Derek Juinn Chieh Chan

Influences of diatom frustule morphologies on protein adsorption behavior

Diatom frustules are a potential protein adsorbent substitute for conventional silica to address synthesis limitations of synthetic silica particles such as high energy consumption, long synthesis duration, and usage of toxic compounds. Diatom frustules have been used in many applications including separation of heavy metals, enzyme immobilization, and drug delivery; however, research into diatom frustules as a substrate for selective protein adsorption is limited only to functionalized frustules as a general adsorbent. Hence, in this paper, the morphology of diatom frustules and their protein adsorption were studied. The protein adsorption experiments were conducted using three different diatom frustules, namely, Thalassiosira weissflogii, Navicula sp., and diatomaceous earth (DE). Bovine serum albumin and lysozyme were used as model proteins. The surface chemistry of diatom frustules and protein was manipulated to investigate the interplay between surface charge and adsorption capacity. The adsorption behavior was further evaluated and is discussed through isotherm model and kinetic fitting. The result revealed that among these three diatom frustules, the centric diatom, T. weissflogii frustules have the highest adsorption capability. This can be attributed to their morphology with larger surface area, pore volume, and the presence of silanol groups. Besides that, the kinetic and isotherm model fitting indicate that protein adsorption on these three diatom frustules is a monolayer chemisorption. These results indicate the possibility of diatom frustules as a potential substrate in immunoassay 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.

Artificial Magnetotaxis of Microbot: Magnetophoresis versus Self-Swimming

An artificial magnetotactic microbot was created by integrating the microalgal cell with magnetic microbead for its potential application as biomotor in microscale environment. Here, we demonstrate the remote magnetotactic control of the microbot under a low gradient magnetic field (<100 T/m). We characterize the kinematic behavior of the microbots carrying magnetic microbeads of two different sizes, with diameter of 2 and 4.5 μm, in the absence and presence of magnetic field. In the absence of magnetic field, we observed the microbot showed a helical motion as a result of the misalignment between the thrust force and the symmetry axis after the attachment. The microbot bound with a larger magnetic microbead moved with higher translational velocity but rotated slower about its axis of rotation. The viscous force was balanced by the thrust force of the microbot, resulting in a randomized swimming behavior of the microbot at its terminal velocity. Meanwhile, under the influence of a low gradient magnetic field, we demonstrated that the directional control of the microbot was based on following principles: (1) magnetophoretic force was insignificant on influencing its perpendicular motion and (2) its parallel motion was dependent on both self-swimming and magnetophoresis, in which this cooperative effect was a function of separation distance from the magnet. As the microbot approached the magnet, the magnetophoretic force suppressed its self-swimming behavior, leading to a positive magnetotaxis of the microbot toward the source of magnetic field. Our experimental results and kinematic analysis revealed the contribution of mass density variation of particle-and-cell system on influencing its dynamical behavior.

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...