Green microfluidic devices made of corn proteins

An alternative green microfluidic device made of zein, a prolamin of corn, can be utilized as a disposable environmentally friendly microchip especially in agriculture applications. Using standard soft lithography and stereo lithography techniques, we fabricated thin zein films with microfluidic chambers and channels. These were bonded to both a glass slide and another zein film. The zein film with microfluidic features bonds irreversibly with other surfaces by vapor-deposition of ethanol to create an adhesive layer resulting in very little or no trapped air and small shape distortion. Zein-zein and zein-glass microfluidic devices demonstrated sufficient strength to facilitate fluid flow in a complex microfluidic design that showed no leakage under high hydraulic pressure. Zein-glass microfluidic devices with serpentine mixing design showed successful fluid manipulation as a concentration gradient of Rhodamine B solution was generated. The ease of fabrication and bonding and the flexibility and moldability of zein offer attractive possibilities for microfluidic device design and manufacturing. These devices can include several unit operations with mixing being one of the most commonly used. The zein-based microfluidic devices, made entirely from a biopolymer from agricultural origin, offer alternative environmentally friendly material choices that are less dependent on limited petroleum based polymer resources.     

Adsorption of bovine serum albumin (BSA) on polystyrene (PS) and its acid copolymer

The effect of surface polarity on the adsorption of bovine serum albumin (BSA) on polystyrene (PS), 7% polystyrene-co-maleic anhydride (7%PSMAn) and 50% polystyrene-co-maleic acid (50%PSMA), at pH 7.4, was investigated. Polystyrene represented the non-polar surface while 7%PSMAn and 50%PSMA represented a low and high acid content copolymer. The amount of the adsorbed BSA depended on the amount of the acid content in the copolymer. BSA formed a monolayer with a side-on orientation on the low polarity PS surface, a mixed side-on and end-on orientation on 7%PSMAn and a predominantly side-on orientation on 50%PSMA. The thickness of adsorbed BSA, measured with an atomic force microscope (AFM), varied from 3 nm to 5 nm for the side-on orientation and from 10 nm to 15 nm for the end-on orientation. The average area occupied per BSA molecule was consistent with the proposed orientation, and was 34.8 nm², 27.8 nm² and 18.0 nm² for PS, 7%PSMAn and 50%PSMA, respectively. The adsorption showed a concentration dependency following the Freundlich isotherm, which indicated the interactions among adsorbed BSA molecules on the polymer surface. The adsorption took place as an island-like morphology and started to fuse into a patch-like morphology at higher concentrations before achieving a complete monolayer formation. A non-uniform surface coverage and defects were observed in all cases. It is recommended that for an effective blocking of PS, 7%PSMAn and 50%PSMA, the BSA concentration should be higher than 3 mg/mL.