Molding a silver nanoparticle template on polydimethylsiloxane to efficiently capture mammalian cells.

Herein, a functional template made up of in situ synthesized silver nanoparticles (AgNPs) is prepared on polydimethylsiloxane (PDMS) for the spatial control of cell capture, where the residual Si-H groups in the PDMS matrix are used as reductants to reduce AgNO(3) for forming AgNPs. In virtue of microfluidic system, a one-dimensional array pattern of AgNPs is obtained easily. Further combining with plasma treatment, a two-dimensional array pattern of AgNPs could be achieved. The obtained PDMS-AgNPs composite is characterized in detail. The PDMS-AgNPs composite shows good antibacterial property in E. coli adhesion tests. The patterns possess hifi and high resolution (ca. 8 microm). Cell patterns with high efficiency and spatial selectivity are further formed with the aid of H-Arg-Gly-Asp-Cys-OH (RGDC) tetrapeptide which is grafted on the AgNPs template. Cells immobilized on the template show a good ability for adhesion, spreading, migration, and growth.

Thermal/plasma-driven reversible wettability switching of a bare gold film on a poly(dimethylsiloxane) surface by electroless plating.

We report an approach for fabricating a tunable wettability surface by electroless gold plating on poly(dimethylsiloxane) (PDMS). A two-layer structured gold film with a tight layer and a loose layer can be obtained on the surface of a PDMS chip when the PDMS chip is immersed in a gold plating solution at 30 degrees C for 4 h. Its wettability can be rapidly switched between superhydrophilicity and superhydrophobicity by plasma and heat treatments without any self-assembled monolayer, and the superhydrophobicity can be even changed from the gecko-foot-hair-like character to the lotus-leaf-like character. Benefiting from the various wettabilities of the prepared gold/PDMS composites, protein patterning is successfully achieved on a patterned superhydrophobic/superhydrophilic gold/PDMS composite; a superhydrophobic needle for transferring supersmall water droplets (1 microL) to a superhydrophobic surface is successfully fabricated.

[The spectroscopic studies on the binding of Al(III) to EHPG].

Interaction of ethylene-N,N'-bis(o-hydioxyphenylglycine) (EHPG) with Al3+ has been investigated by both UV difference and fluorescent spectra. Both results show that the molar ration of the complex is most likely 1:1. Aluminum binding produces peaks at 235 and 291 nm. The molar absorptivity of aluminum ions to EHPG at 235 nm is 1.27 x 10(4) cm-1.mol-1.L. The conditional stability constant for Al3+ binding to EHPG is determined to be IgK = 14.20 +/- 0.03 in 0.1 mol.L-1 Hepes buffer at room temperature, pH 7.4 by UV difference spectra. At the same condition, the fluorescent intensity of EHPG at 310 nm has been monitored. In result, the fluorescent intensity of EHPG at 310 nm is decreased with the addition of Al3+. Then the quench of the fluorescent intensity is ascribed to deprotonated phenolic groups coordinated to aluminum ions.

A photoelectrochemical sensor based on CdS-polyamidoamine nano-composite film for cell capture and detection.

We demonstrated herein a newly developed photoelectrochemical cell-sensor for the determination of SMMC-7721 human hepatoma carcinoma cells (SMMC-7721 cells) by using a photosensitive CdS-polyamidoamine (G4) nano-composite film (CdS-PAMAM). The film was generated by electrodeposition method. The presence of PAMAM in the film eliminated the surface defects of CdS nanoparticles and therefore resulted in a greatly enhanced photocurrent and a reduced dark current. In the presence of the electron donor ascorbic acid (AA), the photoexcitation of this modified electrode potentiostated at 0 V versus Ag/AgCl led to an anodic photocurrent. As a result of the covalent coupling reactions, a layer of concanavalin A (ConA) was firmly bound to the functionalized CdS-PAMAM film via glutaraldehyde bridges. The resulting modified electrodes were tested as sensors for SMMC-7721 cell capture and detection via affinity interactions between ConA and mannosyl groups on cell surface. The cell concentration was measured from 5.0 x 10(3) to 1.0 x 10(7) cells mL(-1) through the decrease in photocurrent intensity resulting from its specific binding onto the photosensitive film, the detection limit being 5.0 x 10(3) cells mL(-1).

Cytosensing and evaluation of cell surface glycoprotein based on a biocompatible poly(diallydimethylammonium) doped poly(dimethylsiloxane) film.

In this paper, we constructed an interface that not only retains viability of immobilized BGC823 human gastric carcinoma cells (BGC823 cells) but also efficiently resists nonspecific adsorption of the P-glycoprotein antibody and its secondary antibody, which enabled us to sensitively detect the number of cells and P-glycoproteins on the BGC823 cell surface by the immunoassay method. Preparation of the film was quite simple and inexpensive just by spin-coating poly(dimethylsiloxane) (PDMS) doped with poly(diallydimethylammonium) (PDDA) on the surface of gold electrodes. The composite film's biocompatibility, antinonspecific adsorption ability, and the conductivity for electrochemical probe ([Fe(CN)6]3-/4-) were proved by cell culture experiments, blocking experiments, and electrochemical experiments. Compared with PDMS and PDMS doped with poly(sodium 4-styrenesulfonate) (PSS), the PDMS-PDDA composite film showed a predominant ability to capture cells due to electrostatic reaction between the presence of positively charged PDDA and the negatively charged glycocalyx on the surface of cells. On the advantage of electrochemical immunoassay with a signal amplification path by using biocatalytic precipitation of an insoluble product, differential pulse voltammetry (DPV) measurement based on the changes of electron-transfer resistance was introduced to detect the cell amount and monitor growing states of cells like adhesion, spread, proliferation, and apoptosis on the electrodes. Optimally, signal response was proportional to the logarithm of cell concentration ranging from 1.0 x 10(3) to 5.0 x 10(7) cells mL(-1) with a detection limit of 7.2 x 10(2) cells mL(-1). On the basis of the special property for resisting nonspecific adsorption of this composite film, an ultraviolet and visible (UV-vis) absorption spectrum with one-step immunoreaction was employed to evaluate the P-glycoprotein on the BGC823 cell surface. The P-glycoprotein on a single living intact BGC823 cell was detected correspondingly to 4.7 x 10(7) molecules. The work implied that the composite film possessed potential applications for biosensing and convenient evaluation of surface glycoprotein on living cells.

Patterned Au/poly(dimethylsiloxane) substrate fabricated by chemical plating coupled with electrochemical etching for cell patterning.

In this paper, we present a novel approach for preparing patterned Au/poly(dimethylsiloxane) (PDMS) substrate. Chemical gold plating instead of conventional metal evaporation or sputtering was introduced to achieve a homogeneous gold layer on native PDMS for the first time, which possesses low-cost and simple operation. An electrochemical oxidation reaction accompanied by the coordination of gold and chloride anion was then exploited to etch gold across the region covered by electrolyte. On the basis of such an electrochemical etching, heterogeneous Au/PDMS substrate which has a gold "island" pattern or PDMS dots pattern was fabricated. Hydrogen bubbles which were generated in the etching process due to water electrolysis were used to produce a safe region under the Pt auxiliary electrode. The safe region would protect gold film from etching and lead to the formation of the gold "island" pattern. In virtue of a PDMS stencil with holes array, gold could be etched from the exposed region and take on the PDMS dots pattern which was selected to for protein and cell patterning. This patterned Au/PDMS substrate is very convenient to construct cytophobic and cytophilic regions. Self-assembled surface modification of (1-mercaptoundec-11-yl)hexa(ethylene glycol) on gold and adsorption of fibronectin on PDMS are suitable for effective protein and cell patterning. This patterned Au/PDMS substrate would be a potentially versatile platform for fabricating biosensing arrays.