property of GSH. Therefore, the UV absorbance of detection system could be used to estimate the concentration of GSH, and the probe exhibits highly sensitive and selective detection of the concentration of GSH with a wide linear from 13 to 800 nM within 20 min. Meanwhile, a good linear relationship with correlation coefficient of R² = 0.9795 was obtained. It is believed that this research could broaden the choices of GSH detection methods.     

Use of unmodified silver nanoparticles (AgNPs) as colorimetric Hg(II) sensor: A new approach to sensitive and high sample throughput determination of Hg(II) under high influence of ionic suppression

Facile unmodified silver nanoparticles (AgNPs) as colorimetric sensor for determination of Hg(II) ions in aqueous samples were developed using UV-Vis spectrophotometry. Abrupt change in absorbance of the AgNPs was observed, which progressively decreased and slightly shifted to the blue wavelength as the concentration of Hg(II) increased. It appears that the AgNPs were oxidized by Hg(II), resulting in disintegration of the AgNPs and Hg(0). Deposition of Hg(0) on the surface of AgNPs also occurred, resulting in amalgam particles of mercury (Hg-Ag). Interestingly, the developed approach showed a significant enhancement in the Hg(II) analytical sensitivity when formic acid was doped onto the AgNPs, with the linearity range of 0.01–10 mg L^?1 (r² = 0.999) providing the quantitative detection limit of 0.007 mg L^?1 (3SD blank/slope of the calibration curve). Greater selectivity toward Hg(II) over other ions and colour dyes was also observed, likely a result of stabilization by polyvinylpyrrolidone (PVP), which kept the AgNPs well-stabilized and dispersed in the bulk aqueous environment making them resistant to ionic suppression. Under using a 96-well microplate and a smartphone equipped with homemade application as a colorimetric analyzer under controlled lighting, high sample throughput (128 sample h^?1, n = 4) was achieved, establishing its potential for practical analysis. The percentage recoveries of spiked aqueous samples obtained from the microplate-based system were in acceptable range, in agreement with the values obtained from the UV-Vis spectrophotometry-based system. The proposed colorimetric sensor has been shown to provide a rapid, simple, sensitive and selective detection of Hg(II) ions in various aqueous samples.     

A highly selective colorimetric sensor for Hg2+ based on a copper (II) complex of thiosemicarbazone in aqueous solutions

By applying an indirect strategy, a new copper (Ⅱ) complex of a thiosemicarbazone L has been successfully developed as a colorimetric chemosensor for the sensitive detection of mercury (Ⅱ) ions. In the presence of copper (Ⅱ) ions, the colorless solution of L became yellow; however, upon the addition of traces of mercury (Ⅱ) ions, the yellow color faded to colorless immediately. Other ions, including Fe3+ , Ag+ , Ca2+ , Zn2+ , Pb2+ , Cd2+ , Ni2+ , Co2+ , Cr3+ and Mg2+ had a negligible influence on the probe behavior. The detection limits were 5.0×10 -6 M and 3.0×10 -7 M of Hg2+ using the visual color changes and UV-vis changes respectively. Test strips based on Cu-L were fabricated, which could act as a convenient and efficient Hg2+ test kits.