Microfluidic Paper-based Analytical Devices Research Articles

Femtosecond laser ablation of nitrocellulose for spatio-temporal flow control in µPADs

Microfluidic paper-based analytical devices (μPADs) are gaining popularity due to their low cost and ease of use, but controlling fluid flow for more complex biochemical assays within these devices remains challenging. This study investigates femtosecond laser ablation of nitrocellulose (NC), a preferred material for µPADs, to create mechanically switchable barriers and flow controllers. We investigated NC ablation using single laser pulses and spatially overlapping pulses that generate lines. Single pulse ablation thresholds were determined for wavelengths of 1,030 nm, 515 nm and 343 nm. Line ablation characteristics were investigated as a function of the temporal and spatial pulse separation and laser wavelength. High aspect ratio grooves (up to 4.26) were achieved under specific conditions. These grooves can be used to define the spatial separation of the flow in separated microchannels or to form a barrier line perpendicular to the microchannel that can modulate the temporal behavior of the fluid flow. This barrier introduced an additional high flow resistance slowing down the flow or, if it was designed to cut through nitrocellulose at the entire depth, completely stopped the liquid flow. It was further shown that a barrier formed in this way could be switched by mechanically bending the µPAD at the barrier position. The femtosecond laser patterning method presented here provides precise spatio-temporal control not only for flow branching and multiplexing, but also for controlling flow speed and switching flow on and off within the same manufacturing process. Our results open up new possibilities for complex, multi-step assays on µPADs.

A Paper-Based Assay for the Determination of Total Antioxidant Capacity in Human Serum Samples.

Determining the total antioxidant capacity (TAC) of biological samples is a valuable approach to measuring health status under oxidative stress conditions, such as infertility and type 2 diabetes. The Trolox equivalent antioxidant capacity (TEAC) assay is the most common approach to evaluating TAC in biological matrices. This assay is typically performed in clinical settings on a microtiter plate using a plate reader. However, the instrumentation and expertise requirements, and the resulting delay in the reporting of assay outcomes, make solution-based TEAC assays impractical for point-of-care or at-home testing, where individuals may want to monitor their health status during treatment. This work introduces the first microfluidic paper-based analytical device (µPAD) that measures TAC in human serum using TEAC assay chemistry. TAC was determined through a colorimetric image analysis of the degree of decolorization of 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radical cations (ABTS●+) by serum antioxidants. The µPAD showed a linear response to Trolox, ranging from 0.44 to 2.4 mM, (r = 0.999). The performance of paper-based TEAC assays was validated through direct comparison to solution-based TEAC assays. There was a 0.04 mM difference in TAC values between the two platforms, well within one standard deviation of a standard solution-based assay conducted on an aliquot of the same serum sample (±0.25 mM). The µPAD had a limit of detection (LOD) of 0.20 mM, well below the TAC of normal human serum. The results suggest that the proposed device can be used for biological TAC determination and expands the field of TAC analysis in point-of-care health monitoring.

Development of paper-based microfluidic analytical device (μPAD) for the determination of paracetamol in water samples: Optimization using response surface methodology (RSM)

Detecting and quantifying pharmaceutical compounds in various environmental matrices is complex and challenging. This difficulty stems from the trace levels at which these compounds are found and the lack of analytical methods that are rapid, cost-effective, and portable. To address these challenges, this study aimed to develop microfluidic paper-based analytical devices (μ-PADs) using beeswax screen printing for fabrication. Key parameters, including reaction time, concentration, reagent volume, and channel length, were optimized using response surface methodology. Under optimal conditions of 5 ppm sample concentration, 10 μL reagent volume, 10 min reaction time, and 2 cm channel length, the analytical performance of the μPAD was evaluated and compared with the standard UV–Vis spectrophotometry method. The microfluidic analytical device demonstrated detection limits at 0.03 μg/ml, compared to 0.01 μg/ml for the UV–Vis spectrophotometer. Although the sensitivity of µ-PADs in this study (0.03 μg/ml) is lower than that of UV–Vis (0.01 μg/ml), it represents an improvement over the previous µ-PAD report (1 μg/ml) on the same analytes. Both methods exhibited commendable precision, with a relative standard deviation below 2%. Additionally, recovery rates were acceptable and comparable, ranging from 86.8 to 99.6% for µ-PADs and 96.5–99% for UV–Vis. The analytical performance evaluation suggests that µPADs provide excellent sensitivity, precision, and accuracy for trace-level paracetamol analysis. A paired t-test further confirmed no statistically significant difference between the two methods, underscoring the promising potential of µ-PADs for trace-level paracetamol quantification in water samples without conventional analytical instruments.

Development of a novel ternary MOF nanozyme-based smartphone-integrated colorimetric and microfluidic paper-based analytical device for trace glyphosate detection

Given the significant and potential fatal implications of glyphosate (GLY) residues on human health and the integrity of ecosystems, their presence has garnered substantial global concern and scrutiny. Herein, we introduced a pioneering colorimetric sensing platform, the first of its kind, based on ternary metal-organic frameworks (ZnCo-ZIFs@MIL-101(Fe)). This innovative platform enabled ultra-sensitive, affordable, portable and rapid on-site detection of GLY. This platform achieved a wider linear range for GLY of 0.02–40 μg/mL with an exhibiting remarkable detection limit of 1 ng/mL, which was attributed to the electronic hybridization of the Fe3+, Co2+, and Zn2+ metal centers of ZnCo-ZIFs@MIL-101(Fe), significantly enhancing the composite's catalytic performance. The assay was successfully employed to detect GLY in food and herb samples. Moreover, to meet the demand of in-field detection for GLY, a smartphone detection method based on ZnCo-ZIFs@MIL-101(Fe) with visual, intelligent, and portable features was fabricated. This detection concentration range of GLY was 0–1 μg/mL, and the limit of smartphone detection was 23 ng/mL. Furthermore, this sensor seamlessly integrated with smartphones and paper-based microfluidic chips (μPADs), which constructed a portable test strips-smartphone sensing platform for facilitating real-time and on-site visual quantitative detection of GLY. The detection concentration range was 0–1 μg/mL, and the limit was calculated as low as 75 ng/mL. The assay was highly adaptable in practical applications. In summary, our study paved a novel pathway for the design and utilization of multi-metal MOF nanozymes in on-site pesticide monitoring.

Alcohol ink-modified microfluidic paper-based analytical devices for enhanced white detection in simultaneous determination of multiple water quality indicators.

White detection remains a critical limitation in using colorimetry to determinesubstances with microfluidic paper-based analytical devices (µPADs). Here, we introduced a simple, safe alcohol ink-modified µPAD for the straightforward and facile detection of white color in precipitation reactions. Although absolute alcohol ink was found to cause device leakage, dilution of the ink with water was the key to successfully precoat wax-created µPADs. Device utility was demonstrated through simultaneous detection of sulfate, phosphate, and waterhardness via precipitation reactions. While phosphate interfered with sulfate detection by Ba2+, in situ distance-based quantification of phosphate was implemented. Aside from anions, the modified µPADs could be extended to detect cationic analytes such as total hardness. The limits of detection (LODs) for sulfate, phosphate, and hardness were 0.005mmol L-1, 0.005mmol L-1, and 0.5mmol L-1, respectively, with the linear ranges of 0.01-10.0mmol L-1, 0.005-1.0mmol L-1, and 0.001-0.5mol L-1. The µPADs were applied to real water samples, demonstrating results that were consistent with standard methods at a 95% confidence level. By incorporating white detection, these alcohol ink-modified µPADs offer enhanced versatility for addressing a broader array of analytical challenges in real-world settings.

A Trianalyte µPAD for Simultaneous Determination of Iron, Zinc, and Manganese Ions.

In this work, a microfluidic paper-based analytical device (µPAD) for simultaneous detection of Fe, Zn, and Mn ions using immobilized chromogenic reagents Ferene S, xylenol orange, and 1-(2-pyridylazo)-2-naphthol, respectively, is presented. As the effective recognition of analytes via respective chromogens takes place under extremely different pH conditions, experiments reported in this publication are focused on optimization of the µPAD architecture allowing for the elimination of potential cross effects. The paper-based microfluidic device was fabricated using low-cost and well-reproducible wax-printing technology. For optical detection of color changes, an ordinary office scanner and self-made RGB-data processing program were applied. Optimized and stable over time, µPADs allow fast, selective, and reproducible multianalyte determinations at submillimolar levels of respective heavy metal ions, which was confirmed by results of the analysis of solutions mimicking real samples of wastewater. The presented concept of simultaneous determination of different analytes that required extremely different conditions for detection can be useful for the development of other multianalyte microfluidic paper-based devices in the µPAD format.

Non-enzymatic Determination of Glucose in Artificial Urine Using 3D-µPADs through Silver Nanoparticles Formation

Patients with diabetes often experience blood glucose fluctuations, making monitoring crucial. Traditional blood sampling methods pose risks of infection and pain. An alternative non-invasive approach using urine tests has been explored. Recent studies highlight microfluidic paper-based analytical devices (µPADs) as convenient, simple, and easily fabricated tools for non-invasive glucose measurement. This study aims to develop a concept of measuring glucose in artificial urine using 3D-µPADs in a non-enzymatic manner by utilizing glucose as a reducing agent for silver nanoparticle (AgNPs) formation. Embedding three-dimensional connectors in µPADs links the sample and detection zones to limit reagent mixing and improve glucose detection resolution. The optimal conditions were NaOH 10 M, starch 1%, and AgNO3 30 mM, with sample and detection zone volumes of 10 and 9 µL, respectively. The fifth reaction sequence involved AgNO3 in the detection zone and a solution of glucose, NaOH, and starch in the sample zone at 1:1:1 volume ratio. The reagent drying time was 15 min, with immobilization once and reaction time of 9 min. The method showed excellent linearity (R2 = 0.9905), precision (%RSD = 4.27%), accuracy (77.32–92.58%), and limit of detection (11.11 mg/dL).

Paper-based isotachophoretic preconcentration technique for low-cost determination of glyphosate

Electrophoretic microfluidic paper-based analytical devices (e-µPADs) are promising for low-cost and portable technologies, but quantitative detection remains challenging. In this study, we develop a paper-based isotachophoretic preconcentration and separation method for the herbicide glyphosate as a model analyte. The device, consisting of two electrode chambers filled with leading and terminating electrolytes and a nitrocellulose strip as the separation carrier, was illuminated by a flat light source and operated with a voltage supply of 400 V. Detection was accomplished using a simple camera. Colorimetric detection was optimized through competitive complexation between glyphosate, copper ions, and pyrocatechol violet as a dye. The buffer system was optimized using simulations, (i) ensuring the pH was optimal for the demetallation of the blue pyrocatechol violet-copper complex [PV] to the yellow free dye and (ii) ensuring the electrophoretic migration of glyphosate into the slower [PV] for the colorimetric reaction. A new data evaluation method is presented, analyzing the RGB channel intensities. The linear range was between 0.8 and 25 µM, with a LOD of approximately 0.8 µM. The ITP separation preconcentrated glyphosate by a factor of 820 in numerical simulations. The method may be applied to control glyphosate formulations, especially in developing countries where herbicide sales and applications are poorly regulated.Graphical

Microfluidic paper-based analytical devices for simple and nondestructive durian fruit maturity assessment

Accurately predicting durian maturity is a critically unresolved worldwide issue. Farmers currently determine durian ripeness based on their own observation and experience leading to inconsistencies in harvest timing. This reliance on human judgment often results in premature or overripe harvests, impacting fruit quality, yield, and market value. Existing technological solutions, such as sensors are often complex and require specialized expertise, hindering their adoption by farmers and consumers. Developing sensors that can accurately measure durian ripeness without damaging the fruit, are easy to use, and affordable remains a challenge. We introduce a microfluidic paper-based analytical device (μPAD) for on-site, safe matching to meet the demands of durian maturity evaluation. The μPAD automatically collected peduncle fluid without destroying the durian fruit for dual detection of total sugar and amino acid. For determining total sugar including sucrose, glucose, and fructose, several enzymatic steps were reduced to a single step of invertase for sucrose hydrolysis before total reducing sugar was measured using gold nanoparticle (AuNP) generation. Kinetics study of invertase on the μPAD showed Vmax and Km values of 1.42 mM min−1 and 2.17 mM, respectively, that agreed with the direct study of sucrose conversion. To increase device reliability, amino acid was also simultaneously measured with sugar using the simple ninhydrin test with the addition of SnCl2. The developed sensor provided LODs of 3.50, 3.10, 3.30 μM, and 0.02 mg mL−1 for glucose, fructose, sucrose, and amino acid respectively. The μPADs were able to nondestructively discriminate between the mature and immature durians, showing high linear correlation with the standard dry weight method. The development of this μPAD technology has the potential to revolutionize durian cultivation practices, reduce post-harvest losses, and enhance the overall sustainability and profitability of the durian value chain, and can be further developed for maturity tests of other fruits.

Enhanced sensitivity in acute myocardial infarction diagnosis through optimized multiplex biomarker detection on a paper-based microfluidic platform with individual control capabilities

Acute myocardial infarction (AMI) is a severe condition with high mortality, requiring timely diagnosis, especially in low-resource settings where centralized testing is unavailable. Leveraging our previously developed, reliable, highly integrated on-chip rotary valving system on the microfluidic paper-based analytical device (µPAD), we propose a novel multiplex paper-based microfluidics immunoassay platform for the onsite detection of key cardiac biomarkers—Myoglobin (Myo), cardiac troponin I (cTnI), and creatine kinase-MB (CKMB)—in artificial serum. It enhances assay performance through individually controlled assay conditions, facilitating rapid AMI diagnosis. Compared to existing paper-based multiplex microfluidic ELISA systems, our µPAD uniquely enables the assay of each biomarker under separate, optimally controlled incubation conditions within a single test through the valving system, which leads to optimized signal-to-noise ratio (SNR) performance and introduces more flexibility in multiplex testing. The valving system in the µPAD is driven by a single servo motor, which is controlled via a microcontroller and an interactive touchscreen. These components are integrated into a highly programmable, easy-to-assemble platform that offers fast, low-cost, and user-friendly operation. Utilizing our platform, autonomous ELISA assays were performed on Myo, cTnI, and CKMB for calibration, achieving limits of detection (LOD) of 1.43 ng/mL for Myo, 0.2 ng/mL for cTnI, and 0.735 ng/mL for CKMB. Subsequent spike-and-recovery experiments also confirmed the platform's accuracy and precision in obtaining the test results within 30 minutes and 20 μL serum sample. These results highlight the platform's transformative potential for clinical AMI diagnosis and commercialization, providing a cost-effective and accessible solution for point-of-care testing in diverse settings.

Microfluidic point-of-care testing device for multiplexed detection of liver function blood markers.

In this work, we developed a novel microfluidic paper-based analytical device to quantify the blood markers of liver function from human fingertips and whole blood samples. The device can quickly acquire information for screening liver injury and supporting clinical decision-making by simultaneously performing quantitative tests for alanine aminotransferase, aspartate aminotransferase, and albumin. We evaluated the detection accuracy and the storage stability of the device using fingertip samples. The yielded results of our device correlated well with those from Mindray BS350s, even under the conditions of 35 °C and 90%RH. Thus, it offers an effective platform for clinical assessment of liver injury particularly in resource-limited areas.

Microfluidic Paper-based Analytical Devices for On-site Environmental Analysis

Microfluidic Paper-based Analytical Devices for On-site Environmental Analysis

Gendered farmer perceptions towards soil nutrition and willingness to pay for a cafetière-style filter system for in-situ soil testing: Evidence from Central Kenya

Soil nutrition is a key pillar in agricultural productivity. However, point-of-need testing for soil nutrition is not readily available in resource-limited settings such as Kenya. We set out to study the perceived need for soil testing among farmers in this country. A group of 547 farmers from Murang'a and Kiambu counties in central Kenya were recruited through multi-stage sampling to help assess the perceptions and willingness to pay (WTP) toward a prototype technology for surveillance of in-situ soil nutrition. The technology is based on a cafetière-style filter system for extraction and a microfluidic paper-based analytical device (μPAD) for nutrient readout. We employed the double bounded choice contingent valuation method (CVM) to analyze the willingness of farmers to accept and pay for the prototype if the technology was available on the market. It was found that currently, only 1.5 % of farmers carry out soil testing. The high costs of analysis at testing centers, which are often far from the farmers, are among the main reasons contributing to the majority of farmers not testing their soils. The farmers surveyed were generally willing to make their soil data publicly accessible, especially to extension officers. CVM showed that uncontrolled WTP had a 94.24 % premium above KSh1,000 ($6.60) incurred by using the existing rapid testing method. Factoring the control variables and disaggregating the model into gender categories, the findings showed that youth, women, and men had WTP values of KSh1,612.53 ($10.75), KSh1,558.68 ($10.39), and KSh1,504.83 ($10.03), respectively, indicating that farmers can indeed pay for the convenience to test their soils in situ. Through the democratization of soil nutrition data, extension agents can enhance the improvement of agricultural productivity, which implies that farmers can commercialize their agricultural activities.

Determination of Quercetin in Iraqi Green Walnut Husk via Green Ionic Liquid-Based Digestion Extraction and Gel Filtration Procedures-Spectrophotometry and Microfluidic Paper-Based Analytical Platform Detection

في هذه الدراسة تم استخلاص ،عزل وتقدير الكيورستين الموجود في قشور الجوز العراقي باستخدام طريقة جديدة تعتمد على الاستخلاص بطريقة الهضم المبنية على استخدام السوائل الايونية و طريقة الترشيح بالجل للفصل المقترنة مع المطيافية الضوئية للتقدير ومن ثم مقارنتها مع تقنية جديدة تسمى تقنية السوائل المايكروية الورقية مستهدفة بناء طريقة اقتصادية، صديقة للبيئة وخضراء. ولقد تم اختيار 1 بيوتيل-3-مثيل ايمادزوليم كلورايد كمذيب اخضر بديل للمذيبات التقليدية بسبب خصائصة الذوبانية .ولقد اظهرت النتائج ان 100 ملغرام من القشورتحتاج الى 15 مل من المذيب و30 دقيقة من الهضم عند درجة75°C كظروف مثلى لاعطاء افضل ناتج للمستخلص بطريقة الهضم مقارنه مع طرق الاستخلاص الاخرى .تحت هذه الظروف المثلى تم عزل الكيورستين باستخدام طريقة الترشيح بالجل وتم التاكد من المركب المعزول باستخدام تقنية كروموتوغرافيا السائل عالية الاداء و اشعة فورية تحت الحمراء .تم تقدير الكيورستين المعزول من المستخلص لونيا ( طريقة كلوريد الالمنيوم) باستخدام طريقتي المطيافية الضوئية و وتقنية السوائل المايكروية الورقية معطيا الخطية لمنحنيات المعايرة لكلتا الطريقيتين بين 10-100 مليغرام / لتر مع معامل ارتباط0.9369 و 0.7917 لكلتا الطريقتين. ومن ثم تم تقدير الفعالية المضادة للاكسدة باستخجام طريقة قوة الاختزال للمركب المعزول مظهرة فعالية مضادة للاكسدة جيدة و بين تحليل التباين (ANOVA) عدم وجود فرق كبير بين تقنية المطيافية الضوئية وتقنية السوائل المايكروية الورقية. كخلاصة يمكن اعتبار المذيب الايوني BMIMCLمذيبا امنا ومناسبا لاستخلاص المركبات النباتية ذات الخواص الطبية وكذلك فان تقنية السوائل المايكروية الورقية اثبتت مقدرتها على التحليل بكفاءة مساوية الى طرق التحليل التقليدية بالاضافة الى خصائصها الخضراء.

A novel low-cost and simple fabrication technique for a paper-based analytical device using super glue

BackgroundThe microfluidic paper-based analytical devices (μPADs) have been highly regarded as effective tools that offer a cost-effective and portable solution for point-of-care testing (POCT) and on-site detection. Utilizing paper substrates such as cellulose and nitrocellulose membranes, μPADs have proven beneficial for a range of applications from medical diagnostics to environmental monitoring. Despite their advantages, the fabrication of μPADs often requires sophisticated techniques and equipment, posing challenges for widespread adoption, especially in resource-limited settings. This study addresses the need for a simplified, low-cost method for fabricating μPADs that is accessible without specialized training or equipment. ResultsThis research introduces a novel, efficient method for producing μPADs using 3D-printed slidable chambers and super glue vapor, bypassing traditional, more complex fabrication processes. The method utilizes super glue (ethyl-cyanoacrylate) vapor to create hydrophobic barriers on paper substrates. By optimizing the exposure sequence to super glue and water vapors and the heating conditions, we achieved rapid hydrophobization within 5 min, creating effective hydrophobic barriers and hydrophilic channels on paper substrates. The technique's simplicity allows for use by individuals without specialized training. The practical application of the fabrication method is demonstrated by the fabrication of μPADs that can detect multiple target analytes. We perform the simultaneous detection of glucose, proteins, and also the simultaneous detection of heavy metal ions nickel (Ni2+) and copper (Cu2+), highlighting its potential for broad applications in point-of-care diagnostics. SignificanceThis study is the first to report a method for selective exposure of ethyl-cyanoacrylate vapor for the fabrication of μPADs. This method significantly reduces the complexity, time, and fabrication cost, making it feasible for use in various settings. It also eliminates the need for specialized equipment and can be executed by individuals without specialized training. We believe that the proposed fabrication method contributes to the wider adoption and deployment of μPADs across various sectors.

Unveiling the potential of the capillary-driven microfluidic paper-based device integrated with smartphone-based for simultaneously colorimetric salivary ethanol and △9-tetrahydrocannabinol analysis

Monitoring various biomarkers in saliva samples emerges as a dynamic and non-invasive method. However, the high viscosity of saliva presents a distinct challenge when integrating paper-based platforms for on-site analysis. In addressing this challenge, we introduced the capillary-driven microfluidic paper-based analytical devices (μCD-PAD) designed for user-friendly and simultaneous detection of ethanol and tetrahydrocannabinol (THC) in saliva without a sample preparation step. Employing a colorimetric approach, we quantified both analytes. Synthetic salivas of varying viscosity flowed seamlessly to the detection zone without needing a sample preparation step, and no impact on colorimetric detection due to viscosity was observed (RSD <5 %). Within 10 min after the solution reached the detection zone, the device produced a homogeneous color signal, easily analyzed by a smartphone camera. To extend the application for determination to cover a legal limit concentration of ethanol and concentration of salivary THC even 24 h after marijuana consumption, the detection time of 30 min was optimized. Moreover, a saliva sample containing both analytes was used to demonstrate the capability of the developed device to detect ethanol and THC simultaneously. No cross-talk between ethanol and THC occurred and showed recovery in the 98–102 % for ethanol and 95–105 % for THC with acceptable accuracy. This developed device exhibits excellent potential for forensic applications, providing a user-friendly, cost-effective, and real-time screening tool for detecting ethanol and THC in saliva.

Straightforward high-temperature antibody immobilization for rapid and simple microfluidic paper-based ELISA for detection of β’-component (Onc k 5) protein, a major IgE-binding protein in salmon roe

Detection of allergenic proteins in food is required for maintaining the health of persons with food allergies. Enzyme-linked immunosorbent assay (ELISA) is a common technique for the detection of proteins. However, conventional ELISA is expensive, time-consuming, and needs technical expertise. Here, a microfluidic paper-based analytical device (µPAD) combined with a sandwich ELISA technique is developed for rapid, simple, and sensitive colorimetric detection of β’-component protein, a major allergen in salmon roe. The developed µPAD-ELISA employs a capture antibody and enzyme-labeled detection antibody. In addition to the µPAD, a technique for immobilization of the capture antibody has been developed, which completes the immobilization within 5 min by drying the antibody solution on a paper substrate in an oven at 50 °C without any chemical modification. The immobilized antibody exhibited higher binding capability to an antigen and stability against washing processes than those immobilized at room temperature. Since this technique allows simple and rapid preparation of the ELISA in the µPAD, the present µPAD-ELISA completed the analysis within only 15 min, including the immobilization step, compared to a conventional ELISA, which takes about 19 h. This µPAD-ELISA offered a good limit of detection of 1.59 ng mL−1 and reduced the amounts of reagents by a factor of about 17–67, which decreases the analysis cost. This µPAD-ELISA approach employing the present antibody immobilization is expected to be an effective strategy for the detection of allergenic proteins in food.

Paper chip-based colorimetric biosensor for glucose by using CuFe2O4@GO as nanozyme

The development of nanomaterials with notable enzyme-like activity is of great significance to the field of bioanalysis. Herein, a nanomaterial composed of copper ferrite nanoparticles (CuFe2O4 NPs) and graphene oxide (GO) was successfully prepared (CuFe2O4@GO). The obtained CuFe2O4@GO was proved to have peroxidase-like (POD-like) activity, which could catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) to generate oxidized TMB (ox-TMB) in the presence of H2O2 with an obvious color change. On this basis, a colorimetric biosensor using a UV–vis spectrometer as readout and a paper chip-based colorimetric biosensor using a smartphone as readout was constructed for glucose detection, respectively, as glucose oxidase (GOD) could oxidize glucose to form H2O2. The UV–vis spectrometer-based approach exhibits a linear range of 0 to 1000 μM and a limit of detection (LOD) of 0.79 μM for glucose. The smartphone-based method shows a linear range of 0.1 to 50 mM and a LOD of 0.04 mM for glucose. Moreover, the fabricated colorimetric biosensors have good selectivity towards glucose and the sample matrixes cannot affect the detection of glucose. Finally, the concentration of glucose in human serum samples was successfully detected using two different ways, and the results are close to the clinical values. The proposed method embraces several good merits. Firstly, the colorimetric biosensors combining UV–vis spectrometer and smartphone offer precise results, which could effectively prevent the occurrence of false events. Secondly, paper-based microfluidic analytical device (μPAD) as analytical platform and smartphone as readout provides a versatile approach for constructing sensitive, cost-effective, and simple colorimetric biosensor for the visual monitoring of glucose. Lastly, except for glucose detection, this work also shows great application prospects for other small molecules detection that could generate H2O2.

Non-Enzymatic Detection of Glucose and Ketones in Urine using Paper-Based Analytical Devices

Diabetes, driven by unbalanced diets and unhealthy lifestyles, is highly prevalent. In Indonesia, its prevalence is projected to reach 28.6 million by 2045. Microfluidic paper-based analytical devices (μPADs) are paper-based analytical tools that use hydrophilic paper for measurement and hydrophobic barriers to control fluid flow. This research aims to develop a non-enzymatic method for detecting glucose and ketones in artificial urine using S2Z-μPADs. The fabrication of S2Z-μPADs involves printing the design on Whatman No. 1 paper using wax printing and applying silver nanoparticles for glucose detection and the Schiff base reaction for ketone detection. The results show that the optimum condition for glucose detection is achieved with an AgNO3 concentration of 500 mM. A NaOH concentration of 10 M. Acetoacetate detection is optimized with a glycine concentration of 1 M, sodium nitroprusside concentration of 15%, NaOH concentration of 1 M, a drying time of 8 minutes, and a reaction time of 10 minutes. Validation results demonstrate good linearity for glucose (R² = 0.9821) and ketones (R² = 0.995). High precision was achieved with relative standard deviation (RSD) values of 3.792% for glucose and 1.482% for ketones. The obtained limits of detection (LOD) and limits of quantification (LOQ) indicate that the developed S2Z-μPADs can differentiate between each category of diabetes. The accuracy of glucose and ketone detection ranges from 87.463% to 97.374%. The high accuracy of the μPADs highlights their potential for reliable diabetes management and effective disease monitoring.

Microfluidic paper-based analytical device for measurement of pH using as sensor red cabbage anthocyanins and gum arabic

The objective of this study was to develop and validate a novel microfluidic paper-based analytical device (μPADpH) for determining the pH levels in foods. Anthocyanins from red cabbage aqueous extract (RCAE) were used as its analytical sensor. Whatman No. 1 filter paper was the most suitable for the device due to its porosity and fiber organization, which allows for maximum color intensity and minimal color heterogeneity of the RCAE in the detection zone of the μPADpH. To ensure the color stability of the RCAE for commercial use of the μPADpH, gum arabic was added. The geometric design of the μPADpH, including the channel length and separation zone diameter, was systematically optimized using colored food. The validation showed that the μPADpH did not differ from the pH meter when analyzing natural foods. However, certain additives in processed foods were found to increase the pH values.