Dr Anitha Devadoss, Dr Suman Singh and Dr Murugan Veerapandian introduce the Sensors & Diagnostics themed issue on Advances in Nanomaterials for Sensors in Early Disease Diagnosis.

Efficient isolation and ultrasensitive detection of cancer cell-derived extracellular vesicles (EVs), which carry molecular fingerprints of their parent cells, can enable precise early-stage cancer diagnostics and prognostics. In this study, we developed a label-free impedimetric biosensor using electroactive 3D porous graphene foam (3D-PGF) electrodes to detect CD81 protein and MCF-7 cells-derived EVs in human serum. 1-pyrenebutyric acid N-hydroxysuccinimide ester (PYB-NHS) was non-covalently attached to the 3D-PGF via pi-pi interactions without compromising structural integrity or electrocatalytic performance. Sensor selectivity was achieved by immobilizing anti-CD81 antibodies onto the modified electrode, followed by quenching and blocking with ethanolamine and bovine serum albumin. MCF-7 cells-derived EVs were isolated by ultracentrifugation and characterized using nanoparticle tracking analysis and immunoaffinity plate-based assay. Capture and detection of CD81- and MCF-7-derived EVs were evaluated using electrochemical impedance spectroscopy with a ferro/ferri redox mediator. The sensor demonstrated exceptional sensitivity, with limits of detection of 0.048 fg/mL for CD81 protein and similar to 24 EVs/mL for MCF-7 EVs. Performance was benchmarked against 2D graphene electrodes, highlighting structural and electrochemical advantages. The binder-free 3D-PGF combined with non-covalent functionalization establishes a robust platform for selective, label-free, and ultrasensitive detection of cancer-cell-derived EVs in human serum samples.

Micro- and nanoplastics (MNPs) are ubiquitous environmental pollutants representing a concern for human health. MNPs have been detected in human placentas, indicating that during pregnancy maternal exposure may lead to placental transfer and foetal exposure, with potential for adverse effects on early-life development. However, a comprehensive risk assessment (RA) framework, specific to early-life is lacking. Here, we propose a novel roadmap to assist the development of an early-life health RA of MNPs. This roadmap is designed based on established chemical, mixture, particle, and MNP assessment strategies aligned with standard RA components (problem formulation, hazard identification, hazard characterisation, exposure assessment, risk characterisation). We systematically work through these stages to identify what is needed to progress a RA for the early-life impacts of MNPs, including what information is missing, and what may be used in the interim. While challenges such as complex physicochemical properties of MNPs, limited toxicity data at relevant exposure levels, and uncertainties related to characterising complex exposures have been described elsewhere, our work discusses how these challenges specifically impact early-life stages such as the significance of MNP presence in biological samples and factors influencing bioaccumulation and placental transfer. Additionally, we introduce the development of new technology readiness levels for methods used in the detection of MNPs in complex matrices. Importantly, this review integrates a broad scope of relevant information into one comprehensive document, providing a unified resource. We highlight specific requirements and areas for targeted research, including the development of dose-response relationships specific to early-life stages and novel strategies for assessing bioaccumulation and placental transfer of MNPs. By addressing these gaps, our roadmap aims to advance the development of a robust framework, ultimately enhancing the understanding and mitigation of risks associated with early-life exposure to MNPs.

Advanced economic development and technologies cause worldwide plastic waste to increase many folds, leaving policymakers with the dilemma of managing it. Synthetic solid particles or polymeric matrices of plastics with diverse shapes and sizes are the primary concern of environmental pollution of the marine ecosystem, freshwater, agriculture fields, atmosphere, food, drinking water, and other remote locations. Researchers demonstrated microplastics (MPs) as multifaceted stressors in the ecosystem, carrying toxic chemicals and vectors of transport, and described the implications of these hazardous chemicals on human health. MPs in the environment can adsorb organic, nitrogenous substances and other minerals. This complex system may promote microbial growth and aggregation. Continuous contact of microbes with MPs changes the internal arrangement of ions and atoms, alternating physio-chemical properties and becoming hydrophobic. These properties allow specific bacterial growth on MPs and promote bacterial resistance and transfer of resistance genes. MPs aged by ultra-violet light, temperature, and chemicals increase bacterial adsorption and antibiotic-resistance gene transfer synergistically. MPs are mitigated in the environment by aggregation of microbes, which leads to aging and loss of the crystalline structure of microplastic due to the release of enzymes that cause oxidation, demethylation and desertification, and hydrolysis of MPs. Aerobic conditions are preferred to degrade MPs in different environmental conditions for large-scale degradation of MPs. However, anaerobic degradation requires controlled conditions and specialized equipment. The use of a consortium of bacteria increases biodegradation efficiency. Among the microorganisms, fungi were the most effective at detoxicating xenobiotics in the environment due to their adaptability and ability to tolerate diverse conditions. This critical review analyses microplastic-induced microbial diversity and microbial adaptations to it. Furthermore, it describes MP's role in the cause of diarrhea, antimicrobial resistance, and spread. The potential use of bioremediation methods and pathways for eliminating MPs like phthalates and bisphenol from ecosystems is discussed in detail. Finally, suggestions are put forward for controlling and removing MPs from the environment. Advanced economic development and technologies cause worldwide plastic waste to increase many folds, leaving policymakers with the dilemma of managing it.

The toxic nature of inorganic nanostructured materials as photocatalysts is often not accounted for in traditional wastewater treatment reactions. Particularly, some inorganic nanomaterials employed as photocatalysts may release secondary pollutants in the form of ionic species that leach out due to photocorrosion. In this context, this work is a proof-of-concept study for exploring the environmental toxicity effect of extremely small-sized nanoparticles (<10 nm) like quantum dots (QDs) that are employed as photocatalysts, and in this study, cadmium sulfide (CdS) QDs are chosen. Typically, CdS is an excellent semiconductor with suitable bandgap and band-edge positions that is attractive for applications in solar cells, photocatalysis, and bioimaging. However, the leaching of toxic cadmium (Cd2+) metal ions due to the poor photocorrosion stability of CdS is a matter of serious concern. Therefore, in this report, a cost-effective strategy is devised for biofunctionalizing the active surface of CdS QDs by employing tea leaf extract, which is expected to hinder photocorrosion and prevent the leaching of toxic Cd2+ ions. The coating of tea leaf moieties (chlorophyll and polyphenol) over the CdS QDs (referred to hereafter as G-CdS QDs) was confirmed through structural, morphological, and chemical analysis. Moreover, the enhanced visible-light absorption and emission intensity of G-CdS QDs in comparison to that of C-CdS QDs synthesized through a conventional chemical synthesis approach confirmed the presence of chlorophyll/polyphenol coating. Interestingly, the polyphenol/chlorophyll molecules formed a heterojunction with CdS QDs and enabled the G-CdS QDs to exhibit enhanced photocatalytic activity in the degradation of methylene blue dye molecules over C-CdS QDs while effectively preventing photocorrosion as confirmed from cyclic photodegradation studies. Furthermore, detailed toxicity studies were conducted by exposing zebrafish embryos to the as-synthesized CdS QDs for 72 h. Surprisingly, the survival rate of the zebrafish embryos exposed to G-CdS QDs was equal to that of the control, indicating a significant reduction in the leaching of Cd2+ ions from G-CdS QDs in comparison to C-CdS QDs. The chemical environment of C-CdS and G-CdS before and after the photocatalysis reaction was examined by X-ray photoelectron spectroscopy. These experimental findings prove that biocompatibility and toxicity could be controlled by simply adding tea leaf extract during the synthesis of nanostructured materials, and revisiting green synthesis techniques can be beneficial. Furthermore, repurposing the discarded tea leaves may not only facilitate the control of toxicity of inorganic nanostructured materials but can also help in enhancing global environmental sustainability.

An immunosensor capable of high sensitivity detection of beta-amyloid peptides, shown to be a reliable biomarker for Alzheimer's disease, has been developed using screen printed graphene electrodes (SPGEs) modified with ultra-thin layers of polymerised 1,5-diaminonaphthalene (pDAN). Electropolymerization of 1,5-diaminonaphthalene (DAN) was performed to coat the graphene screen printed electrodes in a continuous polymer layer with controlled thickness. The surface characteristics of pristine graphene and polymer modified graphene electrodes were examined using Raman and X-ray photoelectron spectroscopy. The effects of polymer thickness on the electron transfer rates were investigated. An immunosensor for selective detection of beta amyloid peptides Aβ(1-42) was developed via biofunctionalization of the pDAN modified SPGE with the anti-beta amyloid antibody used as the peptide bioreceptor. The immunosensor has been used for specific detection of Aβ(1-42) with a linear range of 1 pg mL-1 to 1000 pg mL-1 and showed 1.4 pg mL-1 and 4.25 pg mL-1 detection and quantification limit, respectively. The biosensor was further validated for the analysis of spiked human plasma. The immunosensor enables rapid, accurate, precise, reproducible and highly sensitive detection of Aβ(1-42) using a low-cost SPGE platform, which opens the possibilities for diagnostic ex vivo applications and research-based real time studies.

Electrochemical biosensors using carbon-based electrodes are being widely developed for the detection of a range of different diseases. Since their sensitivity depends on the surface coverage of bioreceptor moieties, it necessarily depends on the surface coverage of amine precursors. Electrochemical techniques, using ferrocene carboxylic acid as a rapid and cheap assay, were used to assess the surface coverage of amino-phenyl groups attached to the carbon electrode. While the number of electrons transferred in the first step of diazotisation indicated a surface coverage of 8.02 ± 0.2 × l0−10 (mol/cm2), and those transferred in the second step, a reduction of nitrophenyl to amino-phenyl, indicated an amine surface coverage of 4–5 × l0−10 (mol/cm2), the number of electrons transferred during attachment of the amine coupling assay compound, ferrocene carboxylic acid, indicated a much lower available amine coverage of only 2.2 × l0−11 (mol/cm2). Furthermore, the available amine coverage was critically dependent upon the number of cyclic voltammetry cycles used in the reduction, and thus the procedures used in this step influenced the sensitivity of any subsequent sensor. Amine coupling of a carboxyl terminated anti-beta amyloid antibody specific to Aβ(1-42) peptide, a potential marker for Alzheimer’s disease, followed the same pattern of coverage as that observed with ferrocene carboxylic acid, and at optimum amine coverage, the sensitivity of the differential pulse voltammetry sensor was in the range 0–200 ng/mL with the slope of 5.07 µA/ng·mL−1 and R2 = 0.98.

Affinity biosensors based on graphene field-effect transistor (GFET) or resistor designs require the utilization of graphene's exceptional electrical properties. Therefore, it is critical when designing these sensors, that the electrical properties of graphene are maintained throughout the functionalization process. To that end, non-covalent functionalization may be preferred over covalent modification. Drop-cast 1,5-diaminonaphthalene (DAN) was investigated as a quick and simple method for the non-covalent amine functionalization of carbon-based surfaces such as graphene, for use in biosensor development. In this work, multiple graphene surfaces were functionalized with DAN via a drop-cast method, leading to amine moieties, available for subsequent attachment to receptor molecules. Successful modification of graphene with DAN via a drop-cast method was confirmed using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and real-time resistance measurements. Successful attachment of receptor molecules also confirmed using the aforementioned techniques. Furthermore, an investigation into the effect of sequential wash steps which are required in biosensor manufacture, on the presence of the DAN layer, confirmed that the functional layer was not removed, even after multiple solvent exposures. Drop-cast DAN is thus, a viable fast and robust method for the amine functionalization of graphene surfaces for use in biosensor development.

This chapter provides a generalized overall picture about fundamental electrochemical properties of transition metal dichalcogenides (TMDs) and their recent applications in wide range of energy technologies (battery, supercapacitor, and water splitting). The high surface area, large number of active sites, and remarkable chemical stability offer TMDs with vast opportunities for utilizing as a promising electrocatalysts. However, inadequate electrical conductivity and other deficiencies foster considerable research efforts for further modification. The TMDs showed enhanced electrocatalytic performance through (1) site doping/modification, (2) phase modulation, (3) control of growth morphology, and (4) heterostructure formation. This chapter summarizes the recent demonstration of these methodologies in TMDs towards designing the efficient and benchmarking electrocatalysts. Furthermore, the underlying mechanism of device functionality, materials challenges, and perspectives of TMD based electrocatalysts are also discussed in this chapter.

Herein, we report the influence of gamma-ray irradiation process on the physicochemical properties of partially reduced graphene oxide (PRGO) thin films. It is found that gamma-ray irradiation at 25 kGy alters the surface, chemical environment, and wettability properties of PRGO via inducing edge sites and oxygen moieties, resulting in enhanced water oxidation performance. (C) 2019 Elsevier B.V. All rights reserved.

Green technology for nanoparticles synthesis is considered to be of great significance in biomedical applications. Recently, low dimensional semiconductor cadmium sulfide (CdS) quantum dots (QDs) have raised great attention due to their optical properties and wide usage in biomedical studies. In our present work, we demonstrate a simple green synthesis route for CdS QDs production using waste matured tea leaves (mother leaf) as biosurfactant that are a waste product of the tea leaf industry and not suitable for drinking. The structural and morphological analysis showed waste tea leaf derived CdS QDs range from 2.5 to 4 nm in particle size with a cubic crystalline structure. Interestingly, these CdS QDs exhibit strong fluorescence emission with maximum around 670 nm. We explored the cytotoxic effect of waste tea leaf mediated CdS QDs (MT-CdS QDs) in breast cancer cell lines and compared their viability with standard drug - cisplatin. Our experimental studies strongly suggest that MT-CdS QDs exhibits cytotoxic effect on breast cancer cells and their performance was compared with standard drug cisplatin. To further understand the role of MT-CdS QDs towards cytotoxicity, the fluorescence microscopy and flow cytometry analysis were carried out. The flow cytometry results reveal that MT-CdS QDs induces cell death as it arrests the cell cycle at S phase as well as G2/M phase. Further the apoptosis mechanism was confirmed with the expression of anti-apoptotic and apoptotic proteins. These studies explored that waste tea leaves have dual advantage - both in controlling the particle size of CdS QDs as well as facilitates their cytotoxicity effect in breast cancer cell death. Therefore, it is anticipated that the utilization of MT-CdS QDs produced from waste tea leaves as bi-functional drug and delivery vehicle in cancer treatment will be a promising approach. Also, this is a simple and circular economic route for producing biocompatible QDs at low-cost, which could simultaneously benefit tea and biomedical industries.

Grafting thin polymer layers on graphene enables coupling target biomolecules to graphene surfaces, especially through amide and aldehyde linkages with carboxylic acid and primary amine derivatives, respectively. However, functionalizing monolayer graphene with thin polymer layers without affecting their exceptional electrical properties remains challenging. Herein, we demonstrate the controlled modification of chemical vapor deposition (CVD) grown single layer graphene with ultrathin polymer 1,5-diaminonaphthalene (DAN) layers using the electropolymerization technique. It is observed that the controlled electropolymerization of DAN monomer offers continuous polymer layers with thickness ranging between 5–25 nm. The surface characteristics of pure and polymer modified graphene was examined. As anticipated, the number of surface amine groups increases with increases in the layer thickness. The effects of polymer thickness on the electron transfer rates were studied in detail and a simple route for the estimation of surface coverage of amine groups was demonstrated using the electrochemical analysis. The implications of grafting ultrathin polymer layers on graphene towards horseradish peroxidase (HRP) enzyme immobilization and enzymatic electrochemical sensing of H2O2 were discussed elaborately.

Since the discovery of the two-dimensional (2D) carbon material, graphene, just over a decade ago, the development of graphene-based field effect transistors (G-FETs) has become a widely researched area, particularly for use in point-of-care biomedical applications. G-FETs are particularly attractive as next generation bioelectronics due to their mass-scalability and low cost of the technology’s manufacture. Furthermore, G-FETs offer the potential to complete label-free, rapid, and highly sensitive analysis coupled with a high sample throughput. These properties, coupled with the potential for integration into portable instrumentation, contribute to G-FETs’ suitability for point-of-care diagnostics. This review focuses on elucidating the recent developments in the field of G-FET sensors that act on a bioaffinity basis, whereby a binding event between a bioreceptor and the target analyte is transduced into an electrical signal at the G-FET surface. Recognizing and quantifying these target analytes accurately and reliably is essential in diagnosing many diseases, therefore it is vital to design the G-FET with care. Taking into account some limitations of the sensor platform, such as Debye–Hükel screening and device surface area, is fundamental in developing improved bioelectronics for applications in the clinical setting. This review highlights some efforts undertaken in facing these limitations in order to bring G-FET development for biomedical applications forward.

Graphene (GR) and its derivatives are promising materials on the horizon of nanotechnology and material science and have attracted a tremendous amount of research interest in recent years. The unique atom-thick 2D structure with sp2 hybridization and large specific surface area, high thermal conductivity, superior electron mobility, and chemical stability have made GR and its derivatives extremely attractive components for composite materials for solar energy conversion, energy storage, environmental purification, and biosensor applications. This review gives a brief introduction of GR's unique structure, band structure engineering, physical and chemical properties, and recent energy-related progress of GR-based materials in the fields of energy conversion (e.g., photocatalysis, photoelectrochemical water splitting, CO2 reduction, dye-sensitized and organic solar cells, and photosensitizers in photovoltaic devices) and energy storage (batteries, fuel cells, and supercapacitors). The vast coverage of advancements in environmental applications of GR-based materials for photocatalytic degradation of organic pollutants, gas sensing, and removal of heavy-metal ions is presented. Additionally, the use of graphene composites in the biosensing field is discussed. We conclude the review with remarks on the challenges, prospects, and further development of GR-based materials in the exciting fields of energy, environment, and bioscience.

The solar-to-hydrogen generation from the TiO2-CdS-ZnS-MoS2 (TCZM) heterointerface was demonstrated. We found that a Pt-free CdS quantum dot-sensitized TiO2 mesoporous electrode with a metallic-type 1T MoS2 co-catalyst resulted in 0.11 ml cm(-2) h(-1) H-2 fuel generation in unassisted potential mode, which was strikingly improved to 1.47 ml cm(-2) h(-1) under 1 V applied potential.

We present an effective way to develop superhydrophobic steel surface which shows stable superhydrophobicity under harsh mechanical bending.