Reduced graphene oxide doping with nanometer-sized ferrocene moieties - New active material for glucose redox sensors

Ferrocene-decorated graphene nanosheets built by edge-to-face π-π interaction for room temperature ppb-level NO sensing

The development of materials toward ppb-level nitric oxide (NO) sensing at room temperature remains in high demand for the monitoring of respiratory inflammatory diseases. In order to find an iron-containing molecule without steric hindrance to combine with graphene for room temperature NO gas sensing, here a supramolecular assembly of ferrocene (Fc) and reduced graphene oxide (rGO) was designed and prepared for NO sensing. The assembly of Fc/rGO was characterized using FT-IR, TEM, and XPS measurements. The Fc/rGO-based sensors exhibited superior NO sensing properties at room temperature including high response (Ra/Rg = 1.73, 1 ppm), high selectivity against other exhaled gases, reliable repeatability and stability (less than 4 % decrease after 40 days). A practical limit of detection (LOD) of 200 ppb was achieved. The theoretical simulation demonstrates that ferrocene is assembled via π-π interaction with rGO in edge-to-face configuration which provides relatively lower energy than face-to-face configuration does for the whole assembly. It was first verified that the enhanced adsorption capacity and the charge transfer between NO and Fc/rGO would result in improvement of the assembly's sensitivity toward NO after ferrocene was assembled with graphene. This work provides a fresh approach of anchoring iron on graphene for gas sensing via supramolecular methods.

Label-Free Mode Based on Ferrocene/PEDOT:PSS-PPy for Molecularly Imprinted Electrochemically Ultrasensitive Detection of Amino Acids

Generally, molecularly imprinted (MIP) electrochemical sensors for amino acids operate in a "label-like" mode. That is, after an amino acid is specifically recognized by an imprinted cavity at the sensing interface, the amino acid itself provides the sensing signal for quantitative detection. However, poorly electroactive amino acids impede electron transfer at the sensing interface and require high potentials to drive the reaction; thus, more interfering reactions tend to be triggered in practical applications, causing enhanced background noise in the detection. To address these issues, a "label-free" mode of the MIP sensor based on the ferrocene (Fc)/PEDOT:PSS-polypyrrole (PPy) composite was designed for the first time. The Fc/PEDOT:PSS-PPy is drop coated on the electrode surface as a substrate, and MIP polymers with specific recognition ability are immobilized on the substrate via electrostatic adsorption. As a proof of concept, l-tyrosine (l-Tyr) was selected as a model analyte and the "label-free" mode MIP/Fc/PEDOT:PSS-PPy sensor was constructed. The limit of detection (LOD) and linearity range of the MIP/Fc/PEDOT:PSS-PPy sensor were 2.31 × 10-11 M and from 100 pM to 5 mM, respectively. Compared with the label-like mode, the LOD was three orders of magnitude lower, the linear range was increased by three orders of magnitude, and the sensitivity was improved by more than four times. This work provides a universal and effective concept for MIP electrochemical sensing of amino acids.

Advanced nanomaterials for electrochemical sensors: application in wearable tear glucose sensing technology

In the last few decades, tear-based biosensors for continuous glucose monitoring (CGM) have provided new avenues for the diagnosis of diabetes. The tear CGMs constructed from nanomaterials have been extensively demonstrated by various research activities in this field and are gradually witnessing their most prosperous period. A timely and comprehensive review of the development of tear CGMs in a compartmentalized manner from a nanomaterials perspective would greatly broaden this area of research. However, to our knowledge, there is a lack of specialized reviews and comprehensive cohesive reports in this area. First, this paper describes the principles and development of electrochemical glucose sensors. Then, a comprehensive summary of various advanced nanomaterials recently reported for potential applications and construction strategies in tear CGMs is presented in a compartmentalized manner, focusing on sensing properties. Finally, the challenges, strategies, and perspectives used to design tear CGM materials are emphasized, providing valuable insights and guidance for the construction of tear CGMs from nanomaterials in the future.

A dual-mode biosensor featuring single-atom Fe nanozyme for multi-pesticide detection in vegetables

The single-atom iron nanozyme (SA-Fe-NZ) exhibits high catalytic activity and excellent electron transfer efficiency in biosensors. However, the binding of bioreceptors to the surface of SA-Fe-NZ results in a decrease in the catalytic activity of the nanozyme due to its toxic effects. We utilized the toxic effects and excellent electrochemical properties of the SA-Fe-NZ to successfully construct a smartphone-assisted dual-mode biosensor. The complex formed by the binding of organophosphorus pesticides (OPs) to the aptamer exhibited toxic effects and inhibited the catalytic activity of the nanozyme, preventing the colorimetric substrate from being catalyzed. Simultaneously, the aptamers labeled with electrochemical signal molecules approached the electrode surface, causing a change in the electrochemical signal. The results demonstrated that the constructed broad-spectrum aptamer biosensor exhibited a low limit of detection of 3.55 fM and a wide linear range of 10-13-10-2 M, allowing for qualitative and quantitative detection of multiple OPs in vegetables.

The energetic and physical concept of gold nanorod-dependent fluorescence in cancer treatment and development of new photonic compounds|review

The optical features of gold nanorods (GNR) may be precisely controlled by manipulating their size, shape, and aspect ratio. This review explores the impact of these parameters on the optical tuning of (GNR). By altering the experimental conditions, like the addition of silver ions during the seed-mediated growth process, the aspect ratio of (GNR) may be regulated. The shape is trans from spherical to rod-like structures resulting in noticeable changes in the nanoparticles surface plasmons resonance (SPR) bands. The longitudinal SPR band, associated with electron oscillations along the long axis, exhibits a pronounced red shift into the (NIR) region as the aspect ratio increases. In contrast, the transverse SPR band remains relate unchanged. Using computational methods like the discrete dipole approximation (DDA) allows for analyzing absorption, scattering, and total extinction features of gold (G) nanoparticles. Studies have shown that increasing the aspect ratio enhances the scattering efficiency, indicating a higher scattering quantum yield (QY). These findings highlight the importance of size, shape, and aspect ratio in controlling the optical features of (GNR) providing valuable insights for various uses in nanophotonics and plasmonic-dependent fluorescence in cancer treatment and developing new photonic compound NRs.

Porous nitrogen-doped reduced graphene oxide-supported CuO@Cu2O hybrid electrodes for highly sensitive enzyme-free glucose biosensor

Constructing high-performance enzyme-free biosensors for detecting glucose is essential to preliminary diabetes diagnosis. Here, copper oxide nanoparticles (CuO@Cu₂O NPs) were anchored in porous nitrogen-doped reduced graphene oxide (PNrGO) to construct CuO@Cu₂O/PNrGO/GCE hybrid electrode for sensitive detection of glucose. Benefiting from the remarkable synergistic effects between the multiple high activation sites of CuO@Cu₂O NPs and the dramatic properties of PNrGO with excellent conductivity and large surface area with many accessible pores, the hybrid electrode possesses outstanding glucose sensing performance that is far superior to those of pristine CuO@Cu₂O electrode. The as-fabricated enzyme-free glucose biosensor displays prominent glucose sensitivity of 2,906.07 μA mM^-1 cm^-2, extremely low limit of detection of 0.13 μM, and wide linear detection of 3 μM-6.772 mM. In addition, excellent reproducibility, favorable long-term stability, and distinguished selectivity are obtained in the glucose detection. Importantly, this study provides promising results for continuous improvement of non-enzyme sensing applications.

Progress of Enzymatic and Non-Enzymatic Electrochemical Glucose Biosensor Based on Nanomaterial-Modified Electrode

This review covers the progress of nanomaterial-modified electrodes for enzymatic and non-enzymatic glucose biosensors. Fundamental insights into glucose biosensor components and the crucial factors controlling the electrochemical performance of glucose biosensors are discussed in detail. The metal, metal oxide, and hybrid/composite nanomaterial fabrication strategies for the modification of electrodes, mechanism of detection, and significance of the nanomaterials toward the electrochemical performance of enzymatic and non-enzymatic glucose biosensors are compared and comprehensively reviewed. This review aims to provide readers with an overview and underlying concept of producing a reliable, stable, cost-effective, and excellent electrochemical performance of a glucose biosensor.

Wearable microfluidic-based e-skin sweat sensors

Electronic skins (e-skins) are soft (deformable and stretchable) state-of-the-art wearable devices that emulate the attributes of human skin and act as a Human-Machine Interface (HMI). Recent advances in e-skin for real-time detection of medical signals such as pulse, temperature, electromyogram (EMG), electroencephalogram (EEG), electrooculogram (EOG), electrocardiogram (ECG), and other bioelectric signals laid down an intelligent foundation for early prediction and diagnosis of diseases with a motive of reducing the risk of the ailment reaching to the end stage. In particular, sweat testing has been employed in diverse applications ranging from medical diagnosis of diabetes, cystic fibrosis, tuberculosis, blood pressure, and autonomic neuropathy to evaluating fluid and electrolyte balance in athletes. Typically, sweat testing techniques are done by trained experts and require off-body measurements, which prevent individuals from de-coding health issues quickly and independently. With the onset of soft electronics, wearable sweat sensors overcome this disadvantage via in situ sweat measurements with real-time feedback, timely diagnosis, creating the potential for preventive care and treatment. Over the past few decades, wearable microfluidic-based e-skin sweat sensors have paved a new way, promising sensing interfaces that are highly compatible with arranging medical and electronic applications. The present review highlights the recent research carried out in the microfluidic-based wearable sweat sensors with a critical focus on real-time sensing of lactate, chloride, and glucose concentration; sweat rate, simultaneously with pH, and total sweat loss for preventive care, timely diagnosis, and point-of-care health and fitness monitoring.

Wearable biochemical sensors for human health monitoring: sensing materials and manufacturing technologies

Wearable biochemical sensors are of great interest nowadays due to their powerful potential in personalized medicine and continuous monitoring of human health. Thus, a great deal of effort has been put into the development of such sensors to enable real-time and non-invasive quantification of various chemical constituents in the human body such as sweat, saliva, and tears. Owing to the advances in materials science and mechanical engineering, wearable biochemical sensors have been developed to probe various biomarkers and have been subsequently considered as wearable electronic devices for practical applications. In this review, we present a broad overview on the recent advances in electrochemical wearable sensors towards various organic components and ions closely linked to human health. With an emphasis on materials and manufacturing technologies of the sensing electrodes, the research status is summarized, and the challenges and opportunities in this growing field are prospected.

Wearable Biosensors: An Alternative and Practical Approach in Healthcare and Disease Monitoring

With the increasing prevalence of growing population, aging and chronic diseases continuously rising healthcare costs, the healthcare system is undergoing a vital transformation from the traditional hospital-centered system to an individual-centered system. Since the 20th century, wearable sensors are becoming widespread in healthcare and biomedical monitoring systems, empowering continuous measurement of critical biomarkers for monitoring of the diseased condition and health, medical diagnostics and evaluation in biological fluids like saliva, blood, and sweat. Over the past few decades, the developments have been focused on electrochemical and optical biosensors, along with advances with the non-invasive monitoring of biomarkers, bacteria and hormones, etc. Wearable devices have evolved gradually with a mix of multiplexed biosensing, microfluidic sampling and transport systems integrated with flexible materials and body attachments for improved wearability and simplicity. These wearables hold promise and are capable of a higher understanding of the correlations between analyte concentrations within the blood or non-invasive biofluids and feedback to the patient, which is significantly important in timely diagnosis, treatment, and control of medical conditions. However, cohort validation studies and performance evaluation of wearable biosensors are needed to underpin their clinical acceptance. In the present review, we discuss the importance, features, types of wearables, challenges and applications of wearable devices for biological fluids for the prevention of diseased conditions and real-time monitoring of human health. Herein, we summarize the various wearable devices that are developed for healthcare monitoring and their future potential has been discussed in detail.

A Non-Enzymatic Sensor Based on Fc-CHIT/CNT@Cu Nanohybrids for Electrochemical Detection of Glucose

Herein, a composite structure, consisting of Cu nanoparticles (NPs) deposited onto carbon nanotubes and modified with ferrocene-branched chitosan, was prepared in order to develop a nonenzymatic electrochemical glucose biosensor ferrocene-chitosan/carbon nanotube@ Cu (Fc-CHIT/CNT@Cu). The elemental composition of the carbon nanohybrids, morphology and structure were characterized by various techniques. Electrochemical impedance spectroscopy (EIS) was used to study the interfacial properties of the electrodes. Cyclic voltammetry (CV) and chronoamperometry methods in alkaline solution were used to determine glucose biosensing properties. The synergy effect of Cu NPs and Fc on current responses of the developed electrode resulted in good glucose sensitivity, including broad linear detection between 0.2 mM and 22 mM, a low detection limit of 13.52 μM and sensitivity of 1.256 μA mM⁻¹cm⁻². Moreover, the modified electrode possessed long-term stability and good selectivity in the presence of ascorbic acid, dopamine and uric acid. The results indicated that this inexpensive electrode had potential application for non-enzymatic electrochemical glucose detection.

New Advances in Fabrication of Graphene Glyconanomaterials for Application in Therapy and Diagnosis

Glycoderivatives are an important class of molecules with enormous relevance in numerous biological phenomena; therefore, they have a key role in the learning, understanding, and assessment of different diseases. Nanotechnology, and in particular the design of new nanomaterials, is one of the areas of greatest interest today. In this case, graphene nanomaterials represent very interesting platforms for studying glycosystems, glyconanomaterials that combine the biomolecular recognition and the characteristics of nanoscale objects in the development of early diagnosis systems, and efficient specific therapeutic modalities. In this mini-review, we discuss some results recently described in the literature on the conjugation of graphene materials and carbohydrates through the selective interaction of glycoenzymes in graphene to create new materials with biosensing applications, the development and application of sugar-graphene composites, and finally biosystems combining the properties of graphene with metallic nanoparticles and sugars for the creation of excellent glyconanomaterials as novel systems for the therapy or diagnosis of important diseases such as cancer or diabetes.

Single-Atom Enzyme-Functionalized Solution-Gated Graphene Transistor for Real-Time Detection of Mercury Ion

Mercury ion (Hg²⁺), a bioaccumulating and toxic heavy metal, can cause severe damages to the environment and human health. Therefore, development of high-performance Hg²⁺ sensors is highly desirable. Herein, we construct a uniform dodecahedral shaped N-doped carbon decorated by single Fe site enzyme (Fe-N-C SAE), which exhibits good performance for Hg²⁺ detection. The N atom on Fe-N-C SAE can specifically recognize Hg²⁺ through chelation between Hg²⁺ and N atom, while the catalytic site on the single-atom enzyme acts as a signal amplifier. The Fe-N-C SAE-functionalized solution-gated graphene transistor exhibits a dramatic improvement in the selectivity and sensitivity of the devices. The sensor can rapidly detect Hg²⁺ down to 1 nM within 2 s. Besides, a relatively good repeatability and reproducibility for the detection of Hg²⁺ have also been found in our sensor platform. Our findings expand the application of single-atom catalysts in the field of food safety and environmental monitoring.

Ethanol vs. water: influence of the terminal functional group of the alkyl chain and environment of the self-assembly process on electron transport through the thiol layer

Self-assembly of alkanethiol chains on metallic surfaces is a spontaneous process which leads to the formation of highly ordered layers. However, the organization of the thiol chains on the surface strongly depends on the intermolecular interactions between the terminal groups in the chain. The solution environment also plays an important role. In this paper we present the effect of solution solvent (water and ethanol) and the presence of various hydrophilic terminal groups (–OH, –NH₂ and –COOH) on the quality and electrochemical properties of the formed alkanethiol layers. In the studies we applied voltammetry, atomic force microscopy and quartz crystal microbalance to characterize the morphology, packing density and ability to electron exchange through the thiol layer. The blocking properties of the formed SAMs expressed as the electron-transfer rate constant as well as their organization have been examined using a model electrochemical probe, Fe(CN)₆³⁻. With the increase in the polarity of the terminal functional group the regularity of the thiol layer decreased.

The organization of the thiol chains on the surface strongly depends on the intermolecular interactions between the terminal groups in the chain and the solution environment.