A nanoscale range of surface feature curvatures where lipid membranes lose integrity and form pores has been found experimentally. The pores were experimentally observed in the l-alpha-dimyristoyl phosphatidylcholine membrane around 1.2-22 nm polar nanoparticles deposited on mica surface. Lipid bilayer envelops or closely follows surface features with the curvatures outside of that region. This finding provides essential information for the understanding of nanoparticle-lipid membrane interaction, cytotoxicity, preparation of biomolecular templates and supported lipid membranes on rough and patterned surfaces.

We report the first use of redox nanoparticles of cerium oxide as colorimetric probes in bioanalysis. The method is based on changes in the physicochemical properties of ceria nanoparticles, used here as chromogenic indicators, in response to the analyte. We show that these particles can be fully integrated in a paper-based bioassay. To construct the sensor, ceria nanoparticles and glucose oxidase were coimmobilized onto filter paper using a silanization procedure. In the presence of glucose, the enzymatically generated hydrogen peroxide induces a visual color change of the ceria nanoparticles immobilized onto the bioactive sensing paper, from white-yellowish to dark orange, in a concentration-dependent manner. A detection limit of 0.5 mM glucose with a linear range up to 100 mM and a reproducibility of 4.3% for n = 11 ceria paper strips were obtained. The assay is fully reversible and can be reused for at least 10 consecutive measurement cycles, without significant loss of activity. Another unique feature is that it does not require external reagents, as all the sensing components are fixed onto the paper platform. The bioassay can be stored for at least 79 days at room temperature while maintaining the same analytical performance. An example of analytical application was demonstrated for the detection of glucose in human serum. The results demonstrate the potential of this type of nanoparticles as novel components in the development of robust colorimetric bioassays.

A new signal-responsive interface with switchable/tunable redox properties based on a pH-responding polymer brush was studied. Poly(4-vinyl pyridine), P4VP, functionalized with Os-complex redox units was grafted to an indium tin oxide (ITO) conductive support in the form of a polymer brush. The modified electrode surface was responsive to the changes of the pH value of the electrolyte solution: at acidic pH ) 4.0 the redoxpolymer film demonstrated the reversible electrochemical process, E°) 0.29 V (vs Ag/AgCl), while at neutral pH > 6, the polymer was not electrochemically active. The reversible transformation between the active and the inactive state originated from the structural changes of the polymer support. The protonation of the pyridine units of the polymer backbone at the acidic pH resulted in the swelling of the polymer brush allowing quasidiffusional translocation of the flexible polymer chains, thus providing direct contact of the polymer-bound redox units and the conducting electrode support. The uncharged polymer formed at the neutral pH values existed in the shrunk state, when the mobility of the polymer chains was restricted and the polymer-bound redox units were not electrically accessible from the conducting support, thus resulting in the nonactive state of the modified electrode. The reversible changes of the electrochemical activity of the modified electrode and the respective structural changes of the polymer-brush were characterized in details by electrochemistry, AFM, and ellipsometry. The stepwise changes of the pH value between 3.0 and 7.0 resulted in the reversible switching on and off of the electrode redox activity, respectively. The redox activity of the modified electrode was also tunable upon precise titration of the electrolyte solution between pH 3.0 and 7.0 demonstrating a titration-like curve for the amount of the redox-active group because of the smooth transition between the swollen and the shrunk states. The primary electrochemical activity of the modified electrode was coupled with a biocatalytic oxidation of glucose in the presence of soluble glucose oxidase (GOx), thus allowing reversible activation of the bioelectrocatalytic process. The modified electrode with the pH-controlled switchable/tunable redox activity was proposed as a "smart" interface for a new generation of electrochemical biosensors and biofuel cells with a signal-controlled activity.

Molecular computing based on chemical reactions performed in solutions or at functionalized interfaces became an important part of research in the area of modern unconventional computing. 1 Numerous chemical systems mimicking different gates performing Boolean logic operations and responding to a large variety of activating input signals (e.g., light, electrical, magnetic, and chemical) were developed in the past decade. 2 Scaling-up these systems allowed assembly of simple computing networks capable of operating as molecular computing devices performing arithmetic functions. 3 Molecular systems mimicking other components of electronic devices performing digital operations (e.g., memory units, 4 comparator, 5 demultiplexer 6 ) were reported recently. Further progress in the molecular computing systems resulted in the development of single-molecule-based logic gates 7 and nanosize molecular computing systems. 8 Despite the fact that a very promising future is expected for unconventional chemical computing systems, 9 the development of these systems is limited by their synthetic complexity and difficulty to scale them up for assembling large networking systems. The latter problem originates from incompatibility of most chemical systems performing individual computing operations. This limitation can be solved by the application of biomolecular systems designed by Nature to perform highly specific catalytic or recognition reactions in large ensembles where the individual steps are complementary and the reacting components are compatible. Biomolecular computing (biocomputing) became an important step forward in chemical computing allowing for the solution of complex mathematic problems 10 and assembling large networking systems. 11 Recently developed logic gates based on enzyme-catalyzed reactions 12 allowed assembly of the logic gates in concatenated systems 13 as easily as putting together pieces of a puzzle. The enzyme-based logic gates can be connected with electronic transducers allowing interfacing between biomolecular and electronic systems. 14 The computing networks composed of the enzyme-based concatenated logic gates can be used for mimicking various electronic devices. A molecular keypad lock was designed recently using a system of fluorescent complexes. 15 The present paper reports on a novel approach to the assembly of the biomolecular keypad lock using the enzyme-based networking system. Natural biochemical paths include concert operation of multienzyme systems biocatalyzing chain reactions. Taking out one of the biocatalytic units effectively inhibits the whole chain of the biochemical reactions. This property was used to assemble the enzyme-based biomolecular keypad lock. We designed a model biochemical reaction chain, which included hydrolysis of sucrose to glucose, oxidation of glucose by oxygen to yield hydrogen peroxide, and then oxidation of a synthetic dye, 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS), by H 2 O 2 resulting in the formation of a colored product ABTS ox , Scheme ...