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The signal-guided and sequential assembly of biomolecules onto patterned surfaces is demonstrated. Readily transmittable electric signals are used to guide spatially selective deposition of the pH-responsive polysaccharide, chitosan, and functionalized chitosan conjugates, by generating localized pH gradients. The nucleophilic primary amine groups of chitosan enable facile conjugation of proteins and nucleic acids by two approaches, one an enzymatic approach and the other a standard chemical modification, thus providing flexibility when sequentially assembling biomolecules in a spatially selective manner. Moreover, we developed an agarose gel "biomask" for the sequential assembly of single-stranded DNA and confirmed its functionality through nucleic acid hybridization assays.

A protein's functional properties can be adjusted by conjugating it to other polymers. We used a nature-inspired route to create a protein−polysaccharide conjugate and examined the properties of this conjugate. Specifically, the enzyme tyrosinase was used to oxidize accessible tyrosine residues of the model protein green fluorescent protein (GFP). Oxidation yields quinone residues that are “activated” for the covalent conjugation of GFP to nucleophilic groups of the aminopolysaccharide chitosan. Conjugation to chitosan conferred distinct properties to GFP. The GFP−chitosan conjugate was observed to have pH-responsive, “smart” properties, and GFP could be conjugated onto a gel matrix. Additionally, the GFP−chitosan conjugate can be selectively deposited onto a micropatterned surface in response to an applied voltage. This nature-inspired method provides a simple and safe method to conjugate proteins to chitosan, and these conjugates can be readily assembled onto patterned surfaces.

Hydrogels are increasingly considered for creating three-dimensional structures in miniaturized devices, yet few techniques exist for creating such hydrogel structures. We report a new approach for creating hydrogels using the amine-containing polysaccharide chitosan. Specifically, electrodes are immersed into a slightly acidic chitosan solution and a voltage is applied to promote the proton-consuming hydrogen evolution reaction at the cathode surface. This reaction leads to a high localized pH in the vicinity of the cathode surface, and if this localized pH exceeds about 6.3, then chitosan becomes insoluble and deposits at the cathode surface. As the current density is increased, the region of high pH is expected to extend further from the cathode surface into the bulk solution. Using moderately high current densities (50 A/m2), we observed that chitosan deposited as a thick hydrogel. Measurements of the water content confirmed that the deposited chitosan was a hydrogel. To suggest the potential utility,...

The amine-containing polysaccharide chitosan was selectively deposited onto patterned gold surfaces in response to an applied voltage. Standard microfabrication techniques were used to pattern gold onto silicon wafers, and these gold patterns served as templates for the electric field directed deposition of chitosan. Experiments conducted with a fluorescently labeled chitosan derivative demonstrated the spatially selective deposition of chitosan onto gold surfaces that were polarized to serve as negative electrodes. Studies with unlabeled chitosan demonstrated that a “templated” chitosan, deposited by voltage programming of electrodes, can subsequently react with standard amine-selective functional groups. This indicates that common coupling chemistries can be exploited to assemble a variety of compounds onto the deposited chitosan pattern. Thus, chitosan appears to be a unique interface material that can be “templated” onto patterned inorganic surfaces and is reactive for the subsequent assembly of organ...

We examined the assembly of the amine-rich polysaccharide chitosan from solution onto electrode surfaces as a result of voltage bias on the electrode. Chitosan is positively charged and water soluble under mildly acidic conditions and is uncharged and insoluble under basic conditions. We observed that chitosan is deposited from acidic solution onto the surface of a negative electrode and the thickness of the deposited layer is on the order of a micron. The thickness of the deposited layer was observed to be dependent upon the deposition time, the applied voltage, and the chitosan concentration. No deposition was observed on the positive electrode or on an “electrode” that had no applied voltage. Once deposited and neutralized, the chitosan layer can be retained on the electrode surface without the need for an applied voltage. Infrared (FT-IR) and electrospray mass spectrometry confirmed that the deposited material was chitosan. These results demonstrate that chitosan can be deposited and retained on elect...

An ultrathin palladium membrane was prepared by an improved electroless plating technique on the surface of a porous titania ceramic substrate. A simple yet new and valuable activation technique named photocatalytic deposition (PCD) has been presented. The thickness of the resulting palladium membrane was about 0.3−0.4 μm. Hydrogen permeation through the composite membrane was proportional to the hydrogen partial pressure difference. The hydrogen permeability and H2:N2 selectivity through the palladium composite membrane are 6.3 × 10-6 mol m-2 s-1 Pa-1 and 1140 at 773 K, respectively. The activation energy for hydrogen permeation is 21.27 kJ/mol at the temperature range of 673−773 K. Long-term hydrogen permeation operation at 673 K indicated that the flux through the resulting membrane under hydrogen/nitrogen gradients requires 80 h to reach a steady state. The steady-state hydrogen flux showed no observable changes during the thermal cycles between 673 and 773 K.