Aptamer duo-based portable electrochemical biosensors for early diagnosis of periodontal disease

Portable multimodal platform with carbon nano-onions as colorimetric and fluorescent signal output for trypsin detection

Multimodal biosensors with independent signaling pathways can self-calibrate and improve the reliability of disease biomarker detection. Herein, a colorimetric-fluorescent dual-mode paper-based biosensor with PAN/Fe(III)-CNOs (FPCs) as core components has been developed, which information is recognized by smartphone and naked eye. Using 1-(2-pyridylazo)-2-naphthol (PAN) as a mediator, Fe(III) is enriched on the surface of carbon nano-onions (CNOs), endowing FPCs with excellent mimetic enzyme activity and photothermal conversion ability, which allows it to output amplified colorimetric signals under laser irradiation. In addition, the complexation of PAN with Fe(III) broadens its absorption spectrum, which makes FPCs more suitable to be energy acceptors to quench fluorescence of polymer dots (Pdots), resulting in the changes of output fluorescent signal. Based on the above design, a portable colorimetric-fluorescent dual-mode biosensor is proposed for trypsin detection with Pdots as fluorescence sources and FPCs as fluorescence quenchers and nanoenzymes. This work provides a convenient way for constructing portable visual multimodal biosensors, which is expected to applied in various disease diagnosis.

Aptamer-based sensors for fluid biopsies of protein disease markers

Fluid biopsy technology, characterized by its minimally invasive nature, speed, and continuity, has become a rapidly advancing and widely applied real-time diagnostic technique. Among various biomarkers, proteins represent the most abundant class of disease indicators. The sensitive and accurate detection of protein markers in bodily fluids is significantly influenced by the control exerted by recognition ligands. Aptamers, which are structurally dynamic functional oligonucleotides, exhibit high affinity, specific recognition of targets, and notable characteristics of high editability and modularity. These features make aptamer universal "recognition-capture" components, contribute to a significant leap in their applications within the biosensor domain. In this context, we provide a comprehensive review of the extensive application of aptamer-based biosensors in fluid biopsy. We systematically compile the characteristics and construction strategies of aptamer-based biosensors tailored for fluid biopsy, including aptamer sequences, affinity (KD), fluid background, sensing technologies, sensor construction strategies, incubation time, detection performance, and influencing factors. Furthermore, a comparative analysis of their advantages and disadvantages was conducted. In conclusion, we delineate and deliberate on prospective research trajectories and challenges that lie ahead in the realm of aptamer-based biosensors for fluid biopsy.

Point-of-care diagnostic devices for periodontitis - current trends and urgent need

Point of care (POC) diagnostic devices provide a method for rapid accurate identification of disease through analysis of biologically relevant substances. This review focuses on the utility of POC testing for early detection of periodontitis, a critical factor in treating the disease. Accessing the oral cavity for biological sampling is less invasive when compared to other internal test sites, and oral fluids contain biomarkers indicative of periodontitis. The ease of access makes the mouth an excellent target location for the development of POC devices. In this review, accepted standards in industry by which these devices must adhere, provided by the World Health Organization such as REASSURED and CLIA, are discussed. An overview is provided for many periodontal biomarkers currently being investigated as a means of predicting periodontal disease and its progression. POC devices currently being investigated for the identification and monitoring of periodontal disease such as paper-based and lab-on-a-chip based devices are outlined. Limitations of current POC devices on the market are provided and future directions in leveraging biomarkers as an adjunctive method for oral diagnosis along with AI-based analysis systems are discussed. Here, we present the ESSENCE sensor platform, which combines a porous non-planar electrode with enhanced shear flow to achieve unprecedented sensitivity and selectivity. The combination of the ESENCE chip with an automated platform allows us to meet the WHO's ASSURED criteria. This platform promises to be an exciting POC candidate for early detection of periodontitis.

Periodontal disease and emerging point-of-care technologies for its diagnosis

Periodontal disease (PD), a chronic inflammatory disorder that damages the tooth and its supporting components, is a common global oral health problem. Understanding the intricacies of these disorders, from gingivitis to severe PD, is critical for efficient treatment, diagnosis, and prevention in dental care. Periodontal biosensors and biomarkers are critical in improving oral health diagnostic skills. Clinicians may accomplish early identification, tailored therapy, and efficient tracking of periodontal diseases by using these technologies, ushering in a new age of accurate oral healthcare. Traditional periodontitis diagnostic methods frequently rely on physical probing and visual examinations, necessitating the development of point-of-care (POC) devices. As periodontal disorders necessitate more precise and rapid diagnosis, incorporating novel innovations in biosensors and biomarkers becomes increasingly crucial. These innovations improve our capacity to diagnose, monitor, and adapt periodontal therapies, bringing in the next phase of customized and effective dental healthcare. The review discusses the characteristics and stages of PD, clinical treatment techniques, prominent biomarkers and infection-associated factors that may be employed to determine PD, biomedical sensing, and POC appliances that have been created so far to diagnose stages of PD and its progression profile, as well as predicting future developments in this field.

Realizing the clinical utility of saliva for monitoring oral diseases

In the era of personalized/precision health care, additional effort is being expended to understand the biology and molecular mechanisms of disease processes. How these mechanisms are affected by individual genetics, environmental exposures, and behavioral choices will encompass an expanding role in the future of optimally preventing and treating diseases. Considering saliva as an important biological fluid for analysis to inform oral disease detection/description continues to expand. This review provides an overview of saliva as a diagnostic fluid and the features of various biomarkers that have been reported. We emphasize the use of salivary biomarkers in periodontitis and transport the reader through extant literature, gaps in knowledge, and a structured approach toward validating and determine the utility of biomarkers in periodontitis. A summation of the findings support the likelihood that a panel of biomarkers including both host molecules and specific microorganisms will be required to most effectively identify risk for early transition to disease, ongoing disease activity, progression, and likelihood of response to standard periodontal therapy. The goals would be to develop predictive algorithms that serve as adjunctive diagnostic tools which provide the clinician and patient important information for making informed clinical decisions.

An IoT-based aptasensor biochip for the diagnosis of periodontal disease

Severe periodontitis affects nearly 1 billion individuals worldwide, highlighting the need for early diagnosis. Here, an integrated system consisting of a microfluidic chip and a portable point-of-care (POC) diagnostic device is developed using a polymethyl methacrylate (PMMA) chip fabrication and a three-dimensional printing technique, which is automatically controlled by a custom-designed smartphone application to routinely assess the presence of a specific periodontitis biomarker, odontogenic ameloblast-associated protein (ODAM). A sandwich-type fluorescence aptasensor is developed on a microfluidic chip, utilizing aptamer pair (MB@OD64 and OD35@FAM) selectively binding to target ODAM. Then this microfluidic chip is integrated into an automated Internet of Things (IoT)-based POC device, where fluorescence intensity, as a signal, from the secondary aptamer binding to ODAM in a sandwich-type binding reaction on the microfluidic chip is measured by a complementary metal oxide semiconductor (CMOS) camera with a 488 nm light-emitting diode (LED) excitation source. Obtained signals are processed by a microprocessor and visualized on a wirelessly connected smartphone application. This integrated biosensor system allows the rapid and accurate detection of ODAM within 30 min with a remarkable limit of detection (LOD) of 0.011 nM under buffer conditions. Clinical application is demonstrated by successfully distinguishing between low-risk and high-risk individuals with 100 % specificity. A strong potential in the translation of this fluorescence-based microfluidic aptasensor integrated with an IoT-based POC system is expected to be employed for non-invasive, on-site, rapid, and accurate ODAM detection, facilitating periodontitis diagnosis.

Nanoarchitectonics-based electrochemical aptasensors for highly efficient exosome detection

Exosomes, a type of extracellular vesicles, have attracted considerable attention due to their ability to provide valuable insights into the pathophysiological microenvironment of the cells from which they originate. This characteristic implicates their potential use as diagnostic disease biomarkers clinically, including cancer, infectious diseases, neurodegenerative disorders, and cardiovascular diseases. Aptasensors, which are electrochemical aptamers based biosensing devices, have emerged as a new class of powerful detection technology to conventional methods like ELISA and Western analysis, primarily because of their capability for high-performance bioanalysis. This review covers the current research landscape on the detection of exosomes utilizing nanoarchitectonics strategy for the development of electrochemical aptasensors. Strategies involving signal amplification and biofouling prevention are discussed, with an emphasis on nanoarchitectonics-based bio-interfaces, showcasing their potential to enhance sensitivity and selectivity through optimal conduction and mass transport properties. The ongoing challenges to broaden the clinical applications of these biosensors are also highlighted.

DNA conformational change embrace ultraviolet photolysis: A dual-mode sensing platform for electrochemical and fluorescent signaling

We developed a dual-mode biosensor that utilizes DNA conformational changes and ultraviolet photolysis for electrochemical (EC) and fluorescence (FL) detection. In this study, a stem-loop-structured carcinoembryonic antigen (CEA) aptamer was modified on an Au electrode, and this aptamer contained a redox-labeled methylene blue (MB), short-chain DNA with a 6-carboxylic fluorescein (FAM) and a PC linker that can be cleaved by ultraviolet light. Subsequently, CEA and CEA antibody-modified upconversion nanoparticle bioconjugates (CEA-Ab@UCNPs) were added. In the presence of CEA, Ab@UCNPs can bind CEA and push the MB which was originally close to the electrode surface, away from the electrode surface, resulting in a reduced redox current. Under irradiation with a 980 nm laser, the UCNPs emit ultraviolet light, leading to photocleavage of the PC linker and the release of FAM for FL sensing. Under optimal conditions, the EC and FL modes showed good responses to CEA within 0.01-50 ng/mL and 0.1-80 ng/mL, respectively.

Advances in Electrochemical Biosensors for the Detection of Common Oral Diseases

Limiting and preventing oral diseases remains a major challenge to the health of populations around the world, so finding ways to detect early-stage diseases (e.g., caries, periodontal disease, and oral cancer) and aiding in their prevention has always been an important clinical treatment concept. The development and application of electrochemical detection technology can provide important support for the early detection and non-invasive diagnosis of oral diseases and make up for the shortcomings of traditional diagnostic methods, which are highly sensitive, non-invasive, cost-effective, and less labor-intensive. It detects specific disease markers in body fluids through electrochemical reactions, discovers early warning signals of diseases, and realizes rapid and reliable diagnosis. This paper comprehensively summarizes the development and application of electrochemical biosensors in the detection and diagnosis of common oral diseases in terms of application platforms, sensing types, and disease detection, and discusses the challenges faced by electrochemical biosensors in the detection of oral diseases as well as the great prospects for future applications, in the hope of providing important insights for the future development of electrochemical biosensors for the early detection of oral diseases.

Highly sensitive detection of malaria biomarker through matching channel and gate capacitance of integrated organic electrochemical transistors

Organic electrochemical transistors (OECTs) possess versatile advantages for biochemical and electrophysiological applications due to electrochemical gating and ion-to-electron conversion capability. Although OECTs have been successfully applied for biochemical sensing, the effect of relative capacitance for specific sensing events is still unclear. In the present work, we design integrated interdigitated OECTs (iOECTs) with on-plane gold gate and different channel geometries for point-of-care diagnosis of malaria using aptamer as receptor. The transconductance of the iOECTs gated with micro-size gold electrodes decreased with increasing the channel thicknesses, especially for devices with large channel areas, which is inconsistent with devices gated by typical Ag/AgCl electrodes, attributing to the limited gating efficiency of the micro-size gate electrode. The capacitance of gate electrode was heavily suppressed by receptors but increased with the incubation of targets. In addition, the integrated iOECTs with thin channels exhibited superior sensitivity for malaria detection with the detection limit as low as 3.2 aM, much lower than their thick channel counterpart and other state-of-the-art biosensors. These deviations could be caused by the high relative capacitances, with respect to the gate and channel capacitance (Cg/Cch), resulting in a high gate potential drop over the organic channel and thus entirely gating on the thin channel device. These findings provide guidance to optimize the geometry of OECT devices with on-chip integrated gates and the fabrication of miniaturized OECTs for biosensing applications.

Constructing DNAzyme-driven three-dimensional DNA nanomachine-mediated paper-based photoelectrochemical device for ultrasensitive detection of miR-486-5p

As a unique class of dynamic nanostructures, biomimetic DNA walking machines that exhibit geometrical complexity and nanometre precision have gained great success in photoelectrochemical (PEC) bioanalysis. Despite certain achievements, the slow reaction kinetics and low processivity severely restrict the amplification efficiency of the DNA walker-mediated biosensors. Herein, by taking advantage of efficient DNA rolling machines, a three-dimensional (3D) DNA nanomachine-mediated paper-based PEC device for speedy ultrasensitive detection of miR-486-5p was successfully constructed. To achieve it, a novel In2S3/SnS2 sensitized heterojunction was firstly in-situ grown on the Au-modified paper fibers and implemented as the photoanode with effective separation of photogenerated carriers to achieve an enhanced initial photocurrent. Subsequently, the copper hexacyanoferrate(II)-modified CuO nanosphere was introduced as a multifunctional signal regulator via the competitive capture of electron donors and photon energy with the photoelectric layer for efficiently quenching the PEC signal. With the introduction of targets, the DNAzyme-driven DNA nanomachine with editable motion modes was gradually activated and it could continuously cleave the tracks DNA labeled quenching probes, finally achieving the recovery of PEC signal. As a proof of concept, the elaborated paper-based PEC device presented a wide linear range from 0.1 fM to 100 pM and a detection limit of 35 aM for miR-486-5p bioassay. This work provides an innovative insight to the exploitation of DNA nanobiotechnology and nucleic acid signal amplification strategy.

Sensitive dual-mode sensing platform for Amyloid β detection: Combining dual Z-scheme heterojunction enhanced photoelectrochemistry analysis and dual-wavelength ratiometric electrochemiluminescence strategy

As a tumor biomarker, the accumulation of amyloid β oligomers (Aβo) in the brain has been suggested as a key feature in the pathogenesis and progression of Alzheimer's disease (AD). In this work, we designed a novel photoelectrochemical (PEC) and electrochemiluminescence resonance energy transfer (ECL-RET) dual-mode biosensor to achieve ultra-sensitive detection of Aβo. Specifically, the electrode surface modified Carbon Dots (C Dots) and the electrodeposited polyaniline (PANI) film formed a Z-scheme heterojunction reversing the photocurrent signal, and then the Aβo specific recognition peptide was attached to the surface via amide bonding between the amino group of PANI and carbonyl group of peptide. After that, in the presence of CdTe labeled specific recognition aptamer for Aβ (CdTe-Apt), Aβo was captured to construct a sandwich-type biosensor and exhibited a significantly enhanced cathodic photocurrent response because the formed dual Z-scheme heterojunction promoted charge separation efficiency. Interestingly, the proposed biosensor also caused a ratiometric change in the ECL intensity at 555 nm and 640 nm. Therefore, the developed biosensor achieved dual-mode detection of Aβo, where the PEC detection range of Aβo was from 10 fM to 0.1 μM (with a detection limit of 4.27 fM) and the ECL method provided a linear detection range of 10 fM to 10 nM (with a detection limit of 6.41 fM). The stability and reliability of the experimental results indicate that this has been a promising biosensing pattern and could be extended to the analysis of other biomarkers.

Methylene-Blue-Encapsulated Metal-Organic-Framework-Based Electrochemical POCT Platform for Multiple Detection of Heavy Metal Ions in Milk

Considering the high risk of heavy metal ions (HMIs) transferring through the food chain and accumulating in milk, a flexible and facile point-of-care testing (POCT) platform is urgently needed for the accurate, sensitive, and highly selective on-site quantification of multiple HMIs in milk. In this work, a cost-effective disk with six screen-printed electrodes (SPEs) was designed for hand-held electrochemical detection. Metal organic frameworks (MOFs) were adopted to amplify and enhance the electrochemical signals of methylene blue (MB). Using differential pulse voltammetry (DPV) methods, low limits of detection for four HMIs (Cd2+, 0.039 ppb; Hg2+, 0.039 ppb; Pb2+, 0.073 ppb; and As3+, 0.022 ppb) were achieved within four minutes. Moreover, the quantitative POCT system was applied to milk samples. The advantages of low cost, ease of on-site implementation, fast response, and accuracy allow for the POCT platform to be used in practical monitoring applications for the quantitation of multiple HMIs in milk samples.

A visualized sensor based on layered double hydroxides with peroxidase-like activity for sensitive acetylcholinesterase assay

Acetylcholinesterase (AChE) plays a crucial role in biological neurotransmission. The aberrant expression of AChE is associated with various neurodegenerative diseases. Therefore, it is of great significance to develop a simple and highly sensitive AChE analysis platform. Herein, a simple colorimetric sensor was constructed for sensitive detection of AChE based on the peroxidase-like catalytic activity of Ni/Co layered double hydroxides (Ni/Co LDHs). In this sensor, the fabricated Ni/Co LDHs possess high peroxidase-like activity, enabling rapid catalysis of o-phenylenediamine (OPD) to produce yellow oxOPD in the presence of H₂O₂. This peroxidase-like activity of Ni/Co LDHs was found to be effectively inhibited by the presence of AChE. It is speculated that the combination of AChE on the outer surface of Ni/Co LDHs through non-covalent interaction may cover the active sites and hinder their adsorption to the substrates, leading to the failure of OPD oxidation. As a result, the yellow color from oxOPD is related to the AChE concentration, enabling the direct AChE assay in an equipment-free manner. In addition, the fabricated Ni/Co LDHs could be modified on a paper surface to obtain a paper-based analytical device for visualized colorimetric detection of AChE. The as-proposed sensor shows high sensitivity to AChE with a detection limit down to 6.6 μU mL^-1. Therefore, this naked-eye paper-based sensor is capable of on-site and real-time detection of AChE, and has outstanding application prospects in clinical diagnosis and biomedical fields.

Aptamer-Based Point-of-Care Devices: Emerging Technologies and Integration of Computational Methods

Recent innovations in point-of-care (POC) diagnostic technologies have paved a critical road for the improved application of biomedicine through the deployment of accurate and affordable programs into resource-scarce settings. The utilization of antibodies as a bio-recognition element in POC devices is currently limited due to obstacles associated with cost and production, impeding its widespread adoption. One promising alternative, on the other hand, is aptamer integration, i.e., short sequences of single-stranded DNA and RNA structures. The advantageous properties of these molecules are as follows: small molecular size, amenability to chemical modification, low- or nonimmunogenic characteristics, and their reproducibility within a short generation time. The utilization of these aforementioned features is critical in developing sensitive and portable POC systems. Furthermore, the deficiencies related to past experimental efforts to improve biosensor schematics, including the design of biorecognition elements, can be tackled with the integration of computational tools. These complementary tools enable the prediction of the reliability and functionality of the molecular structure of aptamers. In this review, we have overviewed the usage of aptamers in the development of novel and portable POC devices, in addition to highlighting the insights that simulations and other computational methods can provide into the use of aptamer modeling for POC integration.

An ultrasensitive electrochemical aptasensor using Tyramide-assisted enzyme multiplication for the detection of Staphylococcus aureus

In this study, we aimed to introduce a new electrochemical aptasensor based on the tyramide signal amplification (TSA) technology for a highly-sensitive detection of the pathogenic bacterium, Staphylococcus aureus, as a model of foodborne pathogens. In this aptasensor, the primary aptamer, SA37, was used to specifically capture bacterial cells; the secondary aptamer, SA81@HRP, was used as the catalytic probe; and a TSA-based signal enhancement system comprising of biotinyl-tyramide and streptavidin-HRP as electrocatalytic signal tags was adopted to fabricate the sensor and improve the detection sensitivity. S. aureus cells were selected as the pathogenic bacteria to verify the analytical performance of this TSA-based signal-enhancement electrochemical aptasensor platform. After the simultaneous binding of SA37-S. aureus-SA81@HRP formed on the gold electrode, thousands of @HRP molecules could be bound onto the biotynyl tyramide (TB) displayed on the bacterial cell surface through a catalytic reaction between HRP and H₂O₂, resulting in the generation of the highly amplified signals mediated by HRP reactions. This developed aptasensor could detect S. aureus bacterial cells at an ultra-low concentration, with a limit of detection (LOD) of 3 CFU/mL in buffer. Furthermore, this chronoamperometry aptasensor successfully detected target cells in both tap water and beef broth with LOD to be 8 CFU/mL, which are very high sensitivity and specificity. Overall, this electrochemical aptasensor using TSA-based signal-enhancement could be a very useful tool for the ultrasensitive detection of foodborne pathogens in food and water safety and environmental monitoring.

Integrated dual-channel electrochemical immunosensor for early diagnosis and monitoring of periodontitis by detecting multiple biomarkers in saliva

Periodontitis, as the sixth prevalence chronic inflammation worldwide, has inconspicuous and often-overlooked symptoms at early stage, eventually leading to permanent damage to the teeth and supporting tissues. The timely and accurate diagnosis of periodontitis and monitoring its progress appear to be particularly important for clinical treatment. Herein, a dual-channel electrochemical immunosensor was developed for the synchronized detection of two periodontitis-related biomarkers in saliva: interleukin-1β (IL-1β) and matrix metalloproteinase-8 (MMP-8). Owing to its miniaturization, detachability, and portability, this sensor has the potential to detect multiple biomarkers in a point-of-care manner for the early diagnosis and monitoring of periodontitis. The nanocomposites consisted of iridium oxide nanotubes and two-dimensional MXene nanosheets enhance the electrochemical performance of the sensor, achieving excellent sensitivity with wide detection ranges of 0.1-100 and 1-200 ng mL^-1, low limits of detection of 0.014 and 0.13 ng mL^-1, and relatively high correlation coefficients of 0.9911 and 0.9990 for IL-1β and MMP-8, respectively. Furthermore, this device possesses excellent selectivity in complex samples without cross-talk, as well as high recovery and accuracy in spiked artificial saliva. Importantly, the dual-channel device achieves higher diagnostic accuracy for different stages of periodontitis when MMP-8 and IL-1β were simultaneously monitored within clinicopathological saliva. This work proposes a considerable potential for early diagnosis and severity distinguishment of periodontitis in a point-of-care manner, which would be beneficial for progression prediction, treatment guidance, and prognosis assessment of periodontitis.

Biosensors for healthcare: current and future perspectives

Biosensors are utilized in several different fields, including medicine, food, and the environment; in this review, we examine recent developments in biosensors for healthcare. These involve three distinct types of biosensor: biosensors for in vitro diagnosis with blood, saliva, or urine samples; continuous monitoring biosensors (CMBs); and wearable biosensors. Biosensors for in vitro diagnosis have seen a significant expansion recently, with newly reported clustered regularly interspaced short palindromic repeats (CRISPR)/Cas methodologies and improvements to many established integrated biosensor devices, including lateral flow assays (LFAs) and microfluidic/electrochemical paper-based analytical devices (μPADs/ePADs). We conclude with a discussion of two novel groups of biosensors that have drawn great attention recently, continuous monitoring and wearable biosensors, as well as with perspectives on the commercialization and future of biosensors.

Diboronic-Acid-Based Electrochemical Sensor for Enzyme-Free Selective and Sensitive Glucose Detection

A diboronic acid anthracene-based fluorescent system for detecting blood glucose could be used for 180 days. However, there has not yet been a boronic acid immobilized electrode to selectively detect glucose in a signal-increased way. Considering malfunctions of sensors at high sugar levels, the electrochemical signal should be increased proportionally to the glucose concentration. Therefore, we synthesized a new diboronic acid derivative and fabricated the derivative-immobilized electrodes for the selective detection of glucose. We performed cyclic voltammetry and electrochemical impedance spectroscopy with an Fe(CN)₆^3-/4- redox pair for detecting glucose in the range of 0-500 mg/dL. The analysis revealed increased electron-transfer kinetics such as increased peak current and decreased semicircle radius of Nyquist plots as the glucose concentration increased. The cyclic voltammetry and impedance spectroscopy showed that the linear detection range of glucose was 40 to 500 mg/dL with limits of detection of 31.2 mg/dL and 21.5 mg/dL, respectively. We applied the fabricated electrode to detect glucose in artificial sweat and obtained 90% of the performance of the electrodes in PBS. Cyclic voltammetry measurements of other sugars such as galactose, fructose, and mannitol also showed linear increased peak currents proportional to the concentrations of the tested sugars. However, the slopes of the sugars were lower than that of glucose, indicating selectivity for glucose. These results proved the newly synthesized diboronic acid is a promising synthetic receptor for developing a long-term usable electrochemical sensor system.

Lab-on-a-Chip Electrochemical Biosensors for Foodborne Pathogen Detection: A Review of Common Standards and Recent Progress

Foodborne pathogens are an important diagnostic target for the food, beverage, and health care industries due to their prevalence and the adverse effects they can cause to public health, food safety, and the economy. The standards that determine whether a given type of food is fit for consumption are set by governments and must be taken into account when designing a new diagnostic tool such as a biosensor platform. In order to meet these stringent detection limits, cost, and reliability standards, recent research has been focused on developing lab-on-a-chip-based approaches for detection devices that use microfluidic channels and platforms. The microfluidics-based devices are designed, developed, and used in different ways to achieve the established common standards for food pathogen testing that enable high throughput, rapid detection, low sample volume, and minimal pretreatment procedures. Combining microfluidic approaches with electrochemical biosensing could offer affordable, portable, and easy to use devices for food pathogen diagnostics. This review presents an analysis of the established common standards and the recent progress made in electrochemical sensors toward the development of future lab-on-a-chip devices that will aid 'collection-to-detection' using a single method and platform.

Advances in Electrochemical Biosensors Based on Nanomaterials for Protein Biomarker Detection in Saliva

The focus on precise medicine enhances the need for timely diagnosis and frequent monitoring of chronic diseases. Moreover, the recent pandemic of severe acute respiratory syndrome coronavirus 2 poses a great demand for rapid detection and surveillance of viral infections. The detection of protein biomarkers and antigens in the saliva allows rapid identification of diseases or disease changes in scenarios where and when the test response at the point of care is mandated. While traditional methods of protein testing fail to provide the desired fast results, electrochemical biosensors based on nanomaterials hold perfect characteristics for the detection of biomarkers in point-of-care settings. The recent advances in electrochemical sensors for salivary protein detection are critically reviewed in this work, with emphasis on the role of nanomaterials to boost the biosensor analytical performance and increase the reliability of the test in human saliva samples. Furthermore, this work identifies the critical factors for further modernization of the nanomaterial-based electrochemical sensors, envisaging the development and implementation of next-generation sample-in-answer-out systems.

2D MXene-Based Biosensing: A Review

MXene emerged as decent 2D material and has been exploited for numerous applications in the last decade. The remunerations of the ideal metallic conductivity, optical absorbance, mechanical stability, higher heterogeneous electron transfer rate, and good redox capability have made MXene a potential candidate for biosensing applications. The hydrophilic nature, biocompatibility, antifouling, and anti-toxicity properties have opened avenues for MXene to perform in vitro and in vivo analysis. In this review, the concept, operating principle, detailed mechanism, and characteristic properties are comprehensively assessed and compiled along with breakthroughs in MXene fabrication and conjugation strategies for the development of unique electrochemical and optical biosensors. Further, the current challenges are summarized and suggested future aspects. This review article is believed to shed some light on the development of MXene for biosensing and will open new opportunities for the future advanced translational application of MXene bioassays.

Portable Vertical Graphene@Au-Based Electrochemical Aptasensing Platform for Point-of-Care Testing of Tau Protein in the Blood

Alzheimer's disease (AD) is a long-term neurodegenerative disease that poses a serious threat to human life and health. It is very important to develop a portable quantitative device for AD diagnosis and personal healthcare. Herein, we develop a portable electrochemical sensing platform for the point-of-care detection of AD biomarkers in the blood. Such a portable platform integrates nanoAu-modified vertical graphene (VG@Au) into a working electrode, which can significantly improve sensitivity and reduce detection limit due to the large specific surface, excellent electrical conductivity, high stability, and good biocompatibility. The tau protein, as an important factor in the course of AD, is selected as a key AD biomarker. The results show that the linear range of this sensing platform is 0.1 pg/mL to 1 ng/mL, with a detection limit of 0.034 pg/mL (S/N = 3), indicating that this portable sensing platform meets the demand for the detection of the tau protein in the blood. This work offers great potential for AD diagnosis and personal healthcare.

An Electrochemical-Based Point-of-Care Testing Methodology for Uric Acid Measurement

Point-of-care technology (POCT) is an important method in clinical testing in the future, which can achieve the purpose of rapid analysis. In this work, we assembled an electrochemical POC sensor for uric acid (UA) by surface modification of a screen-printed electrode. Copper nanowires were used as electrode modifiers to achieve high-performance electrochemical oxidation of UA. This electrochemical sensor can achieve linear detection of UA in the range of 10 μM to 2 mM. The detection limit of the sensor was calculated to be 2 μM. Although the detection performance of this sensor is not competitive with high-performance electrochemical sensors, it has been able to meet the needs of POC detection. At the same time, the sensor has excellent anti-interference performance. It has also been used successfully to test urine and serum samples from healthy and gout patients.

One-step high-throughput detection of low-abundance biomarker BDNF using a biolayer interferometry-based 3D aptasensor

Although biosensors for signal monitoring have been extensively developed, their application in one-step high-throughput detection of low-abundance disease biomarkers remains challenging. This study presents a 3D aptasensor based on a biolayer interferometry (BLI) technique, followed by the sensitive and rapid detection of the specific biomarker brain-derived neurotrophic factor (BDNF) for early screening of glaucoma, an irreversible disease that causes blindness. The developed 3D aptasensor enabled one-step batch conversion of the low-abundance biomarker BDNF binding into optical interference signal, which was mainly attributed to the following factors: (1) A dimeric aptamer with extremely high targeting affinity was constructed as a biorecognition molecule, (2) highly sensitive 3D matrix sensors were integrated as signal transduction elements, and (3) the BLI Octet system with automated, high-throughput, and real-time online monitoring capabilities was used for reporting. The 3D aptasensor exhibited a broad detection window from 0.41 to 250 ng/mL BDNF, with a limit of detection of 0.2 ng/mL. Furthermore, detection of BDNF in glaucoma patient serum using the aptasensor showed good agreement with ELISA findings as well as the clinical diagnosis of the patient, demonstrating the feasibility of the system as a screening tool for glaucoma. This one-step high-throughput screening approach provides a valuable solution for the early diagnosis of glaucoma and may reduce the risk of blindness in visually impaired people.

Hybrid Nanobioengineered Nanomaterial-Based Electrochemical Biosensors

Nanoengineering biosensors have become more precise and sophisticated, raising the demand for highly sensitive architectures to monitor target analytes at extremely low concentrations often required, for example, for biomedical applications. We review recent advances in functional nanomaterials, mainly based on novel organic-inorganic hybrids with enhanced electro-physicochemical properties toward fulfilling this need. In this context, this review classifies some recently engineered organic-inorganic metallic-, silicon-, carbonaceous-, and polymeric-nanomaterials and describes their structural properties and features when incorporated into biosensing systems. It further shows the latest advances in ultrasensitive electrochemical biosensors engineered from such innovative nanomaterials highlighting their advantages concerning the concomitant constituents acting alone, fulfilling the gap from other reviews in the literature. Finally, it mentioned the limitations and opportunities of hybrid nanomaterials from the point of view of current nanotechnology and future considerations for advancing their use in enhanced electrochemical platforms.