Selective Colorimetric Sensor Research Articles

High peroxidase-mimicking activity of gold@platinum bimetallic nanoparticle-supported molybdenum disulfide nanohybrids for the selective colorimetric analysis of cysteine.

Herein, gold@platinum (Au@Pt) bimetallic nanoparticles with high catalytic ability were in situ decorated onto a molybdenum disulfide (MoS2) surface to obtain nanocomposites (MoS2-Au@Pt) with high peroxidase-mimicking activity, which were used to construct a colorimetric sensor for cysteine (Cys) detection. Interestingly, this sensor can efficiently distinguish Cys from homocysteine (Hcy), glutathione (GSH) and 19 other amino acids with high sensitivity. As expected, the colorimetric sensor can determine the Cys content in Cys supplement tablets due to its high stability and repeatability. Finally, the detection mechanism was studied.

A Highly Selective Colorimetric Sensor for Cysteine Detection

Introducing a hybrid xanthene as a fluorophore, an ‘ensemble’-based fluorescent sensor (E)-2-(6-(diethylamino)-2-((2-hydroxyphenylimino)methyl)-3-oxo-3H-xanthen-9-yl)benzoic acid (a) was designed and synthesised for detection of cysteine. Cysteine can release CuII ion from the non-fluorescent a-CuII complex. Then hydrolytic cleavage of Schiff base a produces a pink fluorescent compound 2-(6-(diethylamino)-2-formyl-3-oxo-3H-xanthen-9-yl)benzoic acid (2). We call this process a fluorescence off-on change. An obvious color change from purple a to pink 2 can be easily observed by the naked-eye. The calibration curve showed that the fluorescence intensity at 560 nm linearly increased over the cysteine concentration range of 0.379-100 µmol L-1 with a limit of detection of 0.379 µmol L-1. Sensor a-CuII displayed excellent selectivity for cysteine, even homocysteine and glutathione did not show influence. The sensor was also used for detecting cysteine in human breast adenocarcinoma cells, which illustrates the practical value. Overall, the sensor appears to be useful for rapid, convenient and selective cysteine detection in living tissues.

Colorimetric Detection of Iron(III) Ion Based on 4-Aminothiophenol and Schiff Base Naphthalene-2-ol Modified Silver Nanoparticles

A facile, highly selective colorimetric sensor based on 4-aminothiophenol (4-ATP) and Schiff base naphthalene-2-ol (L) modified silver nanoparticles (4-ATP-L-AgNPs) for detection of Fe(III) ion in aqueous solution. The presence of Fe(III) ion induced the aggregation of AgNPs that caused the red-shift from 430 to 440 nm, through a cooperative metal-ligand interaction from the coordination bond between Fe(III) ion and functional groups on AgNPs surface resulting in a colour change from dark brown to dark yellow with increasing absorption at 365 nm. The absorbance at 365 nm is linear with the concentration of Fe(III) ion ranging from 9.0 × 10-6 M to 9.0 × 10-3 M with a correlation coefficient of 0.9991. The detection limit of the developed method was 7.9 × 10-6 M. The practical application of 4-ATP-L-AgNPs for selective sensor for Fe(III) ion in various drinking water samples were demonstrated.

C-dots/Mn3O4 nanocomposite as an oxidase nanozyme for colorimetric determination of ferrous ion

At first, C-dots/manganese oxide nanocomposite was synthesized chemically. The presence of Mn3O4 nanostructures and C-dots in the synthesized nanocomposite was confirmed by using of XRD, EDS, FTIR and TEM. The proposed method for synthesis is easy and cheap. The Mn3O4/C-dots nanocomposite shows oxidase-like activity, which is higher than oxidase-like activity of Mn3O4 nanoparticles. In this manner, detection of ferrous ion was possible by using of a competitive reaction between 3,3′,5,5′-tetramethylbenzidine and Fe2+ ion in the presence of the synthesized nanocomposite. So, a sensitive and selective colorimetric sensor for determination of Fe2+ ion was introduced. The linear range and detection limit for determination of Fe2+ ion were obtained as 0.03–0.83 μM and 0.03 μM, respectively.

A Selective Colorimetric Sensor for Pb2+ Detection by Using Phenylboronic Acid Functionalized Polydiacetylene Liposomes

Due to the high toxicity for brain and the nervous system of humans and other living organisms, the design and fabrication of a robust and sensitive method for the detection of Pb2+ in the aqueous solution has attracted the increasing attention among scientists. Herein, a colorimetric and fluorometric sensor for the detection of Pb2+ in the aqueous solution by incorporating a new phenylboronic acid functionalized polydiacetylene liposome was designed. The molar ratio of 4:1 between the monomers, 10,12-pentacosadiynoic acid (PCDA) and phenylboronic acid functionalized PCDA (PCDA-pBA) not only offered sufficient binding sites for Pb2+, but also interrupted the efficient π-conjugation backbone of polydiacetylene (PDA) chains associated with the color and fluorescence changes. Compared with other metal ions, only Pb2+ could cause the color change and the fluorescence enhancement. Moreover, the hybrid PDA liposomes exhibited high sensitivity, fast response time (10 s), and a reasonable detection limit for Pb2+ (0.1 µM). This work not only provides a versatile methodology for the fabrication of sensors for Pb2+ detection, but also is of great fundamental value for a deeper understanding of the complexion-induced color changes based on polydiacetylene materials, and may pave the way for fabrication a new method for recognizing other metal ions.

Synthesis of Novel N,N′,N″-Tris[aryl(hetaryl)-methylideneamino]guanidine Derivatives as Efficient and Selective Colorimetric Sensors for Fluoride Ion

A series of N,N′,N″-tris[aryl(hetaryl)methylideneamino]guanidines have been synthesized in good yields by condensation of N,N′,N″-triaminoguanidine hydrochloride with aromatic and heteroaromatic aldehydes. All compounds have been characterized by 1H and 13C NMR and FT-IR spectra, and the molecular structure of one compound has been determined by single crystal X-ray diffraction. Study of the optical properties of the title compounds in the presence of fluoride ions has shown selective color change from colorless to yellow and purple due to red shift in their UV-Vis absorption spectra.

Fluorescent and colorimetric dual-readout sensor based on Griess assay for nitrite detection.

In this work, we presented a sensitive and selective colorimetric and fluorescent dual-readout sensor based on Griess assay for nitrite (NO2-) detection under acidic condition. The sensor system was constituted of acid-resistant carbon quantum dots (CQDs) and 3-aminophenol (3-Aph) with acidic condition regulated using HCl. During the sensing procedure, reaction of 3-Aph and NO2- under acidic condition can yield a yellow-colored azoic compound (AZO), which gives the colorimetric readout; meanwhile, the fluorescence of CQDs (fluorescence reporter) quenched due to the strong absorption of AZO, leading to fluorescent readout. Wherein, CQDs were synthesized via hydrothermal method through using polyacrylamide as precursor and characterized by AFM, XRD and XPS. Under the optimized condition, the sensor exhibit broad linear relationships towards NO2- in the range of 10 to 100 nM and 2.5 to 100 μM, with practical detection limits of 10 nM and 2.5 μM for the fluorescent and colorimetric readout, respectively. And the sensor displayed excellent capability of selectivity according to interferences study. Furthermore, testing of sprouts, bacon and ham sausage real samples demonstrated good recoveries and reproducibility of the sensor system. All these results suggested the presented colorimetric and fluorescent dual-readout sensor can be a promising candidate for the NO2- detection in real applications.

Naked Eye Detection of Carbonate, Hydroxide, and Cyanide Ions with 1,4′‐Diazaflavonium Bromides: A Simple Spectrophotometric Method for Cyanide Determination

Anion sensor properties of N‐alkyl‐substituted 1,4′‐diazaflavonium bromides in methanol–water were evaluated by UV–vis spectrometry. Pronounced changes were observed in the absorption spectra of all compounds for only OH−, CO32−, and CN− among F−, Cl−, Br−, I−, OH−, CO32−, NO3−, PO43−, CN−, SO42−, HSO4−, HCO3−, SCN−, NO2−, and P2O72− ions. Two new absorption bands at 385 and 685 nm accompanying the distinct color change for OH−, CO32−, and CN− ions were observed in case of all compounds. The color changes were from pink to blue for CO32− and OH− ions and from pink to purple for CN− ion. Thanks to the distinct color change, the compounds can be used as selective colorimetric anion sensors. Linear changes of absorbance of N‐heptyl‐substituted compound at 385 nm as a function of the ion concentration were used to determine CN− ion in water samples. Detection and quantification limits of the proposed method were 0.94 and 2.82 mg/L, respectively.

Silver oxide nano-colloid based selective colorimetric sensor for the recognition of cystine in aqueous solution

ABSTRACTSodium alginate modified Ag2O (SA@Ag2O) nano-colloid is synthesised and studied colorimetric response towards eight selected amino acids in aqueous medium at room temperature. The synthesised SA@Ag2O nano-colloid showed a surface plasmon band at 469 nm. Distinctive colour change of the dark brown colloid to colourless is observed in the case of Cystine. Among the eight amino acids studied such as D-L- Aspartic acid, L-Glutamic acid, Glycine, Alanine, D-L Methionine, L-Cysteine, L-Cystine and L-Tyrosine. L-Cystine stands out by completely decolorising the brown colloid which can be detected by the ‘naked-eye’. This sensor selectively detects Cystine. To understand the sensing mechanism, the amino acid treated SA@Ag2O colloids were characterised by UV, XRD, FTIR and TEM analysis. This approach offers several advantages such as simplicity, low cost and high sensitivity.

3-Formyl Quinoline Based Reusable Selective Colorimetric Sensor for Cyanide Ion and Its Application to the Molecular Logic Gate

3-Formyl Quinoline Based Reusable Selective Colorimetric Sensor for Cyanide Ion and Its Application to the Molecular Logic Gate

How to implement a selective colorimetric gas sensor with off the shelf components?

We report on how an inexpensive and very selective gas sensor can be implemented, simply combining colorimetric indicators casted on top of Scotch® tape, with a commercial microchip adapted here to measure optical reflectance. The system can be easily reproduced (leading to quantitatively consistent results), refreshed and reconfigured to sense different target gases, just replacing the colorimetric tape.

Ranolazine-Functionalized Copper Nanoparticles as a Colorimetric Sensor for Trace Level Detection of As3.

This study involves environmentally friendly synthesis of copper nanoparticles in aqueous medium without inert gas protection, using ranolazine as a capping material. UV-Visible (UV-Vis) spectrometry showed that ranolazine-derived copper nanoparticles (Rano-Cu NPs) demonstrate a localized surface plasmon resonance (LSPR) band at 573 nm with brick-red color under optimized parameters, including pH, reaction time, and concentrations of copper salt, hydrazine hydrate, and ranolazine. The coating of ranolazine on the surface of Cu NPs was studied via Fourier transform infrared (FTIR) spectroscopy. Scanning electron microscopy (SEM) revealed that Rano-Cu NPs consist of spherical particles. X-ray diffraction (XRD) verified that Rano-Cu NPs are crystalline in nature. Atomic force microscopy (AFM) showed that the average size of Rano-Cu NPs was 40 ± 2 nm in the range of 22–95 nm. Rano-Cu NPs proved to be highly sensitive as a selective colorimetric sensor for As3+ via color change from brick red to dark green, in the linear range of 3.0 × 10−7 to 8.3 × 10−6 M, with an R² value of 0.9979. The developed sensor is simple, cost effective, highly sensitive, and extremely selective for As3+ detection, showing a low detection limit (LDL) of 1.6 × 10−8 M. The developed sensor was effectively tested for detection of As3+ in some water samples.

Sequential detection of Cu2+ and cysteine using an imidazole‐based chemosensor in aqueous solution

A highly substituted imidazole‐based colorimetric and fluorogenic chemosensor, 2‐methoxy‐4‐(4,5‐diphenyl‐1H‐imidazol‐2‐yl)phenol (L), for the detection of Cu2+ ion and subsequent colorimetric detection of an amino acid, cysteine, was investigated. L exhibited a distinct color change from colorless to red in the presence of Cu2+ in an aqueous medium. The L‐Cu2+ complex can also be used to detect cysteine by the naked eye over a series of amino acids. The receptor L behaves as a highly selective colorimetric and fluorescent sensor for Cu2+ ions at concentrations as low as 4.33 and 2.25 μM, respectively. These values are much less compared to the WHO recommended limit of 30 μM for Cu2+ in drinking water. From Job's plot and the ESI‐MS spectrum, a 1:1 stoichiometric complex between L and Cu2+ ions can readily be reckoned. This binding was also substantiated by the EPR spectrum and magnetic susceptibility measurements. Additionally, the binding of L with Cu2+ ions was also manifested in the detection of B16F10 cells. This was substantiated through fluorescence microscopy. The spectrum of the L‐Cu2+ entity was also attempted to reproduce theoretically. The probable structure of this was also propounded through Density Functional Theory.

Sequential displacement strategy for selective and highly sensitive detection of Zn2+, Hg2+ and S2- ions: An approach toward a molecular keypad lock.

A thiocarbonohydrazone locked salicylidene based macrocycle ligand L has been synthesized and its ion sensing properties were examined by UV-visible and fluorescence spectroscopy. The macrocycle serves as a highly selective colorimetric sensor for Hg2+ ions while it acts as an excellent fluorescent sensor for Zn2+ ions by exhibiting a green fluorescence at 498 nm even in the presence of interfering ions. A detailed analysis of binding characteristics such as complex stoichiometry, association constant and detection limits of L toward Hg2+ and Zn2+ ions were evaluated by UV-visible and fluorescence experiments which revealed a stronger binding affinity and higher detection limit of L toward the mercury ions. Further, the sequential displacement strategy for the chromofluorogenic detection of Zn2+, Hg2+ and S2- ions by ligand L, has been studied comprehensively. Finally, the ion-responsive fluorescence output signal of L were employed to design a molecular keypad lock which could be accessible by two users having two different set of chemical passwords (inputs) through distinguishable optical trajectories.

A novel colorimetric sensor based on rhodamine-B derivative and bacterial cellulose for the detection of Cu(II) ions in water

A novel rhodamine B derivative (Rh-2) was synthesized. When used as a selective colorimetric sensor for Cu2+, a visible change from colorless to pink was observed. UV-visible and fluorescence spectroscopy demonstrated linear relationships between the concentrations of Cu2+ and Rh-2 in ethanol/water mixtures. Since naked eye detection is inexpensive and more convenient than spectroscopy, test strips were fabricated by immersing bacterial cellulose (BC) in Rh-2 and applying heat treatment. The resulting solid sensor was able to detect Cu2+ in water, visibly changing from colorless to pink. A linear correlation was found between color strength and Cu2+ concentration, when plotted on a log-log scale. No leaching of Rh-2 from BC was observed due to the strong affinity between the two. The BC had a more uniform nanofiber size and larger surface-area-to-volume-ratio than the commonly-used cellulosic paper, making it a promising material for use in colorimetric sensors.

Colorimetric Detection of Hg2+ Based on Enhancement of Peroxidase‐like Activity of Chitosan‐Gold Nanoparticles

Hg2+ is a serious environmental contaminant that can cause severe damage to the immune and nervous systems, and Hg2+ monitoring is critical. Herein, we report a novel, simple, and sensitive Hg2+ sensor based on the enhanced peroxidase‐like activity of chitosan–gold nanoparticles (CS‐AuNPs). The peroxidase‐like activity of the CS‐AuNPs can be markedly enhanced by Hg2+ as seen by the deeper color and increased absorbance at 652 nm. This improved catalytic ability was used to develop a sensitive and selective colorimetric sensor for Hg2+ detection. The limit of detection via the absorption spectra is as low as 0.02 μM. The mechanism underlying the enhanced catalytic ability is discussed. This approach is label‐free, simple, and offers detection with the naked eye. Thus, it has potential applications for the detection of Hg2+ in environmental and food samples.

A selective colorimetric and fluorescence chemosensing sensor for Cr3+ based on a rhodamine base derivative

A rhodamine-conjugated coumarin (L) was used in designing a selective fluorescence chemosensor for the determination of trace amounts of Cr3+ ions in acetonitrile–water (MeCN/H2O (90:10, %v/v) solutions. The intensity of the fluoresce emission of the chemosensor is intensified upon addition of Cr3+ ions in MeCN/H2O (90:10, %v/v) solutions, due to the formation of a selective 1:1 complex between L and Cr3+ ions. The fluorescence enhancement versus Cr3+ concentration has been found to be linear from 1.0 × 10−7 to 1.8 × 10−5 M and a detection limit of 7.5 × 10−8 M. The proposed fluorescent probe proved to be highly selective towards Cr3+ ions as compared to other common metal ions and could be successfully applied to the determination of Cr3+ concentrations in some water and wastewater samples.

A new colorimetric sensor for visible detection of Cu(II) based on photoreductive ability of quantum dots

Quantum dots (QDs) have been widely used to develop analytical methods due to their unique fluorescent and photoelectrochemical characteristics. However, analytical strategies based on their catalytic property are rarely reported. Here, we demonstrate that the photoreductive ability of QDs can be utilized to develop a sensitive and selective colorimetric sensor for Cu(II). By using UV irradiation, 3,3′,5,5′-tetramethylbenzidine (TMB) is oxidized to its oxidation product, which can be reduced back to TMB by QDs. The presence of Cu(II) decreases the reductive activity of QDs and results in a color change in a signal-on format. The proposed sensor can be activated using a portable UV lamp or direct sunlight. Under optimized conditions, the detection limit (S/N = 3) is 10 nM via spectrophotometry and 0.1 μM by visible color change. This sensing system was applied to quantify Cu(II) in real samples, such as river water and tap water. Results were in agreement with those obtained using inductively coupled plasma spectrometry (ICP). This study may provide new ideas for the development of QD-based sensors.

Silver nanoparticles-based colorimetric array for the detection of Thiophanate-methyl

A simple and selective colorimetric sensor based on citrate capped silver nanoparticles (Cit-AgNPs) is proposed for the detection of Thiophanate-methyl (TM) with high sensitivity and selectivity. The method based on the color change of Cit-AgNPs from yellow to cherry red with the addition of TM to Cit-AgNPs that caused a red-shift on the surface plasmon resonance (SPR) band from 394nm to 525nm due to the hydrogen-bonding and substitution. The density functional theory (DFT) method was also calculated the interactions between the TM and citrate ions. Under the optimized conditions, a linear relationship between the absorption ratio (A525nm/A394nm) and TM concentration was found in the range of 2–100μM with correlation coefficient (R2) of 0.988. The detection limit of TM was 0.12μM by UV–vis spectrometer. Moreover, the applicability of colorimetric sensor is successfully verified by the detection of TM in environmental samples with good recoveries.

Selective optical detection of HSO4− via hydrolysis of a simple Schiff Base

A very simple Schiff Base derived from 1-Naphthylamine and 4-(Trifluoromethy) benzaldehyde (L) was prepared as a selective colorimetric and turn-on fluorescent sensor for hydrogen sulfate. In the CH3CN:H2O (3:2, v/v) solvent system, L shows a highly selective colorimetric response to HSO4− ions by changing its color from yellow to colorless immediately. In addition, the weakly fluorescent receptor L shows a highly selective enhancement of fluorescence intensity at 425 nm for HSO4− upon excitation at 320 nm. The recognition process is proven to be hardly influenced by the other tested competitive anions. The sensing is suggested to involve a hydrolysis process promoted by HSO4− which has been further supported by UV–Vis, 1H NMR and HRMS spectroscopic studies. Applicability of L to detect HSO4− in tap water has been demonstrated. An easy-to-prepare test strip of L has also been made for the naked-eye detection of HSO4− in real samples.