New insights into ROS dynamics: a multi-layered microfluidic chip for ecotoxicological studies on aquatic microorganisms

A wavelength-induced frequency filtering method for fluorescent nanosensors in vivo

Fluorescent nanosensors hold the potential to revolutionize life sciences and medicine. However, their adaptation and translation into the in vivo environment is fundamentally hampered by unfavourable tissue scattering and intrinsic autofluorescence. Here we develop wavelength-induced frequency filtering (WIFF) whereby the fluorescence excitation wavelength is modulated across the absorption peak of a nanosensor, allowing the emission signal to be separated from the autofluorescence background, increasing the desired signal relative to noise, and internally referencing it to protect against artefacts. Using highly scattering phantom tissues, an SKH1-E mouse model and other complex tissue types, we show that WIFF improves the nanosensor signal-to-noise ratio across the visible and near-infrared spectra up to 52-fold. This improvement enables the ability to track fluorescent carbon nanotube sensor responses to riboflavin, ascorbic acid, hydrogen peroxide and a chemotherapeutic drug metabolite for depths up to 5.5 ± 0.1 cm when excited at 730 nm and emitting between 1,100 and 1,300 nm, even allowing the monitoring of riboflavin diffusion in thick tissue. As an application, nanosensors aided by WIFF detect the chemotherapeutic activity of temozolomide transcranially at 2.4 ± 0.1 cm through the porcine brain without the use of fibre optic or cranial window insertion. The ability of nanosensors to monitor previously inaccessible in vivo environments will be important for life-sciences research, therapeutics and medical diagnostics.

A rapid response near-infrared ratiometric fluorescent probe for the real-time tracking of peroxynitrite for pathological diagnosis and therapeutic assessment in a rheumatoid arthritis model

Endogenous ONOO⁻ generation in rheumatoid arthritis mice was visualized and confirmed by the ratiometric fluorescent probe Ratio-A.

Recent Progress in Lab-On-a-Chip Systems for the Monitoring of Metabolites for Mammalian and Microbial Cell Research

Lab-on-a-chip sensing technologies have changed how cell biology research is conducted. This review summarises the progress in the lab-on-a-chip devices implemented for the detection of cellular metabolites. The review is divided into two subsections according to the methods used for the metabolite detection. Each section includes a table which summarises the relevant literature and also elaborates the advantages of, and the challenges faced with that particular method. The review continues with a section discussing the achievements attained due to using lab-on-a-chip devices within the specific context. Finally, a concluding section summarises what is to be resolved and discusses the future perspectives.

Effect of light on the transformation of BDE-47 by living and autoclaved cultures of Microcystis flos-aquae and Chlorella vulgaris

Polybrominated diphenyl ethers (PBDEs) are ubiquitous and toxic contaminants found in high concentrations in watercourses, and are not well removed by conventional wastewater treatment facilities. This study aimed to evaluate the removal and transformation of BDE-47, one of the environmentally predominant PBDE congener, by a green alga (Chlorella vulgaris) and a cyanobacterium (Microcystis flos-aquae) under different light conditions. Living and autoclaved cultures were exposed to BDE-47 at a concentration of 10 μg L^-1 for 7 days. Both species removed >90% of BDE-47 very shortly after spiking. Light intensity affected the transformation of BDE-47 in living cultures of both species, since 5 to 11 times more debromination products were measured at a light intensity of 100 μmol photons m^-2 s^-1 than at 20 μmol photons m^-2 s^-1. Living cultures of M. flos-aquae transformed BDE-47 at a rate of 0.22 day^-1 while no transformation was observed in the respective autoclaved cultures. On the contrary, both living and autoclaved cultures of C. vulgaris had similar BDE-47 transformation rates of 0.05-0.06 day^-1. Debromination of BDE-47 was a predominant transformation pathway in cultures of C. vulgaris, with two times higher BDE-28 concentrations measured than in M. flos-aquae, while hydroxylation was more dominant with the cyanobacterium. Most BDE-47 and its debromination product BDE-28 were found on the cell surface of both species. These results reveal that different transformation mechanisms were involved in C. vulgaris and M. flos-aquae cultures and confirm the importance of species selection for the removal of PBDEs from contaminated environments.

Benzo[a]pyrene (BaP) exposure generates persistent reactive oxygen species (ROS) to inhibit the NF-κB pathway in medaka (Oryzias melastigma)

Benzo[a]pyrene (BaP), a common environmental pollutant, can modulate the immune-associated signal pathway NF-κB, which is one of the critical signal pathways involved in various immune responses. BaP exposure usually generates reactive oxygen species (ROS), but whether ROS are predominantly involved in the modulation mechanism of the NF-κB pathway has not been clearly understood. In this study, an in vivo examination of Oryzias melastigma demonstrated that BaP exposure led to a down-regulation of the NF-κB pathway and increased levels of ROS. Conversely, in vitro results using the medaka liver cell line DIT-29 and a widely applied H₂O₂ method showed the opposite: up-regulation of the NF-κB pathway. However, the down-regulation of NF-κB upon BaP exposure in vitro was inhibited by the addition of a ROS inhibitor, indicating ROS are involved in the modulation of NF-κB. The discrepancy between in vivo and in vitro results of ROS impacts on NF-κB activation might be related to the concentration and persistence of ROS. Using a modified luminol detection system, BaP was found to generate sustained physiological concentrations of ROS for 24 h, while an H₂O₂ bolus generated ROS for less than 30 min. Furthermore, a steady-state sub-micromolar H₂O₂ system (H₂O₂ss) was developed in parallel as a positive control of ROS, by which H₂O₂ could be maintained for 24 h. Comparative evaluation using H₂O₂, H₂O₂ss and BaP exposures on the medaka cell line with pGL4.32 demonstrated that the persistent physiological concentrations of ROS generated upon BaP exposure or treatment with H₂O₂ss inhibited the NF-κB pathway, but direct H₂O₂ exposure had the opposite effect. Moreover, a western-blot assay and EMSA detection further confirmed the modulation of the NF-κB pathway in DIT-29. Taken together, this study shows that BaP exposure inhibits the NF-κB pathway by generating sustained physiological concentrations of ROS.

Microfluidic technology for plankton research

Plankton produces numerous chemical compounds used in cosmetics and functional foods. They also play a key role in the carbon budget on the Earth. In a context of global change, it becomes important to understand the physiological response of these microorganisms to changing environmental conditions. Their adaptations and the response to specific environmental conditions are often restricted to a few active cells or individuals in large populations. Using analytical capabilities at the subnanoliter scale, microfluidic technology has also demonstrated a high potential in biological assays. Here, we review recent advances in microfluidic technologies to overcome the current challenges in high content analysis both at population and the single cell level.

Microenvironment-Cell Nucleus Relationship in the Context of Oxidative Stress

The microenvironment is a source of reactive oxygen species (ROS) that influence cell phenotype and tissue homeostasis. The impact of ROS on redox pathways as well as directly on epigenetic mechanisms and the DNA illustrate communication with the cell nucleus. Changes in gene transcription related to redox conditions also influence the content and structure of the extracellular matrix. However, the importance of microenvironmental ROS for normal progression through life and disease development still needs to be thoroughly understood. We illustrate how different ROS concentration levels trigger various intracellular pathways linked to nuclear functions and determine processes necessary for the differentiation of stem cells. The abnormal predominance of ROS that leads to oxidative stress is emphasized in light of its impact on aging and diseases related to aging. These phenomena are discussed in the context of the possible contribution of extracellular ROS via direct diffusion into cells responsible for organ function, but also via an impact on stromal cells that triggers extracellular modifications and influences mechanotransduction. Finally, we argue that organs-on-a-chip with controlled microenvironmental conditions can help thoroughly grasp whether ROS production is readily a cause or a consequence of certain disorders, and better understand the concentration levels of extracellular ROS that are necessary to induce a switch in phenotype.

Ecotoxicology Goes on a Chip: Embracing Miniaturized Bioanalysis in Aquatic Risk Assessment

Biological and environmental sciences are, more than ever, becoming highly dependent on technological and multidisciplinary approaches that warrant advanced analytical capabilities. Microfluidic lab-on-a-chip technologies are perhaps one the most groundbreaking offshoots of bioengineering, enabling design of an entirely new generation of bioanalytical instrumentation. They represent a unique approach to combine microscale engineering and physics with specific biological questions, providing technological advances that allow for fundamentally new capabilities in the spatiotemporal analysis of molecules, cells, tissues, and even small metazoan organisms. While these miniaturized analytical technologies experience an explosive growth worldwide, with a substantial promise of a direct impact on biosciences, it seems that lab-on-a-chip systems have so far escaped the attention of aquatic ecotoxicologists. In this Critical Review, potential applications of the currently existing and emerging chip-based technologies for aquatic ecotoxicology and water quality monitoring are highlighted. We also offer suggestions on how aquatic ecotoxicology can benefit from adoption of microfluidic lab-on-a-chip devices for accelerated bioanalysis.

Non-invasive continuous monitoring of pro-oxidant effects of engineered nanoparticles on aquatic microorganisms

Engineered nanomaterials (ENMs) are key drivers for the development of highly sophisticated new technologies. As all new attainments, the rapidly increasing used of ENMs raise concerns about their safety for the environment and humans. There is growing evidence showing that if engineered nanomaterials are released into the environment, there is a possibility that they could cause harm to aquatic microorganisms. Among the divers effects triggering their toxicity the ability of ENMs to generate reactive oxygen species (ROS) capable of oxidizing biomolecules is currently considered a central mechanism of toxicity. Therefore, development of sensitive tools for quantification of the ROS generation and oxidative stress are highly sought. After briefly introducing ENMs-induced ROS generation and oxidative stress in the aquatic microorganisms (AMOs), this overview paper focuses on a new optical biosensor allowing sensitive and dynamic measurements of H₂O₂ in real-time using multiscattering enhanced absorption spectroscopy. Its principle is based on sensitive absorption measurements of the heme protein cytochrome c whose absorption spectrum alters with the oxidation state of constituent ferrous Fe^II and ferric Fe^III. For biological applications cytochrome c was embedded in porous random media resulting in an extended optical path length through multiple scattering of light, which lowers the limit of detection to a few nM of H₂O₂. The sensor was also integrated in a microfluidic system containing micro-valves and sieves enabling more complex experimental conditions. To demonstrate its performance, abiotic absorption measurements of low concentrations of dye molecules and 10 nm gold particles were carried out achieving limits of detection in the low nM range. Other biologically relevant reactive oxygen species can be measured at sub-μM concentrations, which was shown for glucose and lactate through enzymatic reactions producing H₂O₂. In ecotoxicological investigations H₂O₂ excreted by aquatic microorganisms exposed to various stressors were measured. Pro-oxidant effects of nano-TiO₂ and nano-CuO towards green alga Chlamydomonas reinhardtii were explored in various exposure media and under different light illuminations. Dynamics of Cd²⁺ induced effects on photosynthetic activity, sensitisation and recovery of cells of C. reinhardtii was also studied.

Pro-oxidant effects of nano-TiO2on Chlamydomonas reinhardtii during short-term exposure

This is the first continuous quantification of abiotic and biotic nano-TiO₂– stimulated H₂O₂revealing that measured extracellular and intracellular pro-oxidant endpoints inC. reinhardtiican differ significantly.