Cloth-based microfluidic devices integrated onto the patch as wearable colorimetric sensors for simultaneous sweat analysis.

Introduction: In this work, a flexible, and wearable point-of-care (POC) device integrated on a pain relief patch as wearable colorimetric sensors have been developed for sweat analysis, such as lactic acid, sodium ions, and pH simultaneously. Herein, the patch has still functioned as pain relief, while it allows for sweat monitoring during exercise, and in daily activities. Methods: It was constructed on cotton cloth using wax printing technology (batik stamp) as cloth-based microfluidic devices (CMDs). Here, it uses micro volumes of samples to perform the reaction in the sensing zones, where the sensitive reagents are immobilized so that it can collect and analyze the sweat (lactic acid, sodium ions, and pH) as the model for sweat analytes. The colorimetric analysis was conducted via a smartphone camera by using a free app (Color Grab) for a color image analysis that uses for quantitative analysis or naked eye for semi-qualitative analysis. Results: The ∆RGB value of the CMDS shows the excellent linear correlation vs analytes concentration, where the coefficient of correlations was found for lactic acid (R2 = 0.994), sodium ion (R2 = 0.998), and pH (R2 = 0.994). The ∆RGB value shows the appropriate color value for the linear correlation of the analyte target concentrations in the sweat samples. Here, the limit of detection (LOD) was found at 45.73 µg/mL for lactic acid and 56.46 µg/mL for sodium ions. The reproducibility was found at 0.79% and 0.89%, for lactic acid and sodium ions respectively. Conclusion: It was applied for sweat analysis during exercise, and the results show in agreement with the standard methods used in a clinical laboratory.

Development of the paper-based colorimetric sensor for simple and fast determination of quercetin in guava leaf extract.

This present study aimed to develop a paper-based colorimetric sensor in the form of paper-microzone plates (PµZP), for simple and fast quercetin determination in guava leaf extract samples. Here, N-bromosuccinimide (NBS) solution was immobilized on the microzone as a sensing probe, where quercetin solution can be dropped on it to form red-purplish color adducts which can be seen by the naked eye or captured using a flatbed scanner. The color intensity of the microzone can be quantified against a blank solution and used as analytical data in scanometric assay. The sensor showed a response time of 8 min, a linear interval of 1-10 mM with a detection limit at 1.274 mM toward quercetin, and exhibited good reproducibility (RSD < 1%) and accuracy (98-99% recovery). The quercetin level of guava leaf extract determined by the PµZP-scanometric method was found comparable with that of the TLC-densitometric method, suggesting its use as an alternative method for quercetin analysis in the guava leaf extract.

Amperometric microbial biosensor for sugars and sweetener classification using principal component analysis in beverages.

Sugar and artificial sweeteners are additives in packaged food and beverage products that are widely used, where excessive sugar consumption can cause an increase in various diseases. Detection and classification of natural sugars sucrose, fructose, glucose, and artificial sweetener aspartame are needed to determine the effects of consuming these sweeteners. This study uses an amperometric biosensor integrated biochip-D, which uses Saccharomyces cerevisiae as a bioreceptor through cellular metabolic respiration activity expressed in dissolved oxygen (DO) levels. The variations of sweetener concentration used were in the range of 50 mM to 250 mM. The measurement results showed that the higher the concentration of sugar and artificial sweeteners, the lower DO levels would be measured. It was due to the yeast cell respiration in consuming oxygen (O2) and producing carbon dioxide (CO2), where the decrease in DO levels of sucrose was 14.24%, fructose was 18.02%, glucose was 16.59%, and aspartame was 20.45% at a concentration of 250 mM. The measurement data was clustered and classified using principal component analysis (PCA), which resulted in data variance percentages of 92.80% and 89.40% for the two main components. In the application studies of the biosensor, sensitive determination of sugar in the beverage samples was investigated. Supplementary Information: The online version contains supplementary material available at 10.1007/s13197-022-05625-8.

Paper-Based Electrochemical Biosensors for Food Safety Analysis.

Nowadays, foodborne pathogens and other food contaminants are among the major contributors to human illnesses and even deaths worldwide. There is a growing need for improvements in food safety globally. However, it is a challenge to detect and identify these harmful analytes in a rapid, sensitive, portable, and user-friendly manner. Recently, researchers have paid attention to the development of paper-based electrochemical biosensors due to their features and promising potential for food safety analysis. The use of paper in electrochemical biosensors offers several advantages such as device miniaturization, low sample consumption, inexpensive mass production, capillary force-driven fluid flow, and capability to store reagents within the pores of the paper substrate. Various paper-based electrochemical biosensors have been developed to enable the detection of foodborne pathogens and other contaminants that pose health hazards to humans. In this review, we discussed several aspects of the biosensors including different device designs (e.g., 2D and 3D devices), fabrication techniques, and electrode modification approaches that are often optimized to generate measurable signals for sensitive detection of analytes. The utilization of different nanomaterials for the modification of electrode surface to improve the detection of analytes via enzyme-, antigen/antibody-, DNA-, aptamer-, and cell-based bioassays is also described. Next, we discussed the current applications of the sensors to detect food contaminants such as foodborne pathogens, pesticides, veterinary drug residues, allergens, and heavy metals. Most of the electrochemical paper analytical devices (e-PADs) reviewed are small and portable, and therefore are suitable for field applications. Lastly, e-PADs are an excellent platform for food safety analysis owing to their user-friendliness, low cost, sensitivity, and a high potential for customization to meet certain analytical needs.

Simple monitoring of pH and urea in whole blood using wearable smart woman pad.

Introduction: In this work, we used a thread-paper microfluidic device (µTPAD) system, where a threaded part for the handling of the whole blood samples and a paper part for the reaction of plasma with immobilized bioreagents integrated into woman pad as a wearable sensing device namely as smart women pad. The µTPAD as a wearable smart woman pad is developed for the detection of pH and urea in mensuration blood as real samples. Methods: This combined device was constructed to cover the elements required, that is, separation of red blood cell, conditioning, analyte reaction, and colorimetric detection. The color change in sensing areas was measured in the RGB values via a smartphone using the Color Grab after a smart woman pad was used. The thread allowed red blood cell sampling and separation, while the paper microfluidic device was used for conditioning, biorecognition, and colorimetric transduction of pH and urea as analytes. Results: The time needed for analysis was measured as 110 s using the equilibrium method for both analytes, with a limit of detection (LOD) of 72.55 µg/mL for urea, with precision around 1.68%, while for pH around 0.80%. The smart woman pad allowed rapid detection of pH and urea in menstruation blood as real samples for monitoring of the kidney functions, and the results showed an agreement with the conventional methods that have been generally used in the clinical laboratory. Conclusion: The smart woman pad has the potential to be used as a wearable device to monitor the health status of the user via its blood mensuration analysis.

Colorimetric Paper-Based Dual Indicator Label for Real-Time Monitoring of Fish Freshness.

Research background: Fish freshness and quality monitoring are of high importance for consumers, retailers and fishing industry. Therefore, developing novel approaches that are simple, fast, non-destructive and inexpensive to monitor fish freshness in real time is of great value. One alternative is using Intelligent or smart packaging to monitor the freshness or conditions of packaged fish. Experimental approach: On-package dual indicator label based on paper-based pH sensors was developed for real-time monitoring of the milkfish (Chanos chanos) freshness. The paper-based pH sensor was prepared using bromocresol purple (BCP) and bromothymol blue (BTB) that were immobilized onto a filter paper by dip coating. Herein, the fish degradation could be monitored visually by the dual indicator label, where the BCP changes from yellow to pink, then finally to purple, while the BTP changes from orange to green-yellow, and finally to green-blue to indicate fresh, medium fresh or spoiled product, respectively. Results and conclusion: The label responds to the pH change caused by the fish degradation and the colour of dual indicator changes to show the fish freshness at room temperature and chiller conditions. This pH change was followed by changes in the other parameters related to fish freshness, such as total volatile basic nitrogen (TVBN), total viable count (TVC), texture and odour. The threshold of fish spoilage at room temperature was observed at 8 h and under chiller conditions at 7 days when the deterioration time point was indicated by the colour changes. Thus, it can be concluded that the dual indicator label can be applied as a simple and low-cost on-package active label for fish freshness monitoring. Novelty and scientific contribution: Increasing consumer concerns about quality and safe food worldwide has boosted the search for a novel approach to food monitoring. In this work, a simple and practical on-package dual indicator label for real-time monitoring of fish freshness was developed. The colorimetric pH sensor was obtained simply by dip-coating of filter paper, yet it enables easy and accurate detection of fish spoilage with the naked eye. Similarly, the dual indicator label changes colour for other freshness parameters, such as TVBN, TVC, texture and odour.

Paper microzone plate based on DPPH as a simple colorimetric assay of the total antioxidant content of herbal extracts.

The human body needs an antioxidant-rich diet that comes from foods, beverages, and herbal products to support the physiological antioxidant systems. Thus, the development of an analytical tool for a simple assay of the total antioxidant capacity (TAC) of the rich antioxidant samples is crucial. The current work demonstrates a simple colorimetric assay of TAC of the herbal extract on the paper microzone plate (PµZP) that was constructed in the 70-well of patterned paper using the screen printing technique. The PµZP was constructed by immobilizing DPPH (2,2-diphenyl-1-picrylhydrazyl) onto 70-well of PµZP as a sensing zone for colorimetric detection. The purple-sensing zone exhibited a good response to gallic acid (GA), by producing slightly gray to pale yellow color that can be captured using a scanner and then analyzed using the ImageJ program. The paper-based sensor showed a linear response toward GA at 0.05-0.6 mM (r = 0.9895), reproducible response (RSD < 4%), and accurate measurement with 91 to 106% recovery for measuring TAC of herbal extract, presented as mM gallic acid equivalent and showed a good agreement with the standard DPPH method. The results suggested that the proposed method can be applied for simple TAC measurement in the herbal extract.

Development of an easy-to-use colorimetric pH label with starch and carrot anthocyanins for milk shelf life assessment.

An intelligent freshness indicator was developed by immobilizing anthocyanins of black carrot (ABC) within the starch matrix (total anthocyanins content of 10 mg/100 mL) to monitor freshness/spoilage of milk. The microstructural, spectral, swelling and solubility properties as well as color stability (as a function of time, temperature and light) of the indicator at different pHs were characterized. The incorporation of ABC did not change the swelling index and water solubility. The prepared label showed visible color changes as a function of pH and excellent color stability after one month storage at different conditions. The total color difference (TCD) value of the indicator corresponded to the pH, acidity, and microbial growth of the pasteurized milk. The Pearson correlation coefficient showed a high correlation between TCD and pH (R = -0.979), while a high and positive correlation between TCD and acidity as well as TMC (R = 0.983 and 0.968, respectively) was observed. The developed label can discriminate fresh milk form the milk entered into the initial (TCD: 7.8 after 24 h) and final (TCD: 34.8 after 48 h) steps of spoilage. The fabricated label opens a new perspective to use anthocyanins-incorporated biopolymers in the milk intelligent packaging as a simple and easy-to-use freshness indicator.

Cellulose/chitosan pH-responsive indicator incorporated with carrot anthocyanins for intelligent food packaging.

In this study, the possible use of anthocyanins of black carrot (ABC) as a chemo-responsive dye to fabricate a colorimetric pH indicator in a cellulose-chitosan matrix was investigated in order to the monitoring of spoilage in pasteurized milk. Cellulose paper was impregnated with a chitosan solution prepared by a sol-gel method containing ABC (total anthocyanins content of 10 mg/100 mL) and characterized. The swelling and water solubility increased by incorporation of ABC into the chitosan-cellulose film. The colorimetric pH indicator showed an obvious color variation from pink to khaki at different pH values (pH 2-11). Stability tests revealed that the indicator had acceptable color stability during one-month storage at 20 °C. The results also confirmed the immobilization of ABC into the matrix of the polymeric indicator with no significant effect on the chemical and super-molecular structure of the samples. In food trial, fresh pasteurized milk was entirely discerned through a perceptible color change from blue to violet rose color after 48 h storage at 20 °C, which was comfortably observable by the naked eye. The results proved that the fabricated indicator could be used as food grade biomaterials to monitor freshness/spoilage of milk.

Monomyristin and Monopalmitin Derivatives: Synthesis and Evaluation as Potential Antibacterial and Antifungal Agents.

In the present work, monoacylglycerol derivatives, i.e., 1-monomyristin, 2-monomyristin, and 2-monopalmitin were successfully prepared from commercially available myristic acid and palmitic acid. The 1-monomyristin compound was prepared through a transesterification reaction between ethyl myristate and 1,2-O-isopropylidene glycerol, which was obtained from the protection of glycerol with acetone, then followed by deprotection using Amberlyst-15. On the other hand, 2-monoacylglycerol derivatives were prepared through enzymatic hydrolysis of triglycerides in the presence of Thermomyces lanuginosa lipase enzymes. The synthesized products were analyzed using fourier transform infrared (FTIR) spectrophotometer, gas or liquid chromatography-mass spectrometer (GC-MS or LC-MS), and proton and carbon nuclear magnetic resonance (¹H- and 13C-NMR) spectrometers. It was found that monomyristin showed high antibacterial and antifungal activities, while 2-monopalmitin did not show any activity at all. The 1-monomyristin compound showed higher antibacterial activity against Staphylococcus aureus and Aggregatibacter actinomycetemcomitans and also higher antifungal activity against Candida albicans compared to the positive control. Meanwhile, 2-monomyristin showed high antibacterial activity against Escherichia coli. The effect of the acyl position and carbon chains towards antibacterial and antifungal activities was discussed.

Characterization of cellulosic paper coated with chitosan-zinc oxide nanocomposite containing nisin and its application in packaging of UF cheese.

A new antimicrobial bilayer film was developed using chitosan, cellulose, and nisin. Chitosan solution containing nisin (500 and 1000µg/mL) was prepared by sol-gel method and then the solution was coated on cellulose paper by dip coating method. A chitosan-cellulose film without antimicrobial had no inhibitory effect on Listeria monocytogenes, whereas, the incorporation of nisin made a significant increase (P<0.05) in antimicrobial characteristics of the films. Moreover, no significant differences were shown on antimicrobial activity of developed films during the storage at 4°C for one month. However, the addition of nisin showed a significant increase in the swelling index and solubility of bilayer film. Scanning electron microscope images revealed a uniform coating of chitosan solution on cellulose paper. The FTIR analysis also confirmed successful introducing and binding of the nisin in double layer film. Films with 1000µg/mL of nisin completely inactivated the initial (∼5log10 CFU/g) counts of L. monocytogenes on the surface of Ultra-filter white cheese after storage at 4°C for 14 days. We concluded that nanocomposite film of chitosan-cellulose containing nisin has novel antibacterial activity and can be used for packaging in cheese.

Rapid test for the determination of total phenolic content in brewed-filtered coffee using colorimetric paper.

This work was aimed to develop a chemical sensor for the determination of total polyphenol content (TPC) of coffee samples. The polyphenol sensor was based on co-immobilization of NaIO4 and MBTH in paper as a test strip. The sensor showed sensitive response to chlorogenic acid by forming pink color adduct which can be scanned and quantified by Imagej program. The sensor had response time of 14 min and a linear range between 0.07 and 0.71 mM of chlorogenic acid with a detection limit at 0.002 mM toward chlorogenic acid. The reproducibility of the sensor was good (RSD = 0.44%) with a life time within 27 days when stored at 4 °C. TPC of coffee samples were determined by the sensor, and the results were in agreement with the Folin-Ciocalteu method suggesting its practical use as a tool for TPC determination in coffee samples.

Scanometry as microplate reader for high throughput method based on DPPH dry reagent for antioxidant assay.

The stable chromogenic radical 1,1'-diphenyl-2-picrylhydrazyl (DPPH) solution was immobilized on the microwell plate as dry reagent to construct a simple antioxidant sensor. Then, a regular flatbed scanner was used as microplate reader to obtain analytical parameters for antioxidant assay using one-shot optical sensors as scanometry technique. Variables affecting the acquisition of the images were optimized and the analytical parameters are obtained from an area of the sensing zone inside microwell using the average luminosity of the sensing zone captured as the mean of red, green, and blue (RGB) value using ImageJ® program. By using this RGB value as sensor response, it is possible to determine antioxidant capacity in the range 1-25 ppm as gallic acid equivalent (GAE) with the response time of 9 min. The reproducibility of sensor was good (RSD<1%) with recovery at 93%-96%. The antioxidant sensor was applied to the plant extracts, such as sappan wood and Turmeric Rhizome. The results are good when compared to the same procedure using a UV/Vis spectrophotometer.

Application of class-modelling techniques to infrared spectra for analysis of pork adulteration in beef jerkys.

The use of chemometrics to analyse infrared spectra to predict pork adulteration in the beef jerky (dendeng) was explored. In the first step, the analysis of pork in the beef jerky formulation was conducted by blending the beef jerky with pork at 5-80 % levels. Then, they were powdered and classified into training set and test set. The second step, the spectra of the two sets was recorded by Fourier Transform Infrared (FTIR) spectroscopy using atenuated total reflection (ATR) cell on the basis of spectral data at frequency region 4000-700 cm(-1). The spectra was categorised into four data sets, i.e. (a) spectra in the whole region as data set 1; (b) spectra in the fingerprint region (1500-600 cm(-1)) as data set 2; (c) spectra in the whole region with treatment as data set 3; and (d) spectra in the fingerprint region with treatment as data set 4. The third step, the chemometric analysis were employed using three class-modelling techniques (i.e. LDA, SIMCA, and SVM) toward the data sets. Finally, the best result of the models towards the data sets on the adulteration analysis of the samples were selected and the best model was compared with the ELISA method. From the chemometric results, the LDA model on the data set 1 was found to be the best model, since it could classify and predict 100 % accuracy of the sample tested. The LDA model was applied toward the real samples of the beef jerky marketed in Jember, and the results showed that the LDA model developed was in good agreement with the ELISA method.

A simple visual ethanol biosensor based on alcohol oxidase immobilized onto polyaniline film for halal verification of fermented beverage samples.

A simple visual ethanol biosensor based on alcohol oxidase (AOX) immobilised onto polyaniline (PANI) film for halal verification of fermented beverage samples is described. This biosensor responds to ethanol via a colour change from green to blue, due to the enzymatic reaction of ethanol that produces acetaldehyde and hydrogen peroxide, when the latter oxidizes the PANI film. The procedure to obtain this biosensor consists of the immobilization of AOX onto PANI film by adsorption. For the immobilisation, an AOX solution is deposited on the PANI film and left at room temperature until dried (30 min). The biosensor was constructed as a dip stick for visual and simple use. The colour changes of the films have been scanned and analysed using image analysis software (i.e., ImageJ) to study the characteristics of the biosensor's response toward ethanol. The biosensor has a linear response in an ethanol concentration range of 0.01%-0.8%, with a correlation coefficient (r) of 0.996. The limit detection of the biosensor was 0.001%, with reproducibility (RSD) of 1.6% and a life time up to seven weeks when stored at 4 °C. The biosensor provides accurate results for ethanol determination in fermented drinks and was in good agreement with the standard method (gas chromatography) results. Thus, the biosensor could be used as a simple visual method for ethanol determination in fermented beverage samples that can be useful for Muslim community for halal verification.

A novel high throughput method based on the DPPH dry reagent array for determination of antioxidant activity.

A stable chromogenic radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) is commonly used for the determination of antioxidant activity. In this paper, DPPH was dried into 96 well microplate to produce DPPH dry reagent array plate, based on which the highly sensitive and high throughput determination of antioxidant activities was achieved. The spectrophotometric characterization of the microplate containing dried or fresh DPPH free radicals was reported. The response of the DPPH dry reagent array towards different standard antioxidants was studied. The reaction for DPPH in fresh or dry reagent array with Trolox was reported and compared. The DPPH dry reagent array was used to study the antioxidant activity of banana, green tea, pink guava, and honeydew and the results were compared to the samples reacted with freshly prepared DPPH. The proposed method is comparable to the classical DPPH method, more convenient, simple to operate with minimal solvent required and excellent sensitivity.

Selective chemosensor for Hg(II) ions based on tris[2-(4-phenyldiazenyl)phenylaminoethoxy]cyclotriveratrylene in aqueous samples.

A novel chemosensor, based on tris[2-(4-phenyldiazenyl)phenylaminoethoxy]cyclotriveratrylene (TPPECTV) as chromophore, has been developed for the colorimetric determination and visual detection of Hg(II) ions. TPPECTV exhibits a pronounced chromogenic behavior toward Hg(II) ions by changing the color of the solution from yellow to red-orange upon its addition, which can be easily detected with the naked-eye. Based on this sensing scheme a colorimetric method was developed, where the absorbance linearly increases as a function of the Hg(II) concentration up to 2.0x10(-4) M, with a detection limit of 0.5 microM. The visual detection, using TPPECTV absorbed on silica, provides a simple, rapid and sensitive method and was used for the detection of Hg(II) ions in water samples with a detection limit of 5.0 microM. The colorimetric results of the detection of Hg(II) ions in environmental water samples (river water) are in good agreement with those obtained by cold vapor atomic absorption spectrometry (CVAAS).

An optical fiber biosensor for chlorpyrifos using a single sol-gel film containing acetylcholinesterase and bromothymol blue.

An optical fiber biosensor consisting of acetylcholinesterase (AChE) and bromothymol blue (BTB) doped sol-gel film was employed to detect organophosphate pesticide chlorpyrifos. The main advantage of this optical biosensor is the use of a single sol-gel film with immobilized AChE and BTB. The compatibility of this mixture (AChE and BTB) with the sol-gel matrix has prevented leaching of the film. The immobilization of the enzyme and indicator was simple without chemical modification. The biosensing element on single sol-gel film has been placed inside the flow-cell for flow system. In the presence of a constant AChE, a color change of the BTB and the measured reflected signal at wavelength 622nm could be related to the pesticide concentration in the sample solutions. The performance of optical biosensor in the flow system has been optimized, including chemical and physical parameters. The response time of the biosensor is 8min. A linear calibration curve of chlorpyrifos against the percentage inhibition of AChE was obtained from 0.05 to 2.0mg/L of chlorpyrifos (18-80% inhibition, R(2)=0.9869, n=6). The detection limit for chlorpyrifos was 0.04mg/L. The results of the analysis of 0.5-1.5mg/L of chlorpyrifos using this optical biosensor agreed well with chromatographic method.

Optical sensing systems for microfluidic devices: a review.

This review deals with the application of optical sensing systems for microfluidic devices. In the "off-chip approach" macro-scale optical infrastructure is coupled, while the "on-chip approach" comprises the integration of micro-optical functions into microfluidic devices. The current progress of the use of both optical sensing approaches in microfluidic devices, as well as its applications is described. In all cases, sensor size and shape profoundly affect the detection limits, due to analyte transport limitation, not to signal transduction limitation. The micro- or nanoscale sensors are limited to picomolar-order detection for practical time scales. The review concludes with an assessment of future directions of optical sensing systems for integrated microfluidic devices.

Development of a disposable mercury ion-selective optode based on trityl-picolinamide as ionophore.

A disposable ion-selective optode for mercury based on trityl-picolinamide (T-Pico) as neutral ionophore was developed. The sensing layer consist of plasticised PVC incorporating T-Pico as a selective ionophore for Hg2+, ETH 5418 as a chromoionophore, and potassium tetrakis[3,5-bis(trifluoromethyl)phenyl] borate as lipophilic salt. The measurement principle is based on an ion-exchange mechanism. When the optode membrane is introduced into a water sample for 5 min, there is a colour change from red to blue, depending on the mercury concentration (pH 4.7), making it possible to use the absorbance at 665 nm as the analytical signal. The optode membrane response to Hg2+ was not fully reversible; however, it reveals a very good selectivity to many cations including alkali, alkaline earth, transition, and heavy metal ions. The detection limit for Hg2+ is 5.0x10(-7) M at pH 4.7. The response characteristics of the sensor including dynamic range, reproducibility, response time, and lifetime are discussed in detail. This sensor was used for the determination of mercury in environmental water samples with satisfactory recovery.