Biological Recognition Element Research Articles

The layer-by-layer assembly of reduced graphene oxide films and their application as solution-gated field-effect transistors

In this study, graphene oxide (GO) has been reduced in two different ways for the production of oppositely charged reduced graphene oxide (rGO) sheets. One reduction route consisted of the covalent modification of GO with (3-aminopropyl) triethoxysilane and subsequent chemical reduction to produce positively charged rGO. In the second route employed, GO was reduced in a domestic microwave oven, in which the presence of urea doped the material with nitrogen, increasing its electrical conductivity considerably. Multilayers of oppositely charged rGO were manufactured using the layer-by-layer (LbL) assembly technique. The kinetics and growth of multilayers were monitored by UV–Vis absorption spectroscopy and quartz crystal microbalance. rGO multilayers on the interdigitated gold electrodes originate high conductive films, in which the number of deposited layers controls the conductivity. As a solution-gated field-effect transistor, the devices presented high transconductance; (90 µS and 55 µS for holes and electrons, respectively). Upon modification of the LbL films with papain, used as a biological recognition element, the devices were capable of detecting Cystatin C protein (a chronic renal disease biomarker) in synthetic urine in concentrations as low as 5 ng.mL−1. Therefore, the proposed transistors proposed here represent interesting alternatives as novel sensors and biosensors platforms.

Insect odorant receptor nanodiscs for sensitive and specific electrochemical detection of odorant compounds

An electrochemical sensing methodology using an insect odorant receptor (iOR) as the biological recognition element for detection of odorant compounds is presented. Or22a from the fruit fly Drosophila melanogaster (DmOr22a) was used as a model receptor for the study. DmOr22a in phospholipid nanodisc preparations was shown to be functionally active toward its known ligand (ethyl hexanoate), as measured by electrochemical impedance spectroscopy (EIS). iOR nanodiscs covalently immobilized on a gold substrate were further characterized by atomic force microscopy (AFM), quartz crystal microbalance with dissipation monitoring (QCM-D) and neutron reflectometry in order to study surface modification and understand the underlying mechanisms associated with ligand binding. The EIS sensor exhibited high sensitivity and specificity towards ethyl hexanoate with a detection limit of 5.5 fM. Neutron reflectometry studies provided evidence to support conformational changes in the receptor upon ligand binding. The EIS based detection strategy provides a facile, sensitive and fast method for detecting odorant compounds and paves the way for further development of odorant biosensors.

Continuous Sweat Lactate Sensor Based on Screen-Printed MgO-Templated Carbon with Integrated Flow System

Lactate has long been known as the indicator for distinguishing aerobic and anaerobic metabolism, and thus is a useful marker for metabolic disorders and the state of exercise [1]. Especially, the continuous monitoring of sweat lactate is a useful non-invasive method for real-time tracking the progress of exercise, e.g. of athletes, or of physical therapy patients. In biosensors for continuous monitoring, the biological recognition element, e.g. lactate oxidase (LOx) has to be immobilized on the electrode. Our group previously reported of a glucose sensor in which glucose dehydrogenase (GDH) was immobilized covalently on screen-printed MgO-templated mesoporous carbon (MgOC) modified by graft polymerization, and showed improved stability [2]. Likewise, in this study, radicals were introduced on the surface of the MgOC by electron beam irradiation. Next, glycidyl methacrylate (GMA) was polymerized on the radicalized MgOC, which resulted in epoxy groups on the surface. Ink was prepared by dispersing this poly(GMA)-MgOC (GMgOC) and a polyvinylidene difluoride (PVdF) derivative in N-methyl-2-pyrrolidone (NMP). The ink then was used for the final layer of the working electrode (WE) of a screen-printed 3-electrode strip. Next, 1,2-naphthoquinone was deposited on the WE as mediator, which is insoluble in water and thus is unlikely to dissolve into sweat during the measurement. Finally, LOx derived from Enterococcus faecium was immobilized on the WE by binding covalently to the epoxy groups. This combination of LOx immobilized on screen-printed GMgOC and naphthoquinone promises the construction of stable lactate biosensors suitable for continuous measurements.Furthermore, in this study, two other points were considered for the design and construction of the sensor device. Firstly, the sensor should be constantly supplied with a minimum amount of sweat, without the supply being interrupted. Secondly, the materials and texture of the parts of the sensor in direct contact with the skin should not be irritating. An integrated flow system can solve both points; it ensures a constant supply of sweat, and limits the material and texture in direct contact with the skin. For the construction of the flow system, first, a mold was formed on a silicon wafer using an epoxy-based negative photoresist. Next a degassed mixture of polydimethylsiloxane (PDMS) monomer and catalyst was poured over the mold and cured at 80°C for 1 hour.In first trials, the sensor and flow system were pressed together tightly onto artificial sweat glands. Leakage was prevented by constructing a connector for the sensor out of conducting adhesive tape. Potassium phosphate buffer (100 mM, pH 7.0) containing various amounts of sodium lactate were pumped through the system at 80 µL/min using a syringe pump. Figure 1a shows the response of this system to varying concentrations of lactate. The spikes at the change of concentration are due to a change in the flow when switching the syringe. The delay between the switch of the syringe and the change in response current is due to the lag time until the lactate reached the sensor. The plot of the response current vs the lactate concentration (Fig. 1b) shows a concentration dependent response up to 20 mM lactate. These results indicate that this system is suitable for measuring sweat lactate continuously. Acknowledgement: This work was partially supported by JST-ASTEP Grant Number JPMJTS1513, JSPS Grant Number 17H02162 and Private University Research Branding Project (2017-2019) from Ministry of Education, Culture, Sports, Science and Technology, and Tokyo University of Science Grant for President's Research Promotion． References [1] M.E. Payne, et al.; Sci. Rep., 9, 13720 (2019).[2] I. Shitanda, et al.; Bull. Chem. Soc. Jpn., 93, 32-36 (2020). Figure 1

Amperometric Monitoring of Glucose Level for Non-Invasive Cell-Based Assays Based on Glucose Dehydrogenase-Modified SWCNT

INTRODUCTION Glucose sensing is widely used as one of the evaluation methods for cellular activities and functions, since glucose plays an important role in principal source of biological energy. A cellular glucose uptake rate is frequently determined from culture media collected at specific times by conventional analytical instruments. However, due to the low time resolution, dynamic cellular responses are not evaluated in detail. Meanwhile, most of glucose sensors in the conventional analytical instruments often utilize glucose oxidase (GOx) as a biological recognition element for the analysis of glucose. From the amount of H2O2 generated via the GOx-catalyzed oxidation of glucose by oxygen, glucose concentration is indirectly determined. However, even if such GOx-based glucose sensor was used for cell culture systems, the accurate concentration of glucose would not be determined due to the cellular oxygen consumption based on respiratory metabolism. Additionally, H2O2 is well-known to induce apoptotic or necrotic cell death. In the present work, we prepared an oxygen-independent glucose dehydrogenase (GDH)-modified single-walled carbon nanotube (SWCNT) electrode, at the surface of which a cellulose dialysis membrane was modified to improve the stability of the electrochemical signal, and demonstrated its performance of direct glucose monitoring in the cell culture system. EXPERIMENTAL An electrode for monitoring of glucose levels based on GDH-adsorbed SWCNTs (GDH/SWCNT electrode) was prepared as follows. SWCNT dispersion was cast onto the surface of a glassy carbon electrode. After physically adsorption of 1,4-naphthoquinone (NQ), which promotes direct electron transfer between GDH and SWCNT, at the surface of SWCNTs, an aliquot of a mixture of aqueous solution containing GDH and hexamethylenediamine was cast onto the NQ-adsorbed SWCNT electrode surface, subsequently followed by casting of a glutaraldehyde solution to conjugate GDH with NQ-adsorbed SWCNTs rigidly. The obtained electrode surface was covered with Nafion, further followed by covering cellulose dialysis membrane (CDM). Monitoring changes in glucose levels during hepatic glucose metabolism was performed by means of amperometry at +0.4 V vs. Ag|AgCl in a Dulbecco’s Modified Eagle Medium (DMEM)-based culture medium containing 5 mM glucose and 10% fetal bovine serum (FBS). The working electrode was located several handled micrometers from human hepatoma cell line Hep G2. RESULTS AND DISCUSSION We first examined the glucose concentration dependence of the steady-state anodic current densities for GDH/SWCNT electrodes with and without CDM in the phosphate buffered saline (pH 7.4). The responses at the both electrodes linearly increased with increasing glucose concentration up to 30 mM and then leveled off. However, the slope for the GDH/SWCNT electrode with CDM was slightly smaller than that without CDM. This indicates that CDM might restrictsupplying glucose to the GDH/SWCNT surface. We next confirmed the feasibility of the GDH/SWCNT electrode to amperometric monitoring of glucose level for real-time cell-based assays. We examined long-term stability of the GDH/SWCNT electrode in the DMEM-based culture medium containing 5 mM glucose and 10% FBS. In the absence of CDM, the anodic current rapidly decreased less than 40% after 23 h, but in the presence of CDM, the anodic current was observed 70% or larger even after 24 h. We therefore employed the GDH/SWCNT electrode with CDM for a real sample. Figure 1 shows anodic current responses observed at the CDM-covered GDH/SWCNT electrode located near the bottom surface of a culture dish in the presence and absence of Hep G2 cells in the DMEM-based culture medium with and without cisplatin, which is well-known as one of the anti-cancer drugs. In the absence of Hep G2, an anodic current in the presence of cisplatin showed the similar behavior for that in the absence of cisplatin, so that cisplatin unaffected to the current responses. Meanwhile, in the presence of Hep G2 cells without cisplatin, anodic current rapidly decreased because of their glucose metabolism. In contrast, a current response first rapidly, and then, slightly decreased in the presence of both Hep G2 and cisplatin. The former current change rate was the similar case to the presence of Hep G2 cells without cisplatin, indicating cellular glucose metabolism because cisplatin hardly worked soon after its exposure to Hep G2 cells. The latter current change rate was almost the same as that in the absence of Hep G2 cells with cisplatin, indicating the inhibition of their glucose metabolism due to damage of Hep G2 cells by cisplatin. Thus, the CDM-covered GDH/SWCNT electrode would be applicable to non-invasive cell-based safety assays as an index of changes in cellular glucose metabolism. Figure 1

Molecular Imprinting Technology for Biomimetic Assemblies

The term biomimetic can be simply defined as the examination of nature. The scientists inspired by the enormous diversity of nature to solve human problems or facilitate daily life by mimicking natural models, systems, and elements especially in the biomedical and therapeutic applications to make better drugs, artificial organs, sensing instruments, etc. 
 
 Biological recognition elements like proteins, antibodies, enzymes, DNA, lectins, aptamers, cells, and viruses have been heavily used to ensure specificity in such applications in spite of their lack of stability and reusability. However, in the last two decades molecularly imprinted polymers, MIPs, have been synthesized as an alternative to mimic natural biological interactions for a broad spectrum of templates by means of coordinating functional monomers around template in the presence of cross-linker. 
 
 This review will outline the broad contours of biomimetics prepared by molecular imprinting techniques and their practical applications in the separation techniques, tissue engineering applications, biomimetic surfaces, sensors, artificial membranes, and drug delivery systems.

Long period grating in double cladding fiber coated with graphene oxide as high-performance optical platform for biosensing

In this work, the development and testing of a novel fiber-optic based label-free biosensor is presented, whose performance were verified through the detection of C-reactive protein (CRP) in serum. The device is based on a long period grating fabricated in a double cladding fiber with a W-shaped refractive index (RI) profile. As a result, the working point of the device was tuned to the mode transition region by chemical etching of the outer fiber cladding, obtaining a significant enhancement of the RI sensitivity and an excellent visibility of the grating resonances due to the mode transition in an all-silica structure. The fiber transducer was coated with a nanometric thin layer of graphene oxide in order to provide functional groups for the covalent immobilization of the biological recognition element. A very low limit of detection of about 0.15 ng/mL was obtained during the detection of CRP in serum, and a large working range (1 ng/mL – 100 μg/mL) of clinical relevance has been also achieved.

Electrochemiluminescence Biosensors Using Screen-Printed Electrodes.

Electrogenerated chemiluminescence (also called electrochemiluminescence (ECL)) has become a great focus of attention in different fields of analysis, mainly as a consequence of the potential remarkably high sensitivity and wide dynamic range. In the particular case of sensing applications, ECL biosensor unites the benefits of the high selectivity of biological recognition elements and the high sensitivity of ECL analysis methods. Hence, it is a powerful analytical device for sensitive detection of different analytes of interest in medical prognosis and diagnosis, food control and environment. These wide range of applications are increased by the introduction of screen-printed electrodes (SPEs). Disposable SPE-based biosensors cover the need to perform in-situ measurements with portable devices quickly and accurately. In this review, we sum up the latest biosensing applications and current progress on ECL bioanalysis combined with disposable SPEs in the field of bio affinity ECL sensors including immunosensors, DNA analysis and catalytic ECL sensors. Furthermore, the integration of nanomaterials with particular physical and chemical properties in the ECL biosensing systems has improved tremendously their sensitivity and overall performance, being one of the most appropriates research fields for the development of highly sensitive ECL biosensor devices.

Electrochemical Biosensors Based on Nanomaterials for Early Detection of Alzheimer's Disease.

Alzheimer’s disease (AD) is an untreatable neurodegenerative disease that initially manifests as difficulty to remember recent events and gradually progresses to cognitive impairment. The incidence of AD is growing yearly as life expectancy increases, thus early detection is essential to ensure a better quality of life for diagnosed patients. To reach that purpose, electrochemical biosensing has emerged as a cost-effective alternative to traditional diagnostic techniques, due to its high sensitivity and selectivity. Of special relevance is the incorporation of nanomaterials in biosensors, as they contribute to enhance electron transfer while promoting the immobilization of biological recognition elements. Moreover, nanomaterials have also been employed as labels, due to their unique electroactive and electrocatalytic properties. The aim of this review is to add value in the advances achieved in the detection of AD biomarkers, the strategies followed for the incorporation of nanomaterials and its effect in biosensors performance.

Electrochemical Biosensors Employing Natural and Artificial Heme Peroxidases on Semiconductors.

Heme peroxidases are widely used as biological recognition elements in electrochemical biosensors for hydrogen peroxide and phenolic compounds. Various nature-derived and fully synthetic heme peroxidase mimics have been designed and their potential for replacing the natural enzymes in biosensors has been investigated. The use of semiconducting materials as transducers can thereby offer new opportunities with respect to catalyst immobilization, reaction stimulation, or read-out. This review focuses on approaches for the construction of electrochemical biosensors employing natural heme peroxidases as well as various mimics immobilized on semiconducting electrode surfaces. It will outline important advances made so far as well as the novel applications resulting thereof.

Enhancement of Biosensors by Implementing Photoelectrochemical Processes.

Research on biosensors is growing in relevance, taking benefit from groundbreaking knowledge that allows for new biosensing strategies. Electrochemical biosensors can benefit from research on semiconducting materials for energy applications. This research seeks the optimization of the semiconductor-electrode interfaces including light-harvesting materials, among other improvements. Once that knowledge is acquired, it can be implemented with biological recognition elements, which are able to transfer a chemical signal to the photoelectrochemical system, yielding photo-biosensors. This has been a matter of research as it allows both a superior suppression of background electrochemical signals and the switching ON and OFF upon illumination. Effective electrode-semiconductor interfaces and their coupling with biorecognition units are reviewed in this work.

Amplification-Free Point-of-Care microRNA Detection in Urine Using Molecular Beacon Based Electrochemiluminescence

The burgeoning field of miRNA detection using electrochemiluminescence (ECL) has garnered a great deal of attention in recent times.1 ECL presents many advantages over alternative detection strategies as ECL analyses generally exhibit low-background signals, high sensitivity, are reproducible and scale-able.2 When combined with magnetic-beads for the immobilisation of biological recognition elements, ECL biosensors offer exceptional sensitivity owing to the ability to disperse the beads in large sample volumes to capture the biological target of interest via mixing then concentrate prior to analysis via magnetic extraction.3, 4 Herein, we present a novel biosensor for the sensitive detection of miRNA-21 comprising a molecular beacon ECL probe immobilised on magnetic beads. We obtained a limit of detection of 500 attomoles for miRNA-21 without enzymatic amplification or the addition of detection probes or intercalating labels, negating the need for lengthy and stringent washing procedures to reduce the background signal. Furthermore, we demonstrate the immense potential for point-of-care applications by developing a fully integrated miRNA detection platform. The platform comprises a mini-potentiostat for ECL generation, integrated silicon photodiode for ECL detection and a custom 3D-printed cell holder to readily interface a disposable screen-printed electrode with the potentiostat and photodiode.We applied our magnetic miRNA extraction technology to the detection of miRNA-21 in human urine, a promising biomarker for the early diagnosis of chronic kidney disease.5 Urine is an ideal sample matrix as it is non-invasive to obtain in large volumes, does not require a phlebotomist to acquire and miRNAs in urine are stable in exosomes. When combined with point-of-care miRNA extraction methods, the molecular beacon based ECL system we have developed presents a promising tool for point-of-care diagnosis and management of numerous diseases. 1. P. K. Kalambate, N. S. Gadhari, X. Li, Z. Rao, S. T. Navale, Y. Shen, V. R. Patil and Y. Huang, TrAC, Trends Anal. Chem., 2019, 115643.2. Y. Cheng, L. Dong, J. Zhang, Y. Zhao and Z. Li, Analyst, 2018, 143, 1758-1774.3. M. H. Shamsi, K. Choi, A. H. Ng, M. D. Chamberlain and A. R. Wheeler, Biosens. Bioelectron., 2016, 77, 845-852.4. W. Liu, X. Zhou and D. Xing, Biosens. Bioelectron., 2014, 58, 388-394.5. M. L. Alvarez, M. Khosroheidari, R. Kanchi Ravi and J. K. DiStefano, Kidney Int., 2012, 82, 1024-1032.

Experimental characterization of a biosensor based on a tapered optical fiber for kisspeptin detection.

This paper presents the development of a biosensor based on optical fiber, using a polyclonal antibody kisspeptin receptor as a biological recognition element that is connected to puberty onset and may also help to suppress metastasis in melanoma breast cancer. The fiber surface was chemically prepared to immobilize the antibody. The structural homogeneity of the biosensor, at each stage of the self-assembly, was characterized by Fourier transform infrared spectroscopy and by measurements of the transmission at the output of the biosensor. The morphological homogeneity analysis was performed by optical microscopy and scanning electron microscopy. The biosensor developed was checked to detect kisspeptin in brain tissues by spectral transmission using a superluminescent diode. The data were analyzed using principal component analysis. The interaction of the kisspeptin with its counterpart by means of the evolution of the transmission spectrum as a function of time was observed.

MoS2 nanostructured materials for electrode modification in the development of a laccase based amperometric biosensor for non-invasive dopamine detection

A novel laccase-based amperometric biosensor was developed through the modification of carbon paper electrodes with layered two-dimensional molybdenum disulfide (MoS2) presented in two different morphologies, flowers (MoS2-F) and ribbons (MoS2-R). Two laccase isoforms from Pycnoporus sanguineus CS43 fungi (LacI and LacII) were evaluated for the first time as a biological recognition element, and their performance was compared with commercial laccase from Trametes versicolor (TvL). The best results were observed with the MoS2-R morphology at a concentration of 2 mg/mL Biosensors modified with MoS2-R and with the three enzymes, showed two linear ranges of detection, from 0.1 to 0.5 µM and from 1 to 5 µM. Biosensors modified with LacII exhibited a high sensitivity of 340.3 nA/µM; and low limit of detection (LOD) of 10 nM, which are the best values reported in the literature for dopamine detection by laccase based biosensor. Optimized electrodes modified with enzymes LacII and TvL were tested in a synthetic urine sample in order to evaluate their practical effectiveness, resulting in LOD of 0.67 and 2.67 µM respectively, which are below the average concentrations of dopamine normally found in real urine samples (around 2 µM).

DNA-based nanobiosensors for monitoring of water quality.

Water pollution is a global concern for human and environmental health. As technology and industries have developed over the past decades, increasingly more complex and diverse pollutants are found even in treated waters. For better management of water resources, continuous and efficient monitoring is needed to detect the broad range of contaminants. Biosensors have the potential to meet this challenge and to overcome the limitations of the conventional methods used for water analysis. They combine a biological recognition element to a transducer in a sensitive and robust device, capable of specific detection of molecules of interest. DNA-based sensing technologies meet this set of specifications and benefit from the progress made in nanoscience and nanotechnology. This mini-review proposes an overview of this upcoming new generation of DNA-based biosensors, focusing on promising innovations having for portable, stable, rapid and sensitive devices for water quality monitoring.

Enzyme-based detection of epoxides using colorimetric assay integrated with smartphone imaging.

Epoxides are widely used chemicals, the determination of which is of paramount importance. Herein, we present an enzyme-based approach for noninstrumental detection of epoxides in standard solution and environmental samples. Halohydrin dehalogenase (HheC) as a biological recognition element and epichlorohydrin as a model analyte were evaluated for sensing. The detection is based on the color change of the pH indicator dye bromothymol blue caused by the HheC-catalyzed ring-opening of the epoxide substrate. The color change is then exploited for the determination of epoxide using a smartphone as an image acquisition and data processing device, eliminating the need for computer-based image analysis software. The color parameters were systematically evaluated to determine the optimum quantitative analytical parameter. Under optimal conditions, the proposed enzyme-based detection system showed a linear range of 0.13-2mM with a detection limit of 0.07mM and an assay time of 8Min. In addition, the repeatability expressed as relative standard deviation was found to be below 5% (n=6). Validation with gas chromatographic analyses showed that the proposed enzyme-based epoxide detection could be an alternative way in the quantitative determination of epoxides, and particularly useful in resource-limited settings.

FET-based nanobiosensors for the detection of smell and taste.

Various nanobiosensors composed of biomaterials and nanomaterials have been developed, due to their demonstrated advantage of showing high performance. Among various biomaterials for biological recognition elements of the nanobiosensor, sensory receptors, such as olfactory and taste receptors, are promising biomaterials for developing nanobiosensors, because of their high selectivity to target molecules. Field-effect transistors (FET) with nanomaterials such as carbon nanotube (CNT), graphene, and conducting polymer nanotube (CPNT), can be combined with the biomaterials to enhance the sensitivity of nanobiosensors. Recently, many efforts have been made to develop nanobiosensors using biomaterials, such as olfactory receptors and taste receptors for detecting various smells and tastes. This review focuses on the biomaterials and nanomaterials used in nanobiosensor systems and studies of various types of nanobiosensor platforms that utilize olfactory receptors and taste receptors which could be applied to a wide range of industrial fields, including the food and beverage industry, environmental monitoring, the biomedical field, and anti-terrorism.

Electrochemical biosensors based on nucleic acid aptamers

During recent decades, nucleic acid aptamers have emerged as powerful biological recognition elements for electrochemical affinity biosensors. These bioreceptors emulate or improve on antibody-based biosensors because of their excellent characteristics as bioreceptors, including limitless selection capacity for a large variety of analytes, easy and cost-effective production, high stability and reproducibility, simple chemical modification, stable and oriented immobilization on electrode surfaces, enhanced target affinity and selectivity, and possibility to design them in target-sensitive 3D folded structures. This review provides an overview of the state of the art of electrochemical aptasensor technology, focusing on novel aptamer-based electroanalytical assay configurations and providing examples to illustrate the different possibilities. Future prospects for this technology are also discussed. Graphical abstract.

In Silico Discovery and Validation of Neuropeptide-Y-Binding Peptides for Sensors.

Wearable sensors for human health, performance, and state monitoring, which have a linear response to the binding of biomarkers found in sweat, saliva, or urine, are of current interest for many applications. A critical part of any device is a biological recognition element (BRE) that is able to bind a biomarker at the surface of a sensor with a high affinity and selectivity to produce a measurable signal response. In this study, we discover and compare 12-mer peptides that bind to neuropeptide Y (NPY), a stress and human health biomarker, using independent and complimentary experimental and computational approaches. The affinities of the NPY-binding peptides discovered by both methods are equivalent and below the micromolar level, which makes them suitable for application in sensors. The in silico design protocol for peptide-based BREs is low cost, highly efficient, and simple, suggesting its utility for discovering peptide binders to a variety of biomarker targets.

Detection of Diabetes using Biosensors

Diabetes is the widespread disease in the world. During the last few decades there is a huge increase in the number of diabetic patients. Biosensor is a device which is used to detect diabetes. It converts biological reading into electrical pursuing that helps the patients to predict their diabetic levels. It consists of a biological recognition element and a chemical sensor. They are high-technology tracking tools that measures sugar levels in a quick, highly sensible fashion. We mainly focus on the glucose-oxidase biosensor which uses machine learning techniques and regression methods. Detection of diabetes can be done in many forms like with a radiofrequency biosensor chip, optical fiber biosensor, micro-fluidic biosensor. Optical biosensor is placed in contact lens to detect glucose levels within the tears and give the accurate prediction. There were some early versions of glucose-sensing devices. There are different existing techniques for the detection. But the preferred method is using the continuous glucose observing system. This method offers a good control of diabetes by using real time data. However, there are few provokes identified with the accomplishment of precise and dependable glucose observing. Further consistency and improvements in the development of biosensors to meet their goals are required.

Nanomaterials towards Biosensing of Alzheimer's Disease Biomarkers.

Alzheimer’s disease (AD) is an incurable and highly debilitating condition characterized by the progressive degeneration and/or death of nerve cells, which leads to manifestation of disabilities in cognitive functioning. In recent years, the development of biosensors for determination of AD’s main biomarkers has made remarkable progress, particularly based on the tremendous advances in nanoscience and nanotechnology. The unique and outstanding properties of nanomaterials (such as graphene, carbon nanotubes, gold, silver and magnetic nanoparticles, polymers and quantum dots) have been contributing to enhance the electrochemical and optical behavior of transducers while offering a suitable matrix for the immobilization of biological recognition elements. Therefore, optical and electrochemical immuno- and DNA-biosensors with higher sensitivity, selectivity and longer stability have been reported. Nevertheless, strategies based on the detection of multiple analytes still need to be improved, as they will play a crucial role in minimizing misdiagnosis. This review aims to provide insights into the conjugation of nanomaterials with different transducers highlighting their crucial role in the construction of biosensors for detection of AD main biomarkers.