Immunosensors--principles and applications to clinical chemistry

Electrochemical biosensors in early leukemia detection

Leukemia, a type of blood cancer marked by an abnormal increase in white blood cells, poses a significant challenge to healthcare. The key to successful treatment lies in early detection. However, traditional methods often fall short. This review investigates the potential of electrochemical biosensors for a more accurate and earlier diagnosis of leukemia. Electrochemical biosensors are compact devices that transform biological interactions into electrical signals. Their small size, ease of use, and minimal sample requirements make them perfectly suited for point-of-care applications. Their remarkable sensitivity and specificity enable the detection of subtle biomolecular changes associated with leukemia, which is crucial for early disease detection. This review delves into studies that have utilized these biosensors to identify various types of leukemia. It examines the roles of electrodes, biorecognition elements, and signal transduction mechanisms. The discussion includes the integration of nanomaterials such as gold nanoparticles and nitrogen-doped graphene into biosensor design. These materials boost sensitivity, enhance signal amplification, and facilitate multi-analyte detection, thereby providing a more holistic view of the disease. Beyond technical advancements, the review underscores the practical benefits of these biosensors. Their portability makes them a promising tool for resource-constrained settings, enabling swift diagnosis in remote areas or at a patient's bedside. The potential for monitoring treatment effectiveness and detecting minimal residual disease to prevent relapse is also explored. This review emphasizes the transformative potential of electrochemical biosensors in combating leukemia. By facilitating earlier and more accurate diagnosis, these biosensors stand to revolutionize patient care and enhance treatment outcomes.

Multiplex antibiotic susceptibility testing of urinary tract infections using an electrochemical lab-on-a-chip

Urinary tract infections (UTIs) represent the most prevalent type of outpatient infection, with significant adverse health and economic burdens. Current culture-based antibiotic susceptibility testing can take up to 72 h resulting in ineffective prescription of broad-spectrum antibiotics, poor clinical outcomes and development of further antibiotic resistance. We report an electrochemical lab-on-a-chip (LOC) for testing samples against seven clinically-relevant antibiotics. The LOC contained eight chambers, each housing an antibiotic-loaded hydrogel (cephalexin, ceftriaxone, colistin, gentamicin, piperacillin, trimethoprim, vancomycin) or antibiotic-free control, alongside a resazurin bulk-modified screen-printed electrode for electrochemical detection of metabolically active bacteria using differential pulse voltammetry. Antibiotic susceptibility in simulated UTI samples or donated human urine with either Escherichia coli or Klebsiella pneumoniae could be established within 85 min. Incorporating electrochemical detection onto a LOC provides an inexpensive, simple method for the sensitive determination of antibiotic susceptibility that is significantly faster than using a culture-based approach.

Nanomaterials for detection of biomolecules and delivering therapeutic agents in theragnosis: A review

Nanomaterials are emerging facts used to deliver therapeutic agents in living systems. Nanotechnology is used as a compliment by implementing different kinds of nanotechnological applications such as nano-porous structures, functionalized nanomaterials, quantum dots, carbon nanomaterials, and polymeric nanostructures. The applications are in the initial stage, which led to achieving several diagnoses and therapy in clinical practice. This review conveys the importance of nanomaterials in post-genomic employment, which includes the design of immunosensors, immune assays, and drug delivery. In this view, genomics is a molecular tool containing large databases that are useful in choosing an apt molecular inhibitor such as drug, ligand and antibody target in the drug delivery process. This study identifies the expression of genes and proteins in analysis and classification of diseases. Experimentally, the study analyses the design of a disease model. In particular, drug delivery is a boon area to treat cancer. The identified drugs enter different phase trails (Trails I, II, and III). The genomic information conveys more essential entities to the phase I trials and helps to move further for other trails such as trails-II and III. In such cases, the biomarkers play a crucial role by monitoring the unique pathological process. Genetic engineering with recombinant DNA techniques can be employed to develop genetically engineered disease models. Delivering drugs in a specific area is one of the challenging issues achieved using nanoparticles. Therefore, genomics is considered as a vast molecular tool to identify drugs in personalized medicine for cancer therapy.

Electrochemical DNA biosensors developed for the monitoring of biointeractions with drugs: a review

The interaction of drugs with DNA is important for the discovery of novel drug molecules and for understanding the therapeutic effects of drugs as well as the monitoring of side effects. For this reason, many studies have been carried out to investigate the interactions of drugs with nucleic acids. In recent years, a large number of studies have been performed to electrochemically detect drug-DNA interactions. The fast, sensitive, and accurate results of electrochemical techniques have resulted in a leading role for their implementation in this field. By means of electrochemical techniques, it is possible not only to demonstrate drug-DNA interactions but also to quantitatively analyze drugs. In this context, electrochemical biosensors for drug-DNA interactions have been examined under different headings including anticancer, antiviral, antibiotic, and central nervous system drugs as well as DNA-targeted drugs. An overview of the studies related to electrochemical DNA biosensors developed for the detection of drug-DNA interactions that were reported in the last two decades in the literature is presented herein along with their applications and they are discussed together with their future perspectives.

Polyethylene Glycol-Mediated Directional Conjugation of Biological Molecules for Enhanced Immunoassays at the Point-of-Care

Rapid and reliable point-of-care (POC) diagnostic tests can have a significant impact on global health. One of the most common approaches for developing POC systems is the use of target-specific biomolecules. However, the conjugation of biomolecules can result in decreased activity, which may compromise the analytical performance and accuracy of the developed systems. To overcome this challenge, we present a polymer-based cross-linking protocol for controlled and directed conjugation of biological molecules. Our protocol utilizes a bifunctional thiol-polyethylene glycol (PEG)-hydrazide polymer to enable site-directed conjugation of IgG antibodies to the surface of screen-printed metal electrodes. The metal surface of the electrodes is first modified with thiolated PEG molecules, leaving the hydrazide groups available to react with the aldehyde group in the Fc fragments of the oxidized IgG antibodies. Using anti-Klebsiella pneumoniae carbapenemase-2 (KPC-2) antibody as a model antibody used for antimicrobial resistance (AMR) testing, our results demonstrate a ~10-fold increase in antibody coupling compared with the standard N-hydroxysuccinimide (NHS)-based conjugation chemistry and effective capture (>94%) of the target KPC-2 enzyme antigen on the surface of modified electrodes. This straightforward and easy-to-perform strategy of site-directed antibody conjugation can be engineered for coupling other protein- and non-protein-based biological molecules commonly used in POC testing and development, thus enhancing the potential for improved diagnostic accuracy and performance.

Real-time environmental surveillance of SARS-CoV-2 aerosols

Real-time surveillance of airborne SARS-CoV-2 virus is a technological gap that has eluded the scientific community since the beginning of the COVID-19 pandemic. Offline air sampling techniques for SARS-CoV-2 detection suffer from longer turnaround times and require skilled labor. Here, we present a proof-of-concept pathogen Air Quality (pAQ) monitor for real-time (5 min time resolution) direct detection of SARS-CoV-2 aerosols. The system synergistically integrates a high flow (~1000 lpm) wet cyclone air sampler and a nanobody-based ultrasensitive micro-immunoelectrode biosensor. The wet cyclone showed comparable or better virus sampling performance than commercially available samplers. Laboratory experiments demonstrate a device sensitivity of 77-83% and a limit of detection of 7-35 viral RNA copies/m³ of air. Our pAQ monitor is suited for point-of-need surveillance of SARS-CoV-2 variants in indoor environments and can be adapted for multiplexed detection of other respiratory pathogens of interest. Widespread adoption of such technology could assist public health officials with implementing rapid disease control measures.

Distributed optical fiber biosensor based on optical frequency domain reflectometry

In situ acquisition of spatial distribution of biochemical substances is important in cell analysis, cancer detection and other fields. Optical fiber biosensors can achieve label-free, fast and accurate measurements. However, current optical fiber biosensors only acquire single-point of biochemical substance content. In this paper, we present a distributed optical fiber biosensor based on tapered fiber in optical frequency domain reflectometry (OFDR) for the first time. To enhance evanescent field at a relative long sensing range, we fabricate a tapered fiber with a taper waist diameter of 6 μm and a total stretching length of 140 mm. Then the human IgG layer is coated on the entire tapered region by polydopamine (PDA) -assisted immobilization as the sensing element to achieve to sense anti-human IgG. We measure shifts of the local Rayleigh backscattering spectra (RBS) caused by the refractive index (RI) change of an external medium surrounding a tapered fiber after immunoaffinity interactions by using OFDR. The measurable concentration of anti-human IgG and RBS shift has an excellent linearity in a range from 0 ng/ml to 14 ng/ml with an effective sensing range of 50 mm. The concentration measurement limit of the proposed distributed biosensor is 2 ng/ml for anti-human IgG. Distributed biosensing based on OFDR can locate a concentration change of anti-human IgG with an ultra-high sensing spatial resolution of 680 μm. The proposed sensor has a potential to realize a micron-level localization of biochemical substances such as cancer cells, which will open a door to transform single-point biosensor to distributed biosensor.

The Applications of Electrochemical Immunosensors in the Detection of Disease Biomarkers: A Review

Disease-related biomarkers may serve as indicators of human disease. The clinical diagnosis of diseases may largely benefit from timely and accurate detection of biomarkers, which has been the subject of extensive investigations. Due to the specificity of antibody and antigen recognition, electrochemical immunosensors can accurately detect multiple disease biomarkers, including proteins, antigens, and enzymes. This review deals with the fundamentals and types of electrochemical immunosensors. The electrochemical immunosensors are developed using three different catalysts: redox couples, typical biological enzymes, and nanomimetic enzymes. This review also focuses on the applications of those immunosensors in the detection of cancer, Alzheimer's disease, novel coronavirus pneumonia and other diseases. Finally, the future trends in electrochemical immunosensors are addressed in terms of achieving lower detection limits, improving electrode modification capabilities and developing composite functional materials.

Affinity-Based Analysis Methods for the Detection of Aminoglycoside Antibiotic Residues in Animal-Derived Foods: A Review

With the increasingly serious problem of aminoglycoside antibiotic residues, it is imperative to develop rapid, sensitive and efficient detection methods. This article reviews the detection methods of aminoglycoside antibiotics in animal-derived foods, including enzyme-linked immunosorbent assay, fluorescent immunoassay, chemical immunoassay, affinity sensing assay, lateral flow immunochromatography and molecular imprinted immunoassay. After evaluating the performance of these methods, the advantages and disadvantages were analyzed and compared. Furthermore, development prospects and research trends were proposed and summarized. This review can serve as a basis for further research and provide helpful references and new insights for the analysis of aminoglycoside residues. Accordingly, the in-depth investigation and analysis will certainly make great contributions to food safety, public hygiene and human health.

MIP-on-a-chip: Artificial receptors on microfluidic platforms for biomedical applications

Lab-on-a-chip (LOC) as an alternative biosensing approach concerning cost efficiency, parallelization, ergonomics, diagnostic speed, and sensitivity integrates the techniques of various laboratory operations such as biochemical analysis, chemical synthesis, or DNA sequencing, etc. on miniaturized microfluidic single chips. Meanwhile, LOC tools based on molecularly imprinted biosensing approach permit their applications in various fields such as medical diagnostics, pharmaceuticals, etc., which are user-, and eco-friendly sensing platforms for not only alternative to the commercial competitor but also on-site detection like point-of-care measurements. In this review, we focused our attention on compiling recent pioneer studies that utilized those intriguing methodologies, the microfluidic Lab-on-a-chip and molecularly imprinting approach, and their biomedical applications.

Advancement in COVID-19 detection using nanomaterial-based biosensors

Coronavirus disease 2019 (COVID-19) pandemic has exemplified how viral growth and transmission are a significant threat to global biosecurity. The early detection and treatment of viral infections is the top priority to prevent fresh waves and control the pandemic. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been identified through several conventional molecular methodologies that are time-consuming and require high-skill labor, apparatus, and biochemical reagents but have a low detection accuracy. These bottlenecks hamper conventional methods from resolving the COVID-19 emergency. However, interdisciplinary advances in nanomaterials and biotechnology, such as nanomaterials-based biosensors, have opened new avenues for rapid and ultrasensitive detection of pathogens in the field of healthcare. Many updated nanomaterials-based biosensors, namely electrochemical, field-effect transistor, plasmonic, and colorimetric biosensors, employ nucleic acid and antigen-antibody interactions for SARS-CoV-2 detection in a highly efficient, reliable, sensitive, and rapid manner. This systematic review summarizes the mechanisms and characteristics of nanomaterials-based biosensors for SARS-CoV-2 detection. Moreover, continuing challenges and emerging trends in biosensor development are also discussed.

A Novel Strategy for Selective Thyroid Hormone Determination Based on an Electrochemical Biosensor with Graphene Nanocomposite

This article presents a novel and selective electrochemical bioassay with antibody and laccase for the determination of free thyroid hormone (free triiodothyronine, fT3). The biosensor was based on a glassy carbon electrode modified with a Fe₃O₄@graphene nanocomposite with semiconducting properties, an antibody (anti-PDIA3) with high affinity for fT3, and laccase, which was responsible for catalyzing the redox reaction of fT3. The electrode modification procedure was investigated using a cyclic voltammetry technique, based on the response of the peak current after modifications. All characteristic working parameters of the developed biosensor were analyzed using differential pulse voltammetry. Obtained experimental results showed that the biosensor revealed a sensitive response to fT3 in a concentration range of 10-200 µM, a detection limit equal to 27 nM, and a limit of quantification equal to 45.9 nM. Additionally, the constructed biosensor was selective towards fT3, even in the presence of interference substances: ascorbic acid, tyrosine, and levothyroxine, and was applied for the analysis of fT3 in synthetic serum samples with excellent recovery results. The designed biosensor also exhibited good stability and can find application in future medical diagnostics.

Immunosensors-The Future of Pathogen Real-Time Detection

Pathogens and their toxins can cause various diseases of different severity. Some of them may be fatal, and therefore early diagnosis and suitable treatment is essential. There are numerous available methods used for their rapid screening. Conventional laboratory-based techniques such as culturing, enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR) are dominant. However, culturing still remains the "gold standard" for their identification. These methods have many advantages, including high sensitivity and selectivity, but also numerous limitations, such as long experiment-time, costly instrumentation, and the need for well-qualified personnel to operate the equipment. All these existing limitations are the reasons for the continuous search for a new solutions in the field of bacteria identification. For years, research has been focusing on the use of immunosensors in various types of toxin- and pathogen-detection. Compared to the conventional methods, immunosensors do not require well-trained personnel. What is more, immunosensors are quick, highly selective and sensitive, and possess the potential to significantly improve the pathogen and toxin diagnostic-processes. There is a very important potential use for them in various transport systems, where the risk of contamination by bioagents is very high. In this paper, the advances in the field of immunosensor usage in pathogenic microorganism- and toxin-detection, are described.

Recent Advances in Wearable Biosensors for Non-Invasive Detection of Human Lactate

Lactate, a crucial product of the anaerobic metabolism of carbohydrates in the human body, is of enormous significance in the diagnosis and treatment of diseases and scientific exercise management. The level of lactate in the bio-fluid is a crucial health indicator because it is related to diseases, such as hypoxia, metabolic disorders, renal failure, heart failure, and respiratory failure. For critically ill patients and those who need to regularly control lactate levels, it is vital to develop a non-invasive wearable sensor to detect lactate levels in matrices other than blood. Due to its high sensitivity, high selectivity, low detection limit, simplicity of use, and ability to identify target molecules in the presence of interfering chemicals, biosensing is a potential analytical approach for lactate detection that has received increasing attention. Various types of wearable lactate biosensors are reviewed in this paper, along with their preparation, key properties, and commonly used flexible substrate materials including polydimethylsiloxane (PDMS), polyethylene terephthalate (PET), paper, and textiles. Key performance indicators, including sensitivity, linear detection range, and detection limit, are also compared. The challenges for future development are also summarized, along with some recommendations for the future development of lactate biosensors.

Significance of an Electrochemical Sensor and Nanocomposites: Toward the Electrocatalytic Detection of Neurotransmitters and Their Importance within the Physiological System

A prominent neurotransmitter (NT), dopamine (DA), is a chemical messenger that transmits signals between one neuron to the next to pass on a signal to and from the central nervous system (CNS). The imbalanced concentration of DA may cause numerous neurological sicknesses and syndromes, for example, Parkinson's disease (PD) and schizophrenia. There are many types of NTs in the brain, including epinephrine, norepinephrine (NE), serotonin, and glutamate. Electrochemical sensors have offered a creative direction to biomedical analysis and testing. Researches are in progress to improve the performance of sensors and develop new protocols for sensor design. This review article focuses on the area of sensor growth to discover the applicability of polymers and metallic particles and composite materials as tools in electrochemical sensor surface incorporation. Electrochemical sensors have attracted the attention of researchers as they possess high sensitivity, quick reaction rate, good controllability, and instantaneous detection. Efficient complex materials provide considerable benefits for biological detection as they have exclusive chemical and physical properties. Due to distinctive electrocatalytic characteristics, metallic nanoparticles add fascinating traits to materials that depend on the material's morphology and size. Herein, we have collected much information on NTs and their importance within the physiological system. Furthermore, the electrochemical sensors and corresponding techniques (such as voltammetric, amperometry, impedance, and chronoamperometry) and the different types of electrodes' roles in the analysis of NTs are discussed. Furthermore, other methods for detecting NTs include optical and microdialysis methods. Finally, we show the advantages and disadvantages of different techniques and conclude remarks with future perspectives.

Various types of electrochemical biosensors for leukemia detection and therapeutic approaches

Leukemia often initiates following dysfunctions in hematopoietic stem cells lineages. Various types of leukemia, including acute lymphoblastic leukemia (ALL), chronic myelogenous leukemia (CML), acute promyelocytic leukemia (APL), and human T-cell leukemia/lymphoma virus type 1 (HTLV-1) can thus call for different diagnosis and treatment options. One of the most important subjects in leukemia is the early detection of the disease for effective therapeutic purposes. In this respect, biosensors detecting the molecules of deoxyribonucleic acid (DNA) as analytes are called genosensors or DNA biosensors. Electrochemical sensors, as the most significant approach, also involve reacting of chemical solutions with sensors to generate electrical signals proportional to analyte concentrations. Biosensors can further help detect cancer cells in the early stages of the disease. Moreover, electrochemical biosensors, developed based on various nanomaterials (NMs), can increase sensitivity to the detection of leukemia-related genes, e.g., BCR/ABL as a fusion gene and promyelocytic leukemia/retinoic acid receptor alpha (PML/RARα). Therefore, the present review reflects on previous studies recruiting different NMs for leukemia detection.

Optimized antibody immobilization on natural silica-based nanostructures for the selective detection of E. coli

This study reports for the first time the surface modification of fluorescent nanoparticles derived from geothermal silica precipitate with Escherichia coli (E. coli) antibody. The immobilization of biomolecules on the inorganic surface has been carried out using two different pathways, namely the silanization and hydrosilylation reactions. The former applied (3-aminopropyl)triethoxysilane (APTES) as the crosslinker, while the latter used N-hydroxysuccinimide coupled with N-ethyl-N′-(3-dimethyl aminopropyl) carbodiimide hydrochloride (EDC/NHS). Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy with energy dispersive X-ray spectroscopy (FESEM-EDX), and fluorescence spectroscopy were used to confirm the chemical, physical, and optical properties of the surface-modified fluorescent silica nanoparticles (FSNPs). Based on the results of the FTIR, fluorescence spectroscopy and stability tests, the modified FSNPs with EDC/NHS with a ratio of 4 : 1 were proven to provide the optimum results for further conjugation with antibodies, affording the FSNP-Ab2 sample. The FSNP-Ab2 sample was further tested as a nanoplatform for the fluorescence-quenching detection of E. coli, which provided a linear range of 10² to 10⁷ CFU mL⁻¹ for E. coli with a limit of detection (LoD) of 1.6 × 10² CFU mL⁻¹. The selectivity of the biosensor was observed to be excellent for E. coli compared to that for P. aeruginosa and S. typhimurium, with reductions in the maximum fluorescence intensity at 588 nm of 89.22%, 26.23%, and 54.06%, respectively. The inorganic nanostructure–biomolecule conjugation with optimized coupling agents showed promising analytical performance as a selective nanoplatform for detecting E. coli bacteria.

This work describes for the first time the surface modification of natural-based fluorescent nanoparticles with antibodies as optical biosensing platforms.

Lifting the Veil: Characteristics, Clinical Significance, and Application of β-2-Microglobulin as Biomarkers and Its Detection with Biosensors

Because β-2-microglobulin (β₂M) is a surface protein that is present on most nucleated cells, it plays a key role in the human immune system and the kidney glomeruli to regulate homeostasis. The primary clinical significance of β₂M is in dialysis-related amyloidosis, a complication of end-stage renal disease caused by a gradual accumulation of β₂M in the blood. Therefore, the function of β₂M in kidney-related diseases has been extensively studied to evaluate its glomerular and tubular functions. Because increased β₂M shedding due to rapid cell turnover may indicate other underlying medical conditions, the possibility to use β₂M as a versatile biomarker rose in prominence across multiple disciplines for various applications. Therefore, this work has reviewed the recent use of β₂M to detect various diseases and its progress as a biomarker. While the use of state-of-the-art β₂M detection requires sophisticated tools, high maintenance, and labor cost, this work also has reported the use of biosensor to quantify β₂M over the past decade. It is hoped that a portable and highly efficient β₂M biosensor device will soon be incorporated in point-of-care testing to provide safe, rapid, and reliable test results.

Observational Study of Receptor Binding Domain Spike Antibody Responses to 3 SARS-CoV-2 Vaccinations in Noninfected Subjects: Parallel Neutralizing Antibody and Cardiac Troponin I and T Observations

Background

Our goals were to demonstrate receptor binding domain spike 1 (RBD S1) protein antibody (Ab) kinetic responses to multiple vaccines over approximately 180 days, neutralizing Ab effectiveness, and high-sensitivity cardiac troponin I (hs-cTnI) and T (hs-cTnT) responses in postvaccinated, non-SARS-CoV-2–infected subjects.

Methods

Blood specimens were collected pre- and postvaccinations from seronegative subjects. RDB S1 Abs were measured by the novel Qorvo Biotechnologies Omnia platform. Neutralizing Abs and hs-cTnI and hs-cTnT were measured on the ET Healthcare Pylon 3D.

Results

Two-dose vaccines (Pfizer, Moderna) had peak RBD S1 Ab concentrations about 45 to 55 days after both doses and showed declines over the next 50 to 70 days. The Janssen vaccine showed lower RBD S1 Ab peak concentrations, continued to increase over time, and plateaued after 60 days. There was strong neutralizing Ab response post vaccinations, with only 3 specimens, shortly before and shortly after vaccination, not showing a response. Specimens showed no hs-cTnI (all < 3 ng/L) and hs-cTnT (all < 6 ng/L) increases or changes over time.

Conclusions

We demonstrate in seronegative SARS-CoV-2 subjects that Pfizer and Moderna vaccinations provide strong, neutralizing RBD S1 Ab effectiveness, based on 2 different assays after 2 doses, with the Janssen single-dose vaccine showing a lower RBD S1 Ab response over 4 to 6 months. No myocardial injury was associated with the Pfizer postvaccination. The Qorvo Biotechnologies RBD S1 Ab assay measured on the Omnia platform has potential as a point-of-care platform.

Characterization of rabbit polyclonal antibody against camel recombinant nanobodies

Nanobodies (Nbs) are recombinant single-domain fragments derived from camelids’ heavy-chain antibodies (HCAbs). Nanobodies are increasingly used in numerous biotechnological and medical applications because of their high stability, solubility, and yield. However, one major obstacle prohibiting Nb expansion is the affordability of specific detector antibodies for their final revelation. In this work, the production of a specific anti-Nb antibody as a general detector for camel antibodies, conventional cIgG, and HCAb, and their derived Nbs was sought. Thus, a T7 promoter plasmid was constructed and used to highly express six different Nbs that were used in a successful rabbit immunization. Affinity-purified rabbit anti-Nb rIgG was able to detect immobilized or antigen-bound Nbs via enzyme-linked immunosorbent assay, and its performance was comparable to that of a commercial anti-6× His antibody. Its capacities in dosing impure Nbs, detecting Nbs displayed on M13 phages, and revealing denatured Nbs in immune blotting were all proven. As expected, and because of shared epitopes, rabbit anti-Nb cross-reacted with cIgG, HCAbs, and 6× His-tagged proteins, and the percentage of each fraction within anti-Nb rIgG was determined. Anti-Nb is a promising tool for the checkpoints throughout the recombinant Nb technology.

Transducer Technologies for Biosensors and Their Wearable Applications

The development of new biosensor technologies and their active use as wearable devices have offered mobility and flexibility to conventional western medicine and personal fitness tracking. In the development of biosensors, transducers stand out as the main elements converting the signals sourced from a biological event into a detectable output. Combined with the suitable bio-receptors and the miniaturization of readout electronics, the functionality and design of the transducers play a key role in the construction of wearable devices for personal health control. Ever-growing research and industrial interest in new transducer technologies for point-of-care (POC) and wearable bio-detection have gained tremendous acceleration by the pandemic-induced digital health transformation. In this article, we provide a comprehensive review of transducers for biosensors and their wearable applications that empower users for the active tracking of biomarkers and personal health parameters.

Advanced wearable biosensors for the detection of body fluids and exhaled breath by graphene

Given the huge economic burden caused by chronic and acute diseases on human beings, it is an urgent requirement of a cost-effective diagnosis and monitoring process to treat and cure the disease in their preliminary stage to avoid severe complications. Wearable biosensors have been developed by using numerous materials for non-invasive, wireless, and consistent human health monitoring. Graphene, a 2D nanomaterial, has received considerable attention for the development of wearable biosensors due to its outstanding physical, chemical, and structural properties. Moreover, the extremely flexible, foldable, and biocompatible nature of graphene provide a wide scope for developing wearable biosensor devices. Therefore, graphene and its derivatives could be trending materials to fabricate wearable biosensor devices for remote human health management in the near future. Various biofluids and exhaled breath contain many relevant biomarkers which can be exploited by wearable biosensors non-invasively to identify diseases. In this article, we have discussed various methodologies and strategies for synthesizing and pattering graphene. Furthermore, general sensing mechanism of biosensors, and graphene-based biosensing devices for tear, sweat, interstitial fluid (ISF), saliva, and exhaled breath have also been explored and discussed thoroughly. Finally, current challenges and future prospective of graphene-based wearable biosensors have been evaluated with conclusion. Graphene is a promising 2D material for the development of wearable sensors. Various biofluids (sweat, tears, saliva and ISF) and exhaled breath contains many relevant biomarkers which facilitate in identify diseases. Biosensor is made up of biological recognition element such as enzyme, antibody, nucleic acid, hormone, organelle, or complete cell and physical (transducer, amplifier), provide fast response without causing organ harm.

Enzyme assays with supramolecular chemosensors - the label-free approach

Enzyme activity measurements are essential for many research areas, e.g., for the identification of inhibitors in drug discovery, in bioengineering of enzyme mutants for biotechnological applications, or in bioanalytical chemistry as parts of biosensors. In particular in high-throughput screening (HTS), sensitive optical detection is most preferred and numerous absorption and fluorescence spectroscopy-based enzyme assays have been developed, which most frequently require time-consuming fluorescent labelling that may interfere with biological recognition. The use of supramolecular chemosensors, which can specifically signal analytes with fluorescence-based read-out methods, affords an attractive and label-free alternative to more established enzyme assays. We provide herein a comprehensive review that summarizes the current state-of-the-art of supramolecular enzyme assays ranging from early examples with covalent chemosensors to the most recent applications of supramolecular tandem enzyme assays, which utilize common and often commercially available combinations of macrocyclic host molecules (e.g. cyclodextrins, calixarenes, and cucurbiturils) and fluorescent dyes as self-assembled reporter pairs for assaying enzyme activity.

New insights for integration of nano particle with microfluidic systems for sensor applications

A biosensor is a compact device, which utilizes biological derived recognition component, immobilized on a transducer to analyze an analyte. Nanoparticles with their unique chemical and physical properties are versatile in their applications to develop as sensors. Different nanoparticles play different roles in the sensing systems like metal and metal oxide nanoparticles. The application of Gold, Silver and Copper nanoparticles will be discussed in brief. The nanoparticles typically function as substrates for immobilization of biomolecules, as catalytic agent, electron transfer agent between electrode surface and the biomolecules, and as reactants. Microfluidic deals with manipulating very small volumes of fluids (micro and nanoliters). This miniaturized platform enhances control of flow conditions and mixing rate of fluids. The microfluidics improves the sensitivity of the analysis, and reduces the volumes of sample and reagent in the analysis. The review specifically aims at representing microfluidics-based sensors and nanoparticle based sensors. This review will also focus on probable merger of these two fields to take advantage of both the fields and this will help in pushing the boundaries of these fields further more.

Design of a photoelectrochemical lab-on-a-chip immunosensor based on enzymatic production of quantum dots in situ

We present a new photoelectrochemical immunoassay based on a microfluidic device. Its operation employs enzymatic generation of CdS quantum dots.

Nanowire-based sensor electronics for chemical and biological applications

Detection and recognition of chemical and biological species via sensor electronics are important not only for various sensing applications but also for fundamental scientific understanding. In the past two decades, sensor devices using one-dimensional (1D) nanowires have emerged as promising and powerful platforms for electrical detection of chemical species and biologically relevant molecules due to their superior sensing performance, long-term stability, and ultra-low power consumption. This paper presents a comprehensive overview of the recent progress and achievements in 1D nanowire synthesis, working principles of nanowire-based sensors, and the applications of nanowire-based sensor electronics in chemical and biological analytes detection and recognition. In addition, some critical issues that hinder the practical applications of 1D nanowire-based sensor electronics, including device reproducibility and selectivity, stability, and power consumption, will be highlighted. Finally, challenges, perspectives, and opportunities for developing advanced and innovative nanowire-based sensor electronics in chemical and biological applications are featured.

Graphenoxide Cross-Linker Based Potentiometric Biosensor Design For Sarcosine Determination

BACKGROUND

Sarcosine, also known as N-methyl glycine, is a natural amino acid that is an intermediate and by product in glycine synthesis and degradation. Recently found in many peptides, sarcosine has been researched as a newly accepted prostate cancer marker. The increased concentration of sarcosine in blood serum and the urine showed that malignancy of measured prostate cancer cells is active.

OBJECTIVE

In this article, we aimed to design a potentiometric biosensor for detection of sarcosine with a low detection limit, high selectivity, short response time, wide linear range, and satisfactory long-term stability.

METHODS

In this article, we developed a new Graphene oxide (GFOX) photosensitive cross- linker based potentiometric biosensor based on the AmiNoAcid (monomer) Decorated and Light Underpinning Conjugation Approach (ANADOLUCA) method. The functional groups determined using Raman, FT-IR, XPS analyzes, and surface characterization, the morphology of synthesized GFOX photosensitive cross-linker were determined by TEM and AFM studies. Then, the performance of the GFOX based potentiometric biosensor has been evaluated.

RESULTS

When the usage of the developed GFOX doped potentiometric biosensor against sarcosine determination, it was found that 10 -4 mM sarcosine was determined in 60 seconds in the solution. In addition, the detection limit of the GFOX doped potentiometric biosensor was found to be 9.45x10 -7 mM, and the linear potentiometric biosensor was found to be in the concentration range of 10 -1 to 10 -5 mM. The selectivity studies of the developed potentiometric biosensor were investigated using glycine solutions, and it was determined that GFOX doped potentiometric biosensor was more selective against sarcosine. Besides this, a reusability test using 10 -3 mM sarcosine solution showed that reproducible studies were performed without the loss of potential of designed potentiometric biosensor and no loss of sensitivity.

CONCLUSION

After applying the framework, we get a new potentiometric biosensor for sarcosine determination. GFOX photosensitive cross-linker was used in designing potentiometric biosensors, and this increased the stability and efficiency of the biosensor. Therefore, the developed potentiometric biosensor for sarcosine determination could be easily used for the early diagnosis of prostate cancer.

Trend in creatinine determining methods: Conventional methods to molecular‐based methods

Renal failure (RF) disease is ranked as one of the most prevalent diseases with severe morbidity and mortality. Early diagnosis of RF leads to subsequent control of disease to reduce the poor prognosis. The level of sera creatinine is considered as a significant biomarker for kidney biofunction, which is routinely detected by the Jaffe reaction. The normal range for creatinine in the blood may be 0.84‐1.21 mg/dL. Low accuracy, insufficient sensitivity, explosive and toxicity of picric acid, and pseudo‐interaction with nonspecific elements such as ammonium ions in the Jaffe method lead to the development of various techniques for precise detection of creatinine such as spectroscopic, electrochemical, and chromatography approaches and sensors based on enzymes, molecular imprinted polymer and nanoparticles, etc. Based on previously established results, they are trying to construct sensors with high accuracy, optimum sensitivity, acceptable linear/calibration range, and limit of detection, which are small in size and applicable by the patient him/herself (point‐of‐care testing). By comparing the results of research, a molecularly imprinted electrochemiluminescence‐based sensor with linear/calibration range of 5‐1 mMconcentration of creatinine and the detection limit of 0.5 nM has the best detectable resolution with 2 million measurable points. In this paper, we will review the recently developed methods for measuring creatinine concentration and renal biofunction.

A Bifunctional Nanosilver-Reduced Graphene Oxide Nanocomposite for Label-Free Electrochemical Immunosensing

A bi-functional material based on silver nanoparticles (AgNPs)-reduced graphene oxide (rGO) composite for both electrode modification and signal generation is successfully synthesized for use in the construction of a label-free electrochemical immunosensor. An AgNPs/rGO nanocomposite is prepared by a one-pot wet chemical process. The AgNPs/rGO composite dispersion is simply cast on a screen-printed carbon electrode (SPCE) to fabricate the electrochemical immunosensor. It possesses a sufficient conductivity/electroreactivity and improves the electrode reactivity of SPCE. Moreover, the material can generate an analytical response due to the formation of immunocomplexes for detection of human immunoglobulin G (IgG), a model biomarker. Based on electrochemical stripping of AgNPs, the material reveals signal amplification without external redox molecules/probes. Under optimized conditions, the square wave voltammetric peak current is responded to the logarithm of IgG concentration in two wide linear ranges from 1 to 50 pg.ml-1 and 0.05 to 50 ng.ml-1, and the limit of detection (LOD) is estimated to be 0.86 pg.ml-1. The proposed immunosensor displays satisfactory sensitivity and selectivity. Importantly, detection of IgG in human serum using the immunosensor shows satisfactory accuracy, suggesting that the immunosensor possesses a huge potential for further development in clinical diagnosis.

Laser-induced breakdown spectroscopy as a readout method for immunocytochemistry with upconversion nanoparticles

Immunohistochemistry (IHC) and immunocytochemistry (ICC) are widely used to identify cancerous cells within tissues and cell cultures. Even though the optical microscopy evaluation is considered the gold standard, the limited range of useful labels and narrow multiplexing capabilities create an imminent need for alternative readout techniques. Laser-induced breakdown spectroscopy (LIBS) enables large-scale multi-elemental analysis of the surface of biological samples, e.g., thin section or cell pellet. It is, therefore, a potential alternative for IHC and ICC readout of various labels or tags (Tag-LIBS approach). Here, we introduce Tag-LIBS as a method for the specific determination of HER2 biomarker. The cell pellets were labeled with streptavidin-conjugated upconversion nanoparticles (UCNP) through a primary anti-HER2 antibody and a biotinylated secondary antibody. The LIBS scanning enabled detecting the characteristic elemental signature of yttrium as a principal constituent of UCNP, thus indirectly providing a reliable way to differentiate between HER2-positive BT-474 cells and HER2-negative MDA-MB-231 cells. The comparison of results with upconversion optical microscopy and luminescence intensity scanning confirmed that LIBS is a promising alternative for the IHC and ICC readout.

Biosensing strategies for the electrochemical detection of viruses and viral diseases - A review

Viruses are the causing agents for many relevant diseases, including influenza, Ebola, HIV/AIDS, and COVID-19. Its rapid replication and high transmissibility can lead to serious consequences not only to the individual but also to collective health, causing deep economic impacts. In this scenario, diagnosis tools are of significant importance, allowing the rapid, precise, and low-cost testing of a substantial number of individuals. Currently, PCR-based techniques are the gold standard for the diagnosis of viral diseases. Although these allow the diagnosis of different illnesses with high precision, they still present significant drawbacks. Their main disadvantages include long periods for obtaining results and the need for specialized professionals and equipment, requiring the tests to be performed in research centers. In this scenario, biosensors have been presented as promising alternatives for the rapid, precise, low-cost, and on-site diagnosis of viral diseases. This critical review article describes the advancements achieved in the last five years regarding electrochemical biosensors for the diagnosis of viral infections. First, genosensors and aptasensors for the detection of virus and the diagnosis of viral diseases are presented in detail regarding probe immobilization approaches, detection methods (label-free and sandwich), and amplification strategies. Following, immunosensors are highlighted, including many different construction strategies such as label-free, sandwich, competitive, and lateral-flow assays. Then, biosensors for the detection of viral-diseases-related biomarkers are presented and discussed, as well as point of care systems and their advantages when compared to traditional techniques. Last, the difficulties of commercializing electrochemical devices are critically discussed in conjunction with future trends such as lab-on-a-chip and flexible sensors.

Affinity biosensors developed with quantum dots in microfluidic systems

Quantum dots (QDs) are synthetic semiconductor nanocrystals with unique optical and electronic properties due to their size (2-10 nm) such as high molar absorption coefficient (10-100 times higher than organic dyes), resistance to chemical degradation, and unique optoelectronic properties due to quantum confinement (high quantum yield, emission color change with size). Compared to organic fluorophores, the narrower emission band and wider absorption bands of QDs offer great advantages in cell imaging and biosensor applications. The optoelectronic features of QDs have prompted their intensive use in bioanalytical, biophysical, and biomedical research. As the nanomaterials have been integrated into microfluidic systems, microfluidic technology has accelerated the adaptation of nanomaterials to clinical evaluation together with the advantages such as being more economical, more reproducible, and more susceptible to modification and integration with other technologies. Microfluidic systems serve an important role by being a platform in which QDs are integrated for biosensing applications. As we combine the advantages of QDs and microfluidic technology for biosensing technology, QD-based biosensor integrated with microfluidic systems can be used as an advanced and versatile diagnostic technology in case of pandemic. Specifically, there is an urgent necessity to have reliable and fast detection systems for COVID-19 virus. In this review, affinity-based biosensing mechanisms which are developed with QDs are examined in the domain of microfluidic approach. The combination of microfluidic technology and QD-based affinity biosensors are presented with examples in order to develop a better technological framework of diagnostic for COVID-19 virus.

Microbial biosensor for Salmonella using anti-bacterial antibodies isolated from human serum

In this work, we present a novel microbial biosensor for Salmonella based on impedance spectrometry by using isolated antibodies against a specific bacterial strain from human serum. Anti-Salmonella (or BL21(DE3)) antibodies were isolated from human serum using S. enteritidis (or BL21(DE3)) and the mutant strain ClearColi. After the purification steps, the purification yield of the antibodies was calculated to be 0.2 %. From the FACS analysis, the isolated anti-Salmonella antibodies were estimated to have more than 6-fold higher binding affinity for S. enteritidis compared to antibodies against other kinds of Gram-negative bacterial strains, including HB101, ClearColi, JM110, DH5α, and BL21(DE3). Finally, the anti-Salmonella antibodies isolated herein were used for bacterial detection using electrochemical biosensors based on impedance spectrometry and the R_ct value of the antibodies was estimated for S. enteritidis from the Nyquist plot. The limit of detection of the isolated anti-Salmonella antibodies was estimated to be 1.0 × 10³ cells/mL for S. enteritidis and 1.0 × 10⁶ cells/mL for BL21(DE3), respectively.

Ultrasensitive detection of pathogenic viruses with electrochemical biosensor: State of the art

Last few decades, viruses are a real menace to human safety. Therefore, the rapid identification of viruses should be one of the best ways to prevent an outbreak and important implications for medical healthcare. The recent outbreak of coronavirus disease (COVID-19) is an infectious disease caused by a newly discovered coronavirus which belongs to the single-stranded, positive-strand RNA viruses. The pandemic dimension spread of COVID-19 poses a severe threat to the health and lives of seven billion people worldwide. There is a growing urgency worldwide to establish a point-of-care device for the rapid detection of COVID-19 to prevent subsequent secondary spread. Therefore, the need for sensitive, selective, and rapid diagnostic devices plays a vital role in selecting appropriate treatments and to prevent the epidemics. During the last decade, electrochemical biosensors have emerged as reliable analytical devices and represent a new promising tool for the detection of different pathogenic viruses. This review summarizes the state of the art of different virus detection with currently available electrochemical detection methods. Moreover, this review discusses different fabrication techniques, detection principles, and applications of various virus biosensors. Future research also looks at the use of electrochemical biosensors regarding a potential detection kit for the rapid identification of the COVID-19.

A new potentiometric platform: Antibody cross-linked graphene oxide potentiometric immunosensor for clenbuterol determination

An immunosensor is based on the signal measurement obtained upon the reaction of an antibody antigen complex. It plays a significant role in various fields such as environmental analysis, production monitoring, drug detection or screening, veterinary medicine, and animal food. In this study, an antibody crosslinked graphen oxide (GO)-based potentiometric sensor has been developed for fast, simple, and economical detection of clenbuterol. In this context, the photosensitive amino acid bound GO platform is synthesized and used for the preparation of electrode material. Then, polymeric structure is characterized by infrared spectroscopy, and the performance of immunonano platform prepared by potentiometric sensor is evaluated. The effect of pH, response time, selectivity, and sensitivity is investigated. Under the optimized conditions, a simple and rapid method for the determination of clenbuterol from milk sample is established by immuno-potentiometric sensor. The detection limit has found to be 0.87 × 10^-9 mmol L^-1 for this immuno-potentiometric sensor. This immuno-potentiometric sensor has optimum pH at 7.0, a wide linear response (1.0 × 10^-2 to 1.0 × 10^-9 mmol L^-1 ), rapid response time (2 Min) and 36 weeks operational lifetime.

The application of antibody-aptamer hybrid biosensors in clinical diagnostics and environmental analysis

The growing number of various diseases and the increase of environmental contamination are the causes for the development of novel methods for their detection. The possibility of the application of affinity-based biosensors for such purposes seems particularly promising as they provide high selectivity and low detection limits. Recently, the usage of hybrid antibody-aptamer sandwich constructs was shown to be more advantageous in terms of working parameters in comparison to aptamer-based and immune-based biosensors. This review is focused on the usage of hybrid antibody-aptamer receptor layers for the determination of clinically and environmentally important target molecules. In this work, antibodies and aptamer molecules are characterized and the methods of their immobilization as well as analytical signal generation are shown. This is followed by the critical presentation of examples of hybrid sandwich biosensors that have been elaborated in the past 12 years.