[en] In this work, we study the regional dependence of transport behavior of microalgae Chlorella vulgaris inside microfluidic channel on applied fluid flow rate. The microalgae are treated as spherical naturally buoyant particles. Deviation from the normal diffusion or Brownian transport is characterized based on the scaling behavior of the mean square displacement (MSD) of the particle trajectories by resolving the displacements in the streamwise (flow) and perpendicular directions. The channel is divided into three different flow regions, namely center region of the channel and two near-wall boundaries and the particle motions are analyzed at different flow rates. We use the scaled Brownian motion to model the transitional characteristics in the scaling behavior of the MSDs. We find that there exist anisotropic anomalous transports in all the three flow regions with mixed sub-diffusive, normal and super-diffusive behavior in both longitudinal and transverse directions. (paper)

[en] Highlights: • Future ocean acidification levels have little effect on the growth and photosynthesis of Chlorella sp. • Ocean acidification promoted saturation of fatty acids and amino acid synthesis of Chlorella sp. • Enhancement of energy production and trehalose synthesis could be the acclimation strategies of marine picochlorophytes. -- Abstract: Ocean acidification, due to increased levels of anthropogenic carbon dioxide, is known to affect the physiology and growth of marine phytoplankton, especially in polar regions. However, the effect of acidification or carbonation on cellular metabolism in polar marine phytoplankton still remains an open question. There is some evidence that small chlorophytes may benefit more than other taxa of phytoplankton. To understand further how green polar picoplankton could acclimate to high oceanic CO₂, studies were conducted on an Antarctic Chlorella sp. Chlorella sp. maintained its growth rate (∼0.180 d^-1), photosynthetic quantum yield (Fv/Fm = ∼0.69) and chlorophyll a (0.145 fg cell^-1) and carotenoid (0.06 fg cell^-1) contents under high CO₂, while maximum rates of electron transport decreased and non-photochemical quenching increased under elevated CO₂. GCMS-based metabolomic analysis reveal that this polar Chlorella strain modulated the levels of metabolites associated with energy, amino acid, fatty acid and carbohydrate production, which could favour its survival in an increasingly acidified ocean.

[en] An ecologically important tropical freshwater microalga, Scenedesmus quadricauda, was exposed to Ni toxicity under two temperature regimes, 25 and 35 °C to investigate the interactive effects of warming and different Ni concentrations (0.1, 1.0 and 10.0 ppm). The stress responses were assessed from the growth, photosynthesis, reactive oxygen species (ROS) generation and metabolomics aspects to understand the effects at both the physiological and biochemical levels. The results showed that the cell densities of the cultures were higher at 35 °C compared to 25 °C, but decreased with increasing Ni concentrations at 35 °C. In terms of photosynthetic efficiency, the maximum quantum yield of photosystem II (F_v/F_m) of S. quadricauda remained consistent across different conditions. Nickel concentration at 10.0 ppm affected the maximum rate of relative electron transport (rETR_m) and saturation irradiance for electron transport (E_k) in photosynthesis. At 25 °C, the increase of non-photochemical quenching (NPQ) values in cells exposed to 10.0 ppm Ni might indicate the onset of thermal dissipation process as a self-protection mechanism against Ni toxicity. The combination of warming and Ni toxicity induced a strong oxidative stress response in the cells. The ROS level increased significantly by 40% after exposure to 10.0 ppm of Ni at 35 °C. The amount of Ni accumulated in the biomass was higher at 25 °C compared to 35 °C. Based on the metabolic profile, temperature contributed the most significant differentiation among the samples compared to Ni treatment and the interaction between the two factors. Amino acids, sugars and organic acids were significantly regulated by the combined factors to restore homeostasis. The most affected pathways include sulphur, amino acids, and nitrogen metabolisms. Overall, the results suggest that the inhibitory effect of Ni was lower at 35 °C compared to 25 °C probably due to lower metal uptake and primary metabolism restructuring. The ability of S. quadricauda to accumulate substantial amount of Ni and thrive at 35 °C suggests the potential use of this strain for phycoremediation and outdoor wastewater treatment.

[en] Titanium oxide (TiO₂)/reduced graphene oxide (rGO) composite nanofibers were synthesized via an electrospinning technique and its potential electrochemical activity constructed its realization as an efficient anode catalyst in biophotovoltaic cells (BPV) with Chlorella vulgaris. The uniform adherence of GO sheets over the hydrolyzed Ti⁴⁺ ions, followed by its simultaneous reduction and crystallization, yielded the TiO₂/rGO composite nanofibers. The strong interconnection among the nanofibers and the intimate contact between rGO and TiO₂ in TiO₂/rGO composite improved the efficient electron transportation paths, facilitating the higher oxidation and continuous and stable currents as substantiated, respectively, from the cyclic voltammetry and chronoamperometry studies. By coupling the continuous electron conduction paths, proficient cell interaction, and elevated structural and chemical stabilities, TiO₂/rGO demonstrated the BPV power density of 34.66 ± 1.3 mW m⁻² with excellent durability, outperforming the BPV performances of previous reports. Thus the fundamental understanding achieved on the influences of nanocatalytic system in green energy generation opens up the new horizon of anticipation towards the development of sustainable and high-performance BPVs.

[en] Highlights: • MnS@MoS₂ architectures are prepared by using a simple hydrothermal technique∙MnS@MoS₂ modified TBFP is used as an electrochemical probe for H₂O₂ sensing∙Growth and formation mechanisms of MnS@MoS₂ architectures are illustrated∙Mn(IV)/Mo(IV) centres engaged H₂O₂ electroreduction mechanism is schematized∙MnS@MoS₂/TBFP establishes effectual non-enzymatic H₂O₂ sensing performances∙MnS@MoS₂/TBFP’s real sample H₂O₂ sensing relevancy is actualized in human urine -- Abstract: We report here the rational development of MnO₂ nanorods coated tea bag filter paper (TBFP) as a self-standing, bendable, and disposable electrochemical probe for the sensitive and selective H₂O₂ detection and addresses their challenges in H₂O₂ sensing via the replacement of ‘O’ with ‘S’ in the form of MnS microcubes and its core@shell architecture with MoS₂. The as-configured MnS@MoS₂/TBFP overwhelms the constrains of conventional electrochemical probes including time and cost consumed electrode surface renewability and catalyst loading progression, and the practice of an insulating binder. The hierarchical open porous architectures of MoS₂-shell favour the diffusion of H₂O₂ into the core-MnS microcubes, facilitating an analyte utilization efficacy at both the core and shell architectures. The impacts of core@shell morphological features, replacement of ‘O’ with ‘S’, surface defects, and lattice distribution of MnS@MoS₂ toward non-enzymatic H₂O₂ sensing performances are elucidated using variant electrochemical techniques. With the synergism of uniformly implanted and exposed metallic active sites, efficient electron transfer rate, and high analyte utilization efficiency, MnS@MoS₂/TBFP exposes the low detection limit (120 nM), excellent sensitivity (650 μA mM⁻¹ cm⁻²), and wide linear range (500 nM-5 mM) on H₂O₂ detection. Furthermore, the scrutinized non-enzymatic H₂O₂ detection concerts of MnS/MoS₂/TBFP are selective, decisive, repeatable, and stable, constructing the excellent recovery rates in human urine sample analyses. Thus, the collective benefits of free-standing, flexible, binder-less, re-functional, and cost-efficient MnS@MoS₂/TBFP probe actualize the evolution of affordable and high performance H₂O₂ sensors.