Current progress in organic–inorganic hetero-nano-interfaces based electrochemical biosensors for healthcare monitoring

The Exploration of Nanozymes for Biosensing of Pathological States Tailored to Clinical Theranostics

The nanozymes (NZs) are the artificial catalyst deployed for biosensing with their uniqueness (high robustness, surface tenability, inexpensive, and stability) for obtaining a better response/miniaturization of the varied sensors than their traditional ancestors. Nowadays, nanomaterials with their broadened scale such as metal-organic frameworks (MOFs), and metals/metal oxides are widely engaged in generating NZ-based biosensors (BS). Diverse strategies like fluorescent, colorimetric, surface-enhanced Raman scattering (SERS), and electrochemical sensing principles were implemented for signal transduction of NZs. Despite broad advantages, numerous encounters (like specificity, feasibility, stability, and issues in scale-up) are affecting the potentialities of NZs-based BS, and thus need prior attention for a promising exploration for a revolutionary outcome in advanced theranostics. This review includes different types of NZs, and the progress of numerous NZs tailored bio-sensing techniques in detecting abundant bio analytes for theranostic purposes. Further, the discussion highlighted some recent challenges along with their progressive way of possibly overcoming followed by commercial outbreaks.

Electrochemical and optical (bio)sensors for analysis of antibiotic residuals

Antibiotic residuals in foods may lead to crucial health and safety issues in the human body. Rapid and in-time analysis of antibiotics using simple and sensitive techniques is in high demand. Among the most commonly applicable modalities, chromatography-based techniques like HPLC and LC-MS, along with immunological approaches, particularly ELISA have been exampled in the analysis of antibiotics. Despite being highly sensitive, these methods are considerably time-consuming, thus the presence of skilled personnel and costly equipment is essential. Nanomaterial-based (bio)sensors, however, are de novo analytical equipment with some beneficial characteristics, such as simplicity, low price, on-site, high accuracy, and sensitivity for the detection of analytes. This review aimed to collect the latest developments in NM-based sensors and biosensors for the observation of highly used antibiotics like Vancomycin (Van), Linezolid (Lin), and Clindamycin (Clin). The current challenges and developmental perspectives are also debated in detail for future research directions.

Recent advances in biological molecule detection based on a three-dimensional graphene structure

Graphene has become an attractive material in the field of electrochemical detection owing to its unique electrical properties. Although the simple stacking structures of two-dimensional (2D) graphene sheets can provide excellent detection properties, a macroscopic three-dimensional (3D) structure needs to be constructed to enhance its functional properties. Graphene with a 3D structure has elegant functions, unlike graphene with a 2D structure. These properties include a large specific surface area, easy loading of nanomaterials with electrocatalytic and redox functions, and so on. Herein, we outline the preparation methods (self-assembly, chemical vapor deposition, templates, and 3D printing) for 3D graphene structures for obtaining excellent detection performance and applications in detecting biological molecules, bacteria, and cells. Furthermore, this review focuses on the improvement of the detection performance and enhancement of the applicability of graphene-based electrochemical sensors. We hope that this article will provide a reference for the future development of electrochemical sensors based on 3D graphene composites.

Integrated Cu-Au stereo microelectrode arrays and microfluidic channels for the electrochemical detection of glucose

Noble and transition metal nanomaterials are widely used in glucose sensing. However, the fabrication of these sensors still suffers from complex nanomaterial synthesis process and unstable nanomaterial loading on sensing surfaces. Herein, a Cu-Au bimetallic microelectrode array was prepared via local electrochemical deposition and electrochemical reduction without the need for templates and additional nanomaterial preparation processes. Based on the COMSOL computational fluid study, the obtained microelectrode arrays combined with microfluidic channels allow the continuous and rapid detection of glucose. Large number of active sites on the surface of 3D nano-arrays contributes to excellent sensing performance for glucose, with good linear detection ranges in 10 µM to 4 × 102 µM and 4 × 102 µM to 4 × 105 µM, and a low detection limit of 284 nM. The feasibility of sensor in real sample was verified by detecting glucose in beverages with good recoveries ranging from 95.50% to 104.31%.

Mechanically Tough and Highly Stretchable Hydrogels Based on Polyurethane for Sensitive Strain Sensor

Hydrogels with flexible and stretchable properties are ideal for applications in wearable sensors. However, traditional hydrogel-based sensors suffer from high brittleness and low electrical sensitivity. In this case, to solve this dilemma, a macromolecular polyurethane crosslinking agent (PCA) was designed and prepared; after that, PCA and two-dimensional (2D) MXene nanosheets were both introduced into a covalently crosslinked network to enhance the comprehensive mechanical and electrochemical properties of the hydrogels. The macromolecular polyurethane crosslinking agent promotes high-tensile strength and highly stretchable capacity by suitable covalent crosslinking. The optimized hydrogel, which exhibited maximum tensile strength and maximum elongation at break, had results of 1.21 MPa and 644%, respectively. Two-dimensional MXene nanosheets provide hydrogel with high electrical conductivity and strain sensitivity, producing a wearable device for the continuous monitoring of human movements and facial microexpressions. This study demonstrated an efficient structure design strategy for building mechanically tough, highly stretchable, and sensitive dual-mode MXenes-based wearable sensors.

Colorimetric detection of chromium (VI) via its instigation of oxidase-mimic activity of CuO

Extensive use of chromium makes it one of the major pollutants of water resources. Chromium (VI) in particular is toxic and has detrimental health effects. Because of its high toxicity a tolerable concentration limit of chromium (VI) in drinking water has been recommended. Here we report a colorimetric method for determination of chromium (VI) in water based on the oxidase-like activity of solvothermal synthesized copper oxide. The particles have been characterized by X- ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM). Using 3, 3', 5, 5'- tetramethylbenzidine (TMB) as a chromogenic substrate, CuO exhibited a pronounced oxidase-like activity in the presence of chromium (VI). This method enables successful colorimetric detection of chromium (VI). It demonstrated excellent selectivity for detection of chromium (VI) ions against potentially interfering ions. The method's feasibility to real sample analysis has been proven by testing tap water. Hence, we anticipate that the method can be successfully applied for analysis of chromium (VI) in environmental samples.

A hybrid SERS sensing platform constructed by porous carbon/Ag nanoparticles for efficient imatinib detection in bio-environment

Surface enhanced Raman scattering (SERS) is a rapid and non-destructive spectral detection technique, and has been widely implemented on trace-level molecule detection. In this work, a hybrid SERS substrate constructed by porous carbon film and silver nanoparticles (PCs/Ag NPs) was developed and then used for imatinib (IMT) detection in bio-environment. The PCs/Ag NPs was prepared by direct carbonizing the gelatin-AgNO₃ film in the air atmosphere, and an enhancement factor (EF) of 10⁶ was achieved with R6G as the Raman reporter. Hereafter, this SERS substrate was used as the label-free sensing platform to detect the IMT in the serum, and the experimental results indicate that the substrate is conducive to eliminating the interference from the complex biological molecules in the serum, and the characteristic Raman peaks belonging to IMT (10^-4 M) are accurately resolved. Furthermore, the SERS substrate was used to trace the IMT in the whole blood, the trace of ultra-low concertation of IMT is rapidly discovered without any pretreatment. Thus, this work finally suggests that the proposed sensing platform provides a rapid and reliable method for IMT detection in the bio-environment and offers a potential for its application in therapeutic drug monitoring.

Site-selective growth and plasmonic spectral properties of L-shaped Janus Au-Ag gold nanodumbbells for surface-enhanced Raman scattering

Ligand-mediated interface control has been broadly applied as a powerful tool in constructing asymmetric multicomponent nanoparticles (AMNP), and induces the anisotropic growth with fine-tuning morphology, composition, plasmonic property and functionality. As a new kind of AMNP, the synthesis of Janus Au-Ag nanoparticles with tunable negative surface curvature is still a challenge. Here, we demonstrate that the synergistic surface energy effects between gold nanodumbbells (Au NDs) with a negative surface curvature and 4-mercaptobenzoic acid (4-MBA) can direct the site-selective growth of anisotropic silver domains on gold nanodumbbells (Au NDs@Ag NPs). By adjusting the 4-MBA concentration-dependent interfacial energy, the Au NDs@Ag NPs could be continuously tuned from dumbbell-like core-shell structures, to L-shaped Janus, and then rod-like core-shell structures with directional and asymmetric spatial distributions of resizable Ag domains by site-selective growth. Based on the calculation results of discrete dipole approximation (DDA) method, it has been found that the Au NDs@Ag L-shaped Janus NPs with Ag island domains created polarization orientation-dependent plasmonic extinction spectra and hot spots around the negatively curved waist and Ag domains. The L-shaped Janus Au NDs@Ag NPs exhibited significantly plasmonic spectrum properties with four apparent LSPR peaks that cover from visible to near-infrared range and higher surface-enhanced Raman scattering (SERS) activity compared with the original Au NDs. The best SERS enhancement factor of 1.41 × 10⁷ was achieved. This synergistic surface energy effect-based method involving the asymmetric growth of silver coating on gold nanoparticles with negatively curved surface presents a new method to design and fabricate nanometer optical devices based on asymmetric multicomponent nanoparticles.

Advancements in nanomaterial-based aptasensors for the detection of emerging organic pollutants in environmental and biological samples

The combination of nanomaterials (NMs) and aptamers into aptasensors enables highly specific and sensitive detection of diverse pollutants. The great potential of aptasensors is recognized for the detection of diverse emerging organic pollutants (EOPs) in different environmental and biological matrices. In addition to high sensitivity and selectivity, NM-based aptasensors have many other advantages such as portability, miniaturization, facile use, and affordability. This work showcases the recent advances achieved in the design and fabrication of NM-based aptasensors for monitoring EOPs (e.g., hormones, phenolic contaminants, pesticides, and pharmaceuticals). On the basis of their sensing mechanisms, the covered aptasensing systems are classified as electrochemical, colorimetric, PEC, fluorescence, SERS, and ECL. Special attention has been paid to the fabrication processes, analytical achievements, and sensing mechanisms of NM-based aptasensors. Further, the practical utility of aptasensing approaches has also been assessed based on their basic performance metrics (e.g., detection limits, sensing ranges, and response times).

Electrochemical signal amplification strategy based on trace metal ion modified WS2 for ultra-sensitive detection of miRNA-21

Previous researches have suggested the potential correlation between the development of breast cancer and the concentration of miRNA-21 in serum. Theoretically the doping of multivalent metal ions in WS₂ could bring higher electron transfer capacity, but this hasn't been proven. To fill this research gap, through one-pot method we prepared seven nanocomposite structures modified with different metal ions (Co²⁺, Ni²⁺, Mn²⁺, Zn²⁺, Fe³⁺, Cr³⁺, La³⁺). Characterization revealed that ammonia produced by hydrothermal urea exfoliated the multilayer graphene oxide (MGO) and provided a nitrogen source for doping reduction to form a 3D flower-like structure (NrGOF) with high specific surface area. Meanwhile, the modification of WS₂ by Fe³⁺ not only enhanced its electrochemical conductivity but also gave the material an additional peroxidase activity centre. In the composite Fe³⁺-WS₂/NrGOF-AgNPs, NrGOF is used as a conductive loading interface for WS₂, while Fe³⁺ served as the catalytic and electron transfer centre for secondary amplification of the electrochemical signal. The experimental results showed that the sensing platform has a low limit of detection (LOD) of 1.18 aM for miRNA-21 in the concentration range of 10^-17-10^-12 M and has been successfully applied to the detection of real serum samples.

Nanozymes towards Personalized Diagnostics: A Recent Progress in Biosensing

This review highlights the recent advancements in the field of nanozymes and their applications in the development of point-of-care biosensors. The use of nanozymes as enzyme-mimicking components in biosensing systems has led to improved performance and miniaturization of these sensors. The unique properties of nanozymes, such as high stability, robustness, and surface tunability, make them an attractive alternative to traditional enzymes in biosensing applications. Researchers have explored a wide range of nanomaterials, including metals, metal oxides, and metal-organic frameworks, for the development of nanozyme-based biosensors. Different sensing strategies, such as colorimetric, fluorescent, electrochemical and SERS, have been implemented using nanozymes as signal-producing components. Despite the numerous advantages, there are also challenges associated with nanozyme-based biosensors, including stability and specificity, which need to be addressed for their wider applications. The future of nanozyme-based biosensors looks promising, with the potential to bring a paradigm shift in biomolecular sensing. The development of highly specific, multi-enzyme mimicking nanozymes could lead to the creation of highly sensitive and low-biofouling biosensors. Integration of nanozymes into point-of-care diagnostics promises to revolutionize healthcare by improving patient outcomes and reducing costs while enhancing the accuracy and sensitivity of diagnostic tools.

Biosensor integrated brain-on-a-chip platforms: Progress and prospects in clinical translation

Because of the brain's complexity, developing effective treatments for neurological disorders is a formidable challenge. Research efforts to this end are advancing as in vitro systems have reached the point that they can imitate critical components of the brain's structure and function. Brain-on-a-chip (BoC) was first used for microfluidics-based systems with small synthetic tissues but has expanded recently to include in vitro simulation of the central nervous system (CNS). Defining the system's qualifying parameters may improve the BoC for the next generation of in vitro platforms. These parameters show how well a given platform solves the problems unique to in vitro CNS modeling (like recreating the brain's microenvironment and including essential parts like the blood-brain barrier (BBB)) and how much more value it offers than traditional cell culture systems. This review provides an overview of the practical concerns of creating and deploying BoC systems and elaborates on how these technologies might be used. Not only how advanced biosensing technologies could be integrated with BoC system but also how novel approaches will automate assays and improve point-of-care (PoC) diagnostics and accurate quantitative analyses are discussed. Key challenges providing opportunities for clinical translation of BoC in neurodegenerative disorders are also addressed.

Advances in immunoassay-based strategies for mycotoxin detection in food: From single-mode immunosensors to dual-mode immunosensors

Mycotoxin contamination in foods and other goods has become a broad issue owing to serious toxicity, tremendous threat to public safety, and terrible loss of resources. Herein, it is necessary to develop simple, sensitive, inexpensive, and rapid platforms for the detection of mycotoxins. Currently, the limitation of instrumental and chemical methods cannot be massively applied in practice. Immunoassays are considered one of the best candidates for toxin detection due to their simplicity, rapidness, and cost-effectiveness. Especially, the field of dual-mode immunosensors and corresponding assays is rapidly developing as an advanced and intersected technology. So, this review summarized the types and detection principles of single-mode immunosensors including optical and electrical immunosensors in recent years, then focused on developing dual-mode immunosensors including integrated immunosensors and combined immunosensors to detect mycotoxins, as well as the combination of dual-mode immunosensors with a portable device for point-of-care test. The remaining challenges were discussed with the aim of stimulating future development of dual-mode immunosensors to accelerate the transformation of scientific laboratory technologies into easy-to-operate and rapid detection platforms.

Towards hospital-on-chip supported by 2D MXenes-based 5th generation intelligent biosensors

Existing public health emergencies due to fatal/infectious diseases such as coronavirus disease (COVID-19) and monkeypox have raised the paradigm of 5th generation portable intelligent and multifunctional biosensors embedded on a single chip. The state-of-the-art 5th generation biosensors are concerned with integrating advanced functional materials with controllable physicochemical attributes and optimal machine processability. In this direction, 2D metal carbides and nitrides (MXenes), owing to their enhanced effective surface area, tunable physicochemical properties, and rich surface functionalities, have shown promising performances in biosensing flatlands. Moreover, their hybridization with diversified nanomaterials caters to their associated challenges for the commercialization of stability due to restacking and oxidation. MXenes and its hybrid biosensors have demonstrated intelligent and lab-on-chip prospects for determining diverse biomarkers/pathogens related to fatal and infectious diseases. Recently, on-site detection has been clubbed with solution-on-chip MXenes by interfacing biosensors with modern-age technologies, including 5G communication, internet-of-medical-things (IoMT), artificial intelligence (AI), and data clouding to progress toward hospital-on-chip (HOC) modules. This review comprehensively summarizes the state-of-the-art MXene fabrication, advancements in physicochemical properties to architect biosensors, and the progress of MXene-based lab-on-chip biosensors toward HOC solutions. Besides, it discusses sustainable aspects, practical challenges and alternative solutions associated with these modules to develop personalized and remote healthcare solutions for every individual in the world.

Advances in layered double hydroxide based labels for signal amplification in ultrasensitive electrochemical and optical affinity biosensors of glucose

Since the development of enzyme electrodes, the research area of glucose biosensing has seen outstanding progress and improvement. Numerous sensing platforms have been developed based on different immobilization techniques and improved electron transfer between the enzyme and electrode. Interestingly, these platforms have consistently used innovative nanostructures and nanocomposites. In recent years, layered double hydroxides (LDHs) have become key tools in the field of analytical chemistry owing to their outstanding features and benefits, such as facile synthesis, cost-effectiveness, substantial surface area, excellent catalytic performance, and biocompatibility. LDHs are often synthesized as nanomaterial composites or manufactured with specific three-dimensional structures. The purpose of this review is to illustrate the biosensing prospects of LDH-based glucose sensors and the need for improvement. First, various clinical and conventional approaches for glucose determination are discussed. The definitions, types, and various synthetic methodologies of LDHs are then explained. Subsequently, we discuss the various research studies regarding LDH-based electrochemical and optical assays, focusing on modified systems, improved electron transfers pathways (through developments in surface science), and different sensing designs based on nanomaterials. Finally, a summary of the current limitations and future challenges in glucose analysis is described, which may facilitate further development and applications.

ZIF-8 metal organic framework materials as a superb platform for the removal and photocatalytic degradation of organic pollutants: a review

Metal organic frameworks (MOFs) are attracting significant attention for applications including adsorption, chemical sensing, gas separation, photocatalysis, electrocatalysis and catalysis. In particular, zeolitic imidazolate framework 8 (ZIF-8), which is composed of zinc ions and imidazolate ligands, have been applied in different areas of catalysis due to its outstanding structural and textural properties. It possesses a highly porous structure and chemical and thermal stability under varying reaction conditions. When used alone in the reaction medium, the ZIF-8 particles tend to agglomerate, which inhibits their removal efficiency and selectivity. This results in their mediocre reusability and separation from aqueous conditions. Thus, to overcome these drawbacks, several well-designed ZIF-8 structures have emerged by forming composites and heterostructures and doping. This review focuses on the recent advances on the use of ZIF-8 structures (doping, composites, heterostructures, etc.) in the removal and photodegradation of persistent organic pollutants. We focus on the adsorption and photocatalysis of three main organic pollutants (methylene blue, rhodamine B, and malachite green). Finally, the key challenges, prospects and future directions are outlined to give insights into game-changing breakthroughs in this area.

Applications of metal-organic framework-based bioelectrodes

Metal-organic frameworks (MOFs) are an emerging class of porous nanomaterials that have opened new research possibilities. The inherent characteristics of MOFs such as their large surface area, high porosity, tunable pore size, stability, facile synthetic strategies and catalytic nature have made them promising materials for enormous number of applications, including fuel storage, energy conversion, separation, and gas purification. Recently, their high potential as ideal platforms for biomolecule immobilization has been discovered. MOF-enzyme-based materials have attracted the attention of researchers from all fields with the expansion of MOFs development, paving way for the fabrication of bioelectrochemical devices with unique characteristics. MOFs-based bioelectrodes have steadily gained interest, wherein MOFs can be utilized for improved biomolecule immobilization, electrolyte membranes, fuel storage, biocatalysis and biosensing. Likewise, applications of MOFs in point-of-care diagnostics, including self-powered biosensors, are exponentially increasing. This paper reviews the current trends in the fabrication of MOFs-based bioelectrodes with emphasis on their applications in biosensors and biofuel cells.

Electrochemical activity of glassy carbon electrode modified with ZnO nanoparticles prepared Via Senna Alata L. leaf extract towards antiretroviral drug

The phytosynthesis method was used to prepare ZnO nanoparticles (ZnO NPs) via Senna alata L. leaf extract (SALE) by involving alkaloids, which play an essential role as a source of weak bases during the formation reaction of NPs. ZnO NPs on glassy carbon electrodes (GCE/ZnO NP) have been introduced to investigate its electrochemical activity towards the antiretroviral drug, lamivudine (3TC). Several characterization techniques, such as Fourier Transform Infra-Red (FTIR), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDS), and Dynamic Light Scattering (DLS) techniques were employed to analyze the properties of GCE/ZnO NPs. As a result, ZnO NPs in spherical shape showed a high purity crystalline hexagonal wurtzite structure with a particle diameter of 40–60 nm. A Cyclic Voltammetry (CV) measurement confirmed that the electrochemical reduction of 3TC on GCE/ZnO NPs exhibited an excellent linear range of 10–300 µM with a detection limit of 1.902 µM, quantitation limit of 6.330 µM, and sensitivity of 0.0278 µA/µM. Thus, this research suggests a facile method for the preparation of material-based ZnO NPs as a promising antiretroviral drug sensors due to their excellent electrochemical properties.

Perovskite Nanoparticles as an Electrochemical Sensing Platform for Detection of Warfarin

Chemically prepared PrAlO3 perovskite nanoparticles (NPs) were applied for the electrochemical detection of warfarin, which is commonly utilized for preventing blood clots, such as in deep vein thrombosis. PrAlO3 perovskite NPs were synthesized by the co-precipitation process at environmental conditions. Crystallographic structure, phase purity, morphological structure, thermal stability, optical properties, and electrochemical characteristics were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, UV-visible analysis, and cyclic voltammetry techniques. TEM micrographs showed the highly crystalline structure, smooth surface, irregular shape, and size of nanocrystalline particles with an average size of 20–30 nm. Particularly crystalline perovskite NPs were pasted on glassy carbon electrodes (GCE) to electrochemically detect the warfarin contents in liquid samples. The fabricated electrode was electrochemically characterized by different parameters such as different potential, scan rates, same potential with seven consecutive cycles, time response, real-time sample analysis, and as a function of warfarin concentration in phosphate buffer solution (0.1 M PBS, pH 7.2). The electrochemical electrode was further verified with various potentials of 5, 10, 20, 50, 100, and 150 mV/s, which exhibited sequential enhancements in the potential range. For detecting warfarin over a wide concentration range (19.5 µM–5000 µM), the detection devices offered good sensitivity and a low limit of detection (19.5 µM). The time-dependent influence was examined using chronoamperometry (perovskite NPs/GCE) in the absence and presence of warfarin at four distinct voltages of +0.05 to +1.2 V from 0 to 1000 s. The repeatability and reliability of the constructed electrochemical sensing electrode were also evaluated in terms of cyclic response for 30 days, demonstrating that it is substantially more reliable for a longer period. The fabricated perovskite NPs/GCE electrodes could be employed for the rapid identification of other drugs.