Colorimetric Array Research Articles

Indicator Displacement Assay-based Chemosensor Arrays for Saccharides using Off-the-shelf Materials toward Simultaneous On-site Detection on Paper

Chemosensor arrays are useful analytical methods in supramolecular analytical chemistry, which discriminate molecular information such as species and their concentrations based on pattern recognition. Molecular self-assembled systems can provide not only multi-optical response patterns but also easy preparation of chemosensors. In this regard, dynamic covalent bonds play key roles in competitive assays (i.e., indicator displacement assay (IDA)). In this review, we propose an actual approach for simple IDA-based colorimetric and fluorescent chemosensor arrays utilizing only off-the-shelf materials. With chemometrics techniques, the IDA-based chemosensor arrays successfully recognized target saccharides. Toward on-site analysis, we further applied the IDA-based chemosensor array to a paper-based analytical device. The chemosensor array on the paper has achieved an accurate on-site analysis utilizing image processing without spectrophotometric instruments. The off-the-shelf material-based chemosensor arrays with pattern recognition techniques would be a novel analytical method for lab-free detections.

Detection of aldehydes by gold nanoparticle colorimetric array based on Tollens' reagent.

Aldehydes are very common pollutants and many are possible human carcinogens. Herein, we report an easy-to-operate and low-cost method for discrimination of diverse aldehydes. Our colorimetric sensor array based on Tollens' reagent allows discrimination of ten kinds of aldehydes, showing a distinct color change from wine-red to deep yellow. In the presence of aldehydes, Ag shells are coated onto gold nanoparticles (GNPs) functionalized with diverse ligands (including bovine serum albumin, polyvinylpyrrolidone and L-cysteine), forming Au@Ag core-shell nanoparticles. The sensor array has great capacity for differentiating between ten kinds of aldehydes by color change, with accuracy and specificity of over 88%. Under optimal conditions, there is good linear correlation between Euclidean distance and formaldehyde concentrations ranging from 0.1 to 10 000 μM (R2 = 0.9908). The sensor was successfully used to determine formaldehyde content in shrimp, with recovery of 85.8% to 114.82%. Our GNPs sensor shows good potential for fast, reliable identification of aldehydes in food.

Paper-based colorimetric sensor for potassium ion detection in urine by crown ether modified gold nanoparticles

Detection and identification of potassium ion (K+) level in urine is essential for diagnosis of several deseases or for guiding treatments. We have developed a simple, rapid, low cost and naked-eye quantitative method for K+ analysis in urine using a paper-based colorimetric array test strip. The array comprised three sensing elements printed using a wax-printing technique and filled with different amounts of crown ether (4-aminodibenzo-18-crown-6) modified gold nanoparticles (AuNPs). The detection is achieved by measuring the color change (from red to violet) when AuNPs aggregated following crown ether-K+ complexation. Furthermore, the detection sensitivity could be controlled by changing the amount of the crown ether. The strip sensor array based on crown ether modified AuNPs successfully detected K+ level in the ranges of 5-1000 µM by naked eye. Thus, the developed sensor is very simple yet has a potential to be of real use in detecting K+ in real urine samples.

The Optoelectronic Nose.

How does one tell the difference between one molecule or mixture of molecules from another? Chemical sensing seeks to probe physical or chemical properties of molecular or ionic species (i.e., analytes) and transform that information into a useful and distinguishable output. The olfactory system of animals is the prototype of chemical sensing. Even for human beings (who are generally more visual than olfactory creatures), the sense of smell is one of our most basic capabilities, and we can discriminate among many thousands, and possibly even billions, of different odors. The chemical specificity of the olfactory system does not come from specific receptors for specific analytes (i.e., the traditional lock-and-key model of enzyme-substrate interactions), but rather olfaction uses pattern recognition of the combined responses of several hundred olfactory receptors.In analogy to olfaction, colorimetric sensor arrays provide high dimensional data from the color changes of chemically responsive colorants as they are exposed to analytes. These colorants include pH responsive dyes, Lewis acid/base indicators, redox dyes, vapochromics, and surface-modified silver nanoparticles. The color difference maps so created provide chemical sensing with high sensitivity (often down to ppb levels), impressive discrimination among very similar analytes, and exquisite fingerprinting of extremely similar mixtures over a wide range of analyte types, both in the gas and liquid phases. Such colorimetric arrays probe a wide range of the chemical reactivity of analytes, rather than the limited dimensionality of physical properties (e.g., mass) or physisorption (e.g., traditional electronic noses). Our sensor arrays are disposable and simple to produce by either inkjet or robotic dip-pen printing onto the surface of porous polymer membranes or even paper.Design of both sensor arrays and optical readers for their analysis has advanced to a fully self-contained pocket-sized instrument, the optoelectronic nose. Quantitative analysis requires appropriate chemometric methods for pattern recognition of data with inherently high dimensionality, e.g., hierarchical cluster analysis and support vector machines. A wide range of applications for the colorimetric sensor arrays has been developed, including personal dosimetry of toxic industrial chemicals, detection of explosives or fire accelerants, monitoring pollutants for artwork and cultural heritage preservation, quality control of foods and beverages, rapid identification of bacteria and fungi, and detection of disease biomarkers in breath or urine. The development of portable, high-accuracy instrumentation using standard imaging devices with the capability of onboard, real-time analysis has had substantial progress and increasingly meets the expectations for real-world use.

Gradient-Based Colorimetric Array Sensor for Continuous Monitoring of Multiple Gas Analytes.

Colorimetry is widely used in chemical sensing due to its high sensitivity and high selectivity. However, most colorimetric sensors are one-time use because the color-producing reactions or bindings are usually irreversible. In addition, traditional colorimetric sensors like the detection tubes are bulky and packed individually, making parallel sensing of multiple analytes difficult. Here, we demonstrate a gradient-based colorimetric array sensor (GCAS) to overcome these limitations. Different colorimetric sensing elements are inkjet-printed as parallel straight lines on a porous substrate. Lateral transport of analytes across the substrate creates color gradients on the sensing elements. The color gradients shift along the transport direction over time, and GCAS tracks the gradient shifts and converts them into analyte concentrations in real time. Using a low-cost complementary metal-oxide semiconductor imager, we show detection of three air pollutants using a single GCAS chip and 24 h continuous monitoring of ambient ozone.

Fluorescence and colorimetric dual-mode sensor for visual detection of malathion in cabbage based on carbon quantum dots and gold nanoparticles

A dual-mode fluorescence/colorimetric sensor based on carbon quantum dots (CQDs) and gold nanoparticles (GNPs) was developed for visual detection of malathion in cabbage. The CQDs-GNPs nanocomposite exhibited emission wavelength at 527 nm and absorption wavelength at 524 nm. The fluorescence intensity increased and absorption decreased with addition of malathion. Fluorescence and colorimetric calibration curves were established based on fluorescence intensity (R2 = 0.9914) and absorbance (R2 = 0.9608) in the range of 1 × 10−9–1 × 10−2 M, respectively. Furthermore, fluorescence and colorimetric standard arrays were prepared for visual detection of malathion according to the change of fluorescence brightness and color. Finally, the approximate concentrations of malathion in cabbage samples were estimated by the standard arrays and naked eyes. The calibration curves were used for accurate detection in cabbage samples with recoveries of 89.9%–103.4% (fluorescence) and 88.7%–107.6% (colorimetric). The established sensor for visual malathion detection in cabbage was accurate with strong application potential, especially for rapid screening.

Development of a Dye-Based Device to Assess the Poultry Meat Spoilage. Part II: Array on Act.

This work presents a colorimetric dye-based array for naked-eye detection of chicken meat spoilage. The array is obtained by fixing five acid–base indicators, m-cresol purple (1), o-cresol red (2), bromothymol blue (3), thymol blue (4), and chlorophenol red (5), and a sensing molecule specific for thiols, 5,5′-dithiobis(2-nitrodibenzoic acid), called Ellman’s reagent (6), on a cellulose-based support. The dyes, being permanently charged, are fixed on the support via ion-exchange. The entire degradation process of beast poultry meat, at ambient temperature and in a domestic fridge, is followed by the change of the color of the array, placed in the headspace over the meat samples. The device is set after selection of the most suitable starting form, which could be the acidic or the basic color of indicators, being the proper dye concentration and the dimension of the spots already established. Basing on sensors colors, we identified three levels of the degradation process of chicken meat, named SAFE, WARNING, and HAZARD. By instrumental analysis, we demonstrated that sensors response was correlated to volatile organic compounds (VOCs) composition in the headspace and, thus, to meat spoilage progress. We demonstrated that biogenic amines (BAs), commonly considered a critical spoilage marker, are indeed produced into the samples but never present in the headspace, even in traces, during the investigated time-lapse. The VOC evolution nevertheless allows one to assign the sample as WARNING and further HAZARD. Some indicators turned out to be more informative than others, and the best candidates for a future industrial application resulted in a bromothymol blue (3)-, chlorophenol red (5)-, and Ellman’s reagent (6)-based array.

Development of a Colorimetric Sensor for Autonomous, Networked, Real-Time Application

This review describes an ongoing effort intended to develop wireless sensor networks for real-time monitoring of airborne targets across a broad area. The goal is to apply the spectrophotometric characteristics of porphyrins and metalloporphyrins in a colorimetric array for detection and discrimination of changes in the chemical composition of environmental air samples. The work includes hardware, software, and firmware design as well as development of algorithms for identification of event occurrence and discrimination of targets. Here, we describe the prototype devices and algorithms related to this effort as well as work directed at selection of indicator arrays for use with the system. Finally, we review the field trials completed with the prototype devices and discuss the outlook for further development.

Conjugated Polyelectrolyte Based Colorimetric Array for the Discrimination of Primary Amino Acids

AbstractWe report a colorimetric sensor based on the supramolecular complex between a conformation‐sensitive cationic polythiophene derivative, poly(3‐(4‐methyl‐3‐thienyloxy)propyltrimethylammonium) (PMTPA) and 2‐naphthalenesulfonate (NS). It could be applied to discern 19 primary amino acids by the wavelength of PMTPA/NS. The sensing performance and mechanism was investigated by spectroscopic studies such as absorption and emission spectra. This approach relies on the disassembly of PMTPA/NS aggregates induced by the amphiphilic isoindole derivatives of amino acids formed in situ. 100% confidence limits for this discrimination could be achieved by using linear discriminant analysis (LDA).

Detection of Chemical Warfare Agents by Colorimetric Sensor Arrays.

We report the successful use of colorimetric arrays to identify chemical warfare agents (CWAs). Methods were developed to interpret and analyze a 73-indicator array with an entirely automated workflow. Using a cross-validated first-nearest-neighbor algorithm for assessing detection and identification performances on 632 exposures, at 30 min postexposure we report, on average, 78% correct chemical identification, 86% correct class-level identification, and 96% correct red light/green light (agent versus non-agent) detection. Of 174 total independent agent test exposures, 164 were correctly identified from a 30 min exposure in the red light/green light context, yielding a 94% correct identification of CWAs. Of 149 independent non-agent exposures, 139 were correctly identified at 30 min in the red light/green light context, yielding a 7% false alarm rate. We find that this is a promising approach for the development of a miniaturized, field-portable analytical equipment suitable for soldiers and first responders.

A Colorimetric Artificial Olfactory System for Airborne Improvised Explosive Identification

The detection of ultralow or nonvolatile target analytes remains a significant challenge for artificial olfactory systems even after decades of development, which severely limits their widespread application. To overcome this challenge, an artificial olfactory system based on a colorimetric hydrogel array is constructed for the first time as a universal representative. As an effective extension of conventional artificial olfactory systems that integrates the merits of its predecessors, the proposed system accurately mimics olfactory mucosa and specific odorant binding proteins using hydrogels endowed with specific colorimetric reagents for the detection of hypochlorite, chlorate, perchlorate, urea, and nitrate. Therefore, the proposed system is capable of detecting and discriminating between these five airborne improvised explosive microparticulates with a detection limit as low as 39.4 pg. Additionally, the system demonstrates good reusability over ten cycles, rapid response time of ≈0.2 s, and excellent discrimination properties, despite significant variation. This proof-of-concept study on colorimetric artificial olfactory systems yields a novel strategy for the direct and discriminative detection of nonvolatile airborne microparticulates.

An inkjet‐printed sulfonephthalein dye indicator array for volatile amine detection

Colorimetric indicators are versatile for applications such as intelligent food packaging, for reflecting the actual quality and/or monitoring distribution history of food products. In this study, a colorimetric indicator array composed of sulfonephthalein dyes was successfully developed by piezoelectric inkjet printing, for the detection of volatile amines-the primary spoilage gases for fish and seafood products. The printing inks were formulated in water/ethanol/1-butanol mixture. By refilling the printer's cartridges with our formulated inks and controlling the red, green, and blue color parameters, a 7×9 indicator array was printed onto inkjet transparency films. The color response of the indicator array was tested with different volatile amines at various concentrations. The array indicator was capable of discriminating six different volatile amines: ammonia, trimethylamine, dimethylamine, triethylamine, piperidine, and hydrazine. The printability of the inks was investigated by characterizing their density, surface tension, and dynamic viscosity, dictating that all formulated inks were printable fluid. The microstructural morphologies of the printed dyes on transparency films were evaluated using scanning electron microscopy. Interactions of the dye with the volatiles were studied by Fourier transform infrared spectroscopy. In summary, the piezoelectric inkjet printing method presented in this study offers a convenient, efficient, and flexible means to fabricate colorimetric indicators for detecting food spoilage volatiles. These indicators are promising as sensing components in intelligent packaging systems, to reveal the freshness of fish products by correlating with quality parameters such as total volatile basic nitrogen, microbial growth, and sensory attributes. Further studies on the feasibility of using the array indicators in real food packaging systems, development of strategy to mitigate the potential migration of the indicator dyes, and designing array patterns optimal for machine/human interpretation, are important to commercialize the technology. PRACTICAL APPLICATION: Piezoelectric inkjet printing offers a convenient way to fabricate sensing materials and aligns with industrial packaging operations. The use of indicators on food package helps consumers more accurately perceive real-time food quality information.

Colorimetric discriminatory array for detection and discrimination of antioxidants based on HAuCl4/3,3',5,5'-tetramethylbenzidine.

Here, we report a simple but effective nose/tongue-mimic sensor array based on HAuCl4/3,3',5,5'-tetramethylbenzidine (TMB) for colorimetric discrimination and determination of antioxidants. Two concentrations of HAuCl4 were employed as receptor units to construct the colorimetric sensor array. The sensing strategy is based on the fact that HAuCl4 with different concentrations (0.08 and 0.03 mM) could oxidize TMB to oxidized TMB (oxTMB), resulting in a blue and green color solution, respectively, corresponding to an absorption peak centered at 440 nm and 657 nm. However, the presence of different antioxidants could cause the reduction in HAuCl4, leading to the fading of the blue and green color and the decrease in the absorbance at 440 nm and 657 nm to varying degrees. Based on the above phenomena, by taking advantage of linear discriminant analysis (LDA), five antioxidants (i.e. ascorbic acid (AA), melatonin (MT), uric acid (UA), tannic acid (TCA), and glycine (Gly)) at five concentrations (200, 120, 60, 20, and 1 nM) were successfully discriminated both in buffer and serum. More importantly, this approach is simple, fast, and without the use of any nanomaterials.

Colorimetric identification of lanthanide ions based on two carboxylic acids as an artificial tongue.

We report a colorimetric array, which consists of two carboxylic acids (quinolinic acid (QA), tannic acid (TCA)) as the sensor element and Eriochrome Black T (EBT) as the colorimetric signal readout. The assay is based on coordination binding between lanthanide ions and EBT, and between lanthanide ions and the carboxylic acids. The competitive binding of lanthanide ions with the carboxylic acids and EBT leads to the change in absorbance and color of the solutions. To test the efficacy of our sensor array, the sensor array was exposed to five target lanthanide ions (La3+, Sm3+, Eu3+, Gd3+ and Yb3+) with diverse concentrations (10, 50, 100, 200, 300, 400, and 500 nM). Linear discriminant analysis (LDA) results show that the sensor array can identify the five lanthanide ions, with a low discrimination limit of 10 nM. More importantly, the sensor array realizes fast discrimination of lanthanide ions in river samples, showing potential in environmental monitoring.

White Eggshells: A Potential Biowaste Material for Synergetic Adsorption and Naked-Eye Colorimetric Detection of Heavy Metal Ions from Aqueous Solution.

In the present work, we have utilized a simple, no-cost, unmodified eggshell powder as a naked-eye colorimetric detector, which on simple dispersion in aqueous solution of metal ions exhibited characteristic color change from white to pale green, pale blue, yellow, pale yellow, dark yellow, pale pink, blue, and brown for metal ions V4+, Cr3+, Cr6+, Fe2+, Fe3+, Co2+, Cu2+, and Ag+, respectively. The effects of various parameters like concentration of metal ions, pH, temperature, and adsorbent dosage were investigated by batch sorption experiments. Also, Freundlich and Langmuir models were used to describe the adsorption isotherm. The eggshell powder before and after adsorption was characterized qualitatively by the naked-eye and quantitatively by diffuse reflectance spectroscopy-UV, Fourier transform infrared, atomic absorption spectroscopy, powder X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray spectroscopy, Brunauer-Emmett-Teller, zeta potential, and X-ray photoelectron spectroscopy techniques. In addition, the competitive adsorption of metal ions in mixtures and the recycle experiments were carried out to prove the sustainability of the material. Further, the red, green, and blue alterations were extracted from the colorimetric array and subjected to hierarchical clustering analysis using the Ward method by calculating the Euclidean distance, which displayed facile discrimination of 10 heavy metal ions at 1 mM level. Thus, the unmodified eggshell powder has been proven to be an impressive value-added sustainable material for synergistic metal adsorption and colorimetric naked-eye detection of a series of metal ions with detection limits of 10-4 M for Fe3+, Fe2+, and Cu2+; 10-3 M for Cr3+, Cr6+, Ag+, and Co2+; and 5 × 10-3 M for V4+.

Colorimetric determination of nine metal ions based on the de-aggregation of papain-functionalized gold nanoparticles and using three chelating agents.

A colorimetric array for metal ions is described that is based on the de-aggregation of papain-capped gold nanoparticles (AuNPs) for discrimination of metal ions. The functionalized AuNPs were used as colorimetric probes, and three chelating agents (tripolyphosphate, citrate, and ethylenediamine tetraacetate were employed as the recognition receptors. In the absence of metal ions (Fe3+, Cr3+, Co2+, Mg2+, Pb2+, Ca2+, Zn2+, Ti4+, and Sn4+ were studied), the capped AuNPs are well dispersed in solution. In the presence of these ions, the metal ions bind papain and cause the AuNPs to aggregate. This causes a color change from red to purple. Different chelating agents induce different affinities between metal ions and papain. This results in distinct colorimetric response patterns. Linear discriminant analysis is used to discriminate the various metal ions on a three-dimensional spatial dispersion graph. Graphical abstractA colorimetric method is describedfor discrimination of metal ions. It is based on the chelation reaction between sensing receptors and metal ion-induced papain-functionalized AuNP deaggregation.

Colorimetric and Raman spectroscopic array for detection of hydrogen peroxide and glucose based on etching the silver shell of Au@Ag core-shell nanoparticles.

Gold-silver core-shell nanoparticles (Au@Ag NPs) were prepared by two successive reductions in a seed-growth method. The Au@Ag NPs are used as both a colorimetricandRaman spectroscopic probe for ultrasensitive determination of H2O2 and glucose. It is found that H2O2 (as produced from glucose by the action of glucose oxidase) can directly oxidize and gradually corrode the silver shell of the Au@Ag NPs. This results in a drop in the surface plasmon resonance absorbance at 400nm, and the color of the solution changes from brownish yellow to purple. Without adding any additional chromogenic agents, the color change can be visually observed and detected photometrically. Silver NPs also are an excellent surface-enhanced Raman scattering (SERS) substrate. Due to corrosion of the silver shell, the SERS intensity (measured at 1083cm-1) gradually decreases with increasing glucose concentration. The detection limits are 300nM of glucose for the colorimetric assays, and 20nM for the SERS assay. Graphical abstractSchematic representation of the method forglucose determination. H2O2 can oxidize and gradually corrode the silver shell of the gold-silver core-shell nanoparticles. This results in a distinct color change of the solutionfrom brownish yellow to purple, and a drop in SERS intensity.The effect is applied in colorimetric and Raman spectroscopic assays for glucose.

Colorimetric array freshness indicator and digital color processing for monitoring the freshness of packaged chicken breast

Abstract A colorimetric array freshness indicator was developed to monitor chicken breast spoilage, consisting of an inner poly(ether-block-amide) (PEBA) film, a color-changing layer of eight polymer-immobilized pH dyes, and an outer poly(ethylene terephthalate) film. Simulated experiments with trimethyl amine (TMA) revealed the necessary color changes and the optimum dye concentration for the expected quality range for stored chicken breast was determined. The optimized colorimetric array freshness indicator was then applied to chicken breast packaging and digital images for its color response were acquired using a smartphone camera over storage time. The obtained data were analyzed by both the newly developed chromatic factor and principal component analysis. Chicken breast samples stored at 4 °C and 10 °C could be categorized into two groups, fresh and spoiled states over the storage time. The chromatic parameter X was well correlated with the microorganism counts as well as total volatile base nitrogen (TVBN) and CO2 from the chicken meat samples. Future implementation of the indicator in combination with a smartphone application could provide a low-cost, specific, and sensitive monitoring method for food product freshness.

Colorimetric quantification and discrimination of phenolic pollutants based on peroxidase-like Fe3O4 nanoparticles

Given the great harm of toxic phenolic pollutants toward the environment and human health, exploring efficient and low-cost methods for their monitoring becomes strongly necessary. Herein, we propose a facile and high-performance sensor array for colorimetric quantification and discrimination of phenolic pollutants by employing Fe3O4 nanoparticles (Fe3O4 NPs) as a peroxidase mimic. The small-size Fe3O4 NPs exhibit favorable catalytic activity to promote the reaction of 4-aminoantipyrine, phenolic species and H2O2, giving a remarkable color change to indicate the level of the target. As a result, the approach provided linear response for phenol in the concentration range from 1.67 μM to 1.2 mM, offering a limit of detection down to 3.79 μM. By integrating the colorimetric array with principal component analysis, common phenolic compounds, including phenol, o-chlorophenol, m-chlorophenol, p-chlorophenol, m-aminophenol and o-nitrophenol, were well discriminated even at a very low concentration. These results suggest our sensor array as an effective tool to rapidly detect and differentiate phenolic contaminants in environmental and food matrices.

Simple Colorimetric Chemosensor Array for Oxyanions: Quantitative Assay for Herbicide Glyphosate.

Although the determination of oxyanions due to correlation with metabolic processes and diseases is in high demand, most of the developed methods are suffering from a shortage of a capability of on-site analysis, sensitivity, and user-friendliness. This paper introduces the first colorimetric chemosensor array targeting various anions including glyphosate. The proposed sensor benefits from some notable features such as utilizing only commercially available reagents, recognizing similarly structured compounds by biomaterial-free sensors, and providing a fingerprint-like response originating from pattern recognition. The detection mechanism is based on an anion sensing strategy named coordination binding-based sensor array (CBSA). In CBSA, competitive coordinative bonding of a metal ion (Zn2+) between a catechol dye (i.e., indicator) and target anions occurs, and changes in the optical properties of the dye represent the target's concentration. For data processing, two chemometrical techniques including linear discrimination analysis (LDA) and an artificial neural network (ANN) for pattern classification and regression/prediction purposes were successfully employed, respectively. Finally, the proposed chemosensor was subjected to glyphosate samples (commercial herbicide and tap water samples) and produced satisfactory results.