Pey Yi Toh

Rapid Magnetophoretic Separation of Microalgae

Magnetic collection of the microalgae Chlorella sp. from culture media facilitated by low-gradient magnetophoretic separation is achieved in real time. A removal efficiency as high as 99% is accomplished by binding of iron oxide nanoparticles (NPs) to microalgal cells in the presence of the cationic polyelectrolyte poly(diallyldimethylammonium chloride) (PDDA) as a binder and subsequently subjecting the mixture to a NdFeB permanent magnet with surface magnetic field ≈6000 G and magnetic field gradient <80 T m(-1) . Surface functionalization of magnetic NPs with PDDA before exposure to Chlorella sp. is proven to be more effective in promoting higher magnetophoretic removal efficiency than the conventional procedure, in which premixing of microalgal cells with binder is carried out before the addition of NPs. Rodlike NPs are a superior candidate for enhancing the magnetophoretic separation compared to spherical NPs due to their stable magnetic moment that originates from shape anisotropy and the tendency to form large NP aggregates. Cell chaining is observed for nanorod-tagged Chlorella sp. which eventually fosters the formation of elongated cell clusters.

Magnetophoretic separation of microalgae: the role of nanoparticles and polymer binder in harvesting biofuel

Magnetophoretic separation of Chlorella sp. microalgal biomass is proven to be a feasible downstream processing technology for biofuel production. Kinetic study of cells separation in real time reveals the major steps involved for each stage of low gradient magnetic separation (LGMS) with field gradient (∇B) less than 80 T m−1. Transmission and scanning electron microscopy (TEM & SEM) together with Fourier transforms infrared (FTIR) spectra analysis are employed to confirm the full attachment of surface functionalized iron oxide nanoparticles (SF-IONPs) onto microalgal cells and how the particles distributed on the cells surfaces. From the cross section TEM images of cells, IONPs shown the tendency to be internalized into Chlorella sp. cells but not affect the biofuel quality.

Magnetophoresis of iron oxide nanoparticles at low field gradient: the role of shape anisotropy.

Magnetophoresis of iron oxide magnetic nanoparticle (IOMNP) under low magnetic field gradient (<100 T/m) is significantly enhanced by particle shape anisotropy. This unique feature of magnetophoresis is influenced by the particle concentration and applied magnetic field gradient. By comparing the nanosphere and nanorod magnetophoresis at different concentration, we revealed the ability for these two species of particles to achieve the same separation rate by adjusting the field gradient. Under cooperative magnetophoresis, the nanorods would first go through self- and magnetic field induced aggregation followed by the alignment of the particle clusters formed with magnetic field. Time scale associated to these two processes is investigated to understand the kinetic behavior of nanorod separation under low field gradient. Surface functionalization of nanoparticles can be employed as an effective strategy to vary the temporal evolution of these two aggregation processes which subsequently influence the magnetophoretic separation time and rate.

Toxicity of bare and surfaced functionalized iron oxide nanoparticles towards microalgae

ABSTRACT This study investigates the toxicity of bare iron oxide nanoparticles (IONPs) and surface functionalization iron oxide nanoparticles (SF-IONPs) to the growth of freshwater microalgae Chlorella sp. This study is important due to the increased interest on the application of the magnetic responsive IONPs in various fields, such as biomedical, wastewater treatment, and microalgae harvesting. This study demonstrated that the toxicity of IONPs was mainly contributed by the indirect light shading effect from the suspending nanoparticles which is nanoparticles concentration-dependent, direct light shading effect caused by the attachment of IONPs on cell and the cell aggregation, and the oxidative stress from the internalization of IONPs into the cells. The results showed that the layer of poly(diallyldimethylammonium chloride) (PDDA) tended to mask the IONPs and hence eliminated oxidative stress toward the protein yield but it in turn tended to enhance the toxicity of IONPs by enabling the IONPs to attach on cell surfaces and cause cell aggregation. Therefore, the choice of the polymer that used for surface functionalize the IONPs is the key factor to determine the toxicity of the IONPs.

Effect of the colloidal stability of SF-IONPs on the performance of magnetophoretic separation of microalgae

Microalgae is a potential third generation biofuel resource. The efficiency of magnetophoretic separation of microalgae under inhomogeneous low gradient magnetophoretic separation (LGMS) (< 80 T/m) is depending on the colloidal stability of the surface functionalized iron oxide nanoparticles (SF-IONPs). The colloidal stability of the SF-IONPs is determined by the conformation of the PDDA layer, which is affected by the dosage and molecular weight (MW) of cationic polyelectrolyte poly(diallyldimethylammonium chloride) (PDDA). Result showed that the very low MW of PDDA cationic polyelectrolyte has formed a most colloidally stable suspension of SF-IONPs when in dosage of 100 g/g compared to the other MW of PDDA. The cell separation efficiency is in accordance to the stability of SF-IONPs. From the kinetic separation profile, the separation time (ts) of the SF-IONPs-attached-cells is shortened by the increase of the SF-IONPs concentration, as the magnetic force is proportional to the amount of magnetic partic...