The role of particle-to-cell interactions in dictating nanoparticle aided magnetophoretic separation of microalgal cells

Abstract

Successful application of a magnetophoretic separation technique for harvesting biological cells often relies on the need to tag the cells with magnetic nanoparticles. This study investigates the underlying principle behind the attachment of iron oxide nanoparticles (IONPs) onto microalgal cells, Chlorella sp. and Nannochloropsis sp., in both freshwater and seawater, by taking into account the contributions of various colloidal forces involved. The complex interplay between van der Waals (vdW), electrostatic (ES) and Lewis acid-base interactions (AB) in dictating IONP attachment was studied under the framework of extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) analysis. Our results showed that ES interaction plays an important role in determining the net interaction between the Chlorella sp. cells and IONPs in freshwater, while the AB and vdW interactions play a more dominant role in dictating the net particle-to-cell interaction in high ionic strength media (≥100 mM NaCl), such as seawater. XDLVO predicted effective attachment between cells and surface functionalized IONPs (SF-IONPs) with an estimated secondary minimum of -3.12 kT in freshwater. This prediction is in accordance with the experimental observation in which 98.89% of cells can be magnetophoretically separated from freshwater with SF-IONPs. We have observed successful magnetophoretic separation of microalgal cells from freshwater and/or seawater for all the cases as long as XDLVO analysis predicts particle attachment. For both the conditions, no pH adjustment is required for particle-to-cell attachment.

Tri-functionality of Fe3O4-embedded carbon microparticles in microalgae harvesting

“…KR-1 and magnetic particles both have negative zeta potentials, the low harvesting efficiency (maximum $31.4%) at a high dosage of magnetic particles could be explained by local electrostatic attractions between negative magnetic particles and partially positive sites on the microalgal surface owing to glycoproteins containing NH 3 + . In addition to local electrostatic attractions, London-van der Waals attractions between small-sized particles may also contribute to the adsorption of magnetic particles onto microalgae [35][36][37].…”

Harvesting of freshwater and marine microalgae by common flocculants and magnetic microparticles

“…As mentioned earlier, there is a significant variation of the maximum sorption capacity using magnetic materials, which depends on the magnetic material type, the microalgae species, and the culture media chemistry. The cultivation of microalgae in seawater (high salt concentration) induce short length for electrostatic attractions between algal cells and magnetic particles (Toh et al 2014b). …”

Recent nanoparticle engineering advances in microalgal cultivation and harvesting processes of biodiesel production: A review

“…Therefore, frequently bare Fe 3 O 4 have shown very low magnetic separation efficiencies of $10% at neutral pH, though they varied largely with the microalgal species and medium composition (Prochazkova et al, 2013;Toh et al, 2014b). In order to obtain higher harvesting efficiency irrespective of environmental changes (algal species, pH, medium strength, etc.)…”

“…They also demonstrated, again using PDDA-coated rod-like Fe 3 O 4 nanoparticles, the feasibility of rapid magnetic separation (efficiency: $90% in less than 3 min) of mixed microalgae (Scenedesmus, Spirulina, Chlorella, Tetraedron, Haematococcus, and Dictyosphaerium) from a fishpond (Toh et al, 2012). And in a series of experiments, they studied the complex interplay between van der Waals, electrostatic, and Lewis acid-base interactions for magnetophoretic separation of marine and freshwater microalgal cells based on Extended Derjaguin-Landau-VeweyOverbeek (XDLVO) analysis (Toh et al, 2014b). Their results showed that the electrostatic interaction played a major role in the separation of freshwater Chlorella sp., while the Lewis acid-base and van der Waals interactions played only a dormant role in the separation of marine Nannochloropsis sp.…”

“…and the biological properties of microalgae, and of course performance improvement, currently are the important issues in the nanoparticle harvesting field . Recently, Toh et al (2014b) suggested that the XDLVO analysis model could help to design nanoparticle flocculants for microalgae, especially for the promotion of particle detachment from cell surface in subsequent separation cycles. Physico-chemical surface properties such as the contact angles of probe liquids, surface free energy, and zeta/surface potentials (Ozkan and Berberoglu, 2013), and major constraints such as thermal energy, Stokes drags, and gravitational pulling under low magnetic field were also discussed.…”