Simple Colorimetric Sensor Research Articles

Remarkable colorimetric sensing behavior of pyrazole-based chemosensor towards Cu(ii) ion detection: synthesis, characterization and theoretical investigations.

We report the synthesis of a new imine based ligand, 3-((3-methoxybenzylidene)amino)-1H-pyrazol-5-ol (HL) and its Cu(ii) complexes in 2 : 1 (HL : metal) and 1 : 1 : 1 (HL : metal : HQ) stoichiometric ratio using 8-hydroxyquinoline (HQ) as an additional bidentate ligand. The synthesized ligand (HL) and its Cu(ii) complexes (1 and 2) are structurally characterized using FT-IR, electronic absorption and emission, NMR and MS techniques. Furthermore, the complexation of Cu2+ with HL leads to the immediate formation of brown colour solution which indicates that HL can act as simple colorimetric sensor for Cu2+ ions. We further investigated that the sensor could selectively bind to the Cu2+ ions even in the presence of competitive ions such as Mn2+, Fe2+, Co2+, Ni2+, Zn2+, Ag+ and Na+ ions in aqueous solutions which was studied by electronic absorption spectroscopy. The HL ligand has been investigated for its reactive properties by density functional theory (DFT) calculations. Quantum molecular descriptors describing local reactive properties have been calculated in order to identify the most reactive molecule sites of title compounds. DFT calculations encompassed molecular electrostatic potential (MEP), local average ionization energies (ALIE), Fukui functions and bond dissociation energies for hydrogen abstraction (H-BDE).

Highly selective and ecofriendly colorimetric method for the detection of iodide using green tea synthesized silver nanoparticles

In this work, a simple, selective, sensitive and inexpensive colorimetric sensor has been developed for the detection of iodide ions using green tea (Camellia sinensis) synthesized silver nanoparticles (tea-capped AgNPs). The mechanistic route relied upon the binding of iodide ions to the surface of biosynthesized AgNPs. This binding led to decolorize the yellow color of AgNPs solution along with the disappearance of characteristic surface plasmon (SPR) band at 405nm. The mechanism of interaction of iodide with AgNPs has been discussed by using transmission electron microscopy (TEM) and differential pulse voltammetry (DPV). The biosynthesized AgNPs were capable of detecting iodide in the range from 1×10−7–2.5×10−5M, which exhibited good linear relationships between concentration and absorption change with the correlation coefficient (R2) of 0.994. The detection limit obtained by this tea-capped AgNPs was 6.5×10−8M which is comparable or some better than those obtained by previously reported chemical reduction methods. Moreover, the tea-capped AgNPs demonstrated a selective colorimetric response for iodide in the presence of other potential interfering ions like Br−, F−, Cl−, CH3COO−, NO2−, NO3−, H2PO4− and SO4−. Compared to other colorimetric methods designed for the detection of iodide ions, the proposed method has combined the features of good sensitivity and selectivity, and environment-friendly and cost-effective nature. More importantly, the method does not require any additional chemicals and specific reaction condition.

Recyclable colorimetric sensor of Cr3 + and Pb2 + ions simultaneously using a zwitterionic amino acid modified gold nanoparticles

In this work, a rapid, simple and sensitive colorimetric sensor for simultaneous (or respective) detection of Cr3+ and Pb2+ using tyrosine functionalized gold nanoparticles (AuNPsTyr) has been developed. Tyrosine, a natural and zwitterionic amino acid, could be as a reducing and capping agent to synthesise AuNPs and allow for the simultaneous and selective detection of Cr3+ and Pb2+. Upon the addition of Cr3+ or Pb2+ (a combination of them), the color of AuNPsTyr solution changes from red to blue grey and the characteristic surface plasmon resonance (SPR) band is red-shifted to 580nm due to the aggregation of AuNPs. Interestingly, the aggregated AuNPsTyr can be regnerated and recycled by removing Pb2+ and Cr3+. Even after 3 rounds, AuNPsTyr show almost the same A580nm/A520nm value for the assays of Pb2+ and Cr3+, indicating the good recyclability of the colorimetric sensor. The responding time (within 1min) and sensitivity of the colorimetric sensor are largely improved after the addition of 0.1M NaCl. Moreover, the AuNPsTyr aggregated by Cr3+ or Pb2+ (a combination of them) show excellent selectivity compared to other metal ions (Cr3+, Pb2+, Fe2+,Cu2+,Zn2+,Cr6+,Ni2+,Co2+,Hg2+,Mn2+,Mg2+,Ca2+,Cd2+). More importantly, the developed sensor manifests good stability at room temperature for 3months, which has been successfully used to determine Cr3+ and Pb2+ in the real water samples with a high sensitivity.

Colorimetric recognition of 6-benzylaminopurine in environmental samples by using thioglycolic acid functionalized silver nanoparticles

A simple and selective colorimetric sensor thioglycolic acid capped silver nanoparticles (TGA-AgNPs) was developed for the detection of 6-benzylaminopurine (6-BAP). The synthesized TGA-AgNPs were characterized by UV–vis spectroscopy, dynamic light scattering (DLS), and transmission electron microscopic (TEM) techniques. The TGA-AgNPs as a sensor for binding 6-BAP through hydrogen-bonding and π-π bonding that causes large conjugate clusters, resulting in a color change from yellow to reddish orange. The surface plasmon resonance (SPR) band of TGA-AgNPs at 397nm is red-shifted to 510nm, which confirms that 6-BAP induces the aggregation of TGA-AgNPs. Under the optimized conditions, a linear relationship between the absorption ratio (A510nm/A397nm) and 6-BAP concentration was found in the range of 4–26μM. The detection limit of 6-BAP was 0.2μM, which is lower than the other analytical techniques. Moreover, the proposed sensor was successfully applied for the detection of 6-BAP in environmental samples with good recoveries. The proposed assay provides a simple and cost-effective method for the analysis of 6-BAP in vegetable and water samples.

Colorimetric Sensor Array Based on Gold Nanoparticles with Diverse Surface Charges for Microorganisms Identification.

We report a simple and novel colorimetric sensor array for rapid identification of microorganisms. In this study, four gold nanoparticles (AuNPs) with diverse surface charges were used as sensing elements. The interactions between AuNPs and microorganisms led to obvious color shifts, which could be observed by the naked eye. A total of 15 microorganisms had their own response patterns and were differentiated by linear discriminant analysis (LDA) successfully. Moreover, microorganism mixtures could also be well discerned. The method is simple, fast (within 5 s), effective, and visual, showing the potential applications in pathogen diagnosis and environmental monitoring.

Simple and selective paper-based colorimetric sensor for determination of chloride ion in environmental samples using label-free silver nanoprisms

Simple and selective paper-based colorimetric sensors using silver nanoprism (AgNPrs) were conveniently fabricated and developed for the determination of chloride ions (Cl−) contaminated in the environment. Samples containing different concentrations of Cl− were analyzed. The analysis is based on the oxidative etching of the AgNPrs into smaller silver nanospheres (AgNPss) by Cl−. In the presence of Cl−, the distinctive color change of the AgNPrs from dark-violet to red was rapidly visualized by the naked eye in 5min without the requirement of surface modification. For quantitative measurement using image processing, a good linear relationship (R2 = 0.996) between logarithmic of Cl− concentration and the average mean color intensity was obtained in the range of 10–1000mgL−1 with a detection limit of 1.3mgL−1. The developed sensors were investigated for precision, accuracy, and sensitivity and validated by the classical method. Statistical analysis proved that the developed sensors were precise, sensitive and accurate and can be used effectively for the analysis of Cl− in natural waters.

Co3O4/Reduced Graphene Oxide Nanocomposites as Effective Phosphotriesterase Mimetics for Degradation and Detection of Paraoxon

In this work, Co3O4 nanoparticles supported on reduced graphene oxide (Co3O4/rGO) were prepared through a simple hydrothermal method. The phosphotriesterase (PTE) mimetic activity of the Co3O4/rGO nanocomposites was investigated for the first time, and the catalytic performance was evaluated by hydrolyzing paraoxon. The synergic effects of Co3O4 and rGO greatly improved the binding capacity of the nanocomposites with paraoxon and water molecules, and facilitated electron transfer in the hydrolysis process, resulting in an ∼5-fold enhancement in the hydrolysis efficiency of Co3O4/rGO nanocomposites, compared with that of rGO. Co3O4/rGO nanocomposites also exhibited excellent reusability and stability than other PTE mimetics. Based on the PTE activity of Co3O4/rGO nanocomposites, a simple and sensitive colorimetric sensor of paraoxon was developed and successfully used to determine the paraoxon in cabbage and river water, demonstrating its potential applicability for food and environmental analyses.

A highly sensitive and selective aptamer-based colorimetric sensor for the rapid detection of PCB 77

A highly sensitive, specific and simple colorimetric sensor based on aptamer was established for the detection of polychlorinated biphenyls (PCB 77). The use of unmodified gold nanoparticles as a colorimetric probe for aptamer sensors enabled the highly sensitive and selective detection of polychlorinated biphenyls (PCB 77). A linear range of 0.5nM to 900nM was obtained for the colorimetric assay with a minimum detection limit of 0.05nM. In addition, by the methods of circular dichroism, UV and naked eyes, we found that the 35 base fragments retained after cutting 5 bases from the 5 ‘end of aptamer plays the most significant role in the PCB 77 specific recognition process. We found a novel way to truncated nucleotides to optimize the detection of PCB 77, and the selected nucleotides also could achieve high affinity with PCB 77. At the same time, the efficient detection of the PCB 77 by our colorimetric sensor in the complex environmental water samples was realized, which shows a good application prospect.

Self-sacrificial template synthesis of mixed-valence-state cobalt nanomaterials with high catalytic activities for colorimetric detection of glutathione

Mixed-valence-state cobalt (MVSC) nanomaterials have attracted tremendous interest because of their extraordinarily high electron mobilities and catalytic activities. The design and synthesis of highly active MVSC nanomaterials with appropriate Co2+/Co3+ ratios are extremely desirable. In this work, MVSC nanomaterials with high surface areas and uniform size distributions were fabricated using a self-sacrificial template strategy. The MVSC nanomaterial with the optimum Co2+/Co3+ ratio showed excellent catalytic activity in the oxidation of 3,3′,5,5′-tetramethylbenzidine than other types of nanostructured Co3O4, e.g., nanoplates, nanorods, and nanocubes. Based on the catalytic activity of the MVSC nanomaterial, a simple and sensitive colorimetric sensor of glutathione (GSH) was developed due to the antioxidant ability of GSH. The linear range was 0.5–40μM, and the limit of detection was 0.03μM. The proposed sensor was used to determine GSH in eye drops and health care products. The recoveries ranged from 97.3% to 104.0%, indicating that the proposed colorimetric sensor for GSH quantification is reliable in practical applications.

Fluorescence-based CdTe nanosensor for sensitive detection of cytochrome C

Cytochrome c (Cyt c) is commonly used as intrinsic biomarker for several characteristics of the cell such as respiration, energy level and apoptosis. In the present study a simple colorimetric sensor should be developed and tested for the real-time detection of Cyt c in living cells. We synthesized cadmium telluride quantum dots (CdTe QDs) capped with thioglycolic acid (TGA) as a fluorometric Cyt c nanosensor.The synthesized TGA/CdTe QDs nanosensor was characterized by Fourier transform infrared spectroscopy, transmission electron microscopy, and absorption as well as fluorescence spectrophotometry.We investigated the developed TGA/CdTe QDs sensor with regard to its applicability in the fluorometric detection of Cyt c. Results showed that the TGA/CdTe QDs could be used as a sensitive fluorescence probe for the quantification of different concentrations of Cyt c ranging from 0.5 − 2.5μM. Increased binding of QDs to Cyt c results in decreasing fluorescence. The fluorescence of the QDs is inversely correlated to the Cyt c concentration. Based on these data, a standard curve up to 2.5μM Cyt c was established.Moreover, the developed nanosensor was applied in different concentrations on primary human dermal fibroblasts. Results showed that TGA/CdTe QDs were taken up by cells and could be visualized by fluorescence microscopy. Quantification of Cyt c within living cells via QDs is, however, influenced by various factors such as cell damage, QD aggregation or the level of reactive oxygen species, which have to be taken into account.

Polarity Index Dependence of M13 Bacteriophage-based Nanostructure for Structural Color-based Sensing

Color sensor systems based on M13 bacteriophage are being considerably researched. Although many studies on M13 bacteriophage-based chemical sensing of TNT, endocrine disrupting chemicals, and antibiotics have been undertaken, the fundamental physical and chemical properties of M13 bacteriophagebased nanostructures require further research. A simple M13 bacteriophage-based colorimetric sensor was fabricated by a simple pulling technique, and M13 bacteriophage was genetically engineered using a phage display technique to exhibit a negatively charged surface. Arrays of structurally and genetically modified M13 bacteriophage that can determine the polarity indexes of various alcohols were found. In this research, an M13 bacteriophage-based color sensor was used to detect various types of alcohols, including methanol, ethanol, and methanol/butanol mixtures, in order to investigate the polarity-related property of the sensor. Studies of the fundamental chemical sensing properties of M13 bacteriophage-based nanostructures should result in wider applications of M13 bacteriophage-based colorimetric sensors.

Simple Colorimetric Sensor for Trinitrotoluene Testing

A simple operating colorimetric sensor for trinitrotoluene (TNT) determination using a commercial scanner as a captured image was designed. The sensor is based on the chemical reaction between TNT and sodium hydroxide reagent to produce the color change within 96 well plates, which observed finally, recorded using a commercial scanner. The intensity of the color change increased with increase in TNT concentration and could easily quantify the concentration of TNT by digital image analysis using the Image J free software. Under optimum conditions, the sensor provided a linear dynamic range between 0.20 and 1.00 mg mL-1(r = 0.9921) with a limit of detection of 0.10± 0.01 mg mL-1. The relative standard deviation for eight experiments for the sensitivity was 3.8%. When applied for the analysis of TNT in two soil extract samples, the concentrations were found to be non-detectable to 0.26±0.04 mg mL-1. The obtained recovery values (93-95%) were acceptable for soil samples tested.

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

ABSTRACTGold 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.

Gold Nanoparticle-Based Probe for Colorimetric Detection of Copper Ions.

A new ligand 10-mercaptodecyl-1-iminodiacetic acid (MDIA) was synthesized and used to modify gold nanoparticles to provide a simple assay to repeatedly sense Cu²⁺ in the solution at room temperature. This functionalized gold nanosensor was applied for the detection of Cu²⁺ in water samples with sensitivity and simplicity. The chelation/aggregation process is reversible via addition of a strong metal ion chelator such as EDTA. This simple and fast colorimetric sensor is important in the application of copper ion detection in water quality during the emergency and early warning monitoring.

A smartphone readable colorimetric sensing platform for rapid multiple protein detection.

A simple, visible and smartphone readable strategy has been proposed for the sensitive detection and discrimination of multiple proteins. By employing five different concentrations of NaCl salt, AuNP exhibited different aggregation behavior for different proteins because of differential ion strength, leading to diverse color changes. The sensing system could not only discriminate twelve proteins at the concentration of 50 nM in aqueous solution, but it could also discriminate these proteins at 200 nM in the presence of human urine with an accuracy of 100%. More importantly, based on the theory of chromatics, we could directly read out the color value using a smartphone to distinguish twelve proteins, pure Lys and HSA at various concentrations, and the mixture of these two proteins in the presence of human urine with no confusion after a hierarchical clustering analysis (HCA). The inexpensive and convenient colorimetric sensor array using the ubiquitous smartphone for signal readout has great potential for the point-of-care diagnosis without additional devices.

A RGB-Type Quantum Dot-based Sensor Array for Sensitive Visual Detection of Trace Formaldehyde in Air.

A simple colorimetric sensor array based on red-emitting CdTe QDs and green-colored fluorescein that exhibited RGB-type color change was proposed for visual detection of trace formaldehyde. In the presence of formaldehyde, the red fluorescence from CdTe QDs was quenched while the green fluorescein was inert thus as a reference. Through harvesting the varied quenching efficiency of different ligand-capped CdTe QDs by formaldehyde, a simple sensor array can be constructed for both selective detection of formaldehyde with high sensitivity (LOD of 0.08 ppm) and identification of the existence of potential interference from acetaldehyde. The quenching mechanisms of formaldehyde toward different ligand capped CdTe QDs were studied with fluorescence lifetime, zeta potential, and also theoretical calculations. The results from theoretical calculations were in good agreement with the experimental results. The proposed sensor array was successfully explored for visual analysis of formaldehyde in indoor air samples.

A chemosensor array for the colorimetric identification of some carboxylic acids in human urine samples

A simple colorimetric sensor array containing eight chemosensors from commercial dyes and metal salts was designed to detect a number of important carboxylic acids in human urine. Some common chemometric methods, including principal component analysis (PCA), linear discriminant analysis (LDA) and k-nearest neighbor (kNN) based hierarchical cluster analysis (HCA) were used to test the discriminatory power of the array. The eight-member sensor array perfectly identified eleven carboxylic acids in water with 100% classification accuracy. In order evaluate the potential of sensor array used in biological environments (biofluids), carboxylic acids in human urine were analyzed and 100% classification accuracy was achieved. In addition, the array’s performance in the semi-quantitative identification of carboxylic acids was investigated, and the results showed that the sensor array can discriminate seven typical carboxylic acids at concentrations ranging from 100 to 1000μmolL−1. These results illustrate the potential use of the sensor array for disease diagnosis and other biomedical monitoring applications.

Identification of Endocrine Disrupting Chemicals using a Virus-Based Colorimetric Sensor.

A simple and portable colorimetric sensor based on M13 bacteriophage (phage) was devised to identify a class of endocrine disrupting chemicals, including benzene, phthalate, and chlorobenzene derivatives. Arrays of structurally and genetically modified M13 bacteriophage were fabricated so as to produce a biomimetic colorimetric sensor, and color changes in the phage arrays in response to several benzene derivatives were characterized. The sensor was also used to classify phthalate and chlorobenzene derivatives as representatives of endocrine disrupting chemicals. The characteristic color patterns obtained on exposure to various benzene derivatives enabled similar chemical structures in the vapor phase to be classified. Our sensing approach based on the use of a genetically surface modified M13 bacteriophage offers a promising platform for portable, simple environmental monitors that could be extended for use in numerous application areas, including food monitoring, security monitoring, explosive risk assessment, and point of care testing.

A simple and selective colorimetric mercury (II) sensing system based on chitosan stabilized gold nanoparticles and 2,6-pyridinedicarboxylic acid

The development of simple and cost-effective methods for the detection and treatment of Hg2+ in the environment is an important area of research due to the serious health risk that Hg2+ poses to humans. Colorimetric sensing based on the induced aggregation of nanoparticles is of great interest since it offers a low cost, simple, and relatively rapid procedure, making it perfect for on-site analysis. Herein we report the development of a simple colorimetric sensor for the selective detection and estimation of mercury ions in water, based on chitosan stabilized gold nanoparticles (AuNPs) and 2,6-pyridinedicarboxylic acid (PDA). In the presence of Hg2+, PDA induces the aggregation of AuNPs, causing the solution to change colors varying from red to blue, depending on the concentration of Hg2+. The formation of aggregated AuNPs in the presence of Hg2+ was confirmed using transmission electron microscopy (TEM) and UV–Vis spectroscopy. The method exhibits linearity in the range of 300nM to 5μM and shows excellent selectivity towards Hg2+ among seventeen different metal ions and was successfully applied for the detection of Hg2+ in spiked river water samples. The developed technique is simple and superior to the existing techniques in that it allows detection of Hg2+ using the naked eye and simple and rapid colorimetric analysis, which eliminates the need for sophisticated instruments and sample preparation methods.

Colorimetric detection of Cr (VI) based on the leaching of gold nanoparticles using a paper-based sensor

Herein, we have developed a simple, sensitive and paper-based colorimetric sensor for the selective detection of Chromium (Ⅵ) ions (Cr (VI)). Silanization-titanium dioxide modified filter paper (STCP) was used to trap bovine serum albumin capped gold nanoparticles (BSA-Au NPs), leading to the fabrication of BSA-Au NPs decorated membrane (BSA-Au NPs/STCP). The BSA-Au NPs/STCP operated on the principle that BSA-Au NPs anchored on the STCP were gradually etched by Cr (VI) as the leaching process of gold in the presence of hydrobromic acid (HBr) and hence induced a visible color change. Under optimum conditions, the paper-based colorimetric sensor showed clear color change after reaction with Cr (VI) as well as with favorable selectivity to a variety of possible interfering counterparts. The amount-dependent colorimetric response was linearly correlated with the Cr (VI) concentrations ranging from 0.5µM to 50.0µM with a detection limit down to 280nM. Moreover, the developed cost-effective colorimetric sensor has been successfully applied to real environmental samples which demonstrated the potential for field applications.