Spheroid-3D and Monolayer-2D Intestinal Electrochemical Biosensor for Toxicity/Viability Testing: Applications in Drug Screening, Food Safety, and Environmental Pollutant Analysis

In situ biosensing for cell viability and drug evaluation in 3D extracellular matrix cultures: Applications in cytoprotection of oxidative stress injury

The rise of extracellular matrix (ECM)-supported three-dimensional (3D) cell culture systems which bridge the gap between in vitro culture and in vivo living tissue for pharmacological models has increased the need for simple and robust cell viability assays. This study presents the development of an effective biosensing assay for in situ monitoring of the catecholamine neurotransmitter exocytosis levels for cell viability assessment within complicated cell-encapsulated hydrogel milieu. Firstly, the biosensing assay demonstrated the distinction among four pheochromocytoma (PC12) cell lines with varying degrees of differentiation and the discrepancy in cellular neurosecretory capacity between two-dimensional (2D) monolayer and 3D agarose hydrogel culture conditions, accompanied by morphological distinctions. Secondly, the electrochemical biosensing assay was performed for viability monitoring of PC12 cell lines following various treatments, including oxidative stress injury (OSI) induced by H2O2 and intervention protected by nimodipine, bone marrow mesenchymal stem cells (BMMSC) supernatant and BMMSC-derived exosomes under 2D and 3D milieus. Of note, BMMSC-derived exosomes exhibited high cytoprotection, anti-oxidation effect, endogenous esterase activity and membrane integrity against OSI. Collectively, the biosensing assay results showed principal but not entire consistency with that of conventional cell-counting kit-8 assay. Therefore, the developed biosensing assay allows for sensitive and in situ cell viability assays in spatial ECM environment, which has broad applications in monitoring physiological and pathological processes.

Transcriptomic investigation of NP toxicity on HepaRG spheroids

Metal nanoparticles (NPs) are commonly used nanomaterials, however concerns have been raised about their toxicity. Although a few studies have reported the toxicity of NPs on cells, they have generally been restricted to a limited variety of NPs, inappropriate cell lines, or culture methods. Thus, the adverse effects remain inadequately understood, necessitating further analysis. This study focuses on assessing the impacts of diverse NPs of varying materials and sizes on HepaRG spheroids to determine the genes that respond to acute NP toxicity. HepaRG cells, the most appropriate alternative to primary hepatocytes, were cultured in 3D spheroids to better mimic the cellular microenvironment of the liver. To elucidate the toxicity mechanisms of NPs on HepaRG spheroids, transcriptome analysis was conducted by using RNA sequencing (RNA-seq). Among all NPs, lowest and highest numbers of differentially expressed genes (DEGs) were found for 40 nm AuNP (118 genes) and InP/ZnS (1904 genes), respectively. Remarkably, processes such as drug metabolism, sensitivity to metal ions, oxidative stress, endothelial-mesenchymal transition (EMT) and apoptosis consistently exhibited significant enrichment across all NPs of different materials. Pathways related to stress responses of the cells such as the MAPK, p53 and mTOR pathways are found to be dysregulated upon exposure to various NPs. The genes that are common and unique between DEGs of different NPs were identified. These results provide novel insights into the toxicological mechanisms of NPs on HepaRG spheroids.

In-situ monitoring of cellular H2O2 within 3D cell clusters using conductive scaffolds

Accurately monitoring H2O2 concentrations in 3D cell clusters is challenging due to limited diffusion and rapid degradation of H2O2 in the culture medium. Despite the incorporation of three-dimensional cell culture approaches, the detection technology has largely remained as a 2D planar system. In this study, we present a versatile approach of 3D electrochemical sensing utilizing carbon nanotubes as conductive scaffolds for in-situ monitoring of H2O2 in cell clusters. These scaffolds enabled direct contact between H2O2 released from cells and the electrodes, thereby improving sensitivity and ensuring biocompatibility for cell aggregates. The scaffolds exhibited electrocatalytic behavior with a limit of detection of 6.7 nM H2O2. Additionally, the electrochemical responses of cell clusters with the scaffolds exhibited significantly higher current compared to clusters without scaffolds when stimulated with model drugs. This study underscores the potential of conductive scaffolds for real-time monitoring of H2O2 released from cell clusters in 3D microenvironments.

Banked Primary Progenitor Cells for Allogeneic Intervertebral Disc (IVD) Therapy: Preclinical Qualification and Functional Optimization within a Cell Spheroid Formulation Process

Background/Objectives: Biological products are emerging as therapeutic management options for intervertebral disc (IVD) degenerative affections and lower back pain. Autologous and allogeneic cell therapy protocols have been clinically implemented for IVD repair. Therein, several manufacturing process design considerations were shown to significantly influence clinical outcomes. The primary objective of this study was to preclinically qualify (chondrogenic potential, safety, resistance to hypoxic and inflammatory stimuli) cryopreserved primary progenitor cells (clinical grade FE002-Disc cells) as a potential cell source in IVD repair/regeneration. The secondary objective of this study was to assess the cell source's delivery potential as cell spheroids (optimization of culture conditions, potential storage solutions). Methods/Results: Safety (soft agar transformation, β-galactosidase, telomerase activity) and functionality-related assays (hypoxic and inflammatory challenge) confirmed that the investigated cellular active substance was highly sustainable in defined cell banking workflows, despite possessing a finite in vitro lifespan. Functionality-related assays confirmed that the retained manufacturing process yielded strong collagen II and glycosaminoglycan (GAG) synthesis in the spheroids in 3-week chondrogenic induction. Then, the impacts of various process parameters (induction medium composition, hypoxic incubation, terminal spheroid lyophilization) were studied to gain insights on their criticality. Finally, an optimal set of technical specifications (use of 10 nM dexamethasone for chondrogenic induction, 2% O2 incubation of spheroids) was set forth, based on specific fine tuning of finished product critical functional attributes. Conclusions: Generally, this study qualified the considered FE002-Disc progenitor cell source for further preclinical investigation based on safety, quality, and functionality datasets. The novelty and significance of this study resided in the establishment of defined processes for preparing fresh, off-the-freezer, or off-the-shelf IVD spheroids using a preclinically qualified allogeneic human cell source. Overall, this study underscored the importance of using robust product components and optimal manufacturing process variants for maximization of finished cell-based formulation quality attributes.

Visual Eosin Y-Based Photosensitization Sensing Systems for Ultrasensitive Detection of Diclofenac with Single-Atom Co─N2O2 Site-Immobilized g-C3N4 Nanosheets

It is highly desired to develop a visual sensing system for ultrasensitive detection of colorless diclofenac (DCF), yet with a significant challenge. Herein, a novel dye-based photosensitization sensing system has been successfully developed for detecting DCF for the first time, in which the used dye eosin Y (DeY) can strongly absorb visible light and then be decolorized obviously by transferring photogenerated electrons to g-C3N4 nanosheets (CN), while the built single-atomic Co─N2O2 sites on CN by boron-oxygen connection can competitively adsorb DCF to impede the photosensitization decoloration of DeY. This system exhibits a broad detection range from 8 ng L-1 to 2 mg L-1 with 535 nm light, an exceptionally low detection limit (3.5 ng L-1), and remarkable selectivity. Through the time-resolved, in situ technologies, and theoretical calculations, the decolorization of DeY is attributed to the disruption of DeY's conjugated structure caused by the triplet excited state electron transfer from DeY to CN, meanwhile, the adsorbed oxygen facilitates the charge transfer process. The preferential adsorption of DCF mainly depends on the strong interactions between the as-constructed single-atom Co and Cl in DCF. This study opens an innovative light-driven sensing system by combining dye and single-atom metal/nanomaterial for visually intuitive detection of environmental pollutants.

Recent advances in electrochemical cell-based biosensors for food analysis: Strategies for sensor construction

Owing to their advantages such as great specificity, sensitivity, rapidity, and possibility of noninvasive and real-time monitoring, electrochemical cell-based biosensors (ECBBs) have been a powerful tool for food analysis encompassing the areas of nutrition, flavor, and safety. Notably, the distinctive biological relevance of ECBBs enables them to mimic physiological environments and reflect cellular behaviors, leading to valuable insights into the biological function of target components in food. Compared with previous reviews, this review fills the current gap in the narrative of ECBB construction strategies. The review commences by providing an overview of the materials and configuration of ECBBs, including cell types, cell immobilization strategies, electrode modification materials, and electrochemical sensing types. Subsequently, a detailed discussion is presented on the fabrication strategies of ECBBs in food analysis applications, which are categorized based on distinct signal sources. Lastly, we summarize the merits, drawbacks, and application scope of these diverse strategies, and discuss the current challenges and future perspectives of ECBBs. Consequently, this review provides guidance for the design of ECBBs with specific functions and promotes the application of ECBBs in food analysis.

Xeno-Free 3D Bioprinted Liver Model for Hepatotoxicity Assessment

Three-dimensional (3D) bioprinting is one of the most promising methodologies that are currently in development for the replacement of animal experiments. Bioprinting and most alternative technologies rely on animal-derived materials, which compromises the intent of animal welfare and results in the generation of chimeric systems of limited value. The current study therefore presents the first bioprinted liver model that is entirely void of animal-derived constituents. Initially, HuH-7 cells underwent adaptation to a chemically defined medium (CDM). The adapted cells exhibited high survival rates (85-92%) after cryopreservation in chemically defined freezing media, comparable to those preserved in standard medium (86-92%). Xeno-free bioink for 3D bioprinting yielded liver models with high relative cell viability (97-101%), akin to a Matrigel-based liver model (83-102%) after 15 days of culture. The established xeno-free model was used for toxicity testing of a marine biotoxin, okadaic acid (OA). In 2D culture, OA toxicity was virtually identical for cells cultured under standard conditions and in CDM. In the xeno-free bioprinted liver model, 3-fold higher concentrations of OA than in the respective monolayer culture were needed to induce cytotoxicity. In conclusion, this study describes for the first time the development of a xeno-free 3D bioprinted liver model and its applicability for research purposes.

In vitro induction of hair follicle signatures using human dermal papilla cells encapsulated in fibrin microgels

Cellular spheroids have been described as an appropriate culture system to restore human follicle dermal papilla cells (hFDPc) intrinsic properties; however, they show a low and variable efficiency to promote complete hair follicle formation in in vivo experiments. In this work, a conscientious analysis revealed a 25% cell viability in the surface of the dermal papilla spheroid (DPS) for all culture conditions, questioning whether it is an appropriate culture system for hFDPc. To overcome this problem, we propose the use of human blood plasma for the generation of fibrin microgels (FM) with encapsulated hFDPc to restore its inductive signature, either in the presence or in the absence of blood platelets. FM showed a morphology and extracellular matrix composition similar to the native dermal papilla, including Versican and Collagen IV and increasing cell viability up to 85%. While both systems induce epidermal invaginations expressing hair-specific keratins K14, K15, K71, and K75 in in vitro skin cultures, the number of generated structures increases from 17% to 49% when DPS and FM were used, respectively. These data show the potential of our experimental setting for in vitro hair follicle neogenesis with wild adult hFDPc using FM, being a crucial step in the pursuit of human hair follicle regeneration therapies.

Recent advances in nanobiosensors for sustainable healthcare applications: A systematic literature review

The need for novel healthcare treatments and drugs has increased due to the expanding human population, detection of newer diseases, and looming pandemics. The development of nanotechnology offers a platform for cutting-edge in vivo non-invasive monitoring and point-of-care-testing (POCT) for rehabilitative disease detection and management. The advancement and uses of nanobiosensors are currently becoming more common in a variety of scientific fields, such as environmental monitoring, food safety, biomedical, clinical, and sustainable healthcare sciences, since the advent of nanotechnology. The identification and detection of biological patterns connected to any type of disease (communicable or not) have been made possible in recent years by several sensing techniques utilizing nanotechnology concerning biosensors and nanobiosensors. In this work, 2218 articles are drawn and screened from six digital databases out of which 17 were shortlisted for this review by using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) technique. As a result, this study uses a systematic methodology to review some recently developed extremely sensitive nanobiosensors, along with their biomedical, point-of-care diagnostics (POCD), or healthcare applications and their capabilities, particularly for the prediction of some fatal diseases based on a few of the most recent publications. The potential of nanobiosensors for medicinal, therapeutic, or other sustainable healthcare applications, notably for ailments diagnostics, is also recognized as a way forward in the manifestation of future trends.

Subcutaneous device-free islet transplantation

Diabetes mellitus is a chronic metabolic disease, characterized by high blood sugar levels; it affects more than 500 million individuals worldwide. Type 1 diabetes mellitus (T1DM) is results from insufficient insulin secretion by islets; its treatment requires lifelong use of insulin injections, which leads to a large economic burden on patients. Islet transplantation may be a promising effective treatment for T1DM. Clinically, this process currently involves directly infusing islet cells into the hepatic portal vein; however, transplantation at this site often elicits immediate blood-mediated inflammatory and acute immune responses. Subcutaneous islet transplantation is an attractive alternative to islet transplantation because it is simpler, demonstrates lower surgical complication risks, and enables graft monitoring and removal. In this article, we review the current methods of subcutaneous device-free islet transplantation. Recent subcutaneous islet transplantation techniques with high success rate have involved the use of bioengineering technology and biomaterial cotransplantation-including cell and cell growth factor co-transplantation and hydrogel- or simulated extracellular matrix-wrapped subcutaneous co-transplantation. In general, current subcutaneous device-free islet transplantation modalities can simplify the surgical process and improve the posttransplantation graft survival rate, thus aiding effective T1DM management.

Multidimensional controllable fabrication of tumor spheroids based on a microfluidic device

Multicellular tumor spheroids (MCTSs) are in vitro solid tumor models with physiological relevance. To achieve robust process control, a MCTS fabrication method that combines cell membrane engineering and droplet microfluidic techniques is designed. The fluidic control and the chemical interactions between biotin and streptavidin enable artificial cell aggregation to be accomplished in seconds. Then, spheroids with a uniform size are fabricated within alginate microcapsules. Microfluidic mixing-based cell aggregation regulates the cell aggregate size and the spheroid composition, and the microcapsules regulate the size of spheroids from 120 to 180 μm. The method shows applicability for various cancer cell lines, including HCT116, HepG2, and A549. In addition, composite colon cancer spheroids consisting of HCT116 and NIH3T3 with predetermined cell ratios and uniform distributions are produced. The generated MCTSs are assessed using the ELISA and UPLC-MS/MS techniques. The release of vascular endothelial growth factor (VEGF) and the 5-fluorouracil (5-FU) resistance differ in the monotypic and cocultured colon cancer models. Our method provides a robust way to produce consistent and customized MCTSs in cancer research and drug screening.

Development of fish liver PLHC-1 spheroids and its applicability to investigate the toxicity of plastic additives

Fish liver cell lines are valuable tools to understand the toxicity of chemicals in aquatic vertebrates. While conventional 2D cell cultures grown in monolayers are well established, they fail to emulate toxic gradients and cellular functions as in in-vivo conditions. To overcome these limitations, this work focuses on the development of Poeciliopsis lucida (PLHC-1) spheroids as a testing platform to evaluate the toxicity of a mixture of plastic additives. The growth of spheroids was monitored over a period of 30 days, and spheroids 2-8 days old and sized between 150 and 250 µm were considered optimal for conducting toxicity tests due to their excellent viability and metabolic activity. Eight-day-old spheroids were selected for lipidomic characterization. Compared to 2D-cells, the lipidome of spheroids was relatively enriched in highly unsaturated phosphatidylcholines (PCs), sphingosines (SPBs), sphingomyelins (SMs) and cholesterol esters (CEs). When exposed to a mixture of plastic additives, spheroids were less responsive in terms of decreased cell viability and generation of reactive oxygen species (ROS), but were more sensitive than cells growing in monolayers for lipidomic responses. The lipid profile of 3D-spheroids was similar to a liver-like phenotype and it was strongly modulated by exposure to plastic additives. The development of PLHC-1 spheroids represents an important step towards the application of more realistic in-vitro methods in aquatic toxicity studies.

Exploitation of In Vivo-Emulated In Vitro System in Advanced Food Science

Reasonable model construction contributes to the accuracy of experimental results. Multiple in vivo models offer reliable choices for effective evaluation, whereas their applications are hampered due to adverse features including high time-consumption, high cost and ethical contradictions. In vivo-emulated in vitro systems (IVE systems) have experienced rapid development and have been brought into food science for about two decades. IVE systems' flexibly gathers the strengths of in vitro and in vivo models into one, reflecting the results in an efficient, systematic and interacted manner. In this review, we comprehensively reviewed the current research progress of IVE systems based on the literature published in the recent two decades. By categorizing the IVE systems into 2D coculture models, spheroids and organoids, their applications were systematically summarized and typically exemplified. The pros and cons of IVE systems were also thoroughly discussed, drawing attention to present challenges and inspiring potential orientation and future perspectives. The wide applicability and multiple possibilities suggest IVE systems as an effective and persuasive platform in the future of advanced food science.

3D models of neurodegeneration: implementation in drug discovery

A lack of in vitro models that robustly represent the complex cellular pathologies underlying neurodegeneration has resulted in a translational gap between in vitro and in vivo results, creating a bottleneck in the development of new therapeutics. In the past decade, new and complex 3D models of the brain have been published at an exponential rate. However, many novel 3D models of neurodegeneration overlook the validation and throughput requirements for implementation in drug discovery. This therefore represents a knowledge gap that could hinder the translation of these models to drug discovery efforts. We review the recent progress in the development of 3D models of neurodegeneration, examining model design benefits and validation techniques, and discuss opportunities and standards for 3D models of neurodegeneration to be implemented in drug discovery and development.

Cell viability and drug evaluation biosensing system based on disposable AuNPs/MWCNT nanocomposite modified screen-printed electrode for exocytosis dopamine detection

Cell viability, as an important index to evaluate drug effects, usually was measured by tetrazolium colorimetric assay, playing a key role in drug development and drug screening. Tedious operating procedures, unsatisfactory sensitivity and abominable environments perplex researchers to acquire more detailed in vivo-relevant biological information. Herein, a simple and low-cost cell viability and drug evaluation biosensing system-based on multiwalled carbon nanotubes, gold nanoparticles and Nafion modified screen-printed electrode (SPE) biosensor was constructed for detection of dopamine (DA) released from living cells to evaluate cytotoxicity of antineoplastic drugs such as cisplatin and resveratrol. The biosensing system was demonstrated to display exceptional selectivity, excellent flexibility and good stability toward DA measurement in complex bio-samples. Additionally, the satisfactory recoveries of DA in real samples revealed the reliability and accuracy of the biosensing system in practical application. The IC₅₀ curves respectively obtained by the biosensing system and tetrazolium colorimetric assay provided similar IC₅₀ value but distinctly different dose-effect relationship, which confirmed the enormous potential of the biosensor in cell viability and described drug efficacy profiles in cell function. In short, the cell viability and drug evaluation system using SPE biosensor paves a new way in drug screening and pharmaceutical application to measure bioactive molecule such as DA.

Applications of electrochemical biosensors based on 2D materials and their hybrid composites in hematological malignancies diagnosis

Hematological malignancies encompass a wide variety of severe diseases that pose a serious threat to human health. Given the fact that hematological malignancies are difficult to treat due to their unpredictable and rapid deterioration and high rates of recurrence, growing attention has been paid to their early screening and diagnosis. However, developing a rapid and effective diagnostic tool featuring a noninvasive sampling technique is still extremely challenging. In recent years, novel nanomaterials-based electrochemical biosensors have attracted great interest because of such advantages as simple operation, low cost, fast response, etc. As a kind of rising nanomaterials, two-dimensional materials have excellent electronic and chemical properties, which have been proven to improve the performance of electrochemical biosensors. This review summarizes the applications of different types of electrochemical biosensors (nucleic acid sensors, immunosensors, aptamer biosensors, and cytosensors) based on two-dimensional materials in the detection of biological molecules related to hematological malignancies. Two-dimensional materials-based electrochemical biosensors designed for the diagnosis of leukemia could rapidly detect the target biomolecules at a trace level and show great merits such as wide linear range, low detection limit, high sensitivity, excellent selectivity, and cost-effectiveness. In addition, these biosensors have also achieved satisfactory results in the diagnosis of lymphoma and multiple myeloma. Thus, two-dimensional materials-based electrochemical biosensors are attractive for the early diagnosis of hematological malignancies in clinical practice. Nevertheless, more efforts are still required to further improve the performance of electrochemical biosensors. In this review, we propose the possible main concerns in the design of future two-dimensional materials-based electrochemical biosensors, involving the development of sensors for synchronous detection of diverse target biomolecules, the exploration of other superior two-dimensional materials, the simplification of the sensors fabrication process, the construction of new hybrid structures and how to avoid possible environmental issues.

Fabrication of a label-free electrochemical cell-based biosensor for toxicity assessment of thiram

Thiram has been widely used in agriculture and may invades the food chain, posing a threat to human health. In this research, a label-free electrochemical cell-based biosensor was presented for in vitro toxicity assessment of thiram. HepG2 cells were cultured on poly-l-lysine@gold nano-flowers functionalized indium tin oxide coated glass electrode (PLL@AuNFs/ITO) to serve as biorecognition elements. AuNFs were electrodeposited on ITO to provide an enlarged specific surface area and benefited the output signal amplification. PLL was selected as an effective biocompatible coating material to facilitate cell adhesion and proliferation, thereby realizing one-step recording of electrochemical signals from thiram-treated cells. With the aid of the differential pulse voltammetry method, the fabricated biosensor was applied to assess the cytotoxicity of thiram. Results showed that the cytotoxicity measured by the fabricated biosensor exhibited a linear relationship related to thiram concentration ranging from 5 to 50 μM with a detection limit of 2.23 μM. The IC₅₀ of thiram obtained by the biosensor was 29.5 μM, which was close to that of conventional MTT assay (30.8 μM). The effects of thiram on HepG2 cells were also investigated via SEM and flow cytometry. Meanwhile, the proposed biosensor was used to evaluate the toxicity of thiram in fruit samples. Results indicated that the toxicity of thiram cannot be ignored even at a low residual concentration in food (≤5 mg/kg). In conclusion, the developed sensor showed excellent sensitivity, stability, and reliability, which provided a great capacity for the convenient toxicity evaluation of thiram residue in food.

Electrochemical microwell sensor with Fe-N co-doped carbon catalyst to monitor nitric oxide release from endothelial cell spheroids

Endothelial cells have been widely used for vascular biology studies; recent progress in tissue engineering have offered three-dimensional (3D) culture systems for vascular endothelial cells which can be considered as physiologically relevant models. To facilitate the studies, we developed an electrochemical device to detect nitric oxide (NO), a key molecule in the vasculature, for the evaluation of 3D cultured endothelial cells. Using an NO-sensitive catalyst composed of Fe-N co-doped reduced graphene oxide, the real-time monitoring of NO release from the endothelial cell spheroids was demonstrated.

Cuprous oxide coated silver/graphitic carbon nitride/cadmium sulfide nanocomposite heterostructure: Specific recognition of carcinoembryonic antigen through sandwich-type mechanism

The development of the effective diagnostic method for the determination of cancer biomarkers is one of the most promising strategies for early clinical diagnosis of cancer. Here, based on the preparation of heterogeneous cuprous oxide coated silver (Ag@Cu₂O) nanocomposites/graphitic carbon nitride (g-C₃N₄)/cadmium sulfide (CdS) nanoarrays structure, a highly sensitive photoelectrochemical (PEC) biosensor for the examination of carcinoembryonic antigen (CEA) has been constructed successfully. The combination of photoactive semiconductor materials g-C₃N₄ and CdS increases the electron transfer rate between them and enhances their photocurrent response, thus greatly increasing the concentration detection range. At the same time, the specific recognition between antigen and antibody is used to form a sandwich structure secondary antibody (Ab₂)/CEA/antibody (Ab₁). And because Ag@Cu₂O has the function of absorbing light and consuming electron donor. Therefore, the successful measurement of CEA was achieved by labeling Ag@Cu₂O on Ab₂ and finally immobilizing it on the sensor to correlate the current reduction with the CEA concentration. The sandwich PEC biosensor proposed by this signal amplification strategy under optimal conditions has good analytical performance for CEA, with a wide linear detection range (from 10^-5 to 1 ng/mL) and a low detection limit of 0.0011 pg/mL. The PEC biosensor constructed by this method showed high sensitivity, excellent anti-interference ability, favourable repeatability, and good stability.

Phenolic water toxins: redox mechanism and method of their detection in water and wastewater

Phenolic pollutants are highly toxic and persistent in the environment. Their efficient detection is a pressing social demand. In this regard we introduce a novel ultrasensitive electroanalytical platform for the individual and synchronized detection of three phenolic isomers commonly known as hydroquinone (HQ), resorcinol (RC), and catechol (CC). The sensing device consists of a glassy carbon electrode (GCE) modified with functionalized carbon nanotubes (fCNTs) and gold-silver (Au-Ag NPs) bimetallic nanoparticles. The sandwiched scaffold represented as fCNTs/Au-Ag NPs/fCNTs/GCE efficiently senses HQ, RC, and CC with detection limits of 28.6 fM, 36.5 fM and 42.8 fM respectively. The designed sensor is more promising than reported sensors for phenolic toxins in the context of high sensitivity, selectivity, and rapid responsiveness. The designed sensor also shows the qualities of stability, reproducibility, reliability, and selective recognition capacity for target analytes in multiple real water samples. Moreover, computational calculations explain the function of the electrode modifier in facilitating charge transfer between the transducer and analytes.

Direct SARS-CoV-2 Nucleic Acid Detection by Y-Shaped DNA Dual-Probe Transistor Assay

Rapid screening of infected individuals from a large population is an effective means in epidemiology, especially to contain outbreaks such as COVID-19. The gold standard assays for COVID-19 diagnostics are mainly based on the reverse transcription polymerase chain reaction, which mismatches the requirements for wide-population screening due to time-consuming nucleic acid extraction and amplification procedures. Here, we report a direct nucleic acid assay by using a graphene field-effect transistor (g-FET) with Y-shaped DNA dual probes (Y-dual probes). The assay relies on Y-dual probes modified on g-FET simultaneously targeting ORF1ab and N genes of SARS-CoV-2 nucleic acid, enabling high a recognition ratio and a limit of detection (0.03 copy μL-1) 1-2 orders of magnitude lower than existing nucleic acid assays. The assay realizes the fastest nucleic acid testing (∼1 min) and achieves direct 5-in-1 pooled testing for the first time. Owing to its rapid, ultrasensitive, easily operated features as well as capability in pooled testing, it holds great promise as a comprehensive tool for population-wide screening of COVID-19 and other epidemics.

[Research advances of high-throughput cell-based drug screening systems based on microfluidic technique]

Drug screening is the process of screening new drugs or leading compounds with biological activity from natural products or synthetic compounds, and it plays an essential role in drug discovery. The discovery of innovative drugs requires the screening of a large number of compounds with appropriate drug targets. With the development of genomics, proteomics, metabolomics, combinatorial chemistry, and other disciplines, the library of drug molecules has been largely expanded, and the number of drug targets is continuously increasing. High-throughput screening systems enable the parallel analysis of thousands of reactions through automated operation, thereby enhancing the experimental scale and efficiency of drug screening. Among them, cell-based high-throughput drug screening has become the main screening mode because it can provide a microenvironment similar to human physiological conditions. However, the current high-throughput screening systems are mainly built based on multiwell plates, which have several disadvantages such as simple cell culture conditions, laborious and time-consuming operation, and high reagent consumption. In addition, it is difficult to achieve complex drug combination screening. Therefore, there is an urgent need for rapid and low-cost drug screening methods to reduce the time and cost of drug development. Microfluidic techniques, which can manipulate and control microfluids in microscale channels, have the advantages of low consumption, high efficiency, high throughput, and automation. It can overcome the shortcomings of screening systems based on multi-well plates and provide an efficient and reliable technical solution for establishing high-throughput cell-based screening systems. Moreover, microfluidic systems can be flexibly changed in terms of cell culture materials, chip structure design, and fluid control methods to enable better control and simulation of cell growth microenvironment. Operations such as cell seeding, culture medium replacement or addition, drug addition and cleaning, and cell staining reagent addition are usually involved in cell-based microfluidic screening systems. These operations are all based on the manipulation of microfluids. This paper reviews the research advances in cell-based microfluidic screening systems using different microfluidic manipulation modes, namely perfusion flow mode, droplet mode, and microarray mode. In addition, the advantages and disadvantages of these systems are summarized. Moreover, the development prospects of high-throughput screening systems based on microfluidic techniques has been looked forward. Furthermore, the current problems in this field and the directions to overcome these problems are discussed.

The utility of biomedical scaffolds laden with spheroids in various tissue engineering applications

A spheroid is a complex, spherical cellular aggregate supporting cell-cell and cell-matrix interactions in an environment that mimics the real-world situation. In terms of tissue engineering, spheroids are important building blocks that replace two-dimensional cell cultures. Spheroids replicate tissue physiological activities. The use of spheroids with/without scaffolds yields structures that engage in desired activities and replicate the complicated geometry of three-dimensional tissues. In this mini-review, we describe conventional and novel methods by which scaffold-free and scaffolded spheroids may be fabricated and discuss their applications in tissue regeneration and future perspectives.

Hepatocellular carcinoma (HepG2/C3A) cell-based 3D model for genotoxicity testing of chemicals

The major weakness of the current in vitro genotoxicity test systems is the inability of the indicator cells to express metabolic enzymes needed for the activation and detoxification of genotoxic compounds, which consequently can lead to misleading results. Thus, there is a significant emphasis on developing hepatic cell models, including advanced in vitro three-dimensional (3D) cell-based systems, which better imitate in vivo cell behaviour and offer more accurate and predictive data for human exposures. In this study, we developed an approach for genotoxicity testing with 21-day old spheroids formed from human hepatocellular carcinoma cells (HepG2/C3A) using the dynamic clinostat bioreactor system (CelVivo BAM/bioreactor) under controlled conditions. The spheroids were exposed to indirect-acting genotoxic compounds, polycyclic aromatic hydrocarbon [PAH; benzo(a) pyrene B(a)P], and heterocyclic aromatic amine [PhIP]) at non-cytotoxic concentrations for 24 and 96 h. The results showed that both environmental pollutants B(a)P and PhIP significantly increased the level of DNA strand breaks assessed by the comet assay. Further, the mRNA level of selected genes encoding metabolic enzymes from phase I and II, and DNA damage responsive genes was determined (qPCR). The 21-day old spheroids showed higher basal expression of genes encoding metabolic enzymes compared to monolayer culture. In spheroids, B(a)P or PhIP induced compound-specific up-regulation of genes implicated in their metabolism, and deregulation of genes implicated in DNA damage and immediate-early response. The study demonstrated that this model utilizing HepG2/C3A spheroids grown under dynamic clinostat conditions represents a very sensitive and promising in vitro model for genotoxicity and environmental studies and can thus significantly contribute to a more reliable assessment of genotoxic activities of pure chemicals, and complex environmental samples even at very low for environmental exposure relevant concentrations.

Recent Advances in Electrochemical Sensors for the Detection of Biomolecules and Whole Cells

Electrochemical sensors are considered an auspicious tool to detect biomolecules (e.g., DNA, proteins, and lipids), which are valuable sources for the early diagnosis of diseases and disorders. Advances in electrochemical sensing platforms have enabled the development of a new type of biosensor, enabling label-free, non-destructive detection of viability, function, and the genetic signature of whole cells. Numerous studies have attempted to enhance both the sensitivity and selectivity of electrochemical sensors, which are the most critical parameters for assessing sensor performance. Various nanomaterials, including metal nanoparticles, carbon nanotubes, graphene and its derivatives, and metal oxide nanoparticles, have been used to improve the electrical conductivity and electrocatalytic properties of working electrodes, increasing sensor sensitivity. Further modifications have been implemented to advance sensor platform selectivity and biocompatibility using biomaterials such as antibodies, aptamers, extracellular matrix (ECM) proteins, and peptide composites. This paper summarizes recent electrochemical sensors designed to detect target biomolecules and animal cells (cancer cells and stem cells). We hope that this review will inspire researchers to increase their efforts to accelerate biosensor progress-enabling a prosperous future in regenerative medicine and the biomedical industry.

Recent progress in micro/nano biosensors for shellfish toxin detection

Shellfish toxins, as one kind of marine toxin, have attracted worldwide attention due to their severe threat to food safety and human health. Therefore, it is highly essential and urgent to develop a low-cost and convenient method to detect these toxins. With the rapid advance in microfabrication processes, micro/nano biosensors provide novel approaches to address this issue. In addition to their features of low cost, portability, easy operation, high efficiency and high bioactivity, micro/nano biosensors have great potential to realize on-the-spot, rapid detection of shellfish toxins. This review focuses on the most recent advances in the development of micro/nano biosensors for shellfish toxin detection. These biosensors are mainly classified into five categories according to their transducer detection principles, which include optical devices, electrochemical sensors, electrochemiluminescence, field-effect transistors, and acoustic devices. Sensor strategies, toxin analytes, biosensitive elements, coupling methods and field detection performance are highlighted to discuss the applications of shellfish toxin detection. With advances in sensor technology, biomaterials, microfabrication and miniaturized electronics, micro/nano biosensors applied to in-field fast detection of shellfish toxins are expected to play a critical role in food safety, environmental monitoring, and foreign trade in the foreseeable future. Finally, the current challenges and future development trends of micro/nano biosensors for shellfish toxin detection are discussed.

Three-Dimensional Spheroids as In Vitro Preclinical Models for Cancer Research

Most cancer biologists still rely on conventional two-dimensional (2D) monolayer culture techniques to test in vitro anti-tumor drugs prior to in vivo testing. However, the vast majority of promising preclinical drugs have no or weak efficacy in real patients with tumors, thereby delaying the discovery of successful therapeutics. This is because 2D culture lacks cell–cell contacts and natural tumor microenvironment, important in tumor signaling and drug response, thereby resulting in a reduced malignant phenotype compared to the real tumor. In this sense, three-dimensional (3D) cultures of cancer cells that better recapitulate in vivo cell environments emerged as scientifically accurate and low cost cancer models for preclinical screening and testing of new drug candidates before moving to expensive and time-consuming animal models. Here, we provide a comprehensive overview of 3D tumor systems and highlight the strategies for spheroid construction and evaluation tools of targeted therapies, focusing on their applicability in cancer research. Examples of the applicability of 3D culture for the evaluation of the therapeutic efficacy of nanomedicines are discussed.

RGD-modified injectable hydrogel maintains islet beta-cell survival and function

OBJECTIVE

A potential solution for islet transplantation and drug discovery vis-à-vis treating diabetes is the production of functional islets in a three-dimensional extracellular matrix. Although several scaffold materials have been reported as viable candidates, a clinically applicable one that is injectable and can maintain long-term functionality and survival of islet pancreatic beta-cells (β-cells) is far from being established.

RESULTS

In the current study, we evaluated a ready-to-use and injectable hydrogel's impact on β-cells' function and viability, both in vitro and in vivo. We found that β-cells in high concentration with hydrogels functionalized via Arg-Gly-Asp (RGD) demonstrated better viability and insulin secretory capacity in vitro. Moreover, it is a biocompatible hydrogel that can maintain β-cell proliferation and vascularization without stimulating inflammation after subcutaneous injection. Meanwhile, modifying the hydrogel with RGD can maintain β-cells' secretion of insulin, regulating the blood glucose levels of mice with streptozotocin-induced diabetes.

CONCLUSIONS

Thus, these preliminary results indicate that this RGD-modified hydrogel is a potential extracellular matrix for islet transplantation at extrahepatic sites, and they also provide a reference for future tissue engineering study.

Machine learning based on holographic scattering spectrum for mixed pollutants analysis

Determination of complex pollutants often involves many high-cost and laborious operations. Today's pop machine-learning (ML) technology has exhibited their amazing successes in image recognition, drug designing, disease detection, natural language understanding, etc. ML-driven samples testing will inevitably promote the development of related subjects and fields, but the biggest challenge ahead for this process is how to provide some intelligible and sufficient data for various algorithms. In this work, we present a full strategy for rapid detecting mixed pollutants through the synergistic application of holographic spectrum and convolutional neural network (CNN). The results have shown that a well-trained CNN model could realize quantitative analysis of the mixed pollutants by extracting spectral information of matters, suggesting the strategy's value in facilitating the study of complex chemical systems.

Advanced biomedical applications based on emerging 3D cell culturing platforms

It is of great value to develop reliable in vitro models for cell biology and toxicology. However, ethical issues and the decreasing number of donors restrict the further use of traditional animal models in various fields, including the emerging fields of tissue engineering and regenerative medicine. The huge gap created by the restrictions in animal models has pushed the development of the increasingly recognized three-dimensional (3D) cell culture, which enables cells to closely simulate authentic cellular behaviour such as close cell-to-cell interactions and can achieve higher functionality. Furthermore, 3D cell culturing is superior to the traditional 2D cell culture, which has obvious limitations and cannot closely mimic the structure and architecture of tissues. In this study, we review several methods used to form 3D multicellular spheroids. The extracellular microenvironment of 3D spheroids plays a role in many aspects of biological sciences, including cell signalling, cell growth, cancer cell generation, and anti-cancer drugs. More recently, they have been explored as basic construction units for tissue and organ engineering. We review this field with a focus on the previous research in different areas using spheroid models, emphasizing aqueous two-phase system (ATPS)-based techniques. Multi-cellular spheroids have great potential in the study of biological systems and can closely mimic the in vivo environment. New technologies to form and analyse spheroids such as the aqueous two-phase system and magnetic levitation are rapidly overcoming the technical limitations of spheroids and expanding their applications in tissue engineering and regenerative medicine.

Opportunities and Challenges for Biosensors and Nanoscale Analytical Tools for Pandemics: COVID-19

Biosensors and nanoscale analytical tools have shown huge growth in literature in the past 20 years, with a large number of reports on the topic of 'ultrasensitive', 'cost-effective', and 'early detection' tools with a potential of 'mass-production' cited on the web of science. Yet none of these tools are commercially available in the market or practically viable for mass production and use in pandemic diseases such as coronavirus disease 2019 (COVID-19). In this context, we review the technological challenges and opportunities of current bio/chemical sensors and analytical tools by critically analyzing the bottlenecks which have hindered the implementation of advanced sensing technologies in pandemic diseases. We also describe in brief COVID-19 by comparing it with other pandemic strains such as that of severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS) for the identification of features that enable biosensing. Moreover, we discuss visualization and characterization tools that can potentially be used not only for sensing applications but also to assist in speeding up the drug discovery and vaccine development process. Furthermore, we discuss the emerging monitoring mechanism, namely wastewater-based epidemiology, for early warning of the outbreak, focusing on sensors for rapid and on-site analysis of SARS-CoV2 in sewage. To conclude, we provide holistic insights into challenges associated with the quick translation of sensing technologies, policies, ethical issues, technology adoption, and an overall outlook of the role of the sensing technologies in pandemics.

Application of electrochemical biosensors in tumor cell detection

Conventional methods for detecting tumors, such as immunological methods and histopathological diagnostic techniques, often request high analytical costs, complex operation, long turnaround time, experienced personnel and high false-positive rates. In addition, these assays are difficult to obtain an early diagnosis and prognosis quickly for malignant tumors. Compared with traditional technology, electrochemical technology has realized the study of interface charge transfer behavior at the atomic and molecular levels, which has become an important analytical and detection tool in contemporary analytical science. Electrochemical technique has the advantages of rapid detection, high sensitivity (single cell) and specificity in the detection of tumor cells, which has not only been successful in differentiating tumor cells from normal cells, but has also achieved targeted detection of localized tumor cells and circulating tumor cells. Electrochemical biosensors provide powerful tools for early diagnosis, staging and prognosis of tumors in clinical medicine. Therefore, this review mainly discusses the development and application of electrochemical biosensors in tumor cell detection in recent years.

An electrochemical aptasensor based on eATRP amplification for the detection of bisphenol A

Herein, a novel aptasensor was constructed for ultrasensitive detection of bisphenol A (BPA). In this method, an electrochemically mediated atom transfer radical polymerization (eATRP) signal amplification strategy was applied to BPA detection for the first time. The 5'-end modified sulfhydryl group and the 3'-end modified azide group hairpin DNA were immobilized on a gold electrode through an Au-S bond. The double-stranded DNA was formed by the hybridization of an aptamer and a single-stranded DNA partially paired with the hairpin DNA. In the presence of BPA, the aptamer combined with BPA and the single-stranded DNA was released to open the hairpin structure, making the azide groups at the 3' end exposed. Subsequently the initiator of eATRP was introduced into hairpin DNA through click chemistry reaction and eATRP was conducted for the polymerization of the electroactive probe ferrocene methyl methacrylate (FMMA). As a result, the ultrasensitive detection of BPA was realized, and the detection limit of this aptasensor was as low as 59 aM and a good selectivity was obtained in the presence of 100-fold structural analogs. The application of this aptasensor was evaluated by detecting BPA in pure water samples, and recoveries were in the range of 95.23-98.40%, holding promising applications in biological analysis.