Jit Kang Lim

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.

Stabilization of superparamagnetic iron oxide core-gold shell nanoparticles in high ionic strength media.

Nanoparticles with monodisperse, spherical magnetic iron oxide cores and contiguous gold shells (Fe/Au NPs) have been synthesized in order to combine magnetophoretic responsiveness and localized surface plasmon resonance in a single nanoparticle. Such particles are sufficiently charged to be stable against flocculation in low ionic strength media, but they require surface modification to be stably dispersed in elevated ionic strength media that are appropriate for biotechnological applications. Dynamic light scattering and ultraviolet-visible spectrophotometry are used to monitor the colloidal stability of Fe/Au NPs in pH 7.4 phosphate buffered saline containing 154 mM NaCl (PBS). While uncoated particles flocculate immediately upon introduction to PBS, Fe/Au NPs with adsorbed layers of bovine serum albumin or the amphiphilic triblock copolymers Pluronic F127 and Pluronic F68 resist flocculation after more than 5 days in PBS. Adsorbed dextran allowed flocculation that was limited to the formation of small clusters, while poly(ethylene glycol) homopolymers ranging in molecular weight from 6000 to 100 000 were ineffective steric stabilizers. The effectiveness of adsorbed Pluronic copolymers as steric stabilizers was interpreted in terms of the measured adsorbed layer thickness and extended Derjaguin-Landau-Verwey-Overbeek (DLVO) theory predictions of interparticle interactions.

Liposome rupture and contents release over coplanar microelectrode arrays.

The vulnerability of vesicles to electroporation and rupture by externally applied electric fields, combined with the ability of dielectrophoresis and/or AC electroosmosis to manipulate suspended vesicles over micropatterned electrodes suggests new techniques to electrically trigger localized chemical reactions at predetermined positions in microfluidic devices. The electric field conditions needed to rupture giant unilamellar phospholipid vesicles were determined as a function of vesicle size in a simple coplanar microelectrode array geometry. Rupture results were interpreted in terms of the spatially varying electric field strength, calculated via the Poisson equation and accounting for frequency effects on electrode impedance, and the experimentally measured vesicle elevation. The vesicle transmembrane voltage scales linearly with the applied electric field strength according to the Schwan theory of electroporation, so that larger vesicles are usually more prone to electric field induced rupture than smaller ones in the uniform electric fields that are typically employed to cause electroporation and rupture. Yet, in the coplanar microelectrode arrangement, larger vesicles preferentially reside at larger elevations where the local field strengths are weaker. As a result, there is a sensitive range of vesicle radii that are most prone to electric field induced rupture over a micropatterned electrode array that leaves the largest vesicles resistant to rupture.

Fluorescent molecularly imprinted polymer based on Navicula sp. frustules for optical detection of lysozyme

The direct correlation between disease and lysozyme (LYZ) levels in human body fluids makes the sensitive and convenient detection of LYZ the focus of scientific research. Fluorescent molecularly imprinted polymer has emerged as a new alternative for LYZ detection in order to resolve the limitation of immunoassays, which are expensive, unstable, require complex preparation, and are time consuming. In this study, a novel fluorescence molecularly imprinted polymer based on Navicula sp. frustules (FITC-MIP) has been synthesized via post-imprinting treatment for LYZ detection. Navicula sp. frustules were used as supported material because of their unique properties of moderate surface area, reproducibility, and biocompatibility, to address the drawbacks of nanoparticle core material with low adsorption capacity. The FITC acts as recognition signal and optical readout, whereas MIP provides LYZ selectivity. The synthesized FITC-MIP showed a response time as short as 5xa0min depending on the concentration of LYZ. It is found that the LYZ template can significantly quench the fluorescence intensity of FITC-MIP linearly withinxa0a concentration range of 0 to 0.025xa0mgxa0mL–1, which is well described by Stern-Volmer equation. The FITC-MIP can selectively and sensitively detect down to 0.0015xa0mgxa0mL–1 of LYZ concentration. The excellent sensing performance of FITC-MIP suggests that FITC-MIP is a potential biosensor in clinical diagnosis applications.

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.

Enhance the Colloidal Stability of Magnetite Nanoparticles Using Poly(sodium 4-styrene sulfonate) Stabilizers

The major challenge in assessing the performance of magnetite nanoparticles (MNPs) in removing pollutants from wastewater is the agglomeration of those nanoparticles into a bulky cluster size. In this study, different concentration of poly (sodium 4-styrene sulfonate) (PSS) were coated around the surface of MNPs to increase the particles’ colloidal stability. Both dynamic light scattering (DLS) and thermogravimetric (TGA) analyses have proved the success coating of PSS onto MNPs, whereby the cluster size of the functionalized MNPs were shown notably depends on the applied dosage of PSS. PSS/MNPs functionalization at molar ratio of 6:1 was found to have the smallest cluster size at 148.4 ± 0.22 nm. These results have provided some insight about the particles’ colloidal stability that could be useful for environmental remediation.

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 100u2005g/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...