A novel premixing strategy for highly sensitive detection of nitrite on paper-based analytical devices

BACKGROUND

Nitrite has been involved in many food processing techniques and its excessive consumption is closely related to the development of different diseases. Therefore, highly sensitive detection of nitrite is significant to ensure food safety.

RESULT

This study presents a simple and novel strategy for the highly sensitive detection of nitrite in food using paper-based analytical devices (PADs). In this proposed strategy, the nitrite present in the sample undergoes efficient diazotization when initially mixed with sulfanilamide solution before reacting with N-(1-naphthyl) ethylenediamine dihydrochloride (NED) coated on the detection region of the PAD, leading to the maximum production of colored azo compounds. Specifically, within the concentration range of 0.1-20 mg/L, the LOD and LOQ for the nitrite assay using the premixing strategy are determined as 0.053 mg/L and 0.18 mg/L, respectively which significantly surpass the corresponding values of 0.18 mg/L (LOD) and 0.61 mg/L (LOQ) achieved with the regular Griess reagent analysis.

SIGNIFICANCE

The study highlights the critical importance of the premixing strategy in nitrite detection. Under optimized conditions, the strategy demonstrates an excellent limit of detection (LOD) and limit of quantification (LOQ) for nitrite detection in eight different meat samples. In addition to its high precision, the strategy is applicable in the field of nitrite analysis. This strategy could facilitate rapid and cost-effective nitrite analysis in real food samples, ensuring food safety and quality analysis.

A spectroscopy based prototype for the noninvasive detection of diabetes from human saliva using nanohybrids acting as nanozyme

The recent prediction of diabetes to be a global pandemic invites a detection strategy preferably non-invasive, and bloodless to manage the disease and the associated complications. Here, we have synthesized chitosan polymer functionalized, organic-inorganic bio-compatible nano-hybrids of Mn3O4 nanoparticles, and characterized it by utilizing several optical methodologies for the structural characterization which shows the Michaelis Menten (MM) kinetics for glucose and alpha-amylase protein (well-known diabetes biomarkers). We have also studied the potentiality for the detection of alpha-amylase in human salivary secretion which is reported to be strongly correlated with uncontrolled hyperglycemia. Finally, we have developed a prototype for the measurement of glucose (LOD of 0.38 mg/dL, LOQ of 1.15 mg/dL) and HbA1c (LOD of 0.15% and LOQ of 0.45%) utilizing the basic knowledge in the study for the detection of uncontrolled hyperglycemia at the point-of-care. With the limited number of clinical trials, we have explored the potential of our work in combating the diabetic pandemic across the globe in near future.

An Update on the Use of Natural Pigments and Pigment Nanoparticle Adducts for Metal Detection Based on Colour Response

Natural pigments occur in plants as secondary metabolites and have been used as safe colourants in food. Studies have reported that their unstable colour intensity might be related to metal ion interaction, which leads to the formation of metal-pigment complexes. This underlines the need for further investigations on the use of natural pigments in metal detection using colorimetric methods, since metals are important elements and can be hazardous when present in large amounts. This review aimed to discuss the use of natural pigments (mainly betalains, anthocyanins, curcuminoids, carotenoids, and chlorophyll) as reagents for portable metal detection based on their limits of detection, to determine which pigment is best for certain metals. Colorimetric-related articles over the last decade were gathered, including those involving methodological modifications, sensor developments, and a general overview. When considering sensitivity and portability, the results revealed that betalains are best applied for copper, using a smartphone-assisted sensor; curcuminoids are best applied for lead, using a curcumin nanofiber; and anthocyanin is best applied for mercury, using anthocyanin hydrogel. This provides a new perspective on the use of colour instability for the detection of metals with modern sensor developments. In addition, a coloured sheet representing metal concentrations may be useful as a standard to support on-site detection with trials on masking agents to improve selectivity.

Near-Field Communication Tag for Colorimetric Glutathione Determination with a Paper-Based Microfluidic Device

Here, we propose a microfluidic paper-based analytical device (µPAD) implemented with a near-field communication (NFC) tag as a portable, simple and fast colorimetric method for glutathione (GSH) determination. The proposed method was based on the fact that Ag⁺ could oxidize 3,3',5,5'-tetramethylbenzidine (TMB) into oxidized blue TMB. Thus, the presence of GSH could cause the reduction of oxidized TMB, which resulted in a blue color fading. Based on this finding, we developed a method for the colorimetric determination of GSH using a smartphone. A µPAD implemented with the NFC tag allowed the harvesting of energy from a smartphone to activate the LED that allows the capture of a photograph of the µPAD by the smartphone. The integration between electronic interfaces into the hardware of digital image capture served as a means for quantitation. Importantly, this new method shows a low detection limit of 1.0 µM. Therefore, the most important features of this non-enzymatic method are high sensitivity and a simple, fast, portable and low-cost determination of GSH in just 20 min using a colorimetric signal.

Paper-based plasmonic nanosensor monitors environmental lead pollution in real field

Development of a low-cost portable colorimetric nanosensor for real field pollution monitoring.

Disposable Paper-Based Biosensors for the Point-of-Care Detection of Hazardous Contaminations-A Review

The fast detection of trace amounts of hazardous contaminations can prevent serious damage to the environment. Paper-based sensors offer a new perspective on the world of analytical methods, overcoming previous limitations by fabricating a simple device with valuable benefits such as flexibility, biocompatibility, disposability, biodegradability, easy operation, large surface-to-volume ratio, and cost-effectiveness. Depending on the performance type, the device can be used to analyze the analyte in the liquid or vapor phase. For liquid samples, various structures (including a dipstick, as well as microfluidic and lateral flow) have been constructed. Paper-based 3D sensors are prepared by gluing and folding different layers of a piece of paper, being more user-friendly, due to the combination of several preparation methods, the integration of different sensor elements, and the connection between two methods of detection in a small set. Paper sensors can be used in chromatographic, electrochemical, and colorimetric processes, depending on the type of transducer. Additionally, in recent years, the applicability of these sensors has been investigated in various applications, such as food and water quality, environmental monitoring, disease diagnosis, and medical sciences. Here, we review the development (from 2010 to 2021) of paper methods in the field of the detection and determination of toxic substances.

A portable instrument for on-site detection of heavy metal ions in water

Based on differential pulse voltammetry technology, we developed a portable and affordable instrument for on-site detection of trace heavy metal pollutants in liquid through a disposable plastic pipette. It mainly consists of a six-electrode electrochemical sensor which is integrated in the instrument. The pipette chip is equipped with a pump valve, and thus, it can avoid contamination. We have analyzed the sensitivity and specificity of the electrochemical sensor for heavy metal detection. Experimental results demonstrated that the limit of detection for Pb, Hg, Cu, and Zn was 2.2 ng/mL, 2.5 ng/mL, 15.5 ng/mL, and 10 ng/mL, respectively. The limit of quantification for them was 10 ng/mL, 25 ng/mL, 25 ng/mL, and 14 ng/mL, respectively. The correlation coefficient between peak current and the target heavy metal concentration was above 0.96. Finally, we have tested the analytical performance of the self-build instrument by measuring heavy metal ions in industrial wastewater and rainwater, respectively. Such an instrument is user-friendly for all users even for the common people, and we can envision its wide application in future heavy metal pollutant detection in groundwater, tap water, and supernatant of soil solution.

Paper-based analytical device for high-throughput monitoring tetracycline residue in milk

A low-cost and portable paper-based analytical device has been developed for high throughput and on-site monitoring TC residue in milk through visualized colorimetric reaction. The filtration and concentration effect induced by the porous nature of paper contribute to strengthen the color intensity, leading to quantitative and sensitive detection of tetracycline reaching 1 ppm detection limit, with the linear range of 1-100 ppm both in water and milk samples. The applicability was demonstrated by detection of TC in 18 different types of real milk samples with good recovery ranging from 88% to 113%. Furthermore, the dynamic degradation behavior of tetracycline was monitored through the device. To the best of our knowledge, this is the first report of colorimetric detection of tetracycline in milk using the paper-based device. This simple, fast, cost-effective (~$0.50 per device) and equipment-free paper-based platform provides a promising tool for future application in food and environmental safety.

Nanomaterial-Integrated Cellulose Platforms for Optical Sensing of Trace Metals and Anionic Species in the Environment

The development of disposable sensors that can be easily adapted to every analytical problem is currently a hot topic that is revolutionizing many areas of science and technology. The need for decentralized analytical measurements at real time is increasing for solving problems in areas such as environment pollution, medical diagnostic, food quality assurance, etc., requiring fast action. Despite some current limitations of these devices, such as insufficient detection capability at (ultra)trace level and risk of interferent effects due to matrix, they allow low-cost analysis, portability, low sample consumption, and fast response. In the last years, development of paper-based analytical devices has undergone a dramatic increase for on-site detection of toxic metal ions and other pollutants. Along with the great availability of cellulose substrates, the immobilization of receptors providing enhanced recognition ability, such as a variety of nanomaterials, has driven the design of novel sensing approaches. This review is aimed at describing and discussing the different possibilities arisen with the use of different nanoreceptors (e.g., plasmonic nanoparticles, quantum dots, carbon-based fluorescent nanoparticles, etc.) immobilized onto cellulose-based substrates for trace element detection, their advantages and shortcomings.

Trace analysis on chromium (VI) in water by pre-concentration using a superhydrophobic surface and rapid sensing using a chemical-responsive adhesive tape

Heavy metal ions in water resources present great threats to human health. Chromium (Cr), as the frequently used heavy metal in industrial processes and everyday life, requires a low-cost, fast and effective means to determine its concentration, especially in drinking water. Conventional colorimetric paper-based analytical devices (PADs), due to the limited sensitivity, are unable to quantify the most harmful heavy metal ions to the drinking water standard. In this work, we present a method of using a superhydrophobic (SH) paper to concentrate Cr⁶⁺ from solutions of very low concentration to obtain the precipitated Cr⁶⁺ salt particulates. A known volume of Cr⁶⁺-containing solution was concentrated to "a spot" on the SH paper through drying, so that trace amount of Cr⁶⁺ can be quantified via the application of a specifically-designed chemical-responsive adhesive tape (CAT) sensor, loaded with Cr⁶⁺- specific indicator, on to the concentrated Cr⁶⁺ spot. The detection limit of the SH-CAT method for Cr⁶⁺ is 0.05 mg/L, which is the permitted maximum concentration in drinking water and is significantly lower than that of conventional PADs. The interference and the accuracy studies also show the reliability of this method for measuring trace amounts of analytes.

Highly sensitive and selective optosensing of quercetin based on novel complexation with yttrium ions

A simple and fast method was developed for the determination of quercetin. The concentration of quercetin can be determined based on the fluorescence emission resulting from the coordinative interactions between quercetin and the yttrium ion (Y³⁺). Notably, a portable platform to quantitatively analyze quercetin was constructed. This platform incorporates our custom-built homemade reader based on a photodiode, and Arduino hardware, which accepts a paper ribbon on which Y³⁺ is deposited as an input. In addition, the color change of the paper ribbon was identified using a smartphone via the hue values of the photographs. The limits of detection for quercetin using spectroscopy, a smartphone, and a custom-built reader were calculated to be 27, 110, and 129 nM, respectively. The use of a custom-built device and a smartphone for detecting quercetin via fluorescence from the prepared paper ribbon reduces the time and cost of quercetin detection. This approach could be employed for on-site sensing of quercetin in real samples.