A disposable, simple, fast and low-cost paper-based biosensor and its application to the determination of glucose in commercial orange juices

Improving pesticide residue detection: Immobilized enzyme microreactor embedded in microfluidic paper-based analytical devices

Orientationally immobilized enzyme microreactors (OIMERs), embedded in microfluidic paper-based analytical devices (μPADs) were developed for improved detection of pesticide residues in food. Acetylcholinesterase (AChE) was orientationally immobilized on the reusable Part I of the μPADs, using the specific affinity binding of concanavalin A (Con A) to a glycosyl group on AChE. Using the disposable Part II, facile colorimetric quantification was performed with a smartphone and software, or qualitative detection by a naked-eye visual test. The AChE immobilized in OIMERs not only had improved activity and stability, but also high sensitivity, with a limit of detection as low as (0.007 ± 0.003) μg/mL. The method was used to detect pesticides residues in real vegetable samples; the recovery (88.6-102.7%) showed high reliability for pesticide residues detection in foods. A molecular docking study and an enzyme kinetic analysis were conducted to characterize the mechanism of action of the OIMERs.

In situ anchored ternary hierarchical hybrid nickel@cobaltous sulfide on poly(3,4-ethylenedioxythiophene)-reduced graphene oxide for highly efficient non-enzymatic glucose sensing

A ternary hierarchical hybrid Ni@CoxSy/poly(3,4-ethylenedioxythiophene)-reduced graphene oxide (Ni@CoxSy/PEDOT-rGO) is rationally designed and in situ facilely synthesized as electrocatalyst to construct a binder-free sensing platform for non-enzymatic glucose monitoring through traditional electrodeposition procedure. The as-prepared Ni@CoxSy/PEDOT-rGO presents unique hierarchical structure and multiple valence states as well as strong and robust adhesion between Ni@CoxSy/PEDOT-rGO and GCE. Profiting from the aforementioned merits, the sensing platform constructed under optimal conditions achieved a wide detection range (0.2 μM ~ 2.0 mM) with high sensitivity (1546.32 μA cm-2 mM-1), a rapid response time (5 s), an ultralow detection limit (0.094 μM), superior anti-interference performance, excellent reproducibility and considerable stability. Furthermore, the sensor demonstrates an acceptable accuracy and appreciable recoveries ranging from 90.0 to 102.0% with less than 3.98% RSD in human blood serum samples, indicating the prospect of the sensor for the real samples analysis. It will provide a strategy to rationally design and fabricate ternary hierarchical hybrid as nanozyme for glucose assay.

Paper-Based Microfluidic Chips for Food Hazard Factor Detection: Fabrication, Modification, and Application

Food safety and quality are paramount concerns for ensuring the preservation of human life and well-being. As the field of food processing continues to advance, there is a growing interest in the development of fast, instant, cost-effective, and convenient methods for detecting food safety issues. In this context, the utilization of paper-based microfluidic chips has emerged as a promising platform for enabling rapid detection, owing to their compact size, high throughput capabilities, affordability, and low resource consumption, among other advantages. To shed light on this topic, this review article focuses on the functionalization of paper-based microfluidic surfaces and provides an overview of the latest research and applications to colorimetric analysis, fluorescence analysis, surface-enhanced Raman spectroscopy, as well as their integration with paper-based microfluidic platforms for achieving swift and reliable food safety detection. Lastly, the article deliberates on the challenges these analytical methods and presents insights into their future development prospects in facilitating rapid food safety assessment.

Recent Advances In the development of enzymatic paper-based microfluidic biosensors

Using microfluidic paper-based analytical devices has attracted considerable attention in recent years. This is mainly due to their low cost, availability, portability, simple design, high selectivity, and sensitivity. Owing to their specific substrates and catalytic functions, enzymes are the most commonly used bioactive agents in μPADs. Enzymatic μPADs are various in design, fabrication, and detection methods. This paper provides a comprehensive review of the development of enzymatic μPADs by considering the methods of detection and fabrication. Particularly, techniques for mass production of these enzymatic μPADs for use in different fields such as medicine, environment, agriculture, and food industries are critically discussed. This paper aims to provide a critical review of μPADs and discuss different fabrication methods as the central parts of the μPADs production categorized into printable and non-printable methods. In addition, state-of-the-art technologies such as fully printed enzymatic μPADs for rapid, low-cost, and mass production and improvement have been considered.

Chitosan-carbon nanofiber based disposable bioelectrode for electrochemical detection of oxytocin

Bioelectrodes with low carbon footprint can provide an innovative solution to the surmounting levels of e-waste. Biodegradable polymers offer green and sustainable alternatives to synthetic materials. Here, a chitosan-carbon nanofiber (CNF) based membrane has been developed and functionalized for electrochemical sensing application. The surface characterization of the membrane revealed crystalline structure with uniform particle distribution, and surface area of 25.52 m²/g and pore volume of 0.0233 cm³/g. The membrane was functionalized to develop a bioelectrode for the detection of exogenous oxytocin in milk. Electrochemical impedance spectroscopy was employed to determine oxytocin in a linear concentration range of 10 to 10⁵ ng/mL. The developed bioelectrode showed an LOD of 24.98 ± 11.37 pg/mL and sensitivity of 2.77 × 10^-10 Ω / log ng mL^-1/mm² for oxytocin in milk samples with 90.85-113.34 percent recovery. The chitosan-CNF membrane is ecologically safe and opens new avenues for environment-friendly disposable materials for sensing applications.

Paper-Based Enzymatic Electrochemical Sensors for Glucose Determination

The general objective of Analytical Chemistry, nowadays, is to obtain best-quality information in the shortest time to contribute to the resolution of real problems. In this regard, electrochemical biosensors are interesting alternatives to conventional methods thanks to their great characteristics, both those intrinsically analytical (precision, sensitivity, selectivity, etc.) and those more related to productivity (simplicity, low costs, and fast response, among others). For many years, the scientific community has made continuous progress in improving glucose biosensors, being this analyte the most important in the biosensor market, due to the large amount of people who suffer from diabetes mellitus. The sensitivity of the electrochemical techniques combined with the selectivity of the enzymatic methodologies have positioned electrochemical enzymatic sensors as the first option. This review, focusing on the electrochemical determination of glucose using paper-based analytical devices, shows recent approaches in the use of paper as a substrate for low-cost biosensing. General considerations on the principles of enzymatic detection and the design of paper-based analytical devices are given. Finally, the use of paper in enzymatic electrochemical biosensors for glucose detection, including analytical characteristics of the methodologies reported in relevant articles over the last years, is also covered.

Versatile potentiometric metabolite sensing without dioxygen interference

The field of electrochemical biosensors has been dominated by amperometric and voltammetric sensors; however, these are limited greatly in their signal dependence on electrode size. Open circuit potentiometric sensors are emerging as an alternative due to their signal insensitivity to electrode size. Here, we present a second-generation biosensor that uses a modified chitosan hydrogel to entrap a dehydrogenase or other oxidoreductase enzyme of interest. The chitosan is modified with a desired electron mediator such that in the presence of the analyte, the enzyme will oxidize or reduce the mediator, thus altering the measured interfacial potential. Using the above design, we demonstrate a swift screening method for appropriate enzyme-mediator pairs based on open circuit potentiometry, as well as the efficacy of the biosensor design using two dehydrogenase enzymes (FADGDH and ADH) and peroxidase. Using 1,2-naphthoquinone as the mediator for FADGDH, dynamic ranges from 0.1 to 50 mM glucose are achieved. We additionally demonstrate the ease of fabrication and modification, a lifetime of ≥28 days, insensitivity to interferents, miniaturization to the microscale, and sensor efficacy in the presence of the enzyme's natural cofactor. These results forge a foundation for the generalized use of potentiometric biosensors for a wide variety of analytes within biologically-relevant systems where oxygen can be an interferent.

Design of an Integrated Microfluidic Paper-Based Chip and Inspection Machine for the Detection of Mercury in Food with Silver Nanoparticles

For most of the fast screening test papers for detecting Hg2+, the obtained results are qualitative. This study developed an operation for the μPAD and combined it with the chemical colorimetric method. Silver nanoparticle (AgNP) colloids were adopted as the reactive color reagent to combine and react with the Hg standards on the paper-based chip. Then, the RGB values for the color change were used to establish the standard curve (R2 > 0.99). Subsequently, this detection system was employed for the detection tests of actual samples, and the detected RGB values of the samples were substituted back to the formula to calculate the Hg2+ contents in the food. In this study, the Hg2+ content and recovery rate in commercially available packaged water and edible salts were measured. The research results indicate that a swift, economical, and simple detection method for Hg2+ content in food has been successfully developed.

Hospitals and Laboratories on Paper-Based Sensors: A Mini Review

With characters of low cost, portability, easy disposal, and high accuracy, as well as bulky reduced laboratory equipment, paper-based sensors are getting increasing attention for reliable indoor/outdoor onsite detection with nonexpert operation. They have become powerful analysis tools in trace detection with ultra-low detection limits and extremely high accuracy, resulting in their great popularity in medical detection, environmental inspection, and other applications. Herein, we summarize and generalize the recently reported paper-based sensors based on their application for mechanics, biomolecules, food safety, and environmental inspection. Based on the biological, physical, and chemical analytes-sensitive electrical or optical signals, extensive detections of a large number of factors such as humidity, pressure, nucleic acid, protein, sugar, biomarkers, metal ions, and organic/inorganic chemical substances have been reported via paper-based sensors. Challenges faced by the current paper-based sensors from the fundamental problems and practical applications are subsequently analyzed; thus, the future directions of paper-based sensors are specified for their rapid handheld testing.

Glucose oxidase-mediated sodium alginate gelation: Equipment-Free detection of glucose in fruit samples

In this study, a paper-based sensor, combined with a visual distance-readout method, was developed to determine glucose in fruit samples based on the glucose oxidase-mediated sodium alginate gelation. The type of filter paper, the concentration of sodium alginate and the enzymatic reaction conditions were systematically investigated. Under optimal conditions, the increase in diffusion diameter showed a good linear relationship with glucose concentration between 1.4-7.0 mM, and the limit of quantification was 1.4 mM. Finally, the applicability of the proposed strategy was successfully verified by measuring glucose concentrations in fruit samples. The results generated by the developed paper-based sensor were in good agreement with the results obtained from a glucose assay kit. The recoveries were 91.8%-99.1%. In short, the present study developed a simple, low-cost and efficient method for assessing fruit quality and for guiding fruit intake for diabetic patients, especially in remote or resource-limited regions.

Recent Advances in Potentiometric Biosensing

Potentiometric biosensors are incredibly versatile tools with budding uses in industry, security, environmental safety, and human health. This mini-review on recent (2018-2020) advances in the field of potentiometric biosensors is intended to give a general overview of the main types of potentiometric biosensors for novices while still providing a brief but thorough summary of the novel advances and trends for experienced practitioners. These trends include the incorporation of nanomaterials, graphene, and novel immobilization materials, as well as a strong push towards miniaturized, flexible, and self-powered devices for in-field or at-home use.

Microwave Planar Resonant Solutions for Glucose Concentration Sensing: A Systematic Review

The measurement of glucose concentration finds interesting potential applications in both industry and biomedical contexts. Among the proposed solutions, the use of microwave planar resonant sensors has led to remarkable scientific activity during the last years. These sensors rely on the changes in the dielectric properties of the medium due to variations in the glucose concentration. These devices show electrical responses dependent on the surrounding dielectric properties, and therefore the changes in their response can be related to variations in the glucose content. This work shows an up-to-date review of this sensing approach after more than one decade of research and development. The attempts involved are sorted by the sensing parameter, and the computation of a common relative sensitivity to glucose is proposed as general comparison tool. The manuscript also discusses the key points of each sensor category and the possible future lines and challenges of the sensing approach.

Paper and Other Fibrous Materials-A Complete Platform for Biosensing Applications

Paper-based analytical devices (PADs) and Electrospun Fiber-Based Biosensors (EFBs) have aroused the interest of the academy and industry due to their affordability, sensitivity, ease of use, robustness, being equipment-free, and deliverability to end-users. These features make them suitable to face the need for point-of-care (POC) diagnostics, monitoring, environmental, and quality food control applications. Our work introduces new and experienced researchers in the field to a practical guide for fibrous-based biosensors fabrication with insight into the chemical and physical interaction of fibrous materials with a wide variety of materials for functionalization and biofunctionalization purposes. This research also allows readers to compare classical and novel materials, fabrication techniques, immobilization methods, signal transduction, and readout. Moreover, the examined classical and alternative mathematical models provide a powerful tool for bioanalytical device designing for the multiple steps required in biosensing platforms. Finally, we aimed this research to comprise the current state of PADs and EFBs research and their future direction to offer the reader a full insight on this topic.

Oxidase-loaded hydrogels for versatile potentiometric metabolite sensing

Continuous monitoring of biological metabolites of interest necessitates sensors that are robust, versatile, miniaturizable, and reliable. Electrochemical biosensors have dominated the field of biosensors for decades due to their robust and inexpensive nature. Classically, these sensors use amperometric and voltammetric methods as the sensing modality. One of the greatest limitations with these methods is the dependence of the signal (current, i) on the electrode size, which can change with respect to time due to fouling. Here, we present open circuit potential, an electrochemical technique that is relatively insensitive to electrode size, as a reliable alternative to amperometric and voltammetric techniques for monitoring metabolites of interest. The sensor operates by trapping an oxidase enzyme in a chitosan hydrogel. The oxidase enzyme is required for metabolite specificity. When the oxidase enzyme meets its substrate, oxygen is consumed, and hydrogen peroxide is generated. Hydrogen peroxide generation dominates a half reaction at the platinum surface, resulting in a change in potential. Using the above criteria, we demonstrate the efficacy, long lifetime, sensitivity, and ease of fabrication of glucose sensors, and miniaturize the sensors from macro- to microelectrodes. Additionally, we demonstrate the ease with which this platform can be extended to detect other analytes in the form of a galactose sensor. Our results set a foundation for the generalized use of potentiometric sensors for a broad range of metabolites and applications.

DNA electrochemical biosensor for detection of Alicyclobacillus acidoterrestris utilizing Hoechst 33258 as indicator

Alicyclobacillus acidoterrestris is an acidophilic and thermophilic bacterium present in the soil, often associated with the spoilage of acidic juices, such as orange juice. Their spores resist pasteurization and, when reactivated, modify the organoleptic properties of the juice, making it unsuitable for consumption, due mainly to production of guaiacol. Biosensors are detection devices that respond quickly and are easy to handle, with great potential for use in the juice production chain. In this context, this work reports an electrochemical genosensor for detection of A. acidoterrestris, based on a graphite electrode modified with electrochemically reduced graphene oxide, a polymer derived from 3-hydroxybenzoic acid and a specific DNA probe sequence complementary with the genomic DNA of A. acidoterrestris. Detection of the target was performed by monitoring the oxidation peak of the Hoechst 33258, a common DNA stainer. The genosensor detection limit was 12 ng mL^-1 and it kept 77% of response after ten weeks, and a test showed that orange juice does not interfere with bacteria lysate detection. This biosensor is the first platform for electrochemical detection of the genomic DNA of A. acidoterrestris in the literature, and the first to use Hoechst 33258 as indicator with whole genomic DNA molecules.

An All-in-One Solid State Thin-Layer Potentiometric Sensor and Biosensor Based on Three-Dimensional Origami Paper Microfluidics

An origami three-dimensional design of a paper-based potentiometric sensor is described. In its simplest form, this electrochemical paper-based analytical device (ePAD) is made from three small parts of the paper. Paper layers are folded on each other for the integration of a solid contact ion selective electrode (here a carbon-paste composite electrode) and a solid-state pseudo-reference electrode (here writing pencil 6B on the paper), which are in contact with a hydrophilic channel fabricated on the middle part (third part) of the paper. In this case, the pseudo-reference and working electrodes are connected to the two sides of the hydrophilic channel and hence the distance between them is as low as the width of paper. The unmodified carbon paste electrode (UCPE) and modification with the crown ether benzo15-crown-5 (B15C5) represented a very high sensitivity to Cu (II) and Cd2+ ions, respectively. The sensor responded to H2O2 using MnO2-doped carbon paste electrode (CPE). Furthermore, a biosensor was achieved by the addition of glucose oxidase to the MnO2-doped CPE and hence made it selective to glucose with ultra-sensitivity. In addition to very high sensitivity, our device benefits from consuming a very low volume of sample (10.0 µL) and automatic sampling without need for sampling devices.

Developing an integrated microfluidic and miniaturized electrochemical biosensor for point of care determination of glucose in human plasma samples

A cost-effective, point of care (POC) device based on highly oriented CNT arrays was developed as an electrochemical assay for real-time and sensitive detection of glucose in complex samples. A low-cost, microcontroller-based potentiostat consisting of Arduino Due and LMP9100-EVM was developed to perform electrochemical measurements such as cyclic voltammetry (CV) and amperometry. A syringe pump based on open-source electronics was designed to direct the flow through a microfluidic chip. Vertically aligned carbon nanotube (VACNT) sensor arrays, in combination with the miniature potentiostat and the syringe pumps, were utilized as a POC device for the rapid and accurate detection of glucose. The structure and morphology of samples were characterized by field emission scanning electron microscopy (FESEM) and attenuated total reflectance Fourier transform infrared spectrometry (ATR-FTIR). CV as well as electrochemical impedance spectroscopy (EIS) was performed to investigate the electrochemical behavior of the electrode with respect to different diffusion regimes. The mediator-less biosensor had a limit of detection of 23 μM and sensitivity of 1462 μA mM-1 cm-2 and 1050 μA mM-1 cm-2 at the linear range of 1.2-7.8 mM and 7.8-11.2 mM, respectively. The presence of other biological compounds such as uric acid (UA) and ascorbic acid (AA) did not interfere with the detection of glucose. Finally, the designed POC device was successfully applied for the determination of glucose in human blood plasma samples.

Paper-Based Electrochemical Sensors Using Paper as a Scaffold to Create Porous Carbon Nanotube Electrodes

Paper-based sensors and assays have evolved rapidly due to the conversion of paper-based microfluidics, functional paper coatings, and new electrical and optical readout techniques. Nanomaterials have gained substantial attraction as key components in paper-based sensors, as they can be coated or printed relatively easily on paper to locally control the device functionality. Here, we report a new combination of methods to fabricate carbon nanotube-based (CNT) electrodes for paper-based electrochemical sensors using a combination of laser cutting, drop-casting, and origami. We applied this process to a range of filter papers with different porosities and used their differences in three-dimensional cellulose networks to study the influence of the cellulose scaffold on the final CNT network and the resulting electrochemical detection of glucose. We found that an optimal porosity exists, which balances the benefits of surface enhancement and electrical connectivity within the cellulose scaffold of the paper-based device and demonstrates a cost-effective process for the fabrication of device arrays.

Pd nanoparticle-decorated graphitic C3N4 nanosheets with bifunctional peroxidase mimicking and ON–OFF fluorescence enable naked-eye and fluorescent dual-readout sensing of glucose

Pd nanoparticle-decorated graphitic C₃N₄ nanosheets with peroxidase mimicking and ON–OFF fluorescence for the naked-eye and fluorescent dual-readout detection of glucose.

A newly designed anthracene and isoindigo based polymer: synthesis, electrochemical characterization and biosensor applications

A novel sensing platform based on a newly designed and synthesized polymer, poly[(E)-6-methyl-6′-(10-methylanthracen-9-yl)-1,1′-diundecyl-[3,3′-biindolinylidene]-2,2′-dione] (namely PIIDAnth), was fabricated and explored as a glucose amperometric biosensor.

Reduced graphene oxide doping with nanometer-sized ferrocene moieties - New active material for glucose redox sensors

Herein, we present that the reduced graphene oxide (rGO) doped with nanometer-sized ferrocene moieties is a new, excellent active material for redox sensors. Two distinct approaches were utilized for the modification of rGO. The first method was based on the covalent decoration of rGO via the addition of azomethine ylide generated from the ferrocenecarboxaldehyde oxime. The second approach utilized the adsorption of 1,1'-ferrocenedicarboxylic acid on the graphene sheet via the π-π stacking. The morphology of the synthesized graphene materials was studied by application of microscopic techniques, whereas the Raman data allowed the characteristics of the tested materials in terms of their structural properties. The tested graphene materials doped with ferrocene moieties were used as a bioactive platform for glucose oxidase (GOx) immobilization. The enzyme was immobilized onto the rGO materials in two ways: (i) using a crosslinking agent - glutaraldehyde (GA) and (ii) by formation of the amide bonds between carboxylic groups of rGO-Fc(COOH)₂ and amine groups from enzyme. Ferrocene moieties present at the graphene surface play the role of mediator in the electron transfer between the redox center of GOx and the electrode surface. The functionality of the constructed biosensors has been tested on real samples. The results of the recovery rates showed a satisfying degree of accuracy toward determination of glucose concentration. Examination of the potential interfering species has demonstrated favorable sensitivity and selectivity of the designed biosensor for the detection of glucose.