Bare Iron Oxide Nanoparticles for Magnetic Harvesting of Microalgae: From Interaction Behavior to Process Realization

Myco-generated and analysis of magnetite (Fe3O4) nanoparticles using Aspergillus elegans extract: A comparative evaluation with a traditional chemical approach

In the past few years, nanotechnology has emerged as one of the most interesting and cutting-edge research areas across all disciplines. Nanotechnology allows progress in all science fields to make novel materials and industry-different devices. Generally, nanoparticle synthesis methods are chemical, physical, and biological. The chemical and physical techniques use potentially harmful compounds, and the expense of these processes renders them unsuitable for nanoparticle synthesis. In light of this, it needs development strategies that are sustainable, economical, and eco-friendly viable. Through, biosynthesis, nanoparticles can overcome these disadvantages. One of the biological strategies is the myco-synthesis method, which connects the fields of mycology and nanotechnology. In this study, magnetite (Fe3O4) NPs have been synthesized using a myco-synthesis method by selecting Aspergillus elegans as a fungal species. Two extracts were used, growth medium and an aqueous extract. A comparative analysis between nanoparticles synthesized through myco-synthesis and those produced using conventional chemical methods has been conducted to substantiate the significance of the biological approach. The results of this study unequivocally establish that myco-synthesized nanoparticles exhibit superior and enhanced characteristics compared to those synthesized through chemical means, as ascertained through a comprehensive array of characterization techniques employed throughout the investigation. This contrast is observable in terms of the aggregation state, the existence of capping and stabilizing agents enveloping the nanoparticles, their magnetic and thermal attributes, and the enduring stability of these nanoparticles. These results highlight the significant promise of employing phytochemicals extracted from Aspergillus elegans as a highly suitable option for the biofabrication of Fe3O4 nanoparticles.

Advancements in Nano-Enhanced microalgae bioprocessing

Microalgae are promising sources of valuable compounds: carotenoids, polyunsaturated fatty acids, lipids, etc. To overcome the feasibility challenge due to low yield and attain commercial potential, researchers merge technologies to enhance algal bioprocess. In this context, nanomaterials are attractive for enhancing microalgal bioprocessing, from cultivation to downstream extraction. Nanomaterials enhance biomass and product yields (mainly lipid and carotenoids) through improved nutrient uptake and stress tolerance during cultivation. They also provide mechanistic insights from recent studies. They also revolutionize harvesting via nano-induced sedimentation, flocculation, and flotation. Downstream processing benefits from nanomaterials, improving extraction and purification. Special attention is given to cost-effective extraction, showcasing nanomaterial integration, and providing a comparative account. The review also profiles nanomaterial types, including metallic nanoparticles, magnetic nanomaterials, carbon-based nanomaterials, silica nanoparticles, polymers, and functionalized nanomaterials. Challenges and future trends are discussed, emphasizing nanomaterials' role in advancing sustainable and efficient microalgal bioprocessing, unlocking their potential for bio-based industries.

Microalgae as a potential natural source for the green synthesis of nanoparticles

The increasing global population is driving the development of alternative sources of food and energy, as well as better or new alternatives for health and environmental care, which represent key challenges in the field of biotechnology. Microalgae represent a very important source material to produce several high-value-added bioproducts. Due to the rapid changes in the modern world, there is a need to build new materials for use, including those in the nanometer size, although these developments may be chronological but often do not occur at a time. In the last few years, a new frontier has opened up at the interface of biotechnology and nanotechnology. This new frontier could help microalgae-based nanomaterials to possess new functions and abilities. Processes for the green synthesis of nanomaterials are being investigated, and the availability of biological resources such as microalgae is continuously being examined. The present review provides a concise overview of the recent advances in the synthesis, characterization, and applications of nanoparticles formed using a wide range of microalgae-based biosynthesis processes. Highlighting their innovative and sustainable potential in current research, our study contributes towards the in-depth understanding and provides latest updates on the alternatives offered by microalgae in the synthesis of nanomaterials.

Synergies of pH-induced calcium phosphate precipitation and magnetic separation for energy-efficient harvesting of freshwater microalgae

Energy- and time-consuming concentration steps currently limit the industrial application of microalgae. Compared to state-of-the-art technologies, magnetic separation shows a high potential for efficient harvesting of microalgae. This study presents a novel approach to combine pH-induced calcium phosphate precipitation with cheap natural magnetite microparticles for magnetic separation of the freshwater microalgae Chlorella vulgaris. Harvesting efficiencies up to 98% were achieved at moderate pH and low particle and calcium phosphate concentrations in a model medium. However, cultivation-dependent high loads of algogenic organic matter can severely inhibit flocculation and particle/algae interactions, requiring higher salt concentrations or pH. Harvesting efficiencies above 90% were still attainable at moderate pH with increased calcium phosphate concentrations of 10mM. Acidification of the suspension to pH 5 allows for simple and reversible particle recycling. The presented process provides a promising path to universal and cost-effective harvesting, advancing the utilization of microalgae as a sustainable bioresource.

Preparation and Application of Magnetic Composites Using Controllable Assembly for Use in Water Treatment: A Review

The use of magnetic composites in wastewater treatment has become widespread due to their high flocculating characteristics and ferromagnetism. This review provides an analysis and summary of the preparation and application of magnetic composites through controllable assembly for use in wastewater treatment. The applications of magnetic composites include the treatment of dye wastewater, heavy metal wastewater, microalgae suspensions, and oily wastewater. Additionally, the recycling and regeneration of magnetic composites have been investigated. In the future, further research could be focused on improving the assembly and regeneration stability of magnetic composites, such as utilizing polymers with a multibranched structure. Additionally, it would be beneficial to explore the recycling and regeneration properties of these composites.

Quantification methods of determining brewer's and pharmaceutical yeast cell viability: accuracy and impact of nanoparticles

For industrial processes, a fast, precise, and reliable method of determining the physiological state of yeast cells, especially viability, is essential. However, an increasing number of processes use magnetic nanoparticles (MNPs) for yeast cell manipulation, but their impact on yeast cell viability and the assay itself is unclear. This study tested the viability of Saccharomyces pastorianus ssp. carlsbergensis and Pichia pastoris by comparing traditional colourimetric, high-throughput, and growth assays with membrane fluidity. Results showed that methylene blue staining is only reliable for S. pastorianus cells with good viability, being erroneous in low viability (R² = 0.945; [Formula: see text] = 5.78%). In comparison, the fluorescence microscopy-based assay of S. pastorianus demonstrated a coefficient of determination of R² = 0.991 at [Formula: see text] ([Formula: see text] = 2.50%) and flow cytometric viability determination using carboxyfluorescein diacetate (CFDA), enabling high-throughput analysis of representative cell numbers; R² = 0.972 ([Formula: see text]; [Formula: see text] = 3.89%). Membrane fluidity resulted in a non-linear relationship with the viability of the yeast cells ([Formula: see text]). We also determined similar results using P. pastoris yeast. In addition, we demonstrated that MNPs affected methylene blue staining by overestimating viability. The random forest model has been shown to be a precise method for classifying nanoparticles and yeast cells and viability differentiation in flow cytometry by using CFDA. Moreover, CFDA and membrane fluidity revealed precise results for both yeasts, also in the presence of nanoparticles, enabling fast and reliable determination of viability in many experiments using MNPs for yeast cell manipulation or separation.

Nano magnetite assisted flocculation for efficient harvesting of lutein and lipid producing microalgae biomass

For commercial scale algal biorefining, harvesting cost is a major bottleneck. Thus, a cost-effective, less-energy intensive, and efficient harvesting method is being investigated. Among several harvesting methods, magnetic flocculation offers the benefits of modest operation, energy savings and quick separation. This study aims to develop novel magnetite-(Fe₃O₄) nanoparticles (MNPs) of 20 nm average size and their high reusability potential to reduce the harvesting cost of microalgae biomass. The MNPs were synthesized and characterized using FTIR, Zeta analyzer, and SEM before performing on Chlorella sorokiniana Kh12 and Tu5. For maximum harvesting efficiency >99%, the optimal culture pH, MNPs concentration, and agitation speed were 3, 200 mg/L, and 450 rpm, respectively. Subsequently, MNPs were recovered via alkaline treatment and reused up to 5 cycles as they retained their reactivity and harvesting efficiency. The studied MNPs-based harvesting method could be adopted at a commercial scale for cost-effective algae biorefinery in the future.

Fe3O4-PEI Nanocomposites for Magnetic Harvesting of Chlorella vulgaris, Chlorella ellipsoidea, Microcystis aeruginosa, and Auxenochlorella protothecoides

Magnetic separation of microalgae using magnetite is a promising harvesting method as it is fast, reliable, low cost, energy-efficient, and environmentally friendly. In the present work, magnetic harvesting of three green algae (Chlorella vulgaris, Chlorella ellipsoidea, and Auxenochlorella protothecoides) and one cyanobacteria (Microcystis aeruginosa) has been studied. The biomass was flushed with clean air using a 0.22 μm filter and fed CO₂ for accelerated growth and faster reach of the exponential growth phase. The microalgae were harvested with magnetite nanoparticles. The nanoparticles were prepared by controlled co-precipitation of Fe²⁺ and Fe³⁺ cations in ammonia at room temperature. Subsequently, the prepared Fe₃O₄ nanoparticles were coated with polyethyleneimine (PEI). The prepared materials were characterized by high-resolution transmission electron microscopy, X-ray diffraction, magnetometry, and zeta potential measurements. The prepared nanomaterials were used for magnetic harvesting of microalgae. The highest harvesting efficiencies were found for PEI-coated Fe₃O₄. The efficiency was pH-dependent. Higher harvesting efficiencies, up to 99%, were obtained in acidic solutions. The results show that magnetic harvesting can be significantly enhanced by PEI coating, as it increases the positive electrical charge of the nanoparticles. Most importantly, the flocculants can be prepared at room temperature, thereby reducing the production costs.

Mass cultivation and harvesting of microalgal biomass: Current trends and future perspectives

Microalgae are unicellular photosynthetic organisms capable of producing high-value metabolites like carbohydrates, lipids, proteins, polyunsaturated fatty acids, vitamins, pigments, and other high-value metabolites. Microalgal biomass gained more interest for the production of nutraceuticals, pharmaceuticals, therapeutics, food supplements, feed, biofuel, bio-fertilizers, etc. due to its high lipid and other high-value metabolite content. Microalgal biomass has the potential to convert trapped solar energy to organic materials and potential metabolites of nutraceutical and industrial interest. They have higher efficiency to fix carbon dioxide (CO₂) and subsequently convert it into biomass and compounds of potential interest. However, to make microalgae a potential industrial candidate, cost-effective cultivation systems and harvesting methods for increasing biomass yield and reducing the cost of downstream processing have become extremely urgent and important. In this review, the current development in different microalgal cultivation systems and harvesting methods has been discussed.

Role of Biofuels in Energy Transition, Green Economy and Carbon Neutrality

Modern civilization is heavily reliant on petroleum-based fuels to meet the energy demand of the transportation sector. However, burning fossil fuels in engines emits greenhouse gas emissions that harm the environment. Biofuels are commonly regarded as an alternative for sustainable transportation and economic development. Algal-based fuels, solar fuels, e-fuels, and CO2-to-fuels are marketed as next-generation sources that address the shortcomings of first-generation and second-generation biofuels. This article investigates the benefits, limitations, and trends in different generations of biofuels through a review of the literature. The study also addresses the newer generation of biofuels highlighting the social, economic, and environmental aspects, providing the reader with information on long-term sustainability. The use of nanoparticles in the commercialization of biofuel is also highlighted. Finally, the paper discusses the recent advancements that potentially enable a sustainable energy transition, green economy, and carbon neutrality in the biofuel sector.

Sustainable resource production for manufacturing bioactives from micro- and macroalgae: Examples from harvesting and cultivation in the Nordic region

Micro- and macroalgae are a great and important source of raw material for manufacturing of bioactives and ingredients for food, feed, cosmetics, or pharmaceuticals. Macroalgae (or seaweeds) have been harvested locally from wild stocks in smaller volumes for a long time, and a production chain based on cultivated seaweed for the harvest of considerably larger amounts is in progress for several species. Microalgae and cyanobacteria such as Spirulina have been produced in "backyard ponds" for use in food and feed also for a long time, and now we see the establishment of large production plants to control the cultivation process and increase the production yields. There is also a shift from harvesting or cultivation centered in warmer, sunnier areas to increasing exploitation of natural resources in temperate to boreal regions. In locations with strong seasonal variations in solar irradiance and temperatures, we need to develop procedures to maximize the biomass production in the productive seasons and ensure efficient stabilization of the biomass for year-round processing and product manufacturing. Industrialized biomass production and large-scale manufacturing of bioactives also mean that we must employ sustainable, cost-effective, and environmentally friendly processing methods, including stabilization and extraction methods such as ensiling and subcritical water extraction (SWE) and advanced analytic tools to characterize the products. These topics are focus areas of the Nordic Centre of Excellence (NCoE) NordAqua, and here we present a review of current activities in the field of micro- and macroalgae biomass production sectors illustrated with some of our experiences from the NordAqua consortium.

A critical review on different harvesting techniques for algal based biodiesel production

The fuels retrieved from renewable sources which are usually employed as both carbon and energy sources are termed as neutral based biofuels. The most promising feedstock from renewable sources with great potentiality in contributing to the inclining energy demand is microalgae. These microalgae can be harnessed readily in terms of obtaining qualitative biodiesel with greater energy consumption under limited operational cost. The process of harvesting or dewatering microalgae could be carried under single or sequential combinations of operations. The major drawback of harvesting such as huge operational cost could be lowered by increasing the level of automation than cost of investments. The present review concentrates and explores on the techno-economic analysis of the microalgal harvesting and dewatering processes on a large scale. Along with these advanced techniques enclosing the utilization of nanoparticles for harvesting has also been explored. And it also adds with the impacts of concerning facts on energy consumption, processing cost and recovery of resources during harvesting.

Optimization of Microalga Chlorella vulgaris Magnetic Harvesting

Harvesting of microalgae is a crucial step in microalgae-based mass production of different high value-added products. In the present work, magnetic harvesting of Chlorella vulgaris was investigated using microwave-synthesized naked magnetite (Fe₃O₄) particles with an average crystallite diameter of 20 nm. Optimization of the most important parameters of the magnetic harvesting process, namely pH, mass ratio (m_r) of magnetite particles to biomass (g/g), and agitation speed (rpm) of the C. vulgaris biomass-Fe₃O₄ particles mixture, was performed using the response surface methodology (RSM) statistical tool. Harvesting efficiencies higher than 99% were obtained for pH 3.0 and mixing speed greater or equal to 350 rpm. Recovery of magnetic particles via detachment was shown to be feasible and the recovery particles could be reused at least five times with high harvesting efficiency. Consequently, the described harvesting approach of C. vulgaris cells leads to an efficient, simple, and quick process, that does not impair the quality of the harvested biomass.

The Effect of pH and Viscosity on Magnetophoretic Separation of Iron Oxide Nanoparticles

Magnetic nanoparticles (MNPs) are used for magnetophoresis-based separation processes in various biomedical and engineering applications. Essential requirements are the colloidal stability of the MNPs and the ability to be separated even in low magnetic field gradients. Bare iron oxide nanoparticles (BIONs) with a diameter of 9.2 nm are synthesized via coprecipitation, exhibiting a high saturation magnetization of 70.84 Am2 kg−1 and no remanence. In our study, zeta potential, dynamic light scattering (DLS), and sedimentation analysis show that the aggregation behavior of BIONs is influenced by pH and viscosity. Small aggregate clusters are formed with either low or high pH values or increased viscosity. Regarding magnetophoresis-based separation, a higher viscosity leads to lower magnetophoretic velocities, similar to how small aggregates do. Additionally, cooperative magnetophoresis, the joint motion of strongly interacting particles, affects the separation of the BIONs, too. Our study emphasizes the effect of pH and viscosity on the physicochemical characteristics of MNPs, resulting in different aggregation behavior. Particularly, for high viscous working media in downstream processing and medicine, respectively, the viscosity should be taken into account, as it will affect particle migration.

Bio-nano interactions: binding proteins, polysaccharides, lipids and nucleic acids onto magnetic nanoparticles

The major interest in nanoparticles as an application platform for biotechnology arises from their high surface-to-volume ratio. Iron oxide nanoparticles (IONPs) are particularly appealing due to their superparamagnetic behavior, which enables bioseparation using external magnetic fields. In order to design advanced biomaterials, improve binding capacities and develop innovative processing solutions, a thorough understanding of the factors governing organic-inorganic binding in solution is critical but has not yet been achieved, given the wide variety of chemical and physical influences. This paper offers a critical review of experimental studies of the interactions between low cost IONPs (bare iron oxides, silica-coated or easily-functionalized surfaces) and the main groups of biomolecules: proteins, lipids, nucleic acids and carbohydrates. Special attention is devoted to the driving forces and interdependencies responsible of interactions at the solid-liquid interface, to the unique structural characteristics of each biomolecular class, and to environmental conditions influencing adsorption. Furthermore, studies focusing on mixtures, which are still rare, but absolutely necessary to understand the biocorona, are also included. This review concludes with a discussion of future work needed to fill the gaps in knowledge of bio-nano interactions, seeking to improve nanoparticles' targeting capabilities in complex systems, and to open the door for multipurpose recognition and bioseparation processes.

Impact of magnetic immobilization on the cell physiology of green unicellular algae Chlorella vulgaris

Cell immobilization on the magnetic nanoparticles (MNPs) and magnetic harvesting is a novel approach for microalgal cells separation. To date, the effect of these nanoparticles on microalgal cells was only studied over a short period of time. More studies are hence needed for a better understanding of the magnetic harvesting proposes or environmental concerns relating to long-term exposure to nanoparticles. In this study, the impact of various concentrations of MNPs on the microalgal cells growth and their metabolic status was investigated over 12 days. More than 60% reduction in mitochondrial activity and pigments (chlorophyll a, chlorophyll b, and carotenoids) content occurred during the first 6 days of exposure to ≥50 µg/mL nanoparticles. However, more than 50% growth inhibitory effect was seen at concentrations higher than 400 µg/mL. Exposure to MNPs gradually induced cellular adaptation and after about 6 days of exposure to stress generating concentrations (˂400 µg/mL) of IONs, microalgae could overcome the imposed damages. This work provides a better understanding regarding the environmental impact of MNPs and appropriate concentrations of these particles for future algal cells magnetic immobilization and harvesting.

Role of C/N ratio on microalgae growth in mixotrophy and incorporation of titanium nanoparticles for cell flocculation and lipid enhancement in economical biodiesel application

Present study aimed to evaluate the influence of carbon/nitrogen ratio (C/N) on mixotrophic growth of microalgae and role of nanomaterial in cell recovery and lipid improvement. In this study, three microalgae species were isolated, screened from local freshwater body for lipid assimilation. The microalgae were identified as Chlorococcum sp., Scenedesmus sp., and Euglena sp. Mixotrophic cultivation of each microalgae strain using various organic carbon sources was preferred in contrast with photoautotrophic mode. Sucrose represented as the preeminent source for enhancing the microalgae biomass of 3.5 g/L and lipid content of 58.35%, which was a significant improvement as compared to control. Later, response surface methodology-central composite design (RSM-CCD), tool was employed to optimize the C/N ratio and demonstrated the maximum biomass production of 5.02 g/L along with the increased lipid content of 60.34%. Ti nanoparticles (Ti nps) were added to the culture for lipid enhancement in the stationary phase and biomass removal was performed by nanoparticle (np)-mediated flocculation technique. Optimized concentration of 15 ppm Ti nps determined the cell harvesting efficacy of 82.46% during 45 min of sedimentation time and 1.23-fold lipid enhancement was reported. Extracted lipid was converted to fatty acid methyl esters (FAME) by the process of transesterification and analyzed by gas chromatography-mass spectrometry (GC-MS). Characterization of FAME revealed the presence of 56.31% of saturated fatty acid (SFA) and 29.06% unsaturated fatty acids (UFA) that could be processed towards sustainable biodiesel production. Hence, our results suggested that integration of mixotrophic cultivation and Ti nps emerged as a new cost-effective approach for biomass and lipid enhancement in microalgae Chlorococcum sp.

Unified View of Magnetic Nanoparticle Separation under Magnetophoresis

The migration process of magnetic nanoparticles and colloids in solution under the influence of magnetic field gradients, which is also known as magnetophoresis, is an essential step in the separation technology used in various biomedical and engineering applications. Many works have demonstrated that in specific situations, separation can be performed easily with the weak magnetic field gradients created by permanent magnets, a process known as low-gradient magnetic separation (LGMS). Due to the level of complexity involved, it is not possible to understand the observed kinetics of LGMS within the classical view of magnetophoresis. Our experimental and theoretical investigations in the last years unravelled the existence of two novel physical effects that speed up the magnetophoresis kinetics and explain the observed feasibility of LGMS. Those two effects are (i) cooperative magnetophoresis (due to the cooperative motion of strongly interacting particles) and (ii) magnetophoresis-induced convection (fluid dynamics instability originating from inhomogeneous magnetic gradients). In this feature article, we present a unified view of magnetophoresis based on the extensive research done on these effects. We present the physical basis of each effect and also propose a classification of magnetophoresis into four distinct regimes. This classification is based on the range of values of two dimensionless quantities, namely, aggregation parameter N* and magnetic Grashof number Gr_m, which include all of the dependency of LGMS on various physical parameters (such as particle properties, thermodynamic parameters, fluid properties, and magnetic field properties). This analysis provides a holistic view of the classification of transport mechanisms in LGMS, which could be particularly useful in the design of magnetic separators for engineering applications.

Microalgae harvesting by magnetic flocculation for biodiesel production: current status and potential

With the increasing demand for energy, microalgae, as one of the promising feedstocks of biodiesel, has raised great awareness. Because of its small size, similar density to water and electrical stability, harvesting methods of microalgae that have low energy consumption and that are highly efficient, easy to large-scale and environmentally friendly have become a bottleneck restricting development of the whole process. Among the numerous possible harvesting methods, magnetic flocculation has the advantages of simple operation, fast separation and energy saving and thus is considered as a promising novel harvesting method. In this review, we have summarized the updated status and application potential of magnetic flocculation, including the principle of magnetic flocculation, magnetic flocculating materials, flocculating efficiency and its effect on downstream process. The major challenges such as magnetic materials recovery, large-scale magnetic flocculation device design, and magnetic flocculation costs are also discussed.

Algal cells harvesting using cost-effective magnetic nano-particles

Innovative iron-based nanoparticles were synthesized, characterized and tested for the first time for harvesting single and mixed algal culture from real wastewater. The tailor-made magnetic nanoparticles (MNPs; Fe-MNP-I and Fe-MNP-II) achieved a percentage algae harvesting efficiency (%AHE) higher than 95% using a concentration of MNPs (C_MNP) of 25 ± 0.3 (std. dev = 0.08) mg.L^-1, mixing speed (M_speed) of 120 ± 2 (std. dev = 0.10) rpm, short contact time (C_t) of 7 ± 0.1 (std. dev = 0.05) min and separation time (SP_t) of 3 ± 0.1 (std. dev = 0.09) min. The optimum operational conditions for harvesting of Chlorella vulgaris (C.v) were determined at (C_MNP = 40 ± 0.4 (std. dev = 0.5) g_MNPs.L^-1, SP_t = 2.5 ± 0.4 (std. dev = 0.1) min, M_speed = 145 ± 3 (std. dev = 1.50) rpm and C_t = 5 ± 0.3 (std. dev = 0.10) min using surface response methodology. Langmuir model describes better the adsorption behavior of algae-Fe-MNP-I system, while both Langmuir and Freundlich fit well the adsorption behavior of algae-Fe-MNP-II. The maximum adsorption capacity of Spirulina platensis (SP.PL) (18.27 ± 0.07 (std. dev = 0.19) mg_DWC.mg_particles^-1) was higher than that for Chlorella vulgaris (C.v) (11.52 ± 0.01 (std. dev = 0.34) mg_DWC.mg_particles^-1) and mixed algal culture (M.X) (17.20 ± 0.07 (std. dev = 0.54) mg_DWC.mg_particles^-1) over Fe-MNP-I. Zeta potential measurements revealed that the adsorption mechanism between MNPs and algal strains is controlled by electrostatic interaction. The synthesized MNPs were recycled 10 times using alkaline-ultrasonic regeneration procedure.

A Study on the Effect of Macro- and Micro- Nutrients on Nannochloropsis oceanica Growth, Fatty Acid Composition and Magnetic Harvesting Efficiency

The effect of iron, manganese, phosphorus and nitrogen on growth and lipid synthesis of the microalgae Nannochloropsis oceanica CCMP1779, as well as their impact on the magnetic harvesting efficiency, are examined under their depriving cell culture conditions. Herein, it is demonstrated that nitrogen and manganese depletion primarily reduced cell growth while phosphorus and iron restriction led to higher dry biomass. Subsequently, the role of those nutrients on fatty acids profile was examined. Phosphorus and nitrogen restriction resulted in lower and higher lipid content, respectively. High amounts of polyunsaturated fatty acids like eicosapentaenoic acid are produced under iron and manganese depletion. Phosphorus deprivation favors monounsaturated fatty acids such as C18:1 and C16:1, while nitrogen restriction favors saturated fatty acid production like C14:0, C16:0 and C18:0. Since the presence/absence of macro- and micro-elements may affect the overall electrostatic charges on the outmost microalgae surface, it was also analyzed how these elements affect the magnetic harvesting efficiency. Results showed that phosphorus deprivation led to the best magnetic harvesting efficiency of N. oceanica cells (93%) as compared to other nutrient starvation as well as standard medium.

Immunomagnetic Separation of Microorganisms with Iron Oxide Nanoparticles

The early detection of Legionella in water reservoirs, and the prevention of their often fatal diseases, requires the development of rapid and reliable detection processes. A method for the magnetic separation (MS) of Legionella pneumophila by superparamagnetic iron oxide nanoparticles is developed, which represents the basis for future bacteria detection kits. The focus lies on the separation process and the simplicity of using magnetic nanomaterials. Iron oxide nanoparticles are functionalized with epoxy groups and Legionella-specific antibodies are immobilized. The resulting complexes are characterized with infrared spectroscopy and tested for the specific separation and enrichment of the selected microorganisms. The cell-particle complexes can be isolated in a magnetic field and detected with conventional methods such as fluorescence detection. A nonspecific enrichment of bacteria is also possible by using bare iron oxide nanoparticles (BIONs), which we used as a reference to the nanoparticles with immobilized antibodies. Furthermore, the immunomagnetic separation can be applied for the detection of multiple other microorganisms and thus might pave the way for simpler bacterial diagnosis.

Interaction Analysis of Commercial Graphene Oxide Nanoparticles with Unicellular Systems and Biomolecules

The ability of commercial monolayer graphene oxide (GO) and graphene oxide nanocolloids (GOC) to interact with different unicellular systems and biomolecules was studied by analyzing the response of human alveolar carcinoma epithelial cells, the yeast Saccharomyces cerevisiae and the bacteria Vibrio fischeri to the presence of different nanoparticle concentrations, and by studying the binding affinity of different microbial enzymes, like the α-l-rhamnosidase enzyme RhaB1 from the bacteria Lactobacillus plantarum and the AbG β-d-glucosidase from Agrobacterium sp. (strain ATCC 21400). An analysis of cytotoxicity on human epithelial cell line A549, S. cerevisiae (colony forming units, ROS induction, genotoxicity) and V. fischeri (luminescence inhibition) cells determined the potential of both nanoparticle types to damage the selected unicellular systems. Also, the protein binding affinity of the graphene derivatives at different oxidation levels was analyzed. The reported results highlight the variability that can exist in terms of toxicological potential and binding affinity depending on the target organism or protein and the selected nanomaterial.

Bare Iron Oxide Nanoparticles: Surface Tunability for Biomedical, Sensing and Environmental Applications

Surface modification is widely assumed as a mandatory prerequisite for the real applicability of iron oxide nanoparticles. This is aimed to endow prolonged stability, electrolyte and pH tolerance as well as a desired specific surface chemistry for further functionalization to these materials. Nevertheless, coating processes have negative consequences on the sustainability of nanomaterial production contributing to high costs, heavy environmental impact and difficult scalability. In this view, bare iron oxide nanoparticles (BIONs) are arousing an increasing interest and the properties and advantages of pristine surface chemistry of iron oxide are becoming popular among the scientific community. In the authors’ knowledge, rare efforts were dedicated to the use of BIONs in biomedicine, biotechnology, food industry and environmental remediation. Furthermore, literature lacks examples highlighting the potential of BIONs as platforms for the creation of more complex nanostructured architectures, and emerging properties achievable by the direct manipulation of pristine iron oxide surfaces have been little studied. Based on authors’ background on BIONs, the present review is aimed at providing hints on the future expansion of these nanomaterials emphasizing the opportunities achievable by tuning their pristine surfaces.

Magnetic Separation in Bioprocessing Beyond the Analytical Scale: From Biotechnology to the Food Industry

Downstream processing needs more innovative ideas to advance and overcome current bioprocessing challenges. Chromatography is by far the most prevalent technique used by a conservative industrial sector. Chromatography has many advantages but also often represents the most expensive step in a pharmaceutical production process. Therefore, alternative methods as well as further processing strategies are urgently needed. One promising candidate for new developments on a large scale is magnetic separation, which enables the fast and direct capture of target molecules in fermentation broths. There has been a small revolution in this area in the last 10–20 years and a few papers dealing with the use of magnetic separation in bioprocessing examples beyond the analytical scale have been published. Since each target material is purified with a different magnetic separation approach, the comparison of processes is not trivial but would help to understand and improve magnetic separation and thus making it attractive for the technical scale. To address this issue, we report on the latest achievements in magnetic separation technology and offer an overview of the progress of the capture and separation of biomolecules derived from biotechnology and food technology. Magnetic separation has great potential for high-throughput downstream processing in applied life sciences. At the same time, two major challenges need to be overcome: (1) the development of a platform for suitable and flexible separation devices and (2) additional investigations of advantageous processing conditions, especially during recovery. Concentration and purification factors need to be improved to pave the way for the broader use of magnetic applications. The innovative combination of magnetic gradients and multipurpose separations will set new magnetic-based trends for large scale downstream processing.

The use of magnetic iron oxide based nanoparticles to improve microalgae harvesting in real wastewater

A novel approach for harvesting Scenedesmus sp. microalgae from real wastewater by using adsorbents of magnetite-based nanoparticles (Fe₃O₄ NPs) was tested in this study for the first time for this microalgae. Using these NPs, the harvesting efficiency was even higher than 95%. The optimal conditions (0.14 gNPs/L, a short magnetic separation time of only 8 min and 27 min of contact time) were found using the response surface methodology. The best fitting of the adsorption equilibrium results was achieved by the Langmuir isotherm model, and the maximum adsorption capacity for Scenedesmus sp. reached 3.49 g dry cell weight (DCW)/g Fe₃O₄ NPs. Zeta potential measurements and the Dubinin-Radushkevich isotherm model analysis pointed out that the main adsorption mechanism between Scenedesmus sp. cells and Fe₃O₄ NPs was electrostatic interaction. Finally, Fe₃O₄ NPs were six times successfully reused by combining an alkaline treatment with an ultrasonication process, which implies microalgae lysis. The results herein obtained highlight the potential for magnetic separation of microalgae from wastewater, which is capable of reaching a high harvesting efficiency in a very short time.