A simple and low-cost paper-based colorimetric method for detecting and distinguishing the GII.4 and GII.17 genotypes of norovirus.

In modern times, viruses still threaten people's lives. Among them, norovirus was the main pathogenic factor in the cause of gastroenteritis and foodborne illness, of which the GII.4 and GII.17 genotypes are prevalent in China and most parts of the world. A simple and low-cost platform for rapid and accurate norovirus detection remains a major challenge. After the cell-free system and paper-based chromogenic system were optimized, a rapid and specific norovirus detection method was established based on norovirus-specific sequences in combination with toehold switch elements. The development of a visible color change during detection eliminates the need for any complicated instruments. We validated this strategy and its specificity in differentiating GII.4, GII.17, Zika virus, and human coronavirus HKU1. The results showed that the optimized detection system not only provided a simple and rapid detection method for the sufficient differentiation of the two norovirus genotypes but also showed high specificity and no cross-reactivity with other viruses. Using nucleic acid isothermal amplification, this assay showed a limit of detection of 0.5 pM for the GII.4 genotype and 2.6 fM for the GII.17 genotype in reactions that could be observed directly with the naked eye. Our results suggested that this paper-based colorimetric method could serve as a simple and low-cost visual detection method for pathogens in clinical samples, especially in remote or rural areas.

Colorimetric detection and bio-magnification of bisphenol A in fish organs and water sources using 3',6'-bis(diethylamino)-2- ((3,4,5trimethyl benzylidene) amino) spiro [isoindoline -1,9'-xanthen ]-3-one (BTSIXO)-Fe3+ ion conjugate.

Current study is focusing mainly on the development of simple, novel, and cost-effective optical sensor to detect and quantify Bisphenol A (BPA) contamination. We designed a very selective and sensitive colorimetric sensor using synthesized 3', 6'- bis(diethylamino) -2- ((3,4,5 trimethyl benzylidene) amino)spiro [isoindoline-1,9'-xanthen] -3-one (BTSIXO) conjugated with Fe3+-ions via very simple eco- friendly synthetic protocol. The sensor has an excellent wide detection range for BPA from 0.1 to 150 ppm with LODs of 0.02 ppm. Finally, the applicability of the sensor was demonstrated in fish samples especially in the organs of Oreochromis mossambicus fingerlings and contaminated industrial water samples. The sensor was also applied for the quantification of BPA present drinking water stored in the plastic bottles. The developed sensor has shown a good agreement and accuracy when compared with ESI-Mass techniques.

Disposable and Low-Cost Colorimetric Sensors for Environmental Analysis.

Environmental contamination affects human health and reduces the quality of life. Therefore, the monitoring of water and air quality is important, ensuring that all areas are acquiescent with the current legislation. Colorimetric sensors deliver quick, naked-eye detection, low-cost, and adequate determination of environmental analytes. In particular, disposable sensors are cheap and easy-to-use devices for single-shot measurements. Due to increasing requests for in situ analysis or resource-limited zones, disposable sensors' development has increased. This review provides a brief insight into low-cost and disposable colorimetric sensors currently used for environmental analysis. The advantages and disadvantages of different colorimetric devices for environmental analysis are discussed.

A Rapid, Simple, Inexpensive, and Mobile Colorimetric Assay COVID-19-LAMP for Mass On-Site Screening of COVID-19.

To control the COVID-19 pandemic and prevent its resurgence in areas preparing for a return of economic activities, a method for a rapid, simple, and inexpensive point-of-care diagnosis and mass screening is urgently needed. We developed and evaluated a one-step colorimetric reverse-transcriptional loop-mediated isothermal amplification assay (COVID-19-LAMP) for detection of SARS-CoV-2, using SARS-CoV-2 isolate and respiratory samples from patients with COVID-19 (n = 223) and other respiratory virus infections (n = 143). The assay involves simple equipment and techniques and low cost, without the need for expensive qPCR machines, and the result, indicated by color change, is easily interpreted by naked eyes. COVID-19-LAMP can detect SARS-CoV-2 RNA with detection limit of 42 copies/reaction. Of 223 respiratory samples positive for SARS-CoV-2 by qRT-PCR, 212 and 219 were positive by COVID-19-LAMP at 60 and 90 min (sensitivities of 95.07% and 98.21%) respectively, with the highest sensitivities among nasopharyngeal swabs (96.88% and 98.96%), compared to sputum/deep throat saliva samples (94.03% and 97.02%), and throat swab samples (93.33% and 98.33%). None of the 143 samples with other respiratory viruses were positive by COVID-19-LAMP, showing 100% specificity. Samples with higher viral load showed shorter detection time, some as early as 30 min. This inexpensive, highly sensitive and specific COVID-19-LAMP assay can be useful for rapid deployment as mobile diagnostic units to resource-limiting areas for point-of-care diagnosis, and for unlimited high-throughput mass screening at borders to reduce cross-regional transmission.

Development and validation of an economical uric acid-Fe3+/Fe2+-ferrozine-based colorimetric assay to estimate uric acid level of pure and biological samples.

This work presents the development and validation of a simple, rapid, and cost-effective spectrophotometric method for quantitative analysis of uric acid in biological samples. The method relies upon uric acid-led reduction of Fe(III) to Fe(II) of sample/standard solutions which stoichiometrically engages ferrozine to form a magenta-colored complex. Different parameters including pH, metal and chelator concentrations, temperature, etc., were optimized for the maximum intensity and stability of the complex. The uric acid concentrations of synthetic/plasma solutions were determined by comparing the color intensity of Fe(ferrozine)3 2+ complex produced by test solution with the standard curve formed by known uric acid concentrations. The method was validated in accordance with ICH guidelines and subjected to human plasma analysis. The results obtained were compared with a reference (enzymatic) method which revealed that there was no significant difference between the two methods at 95% confidence level. The method is highly specific, precise, linear, accurate, and robust.

Label-free and enzyme-free one-step rapid colorimetric detection of DNA methylation based on unmodified gold nanoparticles.

DNA methylation has been identified as one of the important causes of tumorigenesis, so it is important to develop some advanced methods for detecting and quantifying DNA methylation. In this study, a label-free and enzyme-free one-step rapid colorimetric detection of DNA methylation based on unmodified Au nanoparticles(Au NPs)has been proposed. This method can quickly, efficiently, economically and easily colorimetric detect methylated DNA only by the color change of unmodified Au NPs solution without the covalent modification of Au NPs in advance or complicated instruments for implementation with practical limitations or expensive biological enzymes or traditional organic dyes during the reaction. The strategy employed the difference in electrostatic attraction of single-stranded DNA and double-stranded DNA against salt-induced aggregation of Au NPs. The method has a DNA methylated detection limit of 8.47 nM and it is distinctly visible to detect methylated DNA with the naked eye as low as 20 nM. Furthermore, the strategy has an ability to detect methylated DNA in the presence of abundant unmethylated DNA with the detection limit of 0.13% and as low as 1% methylated DNA can be distinguished in heterogeneous samples with the naked eye. Also, the stratagem provides a convenient and rapid platform for methylated DNA detection of human serum samples in one step, which displays a huge potential for clinical diagnosis and treatment of oncological diseases.

On-site and low-cost detection of cyanide by simple colorimetric and fluorogenic sensors: Smartphone and test strip applications.

Cyanide is potentially hazardous and quickly acting chemical used in many fields of industry. Therefore, detection of cyanide is of main health concern due to its serious impacts on living organisms. In this context, we have developed rapid, low-cost and on-site sensory two molecules for the colorimetric and fluorogenic sensing of cyanide ion in aqueous samples and food samples. The prepared probes undergo distinct visual color change and exhibits selective fluorogenic turn-on or turn-off response towards cyanide. Competing anions have little or negligible effect on the detection of cyanide. The limit of detection for cyanide ion was calculated as low as 0.45 µM. Free receptors could be successfully regenerated by treating them with Ag+ ion. Moreover, a new visual colorimetric strip based on paper was fabricated with the pale yellow-to-pink color change signal. The fabricated test strips also demonstrated excellent selectivity towards cyanide ion without interfering possible fluoride and acetate ions. The smartphone-based technique which could directly read out the color value using a smartphone revealed an excellent potential for the cyanide detection without additional device.

A low cost smart system to analyze different types of edible Bird's nest adulteration based on colorimetric sensor array.

This study was performed to develop a low-cost smart system for identification and quantification of adulterated edible bird's nest (EBN). The smart system was constructed with a colorimetric sensor array (CSA), a smartphone and a multi-layered network model. The CSA were used to collect the odor character of EBN and the response signals of CSA were captured by the smartphone systems. The principal component analysis (PCA) and hierarchical cluster analysis (HAC) were used to inquiry the similarity among authentic and adulterated EBNs. The multi-layered network model was constructed to analyze EBN adulteration. In this model, discrimination of authentic EBN and adulterated EBN was realized using back-propagation neural networks (BPNN) algorithm. Then, another BPNN-based model was developed to identify the type of adulterant in the mixed EBN. Finally, adulterated percentage prediction model for each kind of adulterate EBN was built using partial least square (PLS) method. Results showed that recognition rates of the authentic EBN and adulterated EBN was as high as 90%. The correlation coefficient of percentage prediction model for calibration set was 0.886, and 0.869 for prediction set. The low-cost smart system provides a real-time, nondestructive tool to authenticate EBN for customers and retailers.

What are the Main Sensor Methods for Quantifying Pesticides in Agricultural Activities? A Review.

In recent years, there has been an increase in pesticide use to improve crop production due to the growth of agricultural activities. Consequently, various pesticides have been present in the environment for an extended period of time. This review presents a general description of recent advances in the development of methods for the quantification of pesticides used in agricultural activities. Current advances focus on improving sensitivity and selectivity through the use of nanomaterials in both sensor assemblies and new biosensors. In this study, we summarize the electrochemical, optical, nano-colorimetric, piezoelectric, chemo-luminescent and fluorescent techniques related to the determination of agricultural pesticides. A brief description of each method and its applications, detection limit, purpose-which is to efficiently determine pesticides-cost and precision are considered. The main crops that are assessed in this study are bananas, although other fruits and vegetables contaminated with pesticides are also mentioned. While many studies have assessed biosensors for the determination of pesticides, the research in this area needs to be expanded to allow for a balance between agricultural activities and environmental protection.

Simultaneous and direct determination of urea and creatinine in human urine using a cost-effective flow injection system equipped with in-house contactless conductivity detector and LED colorimeter.

This work presents a cost-effective and simple flow injection analysis (FIA) system for simultaneous and direct determination of urea and creatinine in human urine. The FIA system comprises two in-house detectors, a contactless conductivity detector and a light emitting diode (LED) detector. The contactless detector was built as a flow-through detection cell with axial electrodes, commonly known as capacitively coupled contactless conductivity detector (C4D) and the diode detector was fabricated based on the concept of paired emitter detector diodes (PEDD). With appropriate dilution of urine, the sample is directly injected into a stream of glycine-NaOH buffer pH 8.8 (the gas donor stream) and is carried by the carrier through a urease minicolumn for on-line enzymatic hydrolysis. The generated NH3 diffuses from the carrier stream through a porous polytetrafluoroethylene (PTFE) membrane into a stream of deionized water (the acceptor stream) leading to an increase in the signal at the C4D due to the NH3 dissolution in the water. In this system, creatinine is determined based on the Jaffé reaction by merging a stream of alkaline picrate with the gas donor stream. The change in color is detected using the PEDD equipped with two green LEDs. Under the optimum condition, the linear range of urea and creatinine were 30-240 mg L-1 and 10-500 mg L-1, with limits of detection of 9.0 mg L-1 and 0.9 mg L-1, respectively. The proposed system provides satisfactorily good precision (RSD < 3%), with sample throughput of 31 sample h-1 for the two analytes. The FIA system tolerates potential interference commonly found in human urine. The system was successfully applied and validated with selected reference methods.

Vertical flow paper-based plasmonic device for cysteine detection.

Cystinuria, is an autosomal recessive genetic disorder involving increasingly high levels of poorly soluble cysteine in urine leading to formation of stones. Developing a facile, low-cost, point-of-care and selective sensor for diagnosis of cysteine is imperative. Accordingly, for the detection of cysteine, the present study demonstrates an inexpensive colorimetric, paper-based vertical flow plasmonic micro-well device with a two-minute turn-around time. The method encompasses the use of microbially-synthesized silver nanoparticles (AgNPs) that change from light brown / yellow to dark brown upon binding with Sulphur present in cysteine. This technique allows for visual detection up to 1 × 10-5 mM cysteine and can be easily offered as a rapid diagnostic test even at setups with minimal resources.

Three-dimensional paper based platform for automatically running multiple assays in a single step.

Paper based assays are paving the way to automated, simplified, robust and cost-effective point of care testing (POCT). We propose a method for fabricating three dimensional (3D) microfluidic paper based analytical devices (µPADs) via combining thin adhesive films and paper folding, which avoids the use of cellulose powders and the complex folding sequence and simultaneously permits assays in several layers. To demonstrate the effectiveness of this approach, a 3DµPADs was designed to conduct more assays on a small footprint, allowing dual colorimetric and electrochemical detections. More importantly, we further developed a 3D platform for implementing automated and multiplexed ELISA in parallel, since ELISA, a routine and standard laboratory method, has rarely been used in practical analyses outside of the laboratory. In this configuration, complex and multistep diagnostic assays can be carried out with the addition of the sample and buffer in a simple fashion. Using Troponin I as model, the device showed a broad dynamic range of detection with a detection limit of 0.35 ng/mL. Thus, the developed platforms allow for various assays to be cost-effectively carried out on a single 3D device, showing great potential in an academic setting and point of care testing under resource-poor conditions.

A colorimetric hydrogen sulfide sensor based on gellan gum-silver nanoparticles bionanocomposite for monitoring of meat spoilage in intelligent packaging.

A colorimetric hydrogen sulfide (H2S) sensor based on gellan gum capped silver nanoparticles was developed to real-time monitor meat spoilage. The colorimetric sensor strategy was attributed to the ultrastrong binding ability of Ag with H2S to form Ag2S. The sensor enables the analysis of H2S with a limit of detection (LOD) of 0.81 µM, and it exhibited excellent selectivity toward H2S against other volatile components generated from chicken breast and silver carp during spoilage. By these virtues, the sensor presented visible color changes from yellow to colorless by in situ and nondestructively sensing H2S generated from chicken breast and silver carp in a packaging system. This strategy provided a simple but useful, non-destructive, robust, cost-effective, and user-friendly platform to real time monitor meat spoilage for intelligent food packaging.

Recent advances in thread-based microfluidics for diagnostic applications.

Over the past decades, researchers have been seeking attractive substrate materials to keep microfluidics improving to outbalance the drawbacks and issues. Cellulose substrates, including thread, paper and hydrogels are alternatives due to their distinct structural and mechanical properties for a number of applications. Thread have gained considerable attention and become promising powerful tool due to its advantages over paper-based systems thus finds numerous applications in the development of diagnostic systems, smart bandages and tissue engineering. To the best of our knowledge, no comprehensive review articles on the topic of thread-based microfluidics have been published and it is of significance for many scientific communities working on Microfluidics, Biosensors and Lab-on-Chip. This review gives an overview of the advances of thread-based microfluidic diagnostic devices in a variety of applications. It begins with an overall introduction of the fabrication followed by an in-depth review on the detection techniques in such devices and various applications with respect to effort and performance to date. A few perspective directions of thread-based microfluidics in its development are also discussed. Thread-based microfluidics are still at an early development stage and further improvements in terms of fabrication, analytical strategies, and function to become low-cost, low-volume and easy-to-use point-of-care (POC) diagnostic devices that can be adapted or commercialized for real world applications.

A novel, simple and low-cost paper-based analytical device for colorimetric detection of Cronobacter spp.

Cronobacter spp. are recognized as a world-wide emerging opportunistic food-borne pathogens that can persist in various food and processing environment for a long time. Therefore, the prevention and detection of them are particularly important. In this study, a micro-spot paper-based analytical device (µPADs) was created by combining PVC pad with filter paper. Detection is achieved by measuring the color change (from colorless to indigo) when a species-specific enzyme associated with the Cronobacter spp. of interest reacts with a chromogenic substrate. When combined with the optimization of specific enrichment process, the method allows for a testing time of 10 h or less and is capable of detecting live bacteria on the inoculated surface of samples in concentrations as low as 101 CFU cm-2. We are surprised to discover that C. dublinensis species and their subspecies had the highest ability to produce α-glucosidase in all genus of Cronobacter spp.. This work demonstrated that the manufacturing method is novel, simple, well reproducible (RSD less than 5%) and low-cost (less than $ 0.15 per micro-spot).

Skin color-specific and spectrally-selective naked-eye dosimetry of UVA, B and C radiations.

Spectrally-selective monitoring of ultraviolet radiations (UVR) is of paramount importance across diverse fields, including effective monitoring of excessive solar exposure. Current UV sensors cannot differentiate between UVA, B, and C, each of which has a remarkably different impact on human health. Here we show spectrally selective colorimetric monitoring of UVR by developing a photoelectrochromic ink that consists of a multi-redox polyoxometalate and an e- donor. We combine this ink with simple components such as filter paper and transparency sheets to fabricate low-cost sensors that provide naked-eye monitoring of UVR, even at low doses typically encountered during solar exposure. Importantly, the diverse UV tolerance of different skin colors demands personalized sensors. In this spirit, we demonstrate the customized design of robust real-time solar UV dosimeters to meet the specific need of different skin phototypes. These spectrally-selective UV sensors offer remarkable potential in managing the impact of UVR in our day-to-day life.

Morphological control of nanoprobe for colorimetric antioxidant detection.

Colloidal metal nanoparticles (NPs) with remarkable localized surface plasmon resonance (LSPR) have found wide use as probes in sensing. The LSPR that employed as the sensing signal is strongly associated with the morphology of nanoprobes. In this work, morphological change of Au nanocage to Au@Ag nanobox and thus the LSPR evolution are well regulated by trace amount of antioxidant, where the mechanism of seed-mediated growth is used as a powerful means in this process. Based on the linear relationship between morphology-induced LSPR evolution and the concentration of antioxidant, a simple, reliable and highly sensitive colorimetric method is developed for antioxidant detection. The detectable range of this method is 0.01-5 µM and 2-20 µM when a UV-vis spectrophotometer and a smartphone are employed as an analyzer, respectively. It has also been successfully applied in the detection of total antioxidants in green tea. This work provides new insights into developing sensitive LSPR-based sensors through precisely manipulating the morphology of nanoprobes.

Simple, reliable, and time-efficient colorimetric method for the assessment of mitochondrial function and toxicity.

Mitochondria are organelles involved in the production of cellular energy, regulation of Ca2+ and redox signaling, and are critical for normal functioning of eukaryotic cells. The dysfunction of mitochondria has been implicated in a wide range of diseases, including metabolic and neurodegenerative disorders and different types of cancers. To better understand the role of mitochondria in healthy and disease states, the development of efficient and reliable tools for the assessment of mitochondrial function is particularly important. Janus green B (JG-B) is a supravital lipophilic cationic dye which, in its oxidized form, has a green-blue color. As JG-B is taken up and reduced by metabolically active mitochondria, the dye has been used for assessing the purity, integrity and metabolic activity of mitochondria with microscopy-based methods. Here we present a simple, time- and cost-efficient JG-B-based colorimetric assay for assessing mitochondrial function, activity and toxicity. The method is based upon reduction of JG-B by mitochondrial dehydrogenases to diethylsafranine, which is pink colored and has a maximum absorption at 550 nm. In this proof of principle study, using in vitro mitochondrial preparations isolated from rat brain, we provide evidence that monitoring JG-B conversion to diethylsafranine can be used as a reliable and robust indicator of mitochondrial activity and toxicity. Because of its simplicity and efficiency in terms of costs and time, this assay has a wide potential in analytical as well as therapeutic areas of biomedical research.

A colorimetric assay of DNA methyltransferase activity based on peroxidase mimicking of DNA template Ag/Pt bimetallic nanoclusters.

DNA methylation catalyzed by DNA methyl transferase (MTase) is a significant epigenetic process for modulating gene expression. Abnormal levels of DNA MTase enzyme have been regarded as a cancer biomarker or a sign of bacterial diseases. We developed a novel colorimetric method to assay M.SssI MTase activity employing peroxidase-like activity of DNA template Ag/Pt NCs without using restriction enzymes. Based on inhibiting the peroxidase reaction that occurred in the TMB-H2O2 system, in the presence of MTase, a highly sensitive and selective colorimetric biosensor was fabricated with a detection limit (LOD) of 0.05 U/mL and a linear range from 0.5 to 10 U/mL. The changes in absorption intensity were monitored to quantify the M.SssI activity. This strategy had a high selectivity over other proteins. Furthermore, it is also demonstrated that this method can be used for the evaluation and screening of inhibitors for DNA MTase.

Detection of Bacteria in Water with ß-Galactosidase-Coated Magnetic Nanoparticles.

Pathogenic contamination and resistant bacterial infections remain critical concerns in both developed and developing countries. Rapid and sensitive detection of pathogens is still a key requirement for both environmental and clinical settings. This article introduces a simple, colorimetric, cost-effective, and high-throughput system based on a positively charged iron oxide/enzyme complex for the detection of both gram-positive and gram-negative bacteria in water between 103 and 108 cfu/mL. This study provides an effective strategy for the identification and purification of pathogen contamination in drinking water.