Jaeyeon Jung

Thermoresponsive pore structure of biopolymer microspheres for a smart drug carrier.

Triggering changes in surface porosity enabled the controlled release of biomolecules from elastin-like polypeptide (ELP) microspheres. The transition temperature (T(t)) of cross-linked microspheres was determined by differential scanning calorimetry, and T(t) was in agreement with the volume transition observed by changing the external temperature of the incubation media. The thermoresponsive pore structure of ELP microspheres and their surface morphology were examined by field-emission scanning electron microscopy. ELP microspheres were investigated as a smart drug carrier using model drug molecules, bovine serum albumin, and prednisone acetate. The release rate was accelerated by squeezing out the entrapped biomolecules as the temperature was increased above T(t) because of the development of micropores at the surface as well as in the bulk. In addition, the stepwise release confirmed that ELP microspheres could be progammed precisely to control the release of drugs by external stimuli.

Smart biopolymer for a reversible stimuli-responsive platform in cell-based biochips.

The rapid response of a smart material surface to external stimuli is critical for application to cell-based biochips. The sharp and controllable phase transition of elastin-like polypeptide (ELP) enabled reversible cell adhesion on the surface by changing the temperature or salt concentration in the system. First, ELP micropatterns were prepared on a glass surface modified into aldehyde. The lysine-containing ELP (ELP-K) was genetically synthesized from E. coli for conjugation with the aldehyde on the glass surface. The phase transition of ELP was monitored in PBS and cell culture media using UV-visible spectroscopy, and a significant difference in transition temperature (Tt) was observed between the two solution systems. The micropatterning of ELP on the glass surface was performed by microcontact printing a removable polymeric template on the aldehyde-glass followed by incubation in ELP-K aqueous solution. The ELP micropatterns were imaged with atomic force microscopy and showed a monolayer thickness of approximately 4 nm. Imaging from time-of-flight secondary ion mass spectroscopy confirmed that the ELP molecules were successfully immobilized on the highly resolved micropatterns. Cell attachment and detachment could be reversibly controlled on the ELP surfaces by external stimuli. The hydrophobic phase above Tt resulted in the adhesion of fibroblasts, while the detachment of cells was induced by lowering the incubation temperature below Tt. The smart properties of ELP were reliable and reproducible, demonstrating potential applications in cell-based microdevices.

Enhanced surface plasmon resonance by Au nanoparticles immobilized on a dielectric SiO2 layer on a gold surface

This paper introduces strategies for enhancement of a surface plasmon resonance (SPR) signal by adopting colloidal gold nanoparticles (AuNPs) and a SiO(2) layer on a gold surface. AuNPs on SiO(2) on a gold surface were compared with an unmodified gold surface and a SiO(2) layer on a gold surface with no AuNPs attached. The modified surfaces showed significant changes in SPR signal when biomolecules were attached to the surface as compared with an unmodified gold surface. The detection limit of AuNPs immobilized on a SPR chip was 0.1 ng mL(-1) for the prostate-specific antigen (PSA), a cancer marker, as measured with a spectrophotometer. Considering that the conventional ELISA method can detect approximately 10 ng mL(-1) of PSA, the strategy described here is much more sensitive (approximately 100 fold). The enhanced shift of the absorption curve resulted from the coupling of the surface and particle plasmons by the SiO(2) layer and the AuNPs on the gold surface.

Amphiphilic comblike polymers enhance the colloidal stability of Fe3O4 nanoparticles

Stable colloidal dispersions of magnetite (Fe(3)O(4)) nanoparticles (MNPs) were obtained with the inclusion of an amphiphilic comblike polyethylene glycol derivative (CL-PEG) as an amphiphilic polymeric surfactant. Both the size and morphology of the resulting CL-PEG-modified MNPs could be controlled and were characterized by transmission electron microscopy (TEM). The interaction between MNPs and CL-PEG was confirmed by the presence of characteristic infrared absorption peaks, and the colloidal stability of the nanoparticle dispersion in water was evaluated by long-term observation of the dispersion using UV-visible spectroscopy. SQUID measurements confirmed the magnetization of CL-PEG-modified MNPs. The zeta potential of the CL-PEG-modified MNPs showed a dramatic conversion from positive to negative in response to the pH of the surrounding aqueous medium due to the presence of carboxyl groups at the surface. These carboxyl groups can be used to functionalize the MNPs with biomolecules for biotechnological applications. However, regardless of surface electrostatics, the flexible, hydrophilic side chains of CL-PEG-modified MNPs prevented the approach of adjacent nanoparticles, thereby resisting aggregation and resulting in a stable aqueous colloid. The cytotoxicity of MNPs and CL-PEG-modified MNPs was evaluated by a MTT assay.

Simple fabrication of a smart microarray of polystyrene microbeads for immunoassay

We describe a simple method to fabricate an array of polystyrene microbeads (PS microbeads) conjugated with an elastin-like polypeptide (ELP) on a glass surface using a removable polymer template (RPT). A thin layer of adhesive was spun-cast on glass and cured by UV radiation. Micropatterns of an RPT were then transferred onto the surface by microcontact printing. The adhesion of PS microbeads on the surface depended on the adhesion performance of the adhesive layer, which could be adjusted by irradiation time. An array of PS microbeads conjugated with ELP was used for a smart immunoassay of prostate-specific antigen (PSA), a cancer marker. By controlling the phase transition of ELP molecules, PSA molecules were selectively adhered or released from the bead surface. The selective and reversible binding of PSA molecules on the bead surface was characterized with fluorescence microscopy.

Polypeptide-Mediated Switchable Microarray of Bacteria

This paper describes a feasible solution for the bacterial cell death and contamination from cell division that occurs in microfluidic applications. The method adopts a smart thermoresponsive surface, highly resolved micropatterns, and surface-functionalized bacteria tagged with thermoresponsive molecules. We developed a method for controllable bacterial attachment and detachment using an elastin-like polypeptide (ELP). To create a smart surface with switchable properties, the surface of a glass substrate was conjugated with thermoresponsive ELP molecules. The attachment of bacterial cells to the ELP surface was induced by the hydrophobic affinity of the ELPs on the glass surface to tagged ELPs on the bacterial surface. A cell-repellent polymer was micropatterned to create a highly resolved space for specific bacterial adhesion. Reversible bacterial attachment and detachment was achieved by controlling the thermoresponsive phase transition of ELP molecules. Five different types of bacteria were successfully conjugated with ELPs and arrayed on the surface. The viability of the bacteria that had attached to the surface was evaluated by determining colony forming units of released bacteria on an agar plate.

ENHANCEMENT OF SURFACE PLASMON RESONANCE USING COLLOIDAL GOLD NANOPARTICLES EMBEDDED IN A SILICA LAYER

This paper presents a strategy for the signal enhancement of surface plasmon resonance biosensors using colloidal gold nanoparticles and a silica layer. We describe the method for the deposition of a silica-stabilized gold nanoparticle layer on a gold film, namely an enhanced surface plasmon resonance chip. This chip shows significant changes in its surface plasmon resonance signals when biomolecules are attached to its surface as compared to a normal gold surface. These characteristics are closely related to the surface plasmon resonance effect as determined using prostate-specific antigen. The detection limit of the enhanced surface plasmon resonance chip is determined to be 0.01 ng/mL for a prostate-specific antigen immunoassay. The use of an enhanced surface plasmon resonance chip makes it possible to enhance signals 1000-fold compared to the signals obtained by conventional surface plasmon resonance sensing. The enhancement of the surface plasmon resonance spectral shift results from the coupling of the surface and particle plasmons through the application of a silica-stabilized gold nanoparticle layer on the gold surface.

Polystyrene microbeads modified with an elastin-like biopolymer for stimuli-responsive immunodetection.

An efficient and controlled method for immunodetection, using polystyrene (PS) microbeads conjugated with an elastin-like polypeptide (ELP), was investigated. ELP is a temperature-sensitive polymer that exhibits a hydrophilic–hydrophobic phase transition at the lower critical solution temperature. To introduce amine groups, ELP was modified with lysine for conjugation with PS microbeads functionalized with carboxylic groups. Prostate-specific antigen (PSA), a cancer marker, was detected from a biomolecular mixture using ELP-conjugated PS microbeads and ELP-conjugated antiPSA. External stimuli were used to reversibly separate the PSA–antiPSA complex. The stimuli-responsiveness of the ELP provided a designable generic biosurface for diagnostic detection.