Enhanced Colorimetric Signal for Accurate Signal Detection in Paper-Based Biosensors

Development of Functional Biointerface Using Mixed Zwitterionic Silatranes

Strategies to design multifunctional interfaces for biosensors have been extensively investigated to acquire optimal sensitivity, specificity, and accuracy. However, heterogeneous ingredients in clinical samples inevitably generate background signals, exposing challenges in biosensor performance. Polymer coating has been recognized as a crucial method to functionalize biointerfaces by providing tailored properties that are essential for interacting with biological systems. Herein, we introduce for the first time two oligomeric silatranes, MPS-MPCn and MPS-PEGMACOOHm, which were copolymerized from mercaptopropylsilatrane (MPS) with either zwitterionic monomer 2-methacryloyloxyethyl phosphorylcholine (MPC) or carboxylated poly(ethylene glycol) methacrylate (PEGMACOOH) through thiol-ene polymerization. These oligomeric silatranes were prepared individually and in combinations in acidic and nonacid solvents for deposition on silicon wafers. Afterward, coating properties, including wettability, thickness, and elemental composition, were characterized by contact angle meter, ellipsometer, and X-ray photoelectron spectroscopy (XPS), respectively. Importantly, MPS-MPCn polymers were found to form thin films with high hydrophilicity and superior fouling repulsion to bacteria and protein, while mixed coating involving 70% MPS-PEGMACOOH2.5 and 30% MPS-MPC2.5 exhibited thinnest coating with best wettability among COOH-terminated coatings. Furthermore, the functional COOH group in the coated surfaces was exploited for postmodification with biological molecules via intermediated N-hydroxysuccinimide (NHS) ester group by amine coupling chemistry. Once again, the combination of 70% MPS-PEGMACOOH2.5 and 30% MPS-MPC2.5 provided an ultimate reduction in nonspecific adsorption (NSA) and established a finest signal discrimination through enzyme-linked immunosorbent assay. Consequently, these novel mixed oligomeric silatranes offer a promising approach for the construction of biosensor interfaces with dual functions in both nonspecific binding prevention and conjugation of biomolecules.

Piezoelectric PVDF and its copolymers in biomedicine: innovations and applications

In recent years, poly(vinylidene fluoride) (PVDF) has emerged as a versatile polymer with a wide range of applications across various fields. PVDF's piezosensitivity, versatility, crystalline structure, and tunable parameters have established it as a highly sought-after material. Furthermore, PVDF and its copolymers exhibit excellent processability and chemical resistance to a diverse array of substances. Of particular significance is its remarkable structural stability in physiological media, which highlights its potential for use in the development of biomedical products. This review offers a comprehensive overview of the latest advancements in PVDF-based biomedical systems. It examines the fabrication of stimulus-responsive delivery systems, bioelectric therapy devices, and tissue-regenerating scaffolds, all of which harness the piezosensitivity of PVDF. Moreover, the potential of PVDF in the fabrication of both invasive and non-invasive diagnostic tools is investigated, with particular emphasis on its flexibility, transparency, and piezoelectric efficiency. The material's high biocompatibility and physiological stability are of paramount importance in the development of implantable sensors for long-term health monitoring, which is crucial for the management of chronic diseases and postoperative care. Additionally, we discuss a novel approach to photoacoustic microscopy that employs a PVDF sensor, thereby eliminating the necessity for external contrast agents. This technique provides a new avenue for non-invasive imaging in biomedical applications. Finally, we explore the challenges and prospects for the development of PVDF-based systems for a range of biomedical applications. This review is distinctive in comparison to other reviews on PVDF due to its concentrated examination of biomedical applications, including pioneering imaging techniques, long-term health monitoring, and a detailed account of advancements in the field. Collectively, these elements illustrate the potential of PVDF to markedly influence biomedical engineering and patient care, distinguishing it from existing literature. By leveraging the distinctive attributes of PVDF and its copolymers, researchers can continue to advance the frontiers of biomedical engineering, with the potential to transform patient care and treatment outcomes.

A review on solution- and vapor-responsive sensors for the detection of phthalates

Phthalic acid esters, largely referred to as phthalates, are today acknowledged as important pollutants used in the manufacture of polyvinyl chloride (PVC)-based plastics, whose use extends to almost every aspect of modern life. The risk of exposure to phthalates is particularly relevant as high concentrations are regularly found in drinking water, food-contact materials and medical devices, motivating an immense body of research devoted to methods for their detection in liquid samples. Conversely, phthalate vapors have only recently been acknowledged as potentially important atmospheric pollutants and as early fire indicators; additionally, deposition of these vapors can pose significant problems to the proper functioning of spacecraft and diverse on-board devices, leading to major space agencies recognizing the need of developing vapor-responsive phthalate sensors. In this manuscript we present a literature survey on solution- and vapor-responsive sensors and analytical assays for the detection of phthalates, providing a detailed analysis of a vast array of analytical data to offer a clear idea on the analytical performance (limits of detection and quantification, linear range) and advantages provided by each class of sensor covered in this review (electrochemical, optical and vapor-responsive) in the context of their potential real-life applications; the manuscript also gives detailed fundamental information on the various physicochemical responses exploited by these sensors and assays that could potentially be harnessed by new researchers entering the field.

The colors of peroxygenase activity: Colorimetric high-throughput screening assays for directed evolution

Fungal unspecific peroxygenases (UPOs) are arising as versatile biocatalysts for C-H oxyfunctionalization reactions. In recent years, several directed evolution studies have been conducted to design improved UPO variants. An essential part of this protein engineering strategy is the design of reliable colorimetric high-throughput screening (HTS) assays for mutant library exploration. Here, we present a palette of 12 colorimetric HTS assays along with their step-by-step protocols, which have been validated for directed UPO evolution campaigns. This array of colorimetric assays will pave the way for the discovery and design of new UPO variants.

Smart and Multifunctional Materials Based on Electroactive Poly(vinylidene fluoride): Recent Advances and Opportunities in Sensors, Actuators, Energy, Environmental, and Biomedical Applications

From scientific and technological points of view, poly(vinylidene fluoride), PVDF, is one of the most exciting polymers due to its overall physicochemical characteristics. This polymer can crystalize into five crystalline phases and can be processed in the form of films, fibers, membranes, and specific microstructures, being the physical properties controllable over a wide range through appropriate chemical modifications. Moreover, PVDF-based materials are characterized by excellent chemical, mechanical, thermal, and radiation resistance, and for their outstanding electroactive properties, including high dielectric, piezoelectric, pyroelectric, and ferroelectric response, being the best among polymer systems and thus noteworthy for an increasing number of technologies. This review summarizes and critically discusses the latest advances in PVDF and its copolymers, composites, and blends, including their main characteristics and processability, together with their tailorability and implementation in areas including sensors, actuators, energy harvesting and storage devices, environmental membranes, microfluidic, tissue engineering, and antimicrobial applications. The main conclusions, challenges and future trends concerning materials and application areas are also presented.

Simple assay for quantifying xanthine oxidase activity

This paper reports a sensitive method for assaying xanthine oxidase (XO) enzyme activity. XO produces hydrogen peroxide (H₂O₂) and superoxide anion radicals (O₂^•-), promoting the development of oxidative stress-related diseases, and is inhibited by various plant extracts. XO activity is quantified by incubating enzyme samples with an appropriate xanthine concentration as the substrate. The proposed method requires XO activity to be quantified based on H₂O₂ generation using a 3,3',5,5'-tetramethylbenzidine (TMB)-H₂O₂ system catalyzed by cupric ions. After a 30-minute incubation at 37 °C, sufficient cupric ion and TMB amounts are added. The assay produces optical signals that can be visually recognized or detected with a UV-visible spectrometer. A direct correlation was found between XO activity and the absorbance at 450 nm of the resulting di-imine (dication) yellow product. The proposed method uses sodium azide to prevent catalase enzyme interference. The new assay's function was confirmed using the TMB-XO assay and a Bland-Altman plot. The resulting correlation coefficient was 0.9976. The innovative assay was relatively precise and comparable to the comparison protocols. In conclusion, the presented method is very efficient at measuring XO activity.

Signal amplification strategies in biosensing of extracellular vesicles (EVs)

Extracellular vesicles (EVs) are membrane-enclosed vesicles secreted from mammalian cells. EVs act as multicomponent delivery vehicles to carry a wide variety of biological molecular information and participate in intercellular communications. Since elevated levels of EVs are associated with some pathological states such as inflammatory diseases and cancers, probing circulating EVs holds a great potential for early diagnostics. To this end, several detection methods have been developed in which biosensors have attracted great attentions in identification of EVs due to their simple instrumentation, versatile design and portability for point-of-care applications. The concentrations of EVs in bodily fluids are extremely low (i.e. 1-100 per μl) at early stages of a disease, which necessitates the use of signal amplification strategies for EVs detection. In this way, this review presents and discusses various amplification strategies for EVs biosensors based on detection modalities including surface plasmon resonance (SPR), calorimetry, fluorescence, electrochemical and electrochemiluminescence (ECL). In addition, microfluidic systems employed for signal amplification are reviewed and discussed in terms of their design and integration with the detection methods.

Paper-based analytical devices for point-of-need applications

Paper-based analytical devices (PADs) are powerful platforms for point-of-need testing since they are inexpensive devices fabricated in different shapes and miniaturized sizes, ensuring better portability. Additionally, the readout and detection systems can be accomplished with portable devices, allying with the features of both systems. These devices have been introduced as promising analytical platforms to meet critical demands involving rapid, reliable, and simple testing. They have been applied to monitor species related to environmental, health, and food issues. Herein, an outline of chronological events involving PADs is first reported. This work also introduces insights into fundamental parameters to engineer new analytical platforms, including the paper type and device operation. The discussions involve the main analytical techniques used as detection systems, such as colorimetry, fluorescence, and electrochemistry. It also showed recent advances involving PADs, especially combining optical and electrochemical detection into a single device. Dual/combined detection systems can overcome individual barriers of the analytical techniques, making possible simultaneous determinations, or enhancing the devices' sensitivity and/or selectivity. In addition, this review reports on distance-based detection, which is also considered a trend in analytical chemistry. Distance-based detection offers instrument-free analyses and avoids user interpretation errors, which are outstanding features for analyses at the point of need, especially for resource-limited regions. Finally, this review provides a critical overview of the practical specifications of the recent analytical platforms involving PADs, demonstrating their challenges. Therefore, this work can be a highly useful reference for new research and innovation.

Decorating Zirconium on Graphene Oxide to Design a Multifunctional Nanozyme for Eco-Friendly Detection of Hydrogen Peroxide

Peroxidase enzymes are crucial in analytical chemistry owing to significant peroxide analytes and their key role in hydrogen peroxide (H2O2) detection. Therefore, exploiting appropriate catalysts for the peroxidase like reactions has become crucial for achieving desired analytical performance. Zirconium (Zr) has attracted growing interest, as a safe and stable potential eco-friendly catalyst for various organic transformations that address increasing environmental challenges. Hence, aiming at fast, sensitive and selective optical detection of H2O2, a colorimetric platform is presented here, based on the excellent peroxidase enzyme-like activity of Zr decorated on graphene oxide (GO). The synergistic effect achieved due to intimate contact between an enzyme like Zr and the high surface area 0f GO ensures efficient electron transfer that increases the chemical and catalytic activity of the composite and advances the decomposition of H2O2 into hydroxyl radicals. The designed probe, thus, efficiently catalyzes the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB), via hydroxyl radicals, thereby transforming the colorless TMB into blue oxidized TMB within 2 min. The catalytic mechanism of the Zr-GO enzyme mimic is proposed herein and verified using a fluorescent probe terephthalic acid (TA) and other scavenger experiments. The multifunctional optical probe allows sensitive and highly selective recognition of H2O2 in a linear range from 100 to 1000 µM with a low detection limit of 0.57 µM. Essentially, the direct accessibility of Zr prevents having to use the complicated preparation and purification procedures mostly practiced for conventional biozymes and nanozymes. The devised method offers several gains, including being green and an inexpensive catalyst, having lower LOD, being fast, cost-effective and sensitive, and having selective work-up procedures.

Portable biosensors for rapid on-site determination of cannabinoids in cannabis, a review

Recent studies highlight the therapeutic virtues of cannabidiol (CBD). Furthermore, due to their molecular enriched profiles, cannabis inflorescences are biologically superior to a single cannabinoid for the treatment of various health conditions. Thus, there is flourishing demand for Cannabis sativa varieties containing high levels of CBD. Additionally, legal regulations around the world restrict the cultivation and consumption of tetrahydrocannabinol (THC)-rich cannabis plants for their psychotropic effects. Therefore, the use of cannabis varieties that are high in CBD is permitted as long as their THC content does not exceed a low threshold of 0.3%-0.5%, depending on the jurisdiction. These chemovars are legally termed 'hemp'. This controlled cannabinoid requirement highlights the need to detect low levels of THC, already in the field. In this review, cannabis profiling and the existing methods used for the detection of cannabinoids are firstly evaluated. Then, selected valuable biosensor technologies are discussed, which suggest portable, rapid, sensitive, reproducible, and reliable methods for on-site identification of cannabinoids levels, mainly THC. Recent cutting-edge techniques of promising potential usage for both cannabis and hemp analysis are identified, as part of the future cultivation and agricultural improvement of this crop.

Progress and Challenges of Point-of-Need Photonic Biosensors for the Diagnosis of COVID-19 Infections and Immunity

The new coronavirus disease, COVID-19, caused by SARS-CoV-2, continues to affect the world and after more than two years of the pandemic, approximately half a billion people are reported to have been infected. Due to its high contagiousness, our life has changed dramatically, with consequences that remain to be seen. To prevent the transmission of the virus, it is crucial to diagnose COVID-19 accurately, such that the infected cases can be rapidly identified and managed. Currently, the gold standard of testing is polymerase chain reaction (PCR), which provides the highest accuracy. However, the reliance on centralized rapid testing modalities throughout the COVID-19 pandemic has made access to timely diagnosis inconsistent and inefficient. Recent advancements in photonic biosensors with respect to cost-effectiveness, analytical performance, and portability have shown the potential for such platforms to enable the delivery of preventative and diagnostic care beyond clinics and into point-of-need (PON) settings. Herein, we review photonic technologies that have become commercially relevant throughout the COVID-19 pandemic, as well as emerging research in the field of photonic biosensors, shedding light on prospective technologies for responding to future health outbreaks. Therefore, in this article, we provide a review of recent progress and challenges of photonic biosensors that are developed for the testing of COVID-19, consisting of their working fundamentals and implementation for COVID-19 testing in practice with emphasis on the challenges that are faced in different development stages towards commercialization. In addition, we also present the characteristics of a biosensor both from technical and clinical perspectives. We present an estimate of the impact of testing on disease burden (in terms of Disability-Adjusted Life Years (DALYs), Quality Adjusted Life Years (QALYs), and Quality-Adjusted Life Days (QALDs)) and how improvements in cost can lower the economic impact and lead to reduced or averted DALYs. While COVID19 is the main focus of these technologies, similar concepts and approaches can be used and developed for future outbreaks of other infectious diseases.

Colorimetric paper-based sarcosine assay with improved sensitivity

This manuscript reports on a simple paper-based bienzymatic colorimetric assay for sarcosine as an important urinary biomarker of prostate cancer. All required assay reagents are pre-deposited on hydrophilic filter paper spots surrounded by a hydrophobic barrier. Sarcosine in the sample solution is selectively oxidized in the presence of sarcosine oxidase (SOx), resulting in the formation of hydrogen peroxide, which is subsequently detected through the horseradish peroxidase (HRP)-catalyzed conversion of the colorless indicator 3,3',5,5'-tetramethylbenzidine (TMB) into its blue-colored oxidation product. By the modification of the paper with positively charged poly(allylamine hydrochloride) (PAH), a linear response to sarcosine between 0 and 10 μM and a significant lowering of the limit of detection (LOD) (0.6 μM) compared to the unmodified paper substrate (12.6 μM) has been achieved. The improvement of the LOD was attributed to the fact that the presence of the polymer limits the enzyme-driven colorimetric reaction to the surface of the paper substrate, resulting in stronger color development. In experiments in artificial urine matrix, the bicarbonate anion was identified as an inhibitor of the colorimetric reaction. This inhibition was successfully eliminated through on-device sample pH adjustments with pH-buffer components pre-deposited onto assay devices. The LOD for sarcosine achieved in artificial urine matrix (2.5 μM) is below the 5 μM threshold value for this urinary biomarker required for diagnostic purposes. Finally, good selectivity over all 20 natural amino acids and satisfactory long-term storage stability of reagent-modified paper substrates at - 20 °C for a period of 50 days were confirmed.

Development and application of a SARS-CoV-2 colorimetric biosensor based on the peroxidase-mimic activity of γ-Fe2O3 nanoparticles

A practical colorimetric assay was developed for the detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). For this purpose, magnetic γ Fe₂O₃ nanoparticles were synthesized and used as a peroxidase-like mimic activity molecule. In the presence of γ Fe₂O₃ nanoparticles, the color change of H₂O₂ included 3,3',5,5'-tetramethylbenzidine was monitored at the wavelength of 654 nm when spike protein interacted with angiotensin-converting enzyme 2 receptor. This oxidation-reduction reaction was examined both spectroscopically and by using electrochemical techniques. The experimental parameters were optimized and the analytical characteristics investigated. The developed assay was applied to real SARS-CoV-2 samples, and very good results that were in accordance with the real time polymerase chain reaction were obtained.

Embedded Immunodetection System for Fecal Occult Blood

In this paper, a rapid test system with high sensitivity, linearity, and stability is presented for fecal occult blood (FOB) detection. The coloration results of the immune response are used as the basis for the determination of the detection target in combination with an immunochromatographic strip. The rapid test system can be used to detect and calculate the concentration of the sample, so detection of the immune coloration response is more accurate in a quantitative analysis. The system is composed of both hardware and software. The programs used for the analysis and programmed by Python include the main program, polarization calibration, QR Code decoding, Bluetooth transmission, and image processing. After verification of each part of the system, it was found that the rapid test system successfully detects from 0 ng/mL to 400 ng/mL of FOB with coefficients of variation (CV) below 3.7% and 1000 ng/mL with a CV only at 7.41%.

Biological characteristics and biomarkers of novel SARS-CoV-2 facilitated rapid development and implementation of diagnostic tools and surveillance measures

Existing coronavirus named as a severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has speeded its spread across the globe immediately after emergence in China, Wuhan region, at the end of the year 2019. Different techniques, including genome sequencing, structural feature classification by electron microscopy, and chest imaging using computed tomography, are primarily used to diagnose and screen SARS-CoV-2 suspected individuals. Determination of the viral structure, surface proteins, and genome sequence has provided a design blueprint for the diagnostic investigations of novel SARS-CoV-2 virus and rapidly emerging diagnostic technologies, vaccine trials, and cell-entry-inhibiting drugs. Here, we describe recent understandings on the spike glycoprotein (S protein), receptor-binding domain (RBD), and angiotensin-converting enzyme 2 (ACE2) and their receptor complex. This report also aims to review recently established diagnostic technologies and developments in surveillance measures for SARS-CoV-2 as well as the characteristics and performance of emerging techniques. Smartphone apps for contact tracing can help nations to conduct surveillance measures before a vaccine and effective medicines become available. We also describe promising point-of-care (POC) diagnostic technologies that are under consideration by researchers for advancement beyond the proof-of-concept stage. Developing novel diagnostic techniques needs to be facilitated to establish automatic systems, without any personal involvement or arrangement to curb an existing SARS-CoV-2 epidemic crisis, and could also be appropriate for avoiding the emergence of a future epidemic crisis.

Immunoassay detection of tumor-associated autoantibodies using protein G bioconjugated to nanomagnet-silica decorated with Au@Pd nanoparticles

A colorimetric immunosensor was developed for the detection of tumor-associated anti-p53 autoantibodies (anti-p53aAbs). The immunosensor platform was prepared by immobilizing human-protein (p53Ag) onto a high binding 96-well plate. The immunoassay was based on the immunometric sandwich protocol, and protein G functionalized nanomagnet-silica nanoparticles decorated with Au@Pd (Fe₃O₄@SiO₂-NH₂-Au@Pd_0.30NPs-protG) was used as the detection nanobioprobe. The Fe₃O₄@SiO₂-NH₂-Au@Pd_0.30NPs-protG exhibited a high binding affinity for the captured anti-p53aAbs and high catalytic performance towards the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB). The oxidation of TMB resulted in significant color change and a UV-vis absorption signal. The detection was achieved by measuring the changes in UV-Vis absorption as the concentrations of anti-p53aAbs changed. The apparent binding affinity (K_D) between the p53aAbs and Fe₃O₄@SiO₂-NH₂-Au@Pd_0.30NPs-protG was 35.2 ng mL^-1. The plot of change in the absorption intensity against the logarithm of anti-p53aAbs was linear within 1.0-500.0 ng mL^-1 with a correlation coefficient (R²) of 0.98. The detection limit (LoD) using 3σ was calculated to be 15 pg mL^-1, which is lower than the conventional HRP-label based colorimetric immunoassay. The real sample detection was investigated using the serum recovery method. The recovery of the anti-p53aAbs ranges from 98.5% to 105.7%, demonstrating its potential for practical applications.

Paper-based colorimetric detection of pathogenic bacteria in food through magnetic separation and enzyme-mediated signal amplification on paper disc

Herein, we report a colorimetric sensing system for the detection of highly virulent bacteria, Escherichiacoli O157:H7, in sausage by utilizing magnetic separation and enzyme-mediated signal amplification on paper disc. For magnetic separation, Poly-l-lysine coated starch magnetic particles (PLL@SMPs) were synthesized and utilized for the separation and concentration of the bacteria in sample suspension. Horseradish peroxidase-conjugated antibody (HRP-Antibody) and 3,3',5,5'- tetramethylbenzidine (TMB) were employed for the specific signal amplification in the presence of target bacteria. The synthesized PLL@SMPs showed an excellent capture efficiency (>90%) for the pathogenic bacteria in large volume sample suspension. The intrinsic problems associated with the non-specific binding of sensing components that lead to the high background signal and low sensitivity in colorimetric detection was successfully resolved by employing hyaluronic acid as a blocking agent. The effective separation and concentration of target bacteria by PLL@SMPs and target-specific signal amplification with exceptionally high signal to noise ratio enabled the detection of target bacteria with a detection limit in the single digit regime. The sensing system proposed in this study was successfully used for the detection of the target pathogenic bacteria, E. coli O157:H7, in sausage sample with the limit of detection (LOD) as low as 30.8 CFU/mL with 95% probability. The simple nature of paper-based detection system with a great sensitivity and specificity would provide an effective means of evaluating the safety of food and environmental samples.

Blood-Based Biomarkers Are Associated with Different Ischemic Stroke Mechanisms and Enable Rapid Classification between Cardioembolic and Atherosclerosis Etiologies

Stroke is a top leading cause of death, which occurs due to interference in the blood flow of the brain. Ischemic stroke (blockage) accounts for most cases (87%) and is further subtyped into cardioembolic, atherosclerosis, lacunar, other causes, and cryptogenic strokes. The main value of subtyping ischemic stroke patients is for a better therapeutic decision-making process. The current classification methods are complex and time-consuming (hours to days). Specific blood-based biomarker measurements have promising potential to improve ischemic stroke mechanism classification. Over the past decades, the hypothesis that different blood-based biomarkers are associated with different ischemic stroke mechanisms is increasingly investigated. This review presents the recent studies that investigated blood-based biomarker characteristics differentiation between ischemic stroke mechanisms. Different blood-based biomarkers are specifically discussed (b-type natriuretic peptide, d-dimer, c-reactive protein, tumor necrosis factor-α, interleukin-6, interleukin-1β, neutrophil-lymphocyte ratio, total cholesterol, triglycerides, low-density lipoprotein, high-density lipoprotein and apolipoprotein A), as well as the different cut-off values that may be useful in specific classifications for cardioembolic and atherosclerosis etiologies. Lastly, the structure of a point-of-care biosensor device is presented, as a measuring tool on-site. The information presented in this review will hopefully contribute to the major efforts to improve the care for stroke patients.