Development of a Bioactive Paper Sensor for Detection of Neurotoxins Using Piezoelectric Inkjet Printing of Sol−Gel-Derived Bioinks

Hydrogen peroxide stabilization with silica xerogel for paper-based analytical devices and its application to phenolic compounds determination

BACKGROUND

Hydrogen peroxide is a key reagent in many analytical assays. At the same time, it is rather unstable and prone to evaporation. For these reasons, its application in sensors requiring reagents in solid state, for example in paper-based microfluidics, is hindered. Usually in paper-based analytical devices reagents are stored in a dried form within paper matrix until the device is used. This approach is not feasible in case of hydrogen peroxide. Here, hydrogen peroxide stabilization on paper with the aid of silica xerogel was studied and optimized to create long-term stable systems which rapidly deliver hydrogen peroxide.

RESULTS

The variables affecting hydrogen peroxide stability such as gelation time, silica to H2O2 ratio, type of solid support and storage conditions were optimized to find the combination of variables providing stable H2O2 concentration for the longest time possible. Such paper-silica-H2O2 composites allow to maintain steady hydrogen peroxide concentration for at least 27 days in the optimal conditions. Hydrogen peroxide is rapidly released from silica-paper matrix within a few minutes upon contact with water, without any byproducts. The obtained systems were characterized using scanning electron microscopy with energy dispersive spectroscopy and infrared spectroscopy, revealing that silica is present as a thin film covering cellulose fibers. Finally, to test the developed hydrogen peroxide stabilization method in real sensing scenario, a proof-of-concept paper-based sensor was created for phenolic content determination in fruits and wine.

SIGNIFICANCE

The outcome of this research will open new avenues in the development of user-friendly, long-term stable paper-based analytical devices which utilize hydrogen peroxide as one of reagents. Owing to the fact, that silica matrix is insoluble in water, the proposed H2O2 stabilization method is compatible with most detection schemes without the risk of interfering with the assay.

Paper-based sensors: affordable, versatile, and emerging analyte detection platforms

Paper-based sensors, often referred to as paper-based analytical devices (PADs), stand as a transformative technology in the field of analytical chemistry. They offer an affordable, versatile, and accessible solution for diverse analyte detection. These sensors harness the unique properties of paper substrates to provide a cost-effective and adaptable platform for rapid analyte detection, spanning chemical species, biomolecules, and pathogens. This review highlights the key attributes that make paper-based sensors an attractive choice for analyte detection. PADs demonstrate their versatility by accommodating a wide range of analytes, from ions and gases to proteins, nucleic acids, and more, with customizable designs for specific applications. Their user-friendly operation and minimal infrastructure requirements suit point-of-care diagnostics, environmental monitoring, food safety, and more. This review also explores various fabrication methods such as inkjet printing, wax printing, screen printing, dip coating, and photolithography. Incorporating nanomaterials and biorecognition elements promises even more sophisticated and sensitive applications.

Microfluidic paper analytic device (μPAD) technology for food safety applications

Foodborne pathogens, food adulterants, allergens, and toxic chemicals in food can cause major health hazards to humans and animals. Stringent quality control measures at all stages of food processing are required to ensure food safety. There is, therefore, a global need for affordable, reliable, and rapid tests that can be conducted at different process steps and processing sites, spanning the range from the sourcing of food to the end-product acquired by the consumer. Current laboratory-based food quality control tests are well established, but many are not suitable for rapid on-site investigations and are costly. Microfluidic paper analytical devices (μPADs) are a fast-growing field in medical diagnostics that can fill these gaps. In this review, we describe the latest developments in the applications of microfluidic paper analytic device (μPAD) technology in the food safety sector. State-of-the-art μPAD designs and fabrication methods, microfluidic assay principles, and various types of μPAD devices with food-specific applications are discussed. We have identified the prominent research and development trends and future directions for maximizing the value of microfluidic technology in the food sector and have highlighted key areas for improvement. We conclude that the μPAD technology is promising in food safety applications by using novel materials and improved methods to enhance the sensitivity and specificity of the assays, with low cost.

Paper-Based Analytical Device Based on Potentiometric Transduction for Sensitive Determination of Phenobarbital

In medicine, barbiturates are a class of depressive medications used as hypnotics, anticonvulsants, and anxiolytics. For the treatment of specific forms of epilepsy and seizures in young children in underdeveloped countries, the World Health Organization recommends phenobarbital (PBAR), a barbiturate drug. This review describes the fabrication and characterization of a paper-based analytical apparatus for phenobarbital detection that is straightforward, affordable, portable, and disposable. All of the solid-state ion-selective electrodes (ISEs) for PBAR as well as a Ag/AgCl reference electrode were constructed and optimized on a nonconductive paper substrate. Using carbon nanotube ink, the sensors were made to function as an ion-to-electron transducer and to make the paper conductive. A suitable polymeric membrane is drop-cast onto the surface of the carbon ink orifice. The pyrido-tetrapeptide and pyrido-hexapeptide derivatives, which were recently synthesized, functioned as distinct ionophores in the PBAR-membrane sensor, enabling its detection. With a detection limit of 5.0 × 10-7 M, the manufactured analytical device demonstrated a Nernstian response to PBAR anions in 50 mM phosphate buffer, pH 8.5, over a linear range of 1.0 × 10-6 to 1.0 × 10-3 M. The PBAR-based sensors showed quick (less than 5 s) response times for PBAR ion detection. The modified separate solution method was utilized to evaluate the selectivity pattern of these novel ionophores with respect to PBAR ions in comparison to other common anions. The analytical instrument that was exhibited on paper had good precision both within and between days. The suggested technology assisted in the detection of trace amounts of PBAR in real pharmaceutical samples. A comparison was made between the data acquired using the HPLC reference method and the information obtained by the recommended potentiometric approach. The described paper-based analytical device may be a good choice for point-of-care PBAR determination because it is cheap and easy to find and can self-pump (especially when combined with potentiometric detection).

Study of Single and Multipass f-rGO Inkjet-Printed Structures with Various Concentrations: Electrical and Thermal Evaluation

Reduced graphene oxide (rGO) is a derivative of graphene, which has been widely used as the conductive pigment of many water-based inks and is recognized as one of the most promising graphene-based materials for large-scale and low-cost production processes. In this work, we evaluate a custom functionalised reduced graphene oxide ink (f-rGO) via inkjet-printing technology. Test line structures were designed and fabricated by the inkjet printing process using the f-rGO ink on a pretreated polyimide substrate. For the electrical characterisation of these devices, two-point (2P) and four-point (4P) probe measurements were implemented. The results showed a major effect of the number of printed passes on the resulting resistance for all ink concentrations in both 2P and 4P cases. Interesting results can be extracted by comparing the obtained multipass resistance values that results to similar effective concentration with less passes. These measurements can provide the ground to grasp the variation in resistance values due to the different ink concentrations, and printing passes and can provide a useful guide in achieving specific resistance values with adequate precision. Accompanying topography measurements have been conducted with white-light interferometry. Furthermore, thermal characterisation was carried out to evaluate the operation of the devices as temperature sensors and heaters. It has been found that ink concentration and printing passes directly influence the performance of both the temperature sensors and heaters.

Improving printability of hydrogel-based bio-inks for thermal inkjet bioprinting applications via saponification and heat treatment processes

Material jetting bioprinting is a highly promising three-dimensional (3D) bioprinting technique that facilitates drop-on-demand (DOD) deposition of biomaterials and cells at pre-defined positions with high precision and resolution. A major challenge that hinders the prevalent use of the material jetting bioprinting technique is due to its limited range of printable hydrogel-based bio-inks. As a proof-of-concept, further modifications were made to gelatin methacrylate (GelMA), a gold-standard bio-ink, to improve its printability in a thermal inkjet bioprinter (HP Inc. D300e Digital Dispenser). A two-step modification process comprising saponification and heat treatment was performed; the GelMA bio-ink was first modified via a saponification process under highly alkali conditions to obtain saponified GelMA (SP-GelMA), followed by heat treatment via an autoclaving process to obtain heat-treated SP-GelMA (HSP-GelMA). The bio-ink modification process was optimized by evaluating the material properties of the GelMA bio-inks via rheological characterization, the bio-ink crosslinking test, nuclear magnetic resonance (NMR) spectroscopy and the material swelling ratio after different numbers of heat treatment cycles (0, 1, 2 and 3 cycles). Lastly, size-exclusion chromatography with multi-angle light scattering (SEC-MALS) was performed to determine the effect of heat treatment on the molecular weight of the bio-inks. In this work, the 4% H2SP-GelMA bio-inks (after 2 heat treatment cycles) demonstrated good printability and biocompatibility (in terms of cell viability and proliferation profile). Furthermore, thermal inkjet bioprinting of the modified hydrogel-based bio-ink (a two-step modification process comprising saponification and heat treatment) via direct/indirect cell patterning is a facile approach for potential fundamental cell-cell and cell-material interaction studies.

An Atlas for the Inkjet Printing of Large-Area Tactile Sensors

This review aims to discuss the inkjet printing technique as a fabrication method for the development of large-area tactile sensors. The paper focuses on the manufacturing techniques and various system-level sensor design aspects related to the inkjet manufacturing processes. The goal is to assess how printed electronics simplify the fabrication process of tactile sensors with respect to conventional fabrication methods and how these contribute to overcoming the difficulties arising in the development of tactile sensors for real robot applications. To this aim, a comparative analysis among different inkjet printing technologies and processes is performed, including a quantitative analysis of the design parameters, such as the costs, processing times, sensor layout, and general system-level constraints. The goal of the survey is to provide a complete map of the state of the art of inkjet printing, focusing on the most effective topics for the implementation of large-area tactile sensors and a view of the most relevant open problems that should be addressed to improve the effectiveness of these processes.

Dip-and-Fold Device: A Paper-Based Testing Platform for Rapid Assessment of Insecticides in Water Samples

The contamination of water and food in agricultural areas, where an enormous volume of pesticides is widely employed to enhance crop production, is a challenging reality. The rapid assessment of these contaminants is fundamental to assure water and food quality and safety, particularly for local community members. This work presents a nonexpensive and easy-operational paper-based testing device for the fast detection of insecticides (carbamates and organophosphates) in water samples. The structural design "dip-and-fold" allows us to carry out the analysis without introducing reagents or samples. The device is prepared using different high-quality papers to support the active acetylcholinesterase (AChE) and the customized chemical formulation for colorimetric detection. The chemical principle is based on the AChE inhibition reaction and Ellman's method. The experiments using standard solutions of carbofuran, propoxur, and chlorpyriphos indicated satisfactory detection at concentrations between 0.1 and 0.0001 mM, and the color results are revealed within 10 min. Therefore, this technique represents a promising alternative for implementing low-cost and efficient water monitoring and management solutions.

Quantitative Point-of-Care Colorimetric Assay Modeling Using a Handheld Colorimeter

Colorimetric assays typically offer a rapid and convenient method to assess analytes that span healthcare monitoring to water quality testing. However, such tests can only provide qualitative results when employed in resource-limited settings or require bulky and expensive equipment such as lab spectrophotometers to allow quantitative measurements. In this paper, we report on the use of a handheld colorimeter to quantitatively determine the concentration of analytes in a manner that is independent of ambient lighting or initial sample color. The method combines the response of the sensor with first-principles modeling that better describes the nature of the assay compared to linear-in-parameters regression modeling that is typically performed in other studies. This method was successfully demonstrated using a number of colorimetric assays: (1) determination of solution pH using a universal indicator, (2) quantification of the DNase presence using a DNA-gold nanoparticle assay, and (3) quantification of the concentration of the antibiotic tetracycline using a cell-based assay.

Recent advances of environmental pollutants detection via paper-based sensing strategy

Paper has become one of the most promising substrates for building low-cost and powerful sensing platforms due to its self-pumping ability and compatibility with multiple patterning methods. Paper-based sensors have been greatly developed in the field of environmental monitoring. In this review, we introduced the research and application of paper-based sensors in environmental monitoring, focusing on the deposition and patterning methods of building paper-based sensors, and summarized the applications of detecting environmental pollutants, including metal ions, anions, explosives, neurotoxins, volatile organic compounds, and small molecules. In addition, the development prospects and challenges of promoting paper-based sensors are also discussed. The current review will provide references for the construction of portable paper-based sensors, and has implications for the field of on-site real-time detection of the environment.

Formation and Elimination of Satellite Droplets during Monodisperse Droplet Generation by Using Piezoelectric Method

One of the key questions in the generation of monodisperse droplets is how to eliminate satellite droplets. This paper investigates the formation and elimination of satellite droplets during the generation of monodisperse deionized water droplets based on a piezoelectric method. We estimated the effects of two crucial parameters—the pulse frequency for driving the piezoelectric transducer (PZT) tube and the volume flow rate of the pumping liquid—on the generation of monodisperse droplets of the expected size. It was found that by adjusting the pulse frequency to harmonize with the volume flow rate, the satellite droplets can be eliminated through their coalescence with the subsequent mother droplets. An increase in the tuning pulse frequency led to a decrease in the size of the monodisperse droplets generated. Among three optimum conditions (OCs) (OC1: 20 mL/h, 20 kHz; OC2: 30 mL/h, 30 kHz; and OC3: 40 mL/h, 40 kHz), the sizes of the generated monodisperse deionized water droplets followed a bimodal distribution in OC1 and OC2, whereas they followed a Gaussian distribution in OC3. The average diameters were 87.8 μm (OC1), 85.9 μm (OC2), and 84.8 μm (OC3), which were 8.46%, 6.14%, and 4.69% greater than the theoretical one (81.0 μm), respectively. This monodisperse droplet generation technology is a promising step in the production of monodisperse aerosols for engineering applications.

[Applications of microfluidic paper-based chips in environmental analysis and detection]

近年来,微流控纸芯片由于低成本、便携化、检测快等优点,在需要快速检测的环境分析领域中展现出了巨大的应用前景。该综述从微流控纸芯片在环境分析中的应用角度,总结归纳了微流控纸芯片在环境分析中的最新研究进展,并展望了其在未来的发展趋势与挑战。论文内容引用150余篇源于科学引文索引(SCI)与中文核心期刊中的相关论文。该综述包括微流控纸芯片在环境检测中的优势与制造方法介绍;电化学法、荧光法、比色法、表面增强拉曼法、集成传感法等基于纸芯片的先进分析方法介绍;根据环境分析目标物种类,如重金属离子、营养盐、农药、微生物、抗生素以及其他污染物等,对纸芯片的最新应用现状进行了举例评述;基于微流控纸芯片的环境分析研究的未来发展趋势和前景展望。通过综述近期相关研究,表明微流控纸芯片从提出至今虽然只有十几年的发展历程,但其在环境分析研究中的发展却十分迅速。微流控纸芯片可以根据不同的环境条件和检测要求灵活选择制作与分析方法,实现最佳的检测效果。但是微流控纸芯片也面临一些挑战,如纸张机械强度不足、流体控制程度不佳等问题。这些问题指出了微流控纸芯片在环境检测领域的发展趋势,相信随着不断深入的研究,纸芯片将会在未来的环境分析中发挥更大作用。

A novel paper biosensor based on Fe3O4@SiO2-NH2and MWCNTs for rapid detection of pseudorabies virus

In this study, a novel paper biosensor based on Fe₃O₄@SiO₂-NH₂magnetic polymer microspheres and multi walled carbon nanotubes (MWCNTs) for rapid detection of pseudorabies virus (PRV) was first developed. Fe₃O₄@SiO₂-NH₂were functionalized with PRV antibody and doped in cellulose nitrate paper to fabricate the magnetic paper biosensor with good magnetic response and biocompatibility. Using MWCNTs to build conductive network of sensors, PRV antigen binds specifically to the immunomagnetic microspheres on the sensor, and the resulting immune complex changes the magnetic domain structure of the sensor and the structural gap of MWCNTs, causing the magnetic property and impedance change. TEM and EDS characterization proved that the biosensor was successfully doped with Fe₃O₄@SiO₂-NH₂and effectively recognized PRV. Under optimized conditions, the impedance variation was found to be linearly related to the logarithm value of PRV concentrations in the range of 10-1 mg ml^-1, with the detection limit of 10 ng ml^-1. This paper biosensor demonstrated advantages of portability, high sensitivity and specificity, providing a valuable method for early control of PRV.

Optimization of Hybrid Ink Formulation and IPL Sintering Process for Ink-Jet 3D Printing

Ink-jet 3D printing technology facilitates the use of various materials of ink on each ink-jet head and simultaneous printing of multiple materials. It is suitable for manufacturing to process a complex multifunctional structure such as sensors and printed circuit boards. In this study, a complex structure of a SiO₂ insulation layer and a conductive Cu layer was fabricated with photo-curable nano SiO₂ ink and Intense Pulsed Light (IPL)-sinterable Cu nano ink using multi-material ink-jet 3D printing technology. A precise photo-cured SiO₂ insulation layer was designed by optimizing the operating conditions and the ink rheological properties, and the resistance of the insulation layer was 2.43 × 10¹³ Ω·cm. On the photo-cured SiO₂ insulation layer, a Cu conductive layer was printed by controlling droplet distance. The sintering of the IPL-sinterable nano Cu ink was performed using an IPL sintering process, and electrical and mechanical properties were confirmed according to the annealing temperature and applied voltage. Then, Cu conductive layer was annealed at 100 °C to remove the solvent, and IPL sintered at 700 V. The Cu conductive layer of the complex structure had an electrical property of 29 µΩ·cm and an adhesive property with SiO₂ insulation layer of 5B.

Rapid, simultaneous detection of mycotoxins with smartphone recognition-based immune microspheres

How to achieve simultaneous and rapid detection of various mycotoxins in food has important practical significance in the field of food processing and safety. In this paper, a smartphone immunoassay system based on hydrogel microspheres has been constructed to quickly detect two mycotoxins at the same time. The rapid detection system was reflected in the following three processes: (1) rapid separation of free matter after direct competition reaction based on hydrogel solid-phase carrier particles; (2) rapid detection process based on efficient catalytic function of enzymes; (3) fast capture and analysis of images based on smartphone software. Ochratoxin A (OTA) and zearalenone (ZEN) are secondary toxic metabolites of fungi that can contaminate a wide range of foods and feeds. OTA and ZEN were used as detection model molecules to verify the feasibility of the intelligent rapid detection system. The entire detection process was within 30 min, and the results were analyzed in only 10 s. Detection limits of mycotoxins OTA and ZEN are 0.7711 ng L^-1 and 1.0391 ng L^-1. The recoveries of both mycotoxins ranged from 76.72 to 122.05%. This study provides a universal rapid detection method for on-site application of large-scale food security testing. Schematic diagram of the construction of the smartphone detection system: The system is divided into three parts: detection, image capture and analysis, and result.

Paper-Based Enzymatic Colorimetric Assay for Rapid Malathion Detection

Due to their unique properties, paper-based biosensors have attracted attention as inexpensive devices for on-site analysis. To achieve fast and sensitive detection of analytes, immobilization of enzymes with high apparent activities on paper is highly desirable; however, this is challenging. Herein, we report an improved approach to attach a malathion degrading enzyme, PoOPH_M9, on paper via an interlocking network of Pluronic F127 (PF127)-poly(acrylic acid)-enzyme conjugates. The addition of PF127 improved retention of enzymatic activity as the apparent kinetic constant V_max of the immobilized enzyme increased two-fold compared with the paper prepared without PF127. The PF127-poly(acrylic acid)-PoOPH_M9 papers provided rapid colorimetric detection of malathion at 0.1-50 mM. The detection was completed within 5 min using a smartphone and image analysis software. As a proof-of-concept, malathion-contaminated water, plant, and apple samples were analyzed with the papers successfully. This material is promising for on-site rapid analysis of malathion-contaminated samples.

Aptamer-based detection of fumonisin B1: A critical review

Mycotoxin contamination is a current issue affecting several crops and processed products worldwide. Among the diverse mycotoxin group, fumonisin B1 (FB1) has become a relevant compound because of its adverse effects in the food chain. Conventional analytical methods previously proposed to quantify FB1 comprise LC-MS, HPLC-FLD and ELISA, while novel approaches integrate different sensing platforms and fluorescently labelled agents in combination with antibodies. Nevertheless, such methods could be expensive, time-consuming and require experience. Aptamers (ssDNA) are promising alternatives to overcome some of the drawbacks of conventional analytical methods, their high affinity through specific aptamer-target binding has been exploited in various designs attaining favorable limits of detection (LOD). So far, two aptamers specific to FB1 have been reported, and their modified and shortened sequences have been explored for a successful target quantification. In this critical review spanning the last eight years, we have conducted a systematic comparison based on principal component analysis of the aptamer-based techniques for FB1, compared with chromatographic, immunological and other analytical methods. We have also conducted an in-silico prediction of the folded structure of both aptamers under their reported conditions. The potential of aptasensors for the future development of highly sensitive FB1 testing methods is emphasized.

Enzyme embedded microfluidic paper-based analytic device (μPAD): a comprehensive review

Low-cost paper-based analytical devices are the latest generation of portable lab-on-chip designs that offers an innovative platform for the on/off-site analysis (biosensing) of target analytes, especially in rural and remote areas. Recently, microfluidic paper-based analytical devices (μPADs) have attained significant recognition owing to their exciting fundamental features such as: ease of fabrication, rapid operation, and precise interpretations. The incorporation of enzymes with paper-based analytical devices significantly improves analytical performance while exhibiting excellent chemical and storage stability. In addition to that, these devices are highly compact, portable, easy-to-use, and do not require any additional sophisticated equipment for the detection and quantification of target analytes. This review provides a holistic insight into design, fabrication, and enzyme immobilization strategies for the development of enzyme-μPADs, which enables them to be widely implemented for in-field analysis. It also highlights the recent application of enzyme-μPADs in the area of: biomedical, food safety, and environmental monitoring while exploring the mechanisms of detection involved. Further, in order to improve the accuracy of analysis, researchers have designed a smartphone-based scanning tool for multi-variant point-of-care devices, which is summarized in the latter part of the review. Finally, the future perspectives and outlook of major challenges associated with enzyme-μPADs are discussed with their possible solutions. The development of enzyme integrated μPADs will open a new avenue as an exceptional analytical tool to explore various applications.HIGHLIGHTSEnzyme embedded paper-based analytical devices are a revolution in the field of biosensing.The design, fabrication, and enzyme immobilization on μPADs have been comprehensively discussed.The application of enzyme-μPADs food safety, environmental monitoring, and clinical diagnostic have been reviewed.Smartphones can be used as an on-site, user-friendly, and compact next-gen scanning tool for biosensing.

High-Resolution Patterning of Hydrogel Sensing Motifs within Fibrous Substrates for Sensitive and Multiplexed Detection of Biomarkers

There has been an increasing and urgent demand to develop nucleic acid bioassays which not only offer high analytical performance but which are also amenable with point-of-care testing. Hydrogels present a versatile class of materials with biocompatible antifouling properties and the ability to be engineered for a range of advanced sensing applications. Fibrous substrates like nitrocellulose offer low-cost and durable platforms to run complex bioassays while enabling portability and ease of handling. We demonstrate herein the ability to synergistically combine these two materials into a portable biosensing platform by leveraging projection lithography. We demonstrate the direct polymerization of hydrogel sensing motifs within a range of fibrous substrates with precise control over their shape, size, location, and functionality. Spatial encoding of the hydrogel motifs enables the multiplex detection of multiple biomarkers on the same test. As a proof-of-concept, we apply the platform to the detection of microRNA, an emerging class of circulating biomarkers with promising potential for early diagnosis and monitoring of cancer. The assay offers a large dynamic range (over three orders of magnitude), high sensitivity (limit of detection of 2.5 amol), as well as versatility and ease of handling. Finally, the bioassay is validated using real biological samples, namely, total RNA extracted from the sera of late-stage breast cancer patients, demonstrating its utility and compatibility with clinical biosensing applications.

A Novel NiFe2O4/Paper-Based Magnetoelastic Biosensor to Detect Human Serum Albumin

For the first time, a novel NiFe2O4/paper-based magnetoelastic (ME) biosensor was developed for rapid, sensitive, and portable detection of human serum albumin (HSA). Due to the uniquely magnetoelastic effect of NiFe2O4 nanoparticles and the excellent mechanical properties of the paper, the paper-based ME biosensor transforms the surface stress signal induced by the specific binding of HSA and antibody modified on the paper into the electromagnetic signal. The accumulated binding complex generates a compressive stress on the biosensor surface, resulting in a decrease in the biosensor's static magnetic permeability, which correlates to the HSA concentrations. To improve the sensitivity of the biosensor, the concentration of NiFe2O4 nanofluid and the impregnated numbers of the NiFe2O4 nanofluid-impregnated papers were optimized. The experimental results demonstrated that the biosensor exhibited a linear response to HSA concentrations ranging from 10 μg∙mL-1 to 200 μg∙mL-1, with a detection limit of 0.43 μg∙mL-1, which is significantly lower than the minimal diagnosis limit of microalbuminuria. The NiFe2O4/paper-based ME biosensor is easy to fabricate, and allows the rapid, highly-sensitive, and selective detection of HSA, providing a valuable analytical device for early monitoring and clinical diagnosis of microalbuminuria and nephropathy. This study shows the successful integration of the paper-based biosensor and the ME sensing analytical method will be a highly-sensitive, easy-to-use, disposable, and portable alternative for point-of-care monitoring.

Whole-cell paper strip biosensors to semi-quantify tetracycline antibiotics in environmental matrices

A novel, low-cost, and portable paper strip biosensor was developed for the detection of tetracycline antibiotics. Escherichia coli/pMTLacZ containing the tetracycline-mediated regulatory gene used as recognition elements with β-galactosidase as the reporter protein was designed and applied to cheap and portable Whatman filter paper as the carrier to prepare this paper strip biosensor. The detection process was optimized by using EDTA and polymyxin B as a sensitizer to improve the accuracy of detection for complicated matrices. The paper strip biosensor was suitable for tetracycline concentrations in the range of 75-10000 μg/L in water and 75-7500 μg/L in soil extracts. Detection limits of 5.23-17.1 μg/L for water and 5.21-35.3 μg/kg for the EDTA soil extracts were achieved at a response time of 90 min. The standard deviation (SD) of detected values by the biosensor paper strip compared to those determined by HPLC was between 13.4 and 59.6% for tetracycline and 2.01-33.5% for oxytetracycline in water and was between 6.22 and 72.8% for tetracycline and 5.90-43.4% for oxytetracycline in soil. This suggests that the paper strip biosensor was suitable for detecting both tetracycline and oxytetracycline in water, and could provide a suitable detection for extractable oxytetracycline in soils. Therefore, this biosensor provides a simple, economical, and portable piece of field kit for on-site monitoring of tetracyclines in a variety of environmental samples, such as pond water and agricultural soil that are susceptible to tetracycline pollution from feed additives and fertilization with livestock manure.

Cellulose-based Biosensor for Bio-molecules Detection in Medical Diagnosis: A Mini-Review

Background::

Biosensors are widely applied for the detection of bio-molecules in blood glucose , cholesterol, and gene. Cellulose as the most dominating natural polymer has attracted more and more interest, especially in the field of medicine such as advanced medical diagnosis. Cellulose could endow biosensors with improved biocompatibility, biodegradability and nontoxicity, which could help in medical diagnosis. This mini-review summarizes the current development of cellulose-based biosensors as well as their applications in medical diagnosis in recent years.

Methods:

After reviewing recent years’ publications we can say that, there are several kinds of cellulose used in biosensors including different cellulose derivatives, bacterial cellulose and nanocellulose. Different types of cellulose-based biosensors, such as membrane, nano-cellulose and others were briefly described in addition to the detection principle. Cellulose-based biosensors were summarized as in the previous papers. The description of various methods used for preparing cellulose-based biosensors was also provided.

Results:

Cellulose and its derivatives with their unique chemical structure proved to be versatile materials providing a good platform for achieving immobilizing bioactive molecules in biosensors. These cellulose-based biosensors possess various desirable properties such as accuracy, sensitivity, convenience, low cost and fast response. Among them, cellulose paper-based biosensors have the advantages of low cost and easy operation. Nano-cellulose has unique properties such as a large aspect ratio, good dispersing ability and high absorption capacity.

Conclusion:

Cellulose displays a promising application in biosensors which could be used to detect different bio-molecules such as glucose, lactate, urea, gene, cell, amino acid, cholesterol, protein and hydroquinone. In future, the attention will be focused on designing miniaturized, multifunctional, intelligent and integrated biosensors. Creation of low cost and environmentally friendly biosensors is also very important.

Development of low-cost paper-based biosensor of polyphenol oxidase for detection of phenolic contaminants in water and clinical samples

In the present work, polyphenol oxidase (PPO) enzyme was purified from potato peel using three-phase partitioning (TPP). In this method, ammonium sulfate and t-butanol were added to precipitate the protein/enzyme from the crude aqueous extract. The PPO enzyme precipitated as an interfacial layer between the upper organic solvent phase and lower aqueous phase. Different purification parameters such as crude extract to t-butanol ratio, ammonium sulfate concentration, temperature, and pH were optimized for TPP. About 69% PPO enzyme activity was recovered in a single step of TPP with 9.2-fold purification. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis profile of partially purified PPO enzyme showed molecular weight in the range of about 30-40 kDa. The PPO enzyme was then investigated for the fabrication of a portable, cost-effective, and disposable colorimetric paper biosensor or colorimetric "test strips" for detection of phenolic contaminants. PPO and a chromophore reagent (3-methyl-2-benzothiazolinone hydrazine) generated a range of color in the presence of phenolic compounds (catechol, phenol, p-cresol, 4-methyl catechol) within 15 min, and limit of detection was found to be 0.5 μM. The biosensor worked in a broad range of pH from 3 to 11 and showed good storage stability at 25 °C and 4 °C for 30 days with no significant loss of activity. The biosensor was also applied on environmental water and urine sample to show reliability of biosensor.

Microfluidic Pneumatic Printed Sandwiched Microdroplet Array for High-Throughput Enzymatic Reaction and Screening

High-throughput enzyme screening for desired functionality is highly demanded. This paper utilizes a newly developed microfluidic pneumatic printing platform for high-throughput enzyme screening applications. The novel printing platform can achieve distinct features including a disposable cartridge, which avoids crosstalk; a flexible cartridge design, allowing for integration of multiple channels; and fast printing speed with submicroliter spot size. Moreover, a polydimethylsiloxane (PDMS)-based sandwich structure has been proposed and used during the printing and imaging, which can lead to better results, including reduced evaporation as well as a uniform light path during imaging. Using this microfluidic pneumatic printed PDMS sandwiched microdroplet array platform, we have demonstrated the capability of high-throughput generation of a combinatorial droplet array with concentration and volume gradients. Furthermore, the potential for enzymatic study has been validated by quantified cellulose reaction implemented with the printing platform.

Microfluidic cap-to-dispense (μCD): a universal microfluidic-robotic interface for automated pipette-free high-precision liquid handling

Microfluidic devices have been increasingly used for low-volume liquid handling operations. However, laboratory automation of such delicate devices has lagged behind due to the lack of world-to-chip (macro-to-micro) interfaces. In this paper, we have presented the first pipette-free robotic-microfluidic interface using a microfluidic-embedded container cap, referred to as a microfluidic cap-to-dispense (μCD), to achieve a seamless integration of liquid handling and robotic automation without any traditional pipetting steps. The μCD liquid handling platform offers a generic and modular way to connect the robotic device to standard liquid containers. It utilizes the high accuracy and high flexibility of the robotic system to recognize, capture and position; and then using microfluidic adaptive printing it can achieve high-precision on-demand volume distribution. With its modular connectivity, nanoliter processability, high adaptability, and multitask capacity, μCD shows great potential as a generic robotic-microfluidic interface for complete pipette-free liquid handling automation.

Biomimetic Membranes with Transmembrane Proteins: State-of-the-Art in Transmembrane Protein Applications

In biological cells, membrane proteins are the most crucial component for the maintenance of cell physiology and processes, including ion transportation, cell signaling, cell adhesion, and recognition of signal molecules. Therefore, researchers have proposed a number of membrane platforms to mimic the biological cell environment for transmembrane protein incorporation. The performance and selectivity of these transmembrane proteins based biomimetic platforms are far superior to those of traditional material platforms, but their lack of stability and scalability rule out their commercial presence. This review highlights the development of transmembrane protein-based biomimetic platforms for four major applications, which are biosensors, molecular interaction studies, energy harvesting, and water purification. We summarize the fundamental principles and recent progress in transmembrane protein biomimetic platforms for each application, discuss their limitations, and present future outlooks for industrial implementation.

Enzymatic Litmus Test for Selective Colorimetric Detection of C-C Single Nucleotide Polymorphisms

A paper based litmus test has been developed using modulation of urease enzyme activity for detection of C-C mismatch single nucleotide polymorphisms (SNPs) by the naked eye. Urease is first inactivated with silver ions and printed onto paper microzones. Addition of DNA containing C-C mismatches reactivates urease via binding of Ag(I), allowing restoration of urease activity, hydrolysis of urea to produce ammonia, and an increase in pH, which is monitored colorimetrically using a pH indicator with a limit of detection of 11 nM DNA in 40 min. The assay system is easy to use, portable, and stable for at least 30 days at ambient temperature. To assess the versatility and practical application of the paper sensor, we used it to identify a G > C transversion present in human genomic DNA from a ductal carcinoma cell line, a mutation commonly found in breast cancer. We believe this new assay system has the potential to be a low-cost method for rapidly identifying DNA with the C-C mismatch SNP as a means of cancer screening in resource-limited areas.

Point-of-Need DNA Testing for Detection of Foodborne Pathogenic Bacteria

Foodborne pathogenic bacteria present a crucial food safety issue. Conventional diagnostic methods are time-consuming and can be only performed on previously produced food. The advancing field of point-of-need diagnostic devices integrating molecular methods, biosensors, microfluidics, and nanomaterials offers new avenues for swift, low-cost detection of pathogens with high sensitivity and specificity. These analyses and screening of food items can be performed during all phases of production. This review presents major developments achieved in recent years in point-of-need diagnostics in land-based sector and sheds light on current challenges in achieving wider acceptance of portable devices in the food industry. Particular emphasis is placed on methods for testing nucleic acids, protocols for portable nucleic acid extraction and amplification, as well as on the means for low-cost detection and read-out signal amplification.

The design, fabrication, and applications of flexible biosensing devices

Flexible biosensors form part of a rapidly growing research field that take advantage of a multidisciplinary approach involving materials, fabrication and design strategies to be able to function at biological interfaces that may be soft, intrinsically curvy, irregular, or elastic. Numerous exciting advancements are being proposed and developed each year towards applications in healthcare, fundamental biomedical research, food safety and environmental monitoring. In order to place these developments in perspective, this review is intended to present an overview on field of flexible biosensor development. We endeavor to show how this subset of the broader field of flexible and wearable devices presents unique characteristics inherent in their design. Initially, a discussion on the structure of flexible biosensors is presented to address the critical issues specific to their design. We then summarize the different materials as substrates that can resist mechanical deformation while retaining their function of the bioreceptors and active elements. Several examples of flexible biosensors are presented based on the different environments in which they may be deployed or on the basis of targeted biological analytes. Challenges and future perspectives pertinent to the current and future stages of development are presented. Through these summaries and discussion, this review is expected to provide insights towards a systematic and fundamental understanding for the fabrication and utilization of flexible biosensors, as well as inspire and improve designs for smart and effective devices in the future.

Recent advances in and potential utilities of paper-based electrochemical sensors: beyond qualitative analysis

Paper based electrochemical sensors (PESs) are simple, low-cost, portable and disposable analytical sensing platforms that can be applied in clinical diagnostics, food quality control and environmental monitoring.

Precision design of vinyl amine and vinyl alcohol-based copolymers via cobalt-mediated radical polymerization

Controlling the amount and the distribution of vinyl amine and vinyl alcohol units within a copolymer is attractive to modulate the properties of the parent major industrial homopolymers, i.e. poly(vinyl amine) and poly(vinyl alcohol).

Single step and mask-free 3D wax printing of microfluidic paper-based analytical devices for glucose and nitrite assays

Microfluidic paper-based analytical devices (μPADs) have recently emerged as a simple, portable, user-friendly, and affordable alternative to more instrument-intensive analytical approaches for point-of-care testing (POCT), food safety analysis, and environmental monitoring. However, most of the existing methods for the fabrication of μPADs still face a great challenge because of different trade-offs among cost, convenience, and the pattern resolution. In this work, we report a facile one-step approach to prepare a μPAD using an affordable, easy-to-build 3D printer to generate patterns of solid wax on laboratory filter paper. The presented wax printing method did not require the use of predesigned masks and an external heat source to form complete hydrophobic wax barrier through the use of a custom-made extruder. The results revealed a strong linear relationship (R² = 0.985) between the nominal and the printed widths of the wax barriers. The achievable resolution of the wax barrier printed on filter paper was 468 ± 72 µm, which was lower than previously reported minimum barrier feature sizes achieved by wax printing and other wax patterning techniques, such as stamping and screen-printing. The analytical utility of the fabricated μPADs was evaluated for colorimetric nitrite and glucose detection in artificial solutions. It was found that the fabricated μPADs provided adequate accuracy and reproducibility for quantitative determination of nitrite and glucose within concentration ranges relevant to the disease detection in human saliva and urine. The wax printing approach reported here provides a simple, rapid, and cost-effective fabrication method for paper-based microfluidics and may bring benefits to medical diagnostics in the developing world.

Flexible and Highly Sensitive Resistive Pressure Sensor Based on Carbonized Crepe Paper with Corrugated Structure

Recently, cellulose paper based materials have emerged for applications in wearable "green" electronics due to their earth abundance, low cost, light weight, flexibility, and sustainability. Herein, for the first time, we develop an almost all cellulose paper based pressure sensor through a facile, cost-effective, scalable, and environment-friendly approach. The screen-printed interdigital electrodes on the flat printing paper and the carbonized crepe paper (CCP) with good conductivity are integrated into a flexible pressure sensor as substrates and active materials, respectively. The porous and corrugated structure of the CCP endows the pressure sensor with high sensitivity (2.56-5.67 kPa^-1 in the range of 0-2.53 kPa), wide workable pressure range (0-20 kPa), fast response time (<30 ms), low detection limit (∼0.9 Pa), and good durability (>3000 cycles). Additionally, we demonstrate the practical applications of the CCP pressure sensor in detection of finger touching, wrist pulse, respiration, phonation, acoustic vibration, etc., and real-time monitoring of spatial pressure distribution. The proposed CCP pressure sensor has great potentials in various applications as wearable electronics. Moreover, the subtle fabrication of the desired materials based on commercially available products provides new insights into the development of green electronics.

Paper-based biodetection using luminescent nanoparticles

Point-of-care and in-field technologies for rapid, sensitive and selective detection of molecular biomarkers have attracted much interest. Rugged bioassay technology capable of fast detection of markers for pathogens and genetic diseases would in particular impact the quality of health care in the developing world, but would also make possible more extensive screening in developed countries to tackle problems such as those associated with water and food quality, and tracking of infectious organisms in hospitals and clinics. Literature trends indicate an increasing interest in the use of nanomaterials, and in particular luminescent nanoparticles, for assay development. These materials may offer attributes for development of assays and sensors that could achieve improvements in analytical figures of merit, and provide practical advantages in sensitivity and stability. There is opportunity for cost-efficiency and technical simplicity by implementation of luminescent nanomaterials as the basis for transduction technology, when combined with the use of paper substrates, and the ubiquitous availability of cell phone cameras and associated infrastructure for optical detection and transmission of results. Luminescent nanoparticles have been described for a broad range of bioanalytical targets including small molecules, oligonucleotides, peptides, proteins, saccharides and whole cells (e.g., cancer diagnostics). The luminescent nanomaterials that are described herein for paper-based bioassays include metal nanoparticles, quantum dots and lanthanide-doped nanocrystals. These nanomaterials often have broad and strong absorption and narrow emission bands that improve opportunity for multiplexed analysis, and can be designed to provide emission at wavelengths that are efficiently processed by conventional digital cameras. Luminescent nanoparticles can be embedded in paper substrates that are designed to direct fluid flow, and the resulting combination of technologies can offer competitive analytical performance at relatively low cost.

A novel approach for precisely controlled multiple cell patterning in microfluidic chips by inkjet printing and the detection of drug metabolism and diffusion

In this work we report the use of inkjet printing as a precise and convenient means for microscale cell patterning in microfluidic chips followed by cell co-culture, stimulation and analysis. A self-made inkjet printing device was manufactured with adjustable parameters, which was capable of multiple cell printing within biocompatible materials. Sodium alginate was used as a printing matrix for cell encapsulation, and precisely distributed cell arrays on glass slides were obtained by accurate software controlled printing. By covering a PDMS layer with the corresponding microchannels onto the cell array substrate and subsequently injecting an ion cross-linking reagent, the cells containing alginate arrays gelated immediately and were immobilized on the bottom of the microchip, which could be utilized for cell culture and analysis. HepG2 cells and U251 cells were successfully co-patterned in the microchip and used for drug metabolism and diffusion experiment to imitate the in vivo situation, as a means to ascertain the capability of the system for precise microscale cell patterning in a microchip. The prodrug tegafur was metabolized by HepG2 cells into the active anticancer compound 5-fluorouracil and this produced an adverse gradient effect on U251 cells according to the distance from the HepG2 cells. The developed approach presented a feasible way to integrate inkjet cell printing and microfluidic chips for the first time, which is proved to be capable of spatially controlled printing of multiple kinds of cells into a microchip for cell culture, stimulation and analysis, which could be applied to tissue engineering, drug testing and related areas. We envision that the approach will help significantly increase the cell patterning efficacy in microfluidic chips as well as reduce the extent of laborious experimental work.

Covalent Attachment of Enzymes to Paper Fibers for Paper-Based Analytical Devices

Due to its unique material properties, paper offers many practical advantages as a viable platform for sensing devices. In view of paper-based microfluidic biosensing applications, the covalent immobilization of enzymes with preserved functional activity is highly desirable and ultimately challenging. In the present manuscript, we report an efficient approach to achieving the covalent attachment of certain enzymes on paper fibers via a surface-bound network of hydrophilic polymers bearing protein-modifiable sites. This tailor-made macromolecular system consisting of polar, highly swellable copolymers is anchored to the paper exterior upon light-induced crosslinking of engineered benzophenone motifs. On the other hand, this framework contains active esters that can be efficiently modified by the nucleophiles of biomolecules. This strategy allowed the covalent immobilization of glucose oxidase and horseradish peroxidase onto cotton linters without sacrificing their bioactivities and performance upon surface binding. As a proof-of-concept application, a microfluidic chromatic paper-based glucose sensor was developed and achieved successful glucose detection in a simple yet efficient cascade reaction.