Graphene nanoplatelet/graphitized nanodiamond-based nanocomposite for mediator-free electrochemical sensing of urea

The potential of MXene-based materials in fluorescence-based sensing/biosensing of ionic and organic contaminants in environment and food samples: Recent advancements and challenges

MXenes belong to one of the recently developed advanced materials with tremendous potential for diverse sensing applications. To date, various types of MXene-based materials have been developed to generate direct/indirect ultrasensitive sensing signals against various forms of analytes via fluorescence quenching or enhancement. In this work, the fluorescence sensing/biosensing capabilities of the MXene-based materials have been explored and evaluated against a list of ionic/emerging pollutants in environment and food matrices. The suitability of an MXene-based sensing approach is also validated through the assessment of the performance based on the basic quality assurance parameters, e.g., limit of detection (LOD), sensing range, and response time. Accordingly, the best performing MXene-based materials are selected and recommended for the given target(s) to help facilitate their scalable applications under real-world conditions.

Electrochemical needle sensor based on a B, N co-doped graphene microelectrode array for the on-site detection of salicylic acid in fruits and vegetables

In this study, a microelectrode array sensor based on boron and nitrogen co-doped vertical graphene (BNVG) was assembled to quantify salicylic acid (SA) in living plants. The influence of B and N contents on the electrochemical reaction kinetics and SA response signal was investigated. A microneedle sensor with three optimized BNVG microelectrodes (3.57 at.% B and 3.27 at.% N) was used to quantitatively analyze SA in the 0.5-100 μM concentration range and pH 4.0-9.0, with limits of detection of 0.14-0.18 μM. Additionally, a quantitative electrochemical model database based on the BNVG microelectrode sensor was constructed to monitor the growth of cucumbers and cauliflowers, which confirmed that the SA level and plant growth rate were positively correlated. Moreover, the SA levels in various vegetables and fruits purchased from the market were measured to demonstrate the practical application prospects for on-site inspection and evaluation.

Exploring nanodiamonds: leveraging their dual capacities for anticancer photothermal therapy and temperature sensing

Cancer has become a primary global health concern, which has prompted increased attention towards targeted therapeutic approaches like photothermal therapy (PTT). The unique optical and magnetic properties of nanodiamonds (NDs) have made them versatile nanomaterials with promising applications in biomedicine. This comprehensive review focuses on the potential of NDs as a multifaceted platform for anticancer therapy, mainly focusing on their dual functionality in PTT and temperature sensing. The review highlighted NDs' ability to enhance PTT through hybridization or modification, underscoring their adaptability in delivering small molecule reagents effectively. Furthermore, NDs, particularly fluorescent nanodiamonds (FNDs) with negatively charged nitrogen-vacancy centers, enable precise temperature monitoring, enhancing PTT efficacy in anticancer treatment. Integrating FNDs into PTT holds promise for advancing therapeutic efficacy by providing valuable insights into localized temperature variations and cell death mechanisms. This review highlights new insights into cancer treatment strategies, showcasing the potential of NDs to revolutionize targeted therapeutics and improve patient outcomes.

Graphene-based biosensors in milk analysis: A review of recent developments

Cow's milk, an excellent source of fat, protein, amino acids, vitamins and minerals, is currently one of the most consumed products worldwide. Contaminations originating from diverse sources, such as biological, chemical, and physical, cause dairy product quality problems and thus dairy-related disorders, raising public health issues. For this reason, legal authorities have deemed it necessary to classify certain contaminations in commercial milk and keep them within particular limitations; therefore, it is urgent to develop next-generation detection systems that can accurately identify just the contaminants of concern to human health. This review presents a detailed investigation of biosensors based on graphene and its derivatives, which offer superior sensitivity and selectivity, by classifying the contaminants under the headings biological, chemical, and physical, in cow's milk according to their sources. We reviewed the current status of graphene-based biosensor (GBs) technology for milk or dairy analysis, highlighting its strengths and weaknesses with the help of comparative studies, tables, and charts, and we put forward a novel perspective to handle future challenges.

Nanodiamonds: A Cutting-Edge Approach to Enhancing Biomedical Therapies and Diagnostics in Biosensing

Nanodiamonds (NDs) have garnered attention in the field of nanomedicine due to their unique properties. This review offers a comprehensive overview of NDs synthesis methods, properties, and their uses in biomedical applications. Various synthesis techniques, such as detonation, high-pressure, high-temperature, and chemical vapor deposition, offer distinct advantages in tailoring NDs' size, shape, and surface properties. Surface modification methods further enhance NDs' biocompatibility and enable the attachment of bioactive molecules, expanding their applicability in biological systems. NDs serve as promising nanocarriers for drug delivery, showcasing biocompatibility and the ability to encapsulate therapeutic agents for targeted delivery. Additionally, NDs demonstrate potential in cancer treatment through hyperthermic therapy and vaccine enhancement for improved immune responses. Functionalization of NDs facilitates their utilization in biosensors for sensitive biomolecule detection, aiding in precise diagnostics and rapid detection of infectious diseases. This review underscores the multifaceted role of NDs in advancing biomedical applications. By synthesizing NDs through various methods and modifying their surfaces, researchers can tailor their properties for specific biomedical needs. The ability of NDs to serve as efficient drug delivery vehicles holds promise for targeted therapy, while their applications in hyperthermic therapy and vaccine enhancement offer innovative approaches to cancer treatment and immunization. Furthermore, the integration of NDs into biosensors enhances diagnostic capabilities, enabling rapid and sensitive detection of biomolecules and infectious diseases. Overall, the diverse functionalities of NDs underscore their potential as valuable tools in nanomedicine, paving the way for advancements in healthcare and biotechnology.

High-Throughput Automatic Laser Printing Strategy toward Cost-effective Portable Integrated Urea Tele-Monitoring System

A portable sweat urea sensing system is a promising solution to satisfy the booming requirement of kidney function tele-monitoring. However, the complicated manufacturing route and the cumbersome electrochemical testing system still need to be improved to develop the urea point-of-care testing (POCT) and tele-monitoring devices. Here, a universal technical route based on a high-throughput automatic laser printing strategy for fabricating the portable integrated urea monitoring system is proposed. This integrated system includes a high-performance laser-printed urea sensing electrode, a planar three-electrode system, and a self-developed wireless mini-electrochemical workstation. A precursor donor layer is activated by laser scribing and in situ transferred into functional nanoparticles for the drop-on-demand printing of the urea sensing electrode. The obtained electrodes show high sensitivity, low detection limit, fast response time, high selectivity, good average recovery, and long-term stability for urea sensing. Additionally, a laser-induced graphene circuit-based miniature planar three-electrode system and a wireless mini-electrochemical workstation are designed for sensing data collection and transmitting, achieving real-time urea POCT and tele-monitoring. This scalable method provides a universal solution for high-throughput and ultra-fast fabrication of urea-sensing electrodes. The portable integrated urea monitoring system is a competitive option to achieve cost-effective POCT and tele-monitoring for kidney function.

A Review of Electroactive Nanomaterials in the Detection of Nitrogen-Containing Organic Compounds and Future Applications

Electrochemical and impedimetric detection of nitrogen-containing organic compounds (NOCs) in blood, urine, sweat, and saliva is widely used in clinical diagnosis. NOC detection is used to identify illnesses such as chronic kidney disease (CKD), end-stage renal disease (ESRD), cardiovascular complications, diabetes, cancer, and others. In recent years, nanomaterials have shown significant potential in the detection of NOCs using electrochemical and impedimetric sensors. This potential is due to the higher surface area, porous nature, and functional groups of nanomaterials, which can aid in improving the sensing performance with inexpensive, direct, and quick-time processing methods. In this review, we discuss nanomaterials, such as metal oxides, graphene nanostructures, and their nanocomposites, for the detection of NOCs. Notably, researchers have considered nanocomposite-based devices, such as a field effect transistor (FET) and printed electrodes, for the detection of NOCs. In this review, we emphasize the significant importance of electrochemical and impedimetric methods in the detection of NOCs, which typically show higher sensitivity and selectivity. So, these methods will open a new way to make embeddable electrodes for point-of-detection (POD) devices. These devices could be used in the next generation of non-invasive analysis for biomedical and clinical applications. This review also summarizes recent state-of-the-art technology for the development of sensors for on-site monitoring and disease diagnosis at an earlier stage.

Green structure orienting and reducing agents of wheat peel extract induced abundant surface oxygen vacancies and transformed the nanoflake morphology of NiO into a plate-like shape with enhanced non-enzymatic urea sensing application

Researchers are increasingly focusing on using biomass waste for green synthesis of nanostructured materials since green reducing, capping, stabilizing and orientation agents play a significant role in final application. Wheat peel extract contains a rich source of reducing and structure orienting agents that are not utilized for morphological transformation of NiO nanostructures. Our study focuses on the role of wheat peel extract in morphological transformation during the synthesis of NiO nanostructures as well as in non-enzymatic electrochemical urea sensing. It was observed that the morphological transformation of NiO flakes into nanoplatelets took place in the presence of wheat peel extract during the preparation of NiO nanostructures and that both the lateral size and thickness of the nanostructures were significantly reduced. Wheat peel extract was also found to reduce the optical band gap of NiO. A NiO nanostructure prepared with 5 mL of wheat peel extract (sample 2) was highly efficient for the detection of urea without the use of urease enzyme. It has been demonstrated that the induced modification of NiO nanoplatelets through the use of structure-orienting agents in the wheat peel has enhanced their electrochemical performance. A linear range of 0.1 mM to 13 mM was achieved with a detection limit of 0.003 mM in the proposed urea sensor. The performance of the presented non-enzymatic urea sensor was evaluated in terms of selectivity, stability, reproducibility, and practical application, and the results were highly satisfactory. As a result of the high surface active sites on sample 2, the low charge transfer resistance, as well as the high exposure to the surface active sites of wheat peel extract, sample 2 demonstrated enhanced performance. The wheat peel extract could be used for the green synthesis of a wide range of nanostructured materials, particularly metal/metal oxides for various electrochemical applications.

Wastewater treatment using nanodiamond and related materials

Nanodiamonds (NDs) are zero-dimensional (0D) carbon-based nanoparticles with SP3/SP2-hybridized carbon atoms that have shown great potential in wastewater treatment areas due to their high surface area, chemical stability, and unique adsorption properties. They can efficiently remove a wide range of pollutants from water, including heavy metals, organic compounds, and dyes via various mechanisms such as electrostatic interactions, π-π stacking, and ion exchange. NDs can be functionalized following different surface chemistries, enabling tailored surface properties and enhanced pollutant adsorption capabilities. This review covers recent research on the application of nanodiamonds in wastewater treatment domain with a major emphasis on adsorption, photocatalytic degradation, and membrane separation, highlighting their promising performances, challenges, and future directions.

Wearable potentiometric biosensor for analysis of urea in sweat

Herein, we introduce wearable potentiometric biosensors on screen-printed carbon electrodes (SPCEs) for on-body and on-site monitoring of urea in sweat. The biosensor architecture was judiciously designed to detect urea at different pHs and incorporate a pH sensor, thus containing polyaniline ink, urease bioink and a polyvinylchloride membrane. Urea detection could be performed in the wide range from 5 to 200 mM at pH 7.0, encompassing urea levels in human sweat. The biosensor response was fast (incubation time 5 min), with no interference from other substances in sweat. Reliable urea detection could be done in undiluted human sweat with a skin-worn flexible device using the pH correction strategy afforded by the pH sensor. The performance of the epidermal biosensor was not affected by severe bending strains. The feasibility of mass production was demonstrated by fabricating epidermal flexible biosensors using slot-die coating with a roll-to-roll technique.

Fluorescence of nanodiamond cocktails: pH-induced effects through interactions with comestible liquids

Fluorescent nanodiamonds with nitrogen-vacancy centers have become important nanoscale probes for sensing and imaging. The surface chemistry of the nanodiamonds influences their emission, interactions, and quantum properties. In this work, we propose to utilize fluorescent nanodiamonds as photostable markers for investigation of comestible liquids. We prepared nanodiamond/comestibles suspensions/cocktails with a wide range of pH levels and studied the samples via fluorescence, wettability, and zeta potential. The composition of the created cocktails revealed a strong impact on the properties of the nanodiamond and its surface chemistry, mainly induced by pH but also tuned by specific quenching compounds. Moreover, the stability of the nanodiamonds in the cocktail media was studied, along with various nature-originated compounds influencing their surface termination, polarity, and charge states. Thanks to the stability and biocompatibility of the nanodiamond, it can be applied in monitoring the condition of foodstuffs, and in the detection of toxins and pathogens in them.

Use of molecular imprinted polymers as sensitive/selective luminescent sensing probes for pesticides/herbicides in water and food samples

As non-biological molecules, molecular imprinted polymers (MIPs) can be made as antibody mimics for the development of luminescence sensors for various targets. The combination of MIPs with nanomaterials is further recognized as a useful option to improve the sensitivity of luminescence sensors. In this work, the recent progresses made in the fabrication of fluorescence, phosphorescence, chemiluminescence, and electrochemiluminescence sensors based on such combination have been reviewed with emphasis on the detection of pesticides/herbicides. Accordingly, the materials that are most feasible for the detection of such targets are recommended based on the MIP technologies.

Recent trends in the applications of thermally expanded graphite for energy storage and sensors - a review

Carbon nanomaterials such as carbon dots (0D), carbon nanotubes (1D), graphene (2D), and graphite (3D) have been exploited as electrode materials for various applications because of their high active surface area, thermal conductivity, high chemical stability and easy availability. In addition, due to the strong affinity between carbon nanomaterials and various catalysts, they can easily form metal carbides (examples: ionic, covalent, interstitial and intermediate transition metal carbides) and also help in the stable dispersion of catalysts on the surface of carbon nanomaterials. Thermally expanded graphite (TEG) is a vermicular-structured carbon material that can be prepared by heating expandable graphite up to 1150 °C using a muffle or tubular furnace. At high temperatures, the thermal expansion of graphite occurred by the intercalation of ions (examples: SO4 2-, NO3 -, Li+, Na+, K+, etc.) and oxidizing agents (examples: ammonium persulfate, H2O2, potassium nitrate, potassium dichromate, potassium permanganate, etc.) which helped in the exfoliation process. Finally, the obtained TEG, an intumescent form of graphite, has been used in the preparation of composite materials with various conducting polymers (examples: epoxy, poly(styrene-co-acrylonitrile), polyaniline, etc.) and metal chlorides (examples: FeCl3, CuCl2, and ZnCl2) for hydrogen storage, thermal energy storage, fuel cells, batteries, supercapacitors, sensors, etc. The main features of TEG include a highly porous structure, very lightweight with an apparent density (0.002-0.02 g cm-3), high mechanical properties (10 MPa), thermal conductivity (25-470 W m-1 K-1), high electrical conductivity (106-108 S cm-1) and low-cost. The porosity and expansion ratio of graphite layers could be customized by controlling the temperature and selection of intercalation ions according to the demand. Recently, TEG based composites prepared with metal oxides, chlorides and polymers have been demonstrated for their use in energy production, energy storage, and electrochemical (bio-) sensors (examples: urea, organic pollutants, Cd2+, Pb2+, etc.). In this review, we have highlighted and summarized the recent developments in TEG-based composites and their potential applications in energy storage, fuel cells and sensors with hand-picked examples.

Recent advancements in urea biosensors for biomedical applications

The quick progress in health care technology as a recurrent measurement of biochemical factors such as blood components leads to advance development and growth in biosensor technology necessary for effectual patient concern. The review wok of authors present a concise information and brief discussion on the development made in the progress of potentiometric, field effect transistor, graphene, electrochemical, optical, polymeric, nanoparticles and nanocomposites based urea biosensors in the past two decades. The work of authors is also centred on different procedures/methods for detection of urea by using amperometric, potentiometric, conductometric and optical processes, where graphene, polymer etc. are utilised as an immobilised material for the fabrication of biosensors. Further, a comparative revision has been accomplished on various procedures of urea analysis using different materials-based biosensors, and it discloses that electrochemical and potentiometric biosensor is the most promise one among all, in terms of rapid response time, extensive shelf life and resourceful design.

p-Dimethylaminobenzaldehyde-based chemosensor for on-site sensing of ammonia precursor in concrete

A chemosensor for on-site sensing of ammonia precursor in concrete to avoid a problem of ammonia emission into the indoor space of concrete buildings was designed and implemented. It was found that aqueous extracts of concrete samples containing antifreeze additives and excreting ammonia were colored in the presence of p-dimethylaminobenzaldehyde. This phenomenon was used for the fast visual sensing of main ammonia precursor (urea) in concrete for the first time. The developed sensor consisted of a sensing solid phase based on an adsorbent modified with p-dimethylaminobenzaldehyde. Various adsorbents were investigated for the immobilization of the reagent and it was established that silica adsorbent Silochrom C-120 provided effective retention of the reagent and Schiff's base formation during the sampling. Moreover, Silochrom C-120 modified with ascorbic acid was proposed to eliminate the oxidant interference. The sensor displayed excellent selectivity and sensitivity with the visual detection limit of 15 mg kg^-1 in terms of urea. The chemosensor was successfully applied by builders on different construction sites. Sample preparation and sensing times were about 2 min and 1 min, respectively.

An Overview on Recent Progress of Metal Oxide/Graphene/CNTs-Based Nanobiosensors

Nanobiosensors are convenient, practical, and sensitive analyzers that detect chemical and biological agents and convert the results into meaningful data between a biologically active molecule and a recognition element immobilized on the surface of the signal transducer by a physicochemical detector. Due to their fast, accurate and reliable operating characteristics, nanobiosensors are widely used in clinical and nonclinical applications, bedside testing, medical textile industry, environmental monitoring, food safety, etc. They play an important role in such critical applications. Therefore, the design of the biosensing interface is essential in determining the performance of the nanobiosensor. The unique chemical and physical properties of nanomaterials have paved the way for new and improved sensing devices in biosensors. The growing demand for devices with improved sensing and selectivity capability, short response time, lower limit of detection, and low cost causes novel investigations on nanobiomaterials to be used as biosensor scaffolds. Among all other nanomaterials, studies on developing nanobiosensors based on metal oxide nanostructures, graphene and its derivatives, carbon nanotubes, and the widespread use of these nanomaterials as a hybrid structure have recently attracted attention. Nanohybrid structures created by combining these nanostructures will directly meet the future biosensors' needs with their high electrocatalytic activities. This review addressed the recent developments on these nanomaterials and their derivatives, and their use as biosensor scaffolds. We reviewed these popular nanomaterials by evaluating them with comparative studies, tables, and charts.

Urea biosensors: A comprehensive review

Present study is specially designed for the recent advances in biosensors to detect and quantify urea concentration. Urea (carbamide) is an organic compound made up of the carbonyl (C=O) functional group with two -NH₂ groups having chemical formula CO (NH₂ )₂ . In nature, urea is found everywhere as the result of various processes, and in the human body, urea is an end product of nitrogen metabolism. An excessive concentration of urea in the human body is responsible for different critical diseases such as indigestion, acidity, ulcers, cancer, malfunctioning of kidneys, renal failure, urinary tract obstruction, dehydration, shock, burns, gastrointestinal bleeding, and so on. Moreover, below the normal level may cause hepatic failure, nephritic syndrome, cachexia, and so on. As well as in various fields such as fishery, dairy, food preservation, agriculture, and so on, urea is normally found and its detection is necessary. In urea biosensors, enzyme urease (Urs) is used as a bioreceptor element and retains its long last activity is the critical issue in front of the researcher. During recent decades, different nanoparticles (zinc oxide, nickel oxide, iron oxide, titanium dioxide, tin(IV) oxide, etc.), conducting polymer (polyaniline, polypyrrole, etc.), conducting polymer-nanoparticles composites, carbon materials (carbon nanotubes, graphene oxide, reduced graphene oxide graphene), and so on are used in urea biosensors. The main emphasis of the present study is to provide cumulative and comprehensive information about the sensing parameters of urea biosensors based on the materials used for enzyme immobilization. Besides this special task, this review provides a fruitful discussion on the basics of biosensors briefly for new and upcoming researchers. Thus, the present study may act as a gift for a large audience that come from different fields and are working in biosensors research.

Temperature-dependent electrical resistivity of macroscopic graphene nanoplatelet strips

This paper studies the temperature dependence of the electrical resistivity of low-cost commercial graphene-based strips, made from a mixture of epoxy and graphene nanoplatelets. An equivalent homogenous resistivity model is derived from the joint use of experimental data and simulation results obtained by means of a full three-dimensional (3D) numerical electrothermal model. Three different types of macroscopic strips (with surface dimensions of cm²) are analyzed, differing in their percentage of graphene nanoplatelets. The experimental results show a linear trend of resistivity in a wide temperature range (-60°C to +60°C), and a negative temperature coefficient . The derived analytical model of temperature-dependent resistivity follows the simple law commonly adopted for conventional conducting materials, such us copper. The model is then validated by using the graphene strips as heating elements by exploiting the Joule effect. These results suggest that such materials can be used as thermistors in sensing or heating applications.

Detection of food spoilage and adulteration by novel nanomaterial-based sensors

Food industry is always looking for more innovative and accurate ways to monitor the food safety and quality control of final products. Current detection techniques of analytes are costly and time-consuming, and occasionally require professional experts and specialized tools. The usage of nanomaterials in sensory systems has eliminated not only these drawbacks but also has advantages such as higher sensitivity and selectivity. This article first presents a general overview of the current studies conducted on the detection of spoilage and adulteration in foods from 2015 to 2020. Then, the sensory properties of nanomaterials including metal and magnetic nanoparticles, carbon nanostructures (nanotubes, graphene and its derivatives, and nanofibers), nanowires, and electrospun nanofibers are presented. The latest investigations and advancements in the application of nanomaterial-based sensors in detecting spoilage (food spoilage pathogens, toxins, pH changes, and gases) and adulterants (food additives, glucose, melamine, and urea) have also been discussed in the following sections. To conclude, these sensors can be applied in the smart packaging of food products to meet the demand of consumers in the new era.

Urea Biosensor Based on a CO2 Microsensor

Urea sensors based on electrodes in direct contact with the medium have limited long-term stability when exposed to complex media. Here, we present a urea biosensor based on urease immobilized in an alginate polymer, buffered at pH 6, and placed in front of a newly developed fast and sensitive CO2 microsensor, where the electrodes are shielded by a gas-permeable membrane. The CO2 produced by the urease in the presence of urea diffuses into the microsensor and is reduced at a Ag cathode. Oxygen interference is prevented by a Cr2+ trap. The 95% response time to changes in urea concentration was 120 s with a linear calibration curve in the range 0-1000 μM and a detection limit of 1 μM. The Ni2+ cofactor to improve sensor performance was continuously supplied from a reservoir behind the sensor tip. The stability of the urea sensor was optimized by the addition of bovine serum albumin as a stabilizer to the urease/alginate mixture that was cross-linked with glutaraldehyde and Ca2+ ions. This immobilization strategy resulted in about 70% of the initial urea sensor sensitivity after two weeks of continuous operation. The sensor was successfully tested in blood serum.

Nanomaterial-based immunosensors for ultrasensitive detection of pesticides/herbicides: Current status and perspectives

The increasing level of pesticides and herbicides in food and water sources is a growing threat to human health and the environment. The development of portable, sensitive, specific, simple, and cost-effective sensors is hence in high demand to avoid exposure or consumption of these chemicals through efficient monitoring of their levels in food as well as water samples. The use of nanomaterials (NMs) for the construction of an immunosensing system was demonstrated to be an efficient and effective option to realize selective sensing against pesticides/herbicides. The potential of such applications has hence been demonstrated for a variety of NMs including graphene, carbon nanotubes (CNTs), metal nanoparticles, and nano-polymers either in pristine or composite forms based on diverse sensing principles (e.g., electrochemical, optical, and quartz crystal microbalance (QCM)). This article evaluates the development, applicability, and performances of NM-based immunosensors for the measurement of pesticides and herbicides in water, food, and soil samples. The performance of all the surveyed sensors has been evaluated on the basis of key parameters, e.g., detection limit (DL), sensing range, and response time.

An amperometric biosensor based on poly(L-aspartic acid), nanodiamond particles, carbon nanofiber, and ascorbate oxidase-modified glassy carbon electrode for the determination of L-ascorbic acid

An amperometric L-ascorbic acid biosensor utilizing ascorbate oxidase (AOx) immobilized onto poly(L-aspartic acid) (P(L-Asp)) film was fabricated on carbon nanofiber (CNF) and nanodiamond particle (ND)-modified glassy carbon electrode (GCE). Effects of AOx, ND, and CNF amounts were investigated by monitoring the response currents of the biosensor at different amounts of AOx, ND, and CNF. The electropolymerization step of L-aspartic acid on CNF-ND/GCE surface was also optimized. Scanning electron microscopy (SEM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) techniques were used to enlighten the modification steps of the biosensor. The effects of pH and applied potential were studied in detail to achieve the best analytical performance. Under optimized experimental conditions, the AOx/P(L-Asp)/ND-CNF/GCE biosensor showed a linear response to L-ascorbic acid in the range of 2.0 × 10^-7-1.8 × 10^-3 M with a detection limit of 1.0 × 10^-7 M and sensitivity of 105.0 μAmM^-1 cm^-2. The novel biosensing platform showed good reproducibility and selectivity. The strong interaction between AOx and the P(L-Asp)/ND-CNF matrix was revealed by the high repeatability (3.4%) and good operational stability. The AOx/P(L-Asp)/ND-CNF/GCE biosensor was successfully applied to the determination of L-ascorbic acid in vitamin C effervescent tablet and pharmaceutical powder containing ascorbic acid with good results, which makes it a promising approach for quantification of L-ascorbic acid. Graphical abstract.

An AgNP-deposited commercial electrochemistry test strip as a platform for urea detection

We developed an inexpensive, portable platform for urea detection via electrochemistry by depositing silver nanoparticles (AgNPs) on a commercial glucose test strip. We modified this strip by first removing the enzymes from the surface, followed by electrodeposition of AgNPs on one channel (working electrode). The morphology of the modified test strip was characterized by Scanning Electron Microscopy (SEM), and its electrochemical performance was evaluated via Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS). We evaluated the performance of the device for urea detection via measurements of the dependency of peak currents vs the analyte concentration and from the relationship between the peak current and the square root of the scan rates. The observed linear range is 1-8 mM (corresponding to the physiological range of urea concentration in human blood), and the limit of detection (LOD) is 0.14 mM. The selectivity, reproducibility, reusability, and storage stability of the modified test strips are also reported. Additional tests were performed to validate the ability to measure urea in the presence of confounding factors such as spiked plasma and milk. The results demonstrate the potential of this simple and portable EC platform to be used in applications such as medical diagnosis and food safety.

Nanomaterials for Healthcare Biosensing Applications

In recent years, an increasing number of nanomaterials have been explored for their applications in biomedical diagnostics, making their applications in healthcare biosensing a rapidly evolving field. Nanomaterials introduce versatility to the sensing platforms and may even allow mobility between different detection mechanisms. The prospect of a combination of different nanomaterials allows an exploitation of their synergistic additive and novel properties for sensor development. This paper covers more than 290 research works since 2015, elaborating the diverse roles played by various nanomaterials in the biosensing field. Hence, we provide a comprehensive review of the healthcare sensing applications of nanomaterials, covering carbon allotrope-based, inorganic, and organic nanomaterials. These sensing systems are able to detect a wide variety of clinically relevant molecules, like nucleic acids, viruses, bacteria, cancer antigens, pharmaceuticals and narcotic drugs, toxins, contaminants, as well as entire cells in various sensing media, ranging from buffers to more complex environments such as urine, blood or sputum. Thus, the latest advancements reviewed in this paper hold tremendous potential for the application of nanomaterials in the early screening of diseases and point-of-care testing.