Colorimetric Paper Sensor Research Articles

Novel cost-effective Hibiscus flower based colorimetric paper sensor containing anthocyanins to monitoring the quality and freshness of raw fish

This article described the low-cost hibiscus flower based colorimetric paper sensor to monitor the quality and freshness of raw fish. The extract of hibiscus flower was used to develop pH sensing paper strips for qualitative analysis. The sensitivity of paper sensor was checked by colorimetric detection of ammonia gas and then it was implemented to monitor the freshness of fish visually. The extract of hibiscus flower containing anthocyanin molecules are the key molecule for visual detection of spoiled food. The above molecule was spectroscopically analyzed with change in pH of the solution before and after the interaction of food products. We also studied the variation of both color and shade of paper sensor with change in pH at natural and artificial light conditions. The color information extracted from images and their relationship with pH was explored in red, green, blue (RGB) and hue, saturation, and value (HSV) color spaces by the image-J software for qualitative monitoring of food. Anthocyanin based paper sensor is used as a convenient and real time smart food sensor in packaging application.

Glucose Oxidase Activity Colorimetric Assay Using Redox-Sensitive Electrochromic Nanoparticle-Functionalized Paper Sensors.

Glucose oxidase (GOx) activity assays are vital for various applications, including glucose metabolism estimation and fungal testing. However, conventional methods involve time-consuming and complex procedures. In this study, we present a colorimetric platform for in situ GOx activity measurement utilizing redox-sensitive electrochromic nanoparticles based on polyaniline (PAni). The glucose-adsorbed colorimetric paper sensor, herein termed Glu@CPS, is created by immobilizing ferrocene and glucose onto paper substrates that have been functionalized with PAni nanoparticles. Glu@CPS not only demonstrated rapid detection (within 5 min) but also exhibited remarkable selectivity for GOx and a limit of detection as low as 1.25 μM. Moreover, Glu@CPS demonstrated consistent accuracy in the measurement of GOx activity, exhibiting no deviations even after being stored at ambient temperature for a duration of one month. To further corroborate the effectiveness of this method, we applied Glu@CPS in the detection of GOx activity in a moldy red wine. The results highlight the promising potential of Glu@CPS as a convenient and precise platform for GOx activity measurement in diverse applications including food quality control, environmental monitoring, and early detection of fungal contamination.

Development of a Colorimetric Paper Sensor for Hg2+ Detection in Water Using Cyanuric Acid-Conjugated Gold Nanoparticles.

Hg2+ is one of the most dangerous pollutants that can cause damage to organs and the immune system. The common detection methods of Hg2+ require sophisticated instrumentation and a long time for analysis. The purpose of this study was to develop a sensor for the detection of Hg2+ using filter paper immobilized by gold nanoparticles (AuNPs) conjugated with cyanuric acid (CA). The clear color change from pink to bluish purple is the response of the CA-AuNPs filter paper sensor to exposure to Hg2+. Detection can be observed visually with the naked eye and/or with imageJ software; the detection limit is 0.05 µM. The colorimetric response of the sensor was also selective towards Hg2+ after testing with different metal ions. In addition, the response from the sensor was also consistent for lake water samples spiked with Hg2+. The results of this research provide a promising basic technology for the development of sensors that are affordable, fast, portable, and easy to use for the detection and monitoring of Hg2+ levels in water.

Cerium oxide bentonite nanocomposite-based colorimetric paper sensor for aflatoxins detection in cereal nuts, oilseed and legumes

Cerium oxide nanoparticles (NanoCeO2) and bentonite (Bent) based nanocomposite (CeO2-Bent) aqueous sensor drop casted on paper substrate has been used to detect food borne Aflatoxins (AFs) by Curcumin (Cur) functionalized redox reaction mediated colorimetric detection. Optical studies reveal that when chromophore-like Cur is first added to Nano CeO2/Bent, it creates a chelate complex that serves as a mediator for enhanced binding with AFs. Cur fictionalized CeO2-Bent in the presence of AFB1 result in a rapid electronic π - π* transition and showed change in color of the dye from red (pH 9.54) to yellow (pH 7). The Hypochromic shift from ~510 nm to ~433 nm was plotted linearly at 433 nm for increased AFB1 level in foods. The calculated LOD indicated values as 0.5 µg/Kg in corn, 2.4 µg/Kg in rice, 0.2 µg/Kg in peanut, 0.7 µg/Kg in almond, 7.8 µg/Kg in arhar and 9.2 µg/Kg in chana respectively. The results were validated with HPLC-FLD obtaining high accuracy and recovery. The sensor reagent further drop casted on paper showed a quick determination for presence of AFs.

Detection of antibiotic-resistance genes in bacterial pathogens using a Cas12a/3D DNAzyme colorimetric paper sensor

The rapid detection of antibiotic-resistant genes in bacterial pathogens is critical in combating global health crises. Herein, we report a CRISPR/Cas12a-based colorimetric paper sensor, where the trans-cleavage activity of Cas12a was post-amplified by rolling circle replication, resulting in the generation of a 3D DNAzyme. The 3D DNAzyme adhered strongly to the paper surface, creating a highly bioactive paper sensor containing high densities of functional DNAzymes. This assay was effective for the rapid detection of the antibiotic-resistant gene, NDM-1, with high sensitivity. In the absence of the NDM-1 gene, the 3D DNAzyme catalyzed a colorimetric reaction, resulting in a blue-colored signal while in the presence of NDM-1, collateral cleavage activity of Cas12a was activated, leading to cleavage of the circle template, thus preventing the generation of the 3D DNAzyme and producing no colorimetric signal. This paper sensor provides rapid and low-cost detection of antibiotic-resistant genes carried by various pathogenic microorganisms with femtomolar-level sensitivity and results that are visible to the naked eye. The entire analysis requires less than 90 minutes of assay time. Due to the highly programmable design of the CRISPR probe, the platform has significant potential for quick responses to new global epidemics.

A Colorimetric Paper Sensor Based on Self‐assembled Nanocomposite Pd−Pt@hemin‐rGO/CNTs‐COOH for the Detection of H2O2

AbstractNanocomposite enzymes are attracting intensive attention worldwide. In the present study, a novel colorimetric H2O2 paper sensor was developed based on a new type of nanocomposites composed of Pd−Pt nanoparticles, hemin functionalized reduced graphene oxide (hemin‐rGO) and carboxylated carbon nanotubes (CNTs‐COOH). The proposed nanocomposites show a high peroxidase‐like activity. It provides a sensitive platform showing a linear response toward H2O2 in the range of 0.05–500 μM with a determination limit of 0.01 μM. Based on this, the composites were applied to construct a paper sensor for H2O2 detection in real samples. The cost‐effectiveness, simplicity and efficiency of this paper sensor could be developed for “point‐of‐care” analysis and other related areas.

Colorimetric Paper Sensor for Food Spoilage Based on Biogenic Amine Monitoring.

Biogenic amines (BAs), nitrogenous molecules usually present in different foods, can be considered an indicator of freshness and food quality since their amount increases during food spoilage. Their detection, possibly in real time via the use of smart packaging, is therefore of crucial importance to ensure food safety and to fulfill consumers' demand. To this end, colorimetric sensors are considered one of the most feasible solutions. Here, we report a user-friendly colorimetric sensing paper able to detect BAs via the naked eye. The sensing molecule is the aglycone genipin, a natural cross-linking agent extracted from gardenia fruit, able to bind BAs producing water-soluble blue pigments. The paper sensor was applied to chicken meat quality monitoring and a quantitative analysis was performed with image acquisition via a smartphone camera, achieving a limit of detection equivalent to 0.1 mM of putrescine. The suitability of the BA sensing paper was assessed by integrating the sensor into smart packaging and analyzing commercial chicken meat samples stored at different temperatures; the results of the sensor paralleled the "best before date" indicated on the label, confirming the potential applicability of the sensor as a smart label.

Environmental monitoring of trace metal pollutants using cellulosic-paper incorporating color change of azo-chromophore.

An essential requirement for colorimetric paper-sensor is to allow the target analytes (heavy metal ions) to access the chromophore while maintaining strong chromophore immobilization on the porous substrate surface. This work evaluates the selection of sensitive chromophores (dithizone, 1-(2-pyridylazo)2-naphthol and 4-(2-pyridylazo)-resorcinol) and their immobilization strategies on paper sensors. Dithizone (DTz) are capable of producing a significant color transition at unadjusted pH, observed by UV-Vis absorption spectroscopy and visible recognition. After immobilizing DTz on a paper substrate (cellulose acetate/chitosan substrate), the DTz-paper sensor showed a distinctive color change from blue-green to peach-pink upon reaction with Pb2+ ions, and the color intensity was proportional to the metal concentration. Quantitative analysis using RGB (R:Red; G:Green; B:Blue) plots showed that increasing DTz concentration on the CA/CS paper sensor increases the difference in total color intensity (∆IT) and the difference in red code intensity (∆IR). This is due to the formation of more DTz-Pb2+ complexes on the CA/CS paper substrate. The CA/CS paper strips immobilized with 100ppm DTz showed practical potential for rapid detection of heavy metal ions. The DTz-CA/CS paper sensor showed significant color change when detecting spiked heavy metals ions (0.1ppm Pb2+, 2.0ppm Zn2+, and 0.2ppm Cu2+) in river water samples that prepared at the maximum permissible limit for industrial effluent in Malaysia.

A regression-based machine learning approach for pH and glucose detection with redox-sensitive colorimetric paper sensors.

Colorimetric paper sensors are used in various fields due to their convenience and intuitive manner. However, these sensors present low accuracy in practical use because it is difficult to distinguish color changes for a minute amount of analyte with the naked eye. Herein, we demonstrate that a machine learning (ML)-based paper sensor platform accurately determines the color changes. We fabricated a colorimetric paper sensor by adsorbing polyaniline nanoparticles (PAni-NPs), whose color changes from blue to green when the ambient pH decreases. Adding glucose oxidase (GOx) to the paper sensor enables colorimetric glucose detection. Target analytes (10 μL) were aliquoted onto the paper sensors, and their images were taken with a smartphone under the same conditions in a darkroom. The red-green-blue (RGB) data from the images were extracted and used to train and test three regression models: support vector regression (SVR), decision tree regression (DTR), and random forest regression (RFR). Of the three regression models, RFR performed the best at estimating pH levels (R2 = 0.957) ranging from pH 2 to 10 and glucose concentrations (R2 = 0.922) ranging from 0 to 10 mg mL-1.

Non-destructive and Rapid Method for Monitoring Fish Freshness of Grass Carp Based on Printable Colorimetric Paper Sensor in Modified Atmosphere Packaging

Non-destructive and Rapid Method for Monitoring Fish Freshness of Grass Carp Based on Printable Colorimetric Paper Sensor in Modified Atmosphere Packaging

Colorimetric paper sensor for visual detection of date-rape drug γ-hydroxybutyric acid (GHB)

Drug-facilitated crimes using date-rape drugs are on the rise. Gamma-hydroxybutyric acid (GHB), a notorious date-rape drug, is colorless, odorless, and tasteless, and therefore difficult to detect in beverages. The ingestion of GHB can severely incapacitate individuals by inducing dizziness, drowsiness, and unconsciousness, making them vulnerable to crimes. To prevent drug-facilitated crimes, a GHB detection kit is developed in which PCDA-gabazine and PCDA, which strongly interact with GHB, are used as sensing materials, while PEO and PVDF are used as matrix materials that enable rapid GHB detection in a short time by increasing the penetration rate of the liquid samples. Detection kits are fabricated by electrospinning a solution containing the sensing materials and matrix materials mixed in an optimal ratio. The color of the kit distinctly changes from blue to red when a drink spiked with GHB is dropped on it (limit of detection: about 0.0096 wt%). The fabricated GHB detection kit is easy to carry and provides a visually distinguishable detection result without requiring any complicated procedure, equipment, or trained personnel. Importantly, the kit can detect GHB in colored and alcoholic beverages. Furthermore, a mobile application is developed that can aid GHB detection using the kit in diverse environments.

Insight into an Oxidative DNA-Cleaving DNAzyme: Multiple Cofactors, the Catalytic Core Map and a Highly Efficient Variant.

SummaryAn oxidative DNA-cleaving DNAzyme (PL) employs a double-cofactor model “X/Cu2+” for catalysis. Herein, we verified that reduced nicotinamide adenine dinucleotide (NADH), flavin mononucleotide, cysteine, dithiothreitol, catechol, resorcinol, hydroquinone, phloroglucinol, o-phenylenediamine, 3,3′,5,5'-tetramethylbenzidine, and hydroxylamine acted as cofactor X. According to their structural similarities or fluorescence property, we further confirmed that reduced nicotinamide adenine dinucleotide phosphate (NADPH), 2-mercaptoethanol, dopamine, chlorogenic acid, resveratrol, and 5-carboxyfluorescein also functioned as cofactor X. Superoxide anions might be the commonality behind these cofactors. We subsequently determined the conservative change of individual nucleotides in the catalytic core under four different cofactor X. The nucleotides A4 and C5 are highly conserved, whereas the conservative levels of other nucleotides are dependent on the types of cofactor X. Moreover, we observed that the minor change in the PL's secondary structure affects electrophoretic mobility. Finally, we characterized a highly efficient variant T3G and converted its double-cofactor NADH/Cu2+ to sole-cofactor NADH.

Development of a triple channel colorimetric paper sensor array based on quantum dots: A robust tool for process monitoring and quality control of basic liquors of Baijiu

Process analysis of basic liquors of Baijiu is a great challenge in industry due to the complexity fermentation processes and tiny product differentiation of basic liquors. In this work, a new triple channel colorimetric paper sensor array based on quantum dots (QDs) with three color-emission was established for the rapid process monitoring of basic liquors of Baijiu. The fluorescence of QDs can be quenched to varying degrees by the ingredients in basic liquors with different production processes, batches and qualities. Through analyzing color change (RGB value) of QDs under the UV lamp, all the corresponding information that represents basic liquors of Baijiu was extracted and further processed by principal component analysis and partial least squares discriminant analysis. By utilizing this colorimetric paper sensor array, all the production processes, batches and qualities of basic liquors can be monitored quickly and accurately with a recognition rate of 100%. What’s more, this paper sensor array required neither special modification nor complex sample preparation and can implement rapid and precise visualization analysis by the naked eye with the aid of a portable UV lamp using only a simple device and small amount of sample, showing its potential applications in the food industry.

Cation-exchange strategy for a colorimetric paper sensor: Belt-like ZnSe nanoframes toward visual determination of heavy metal ions

A colorimetric paper sensor based on a cation-exchange strategy has been developed for the visual determination of heavy metal ions. Belt-like ZnSe nanoframes as colorimetric reagents were prepared from ZnSe·0.5N2H4 hybrid nanobelts as precursors via a hydrothermal method. With the decomposition and release of N2H4 ligands, the regular belt-like nanostructures of the precursors evolved into belt-like nanoframes, which consisted of numerous ZnSe nanocrystals. Inspired by the cation-exchange characteristic of chalcogenides, the as-prepared belt-like ZnSe nanoframes were employed to fabricate a colorimetric paper sensor for the detection of heavy metal ions. Owing to the color change arising from a composition change, the colorimetric paper was successfully applied to detect Ag+, Cu2+, and Hg2+ at room temperature. Depending on the color change and its intensity, heavy metal ions of Ag+, Cu2+, and Hg2+ can be individually identified and their concentrations can be determined. Particularly for Cu2+, its visually detected concentration can be down to 1 ppm. More importantly, the fabricated colorimetric paper sensor displays excellent anti-interference properties from various typical cations and anions. Considering its low cost and practicality, expectedly it can be used for practical application.

A DNAzyme-Based Colorimetric Paper Sensor for Helicobacter pylori.

The reliable detection of pathogenic bacteria in complex biological samples using simple assays or devices remains a major challenge. Herein, we report a simple colorimetric paper device capable of providing specific and sensitive detection of Helicobacter pylori (H. pylori), a pathogen strongly linked to gastric carcinoma, gastric ulcers, and duodenal ulcers, in stool samples. The sensor molecule, an RNA-cleaving DNAzyme obtained through in vitro selection, is activated by a protein biomarker from H. pylori. The colorimetric paper sensor, designed on the basis of the RNA-cleaving property of the DNAzyme, is capable of sensitive detection of H. pylori in human stool samples with minimal sample processing and provides results in minutes. It remains fully functional under storage at ambient temperature for at least 130 days. This work lays a foundation for developing DNAzyme-enabled paper-based point-of-care diagnostic devices for monitoring pathogens in complex samples.

A DNAzyme‐Based Colorimetric Paper Sensor for Helicobacter pylori

AbstractThe reliable detection of pathogenic bacteria in complex biological samples using simple assays or devices remains a major challenge. Herein, we report a simple colorimetric paper device capable of providing specific and sensitive detection of Helicobacter pylori (H. pylori), a pathogen strongly linked to gastric carcinoma, gastric ulcers, and duodenal ulcers, in stool samples. The sensor molecule, an RNA‐cleaving DNAzyme obtained through in vitro selection, is activated by a protein biomarker from H. pylori. The colorimetric paper sensor, designed on the basis of the RNA‐cleaving property of the DNAzyme, is capable of sensitive detection of H. pylori in human stool samples with minimal sample processing and provides results in minutes. It remains fully functional under storage at ambient temperature for at least 130 days. This work lays a foundation for developing DNAzyme‐enabled paper‐based point‐of‐care diagnostic devices for monitoring pathogens in complex samples.

A colorimetric paper sensor based on the domino reaction of acetylcholinesterase and degradable γ-MnOOH nanozyme for sensitive detection of organophosphorus pesticides

Despite the tremendous achievements of existing sensing techniques, sensitive and portable sensing of organophosphorus pesticides (OPs) in a non-polluting manner remains a challenging issue. This work proposed a facile colorimetric paper sensor using γ-MnOOH nanowires (NWs) as a degradable nanozyme and 3,3′,5,5′-tetramethylbenzidine (TMB) as a chromogenic indicator for rapid and sensitive screening of OPs and acetylcholinesterase (AChE) activity. The sensing mechanism was based on the easy disintegration of the oxidase-like γ-MnOOH NWs into invalid Mn2+ ions by the selective reaction with thiocholine (TCh) produced by AChE and acetylthiocholine iodide (ATCh), triggering a remarkable activity loss of MnOOH nanozymes towards TMB oxidation. The concentration of OPs, as an AChE inhibitor, was measured by the changes in absorbance at 652 nm or blue color of oxTMB products. Such detection platform in solution state achieved relatively low limits of detection (LODs) for AChE activity (0.007 mU mL−1), and for two typical OPs, i.e., omethoate (0.35 ng mL−1) and dichlorvos (0.14 ng mL−1), respectively. Further, the portable assembly of such AChE-nanozyme tandem reaction on test paper performed well, reaching LODs of 0.1 mU mL−1 for AChE, 10 ng mL−1 for omethoate, and 3 ng mL−1 for dichlorvos, respectively. Meanwhile, this sensing system showed great selectivity and anti-interfering capacity in both solution and solid states, and worked well in real serum and vegetable samples. The abovementioned results, along with evidence of its good ecological sustainability, demonstrated the superiority of this well-performing platform for application in the food, environmental, and medical fields.

A novel colorimetric paper sensor based on the layer-by-layer assembled multilayers of surfactants for the sensitive and selective determination of total antioxidant capacity.

Herein, a new colorimetric paper sensor based on the layer-by-layer assembled multilayers of a cationic surfactant, tetrabutylammonium bromide (TBABr), and an anionic surfactant, sodium dodecyl sulfate (SDS), modified on filter paper was developed for the determination of total antioxidant capacity (TAC). In this study, gallic acid (GA) was used as the antioxidant standard. The fabricated (TBABr/SDS)3/PAD was loaded with Fe3+ ions to obtain Fe3+/(TBABr/SDS)3/PAD, exhibiting high selectivity for the detection of GA when compared with the case of other metal ions. The interaction between GA and the Fe3+/(TBABr/SDS)3/PAD sensor occurred rapidly, and the colorimetric paper sensor changed from yellow to purple immediately. The quantitative detection of GA was enabled by taking an image using an ordinary smartphone and applying the ImageJ software based on the change in color. Under optimum conditions, a linear response was obtained between the change in the color of the sensor and the TAC value expressed in terms of gallic acid equivalents. The linear range was from 0.50 μM to 6.50 mM with the detection limit of 0.35 μM. The colorimetric paper sensor was applied to detect the TAC in three kinds of green tea and vegetable samples, which provided the good recoveries of 86.0–109.9%. The proposed sensor is simple, cheap, equipment-free, rapid and environmentally friendly. In addition, the colorimetric sensor Fe3+/(TBABr/SDS)3/PAD has potential applicability for TAC detection in real food samples.

A colorimetric paper sensor for citrate as biomarker for early stage detection of prostate cancer based on peroxidase-like activity of cysteine-capped gold nanoclusters.

Citrate is currently considered a preferred biomarker for the early stage detection of prostate cancer. In the present work, based on the highly efficient catalytic properties of gold nanoclusters, a novel system for optical determination of citrate was successfully established under optimized conditions. Cysteine-capped gold nanoclusters (Cys-AuNCs) are shown to have an intrinsic peroxidase-mimetic activity. In the presence of H2O2, Cys-AuNCs nanostructures are able to catalyse the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) with high efficiency to produce a blue dye (with an absorbance maximum at 650 nm). Citrate has carboxylic and hydroxyl groups that can bind with free amino and free carboxyl cysteine groups via hydrogen bonds, thus creating a coating on the surface of the gold nanocluster and inhibiting the cluster oxidation activity. Accordingly, a visual, sensitive and simple colorimetric method using Cys-AuNCs as peroxidase mimetic was developed for detecting citrate. A suitable linear relationship for citrate was obtained for the range of 0.5 to 1000 μM. The limit of detection (LOD) of the proposed method was calculated as 0.1 μM and the relative standard deviation (RSD) was obtained to be less than 4.0%. Moreover, the biosensor was used to perform a paper assay on a Y-shaped microfluidic device and make use of the distinctive features of microchannels such as short response time, very low reagent volume required, low fabrication cost etc. A detection limit of 0.4 μM was achieved through the paper test and a good linear range was observed between 1.0 μM-10 mM. The proposed method was further applied to citrate detection in the human urine sample.

Development of Colorimetric Paper Sensor for Pesticide Detection Using Competitive-inhibiting Reaction

Contamination by pesticides is an ever-increasing problem associated with fields of environmental management and healthcare. Accordingly, appropriate treatments are in demand. Pesticide detection methods have been researched extensively, aimed at making the detection convenient, fast, cost-effective, and easy to use. Among the various detecting strategies, paper-based assay is potent for real-time pesticide sensing due to its unique advantages including disposability, light weight, and low cost. In this study, a paper-based sensor for chlorpyrifos, an organophosphate pesticide, has been developed by layering three sheets of patterned plates. In colorimetric quantification of pesticides, the blue color produced by the interaction between acetylcholinesterase and indoxyl acetate is inhibited by the pesticide molecules present in the sample solutions. With the optimized paper-based sensor, the pesticide is sensitively detected (limit of detection=8.60 ppm) within 5 min. Furthermore, the shelf life of the device is enhanced to 14 days after from the fabrication, by treating trehalose solution onto the deposited reagents. We expect the paper-based device to be utilized as a first-screening analytic device for water quality monitoring and food analysis.