Hybrid systems consisting of nucleic-acid-functionalized silver nanoclusters (AgNCs) and graphene oxide (GO) are used for the development of fluorescent DNA sensors and aptasensors, and for the multiplexed analysis of a series of genes of infectious pathogens. Two types of nucleic-acid-stabilized AgNCs are used: one type includes the red-emitting AgNCs (616 nm) and the second type is near-infrared-emitting AgNCs (775 nm). Whereas the nucleic-acid-stabilized AgNCs do not bind to GO, the conjugation of single-stranded nucleic acid to the DNA-stabilized AgNCs leads to the adsorption of the hybrid nanostructures to GO and to the fluorescence quenching of the AgNCs. By the conjugation of oligonucleotide sequences acting as probes for target genes, or as aptamer sequences, to the nucleic-acid-protected AgNCs, the desorption of the probe/nucleic-acid-stabilized AgNCs from GO through the formation of duplex DNA structures or aptamer-substrate complexes leads to the generation of fluorescence as a readout signal for the sensing events. The hybrid nanostructures are implemented for the analysis of hepatitis B virus gene (HBV), the immunodeficiency virus gene (HIV), and the syphilis (Treponema pallidum) gene. Multiplexed analysis of the genes is demonstrated. The nucleic-acid-AgNCs-modified GO is also applied to detect ATP or thrombin through the release of the respective AgNCs-labeled aptamer-substrate complexes from GO.

Photosynthesis is a sustainable process that converts light energy into chemical energy. substantial research efforts are directed towards the application of the photosynthetic reaction centres, photosystems I and II, as active components for the light-induced generation of electrical power or fuel products. nonetheless, no integrated photo-bioelectrochemical device that produces electrical power, upon irradiation of an aqueous solution that includes two inter-connected electrodes is known. Here we report the assembly of photobiofuel cells that generate electricity upon irradiation of biomaterial-functionalized electrodes in aqueous solutions. The cells are composed of electrically contacted photosystem II-functionalized photoanodes and an electrically wired bilirubin oxidase/carbon nanotubes-modified cathode. Illumination of the photoanodes yields the oxidation of water to o 2 and the transfer of electrons through the external circuit to the cathode, where o 2 is re-reduced to water.

Graphene oxide (GO) is implemented as a functional matrix for developing fluorescent sensors for the amplified multiplexed detection of DNA, aptamer-substrate complexes, and for the integration of predesigned DNA constructs that activate logic gate operations. Fluorophore-labeled DNA strands acting as probes for two different DNA targets are adsorbed onto GO, leading to the quenching of the luminescence of the fluorophores. Desorption of the probes from the GO, through hybridization with the target DNAs, leads to the fluorescence of the respective label. By coupling exonuclease III, Exo III, to the system, the recycling of the target DNAs is demonstrated, and this leads to the amplified detection of the DNA targets (detection limit 5 × 10(-12) M). Similarly, adsorption of fluorophore-functionalized aptamers against thrombin or ATP onto the GO leads to the desorption of the aptamer-substrate complexes from GO and to the triggering of the luminescence corresponding to the respective fluorophore, thus, allowing the multiplexed analysis of the aptamer-substrate complexes. By designing functional fluorophore-labeled DNA constructs and their interaction with GO, in the presence (or absence) of nucleic acids, or two different substrates for aptamers, as inputs, the activation of the "OR" and "AND" logic gates is demonstrated.

A three-dimensional composite consisting of the oxygen-insensitive flavin-dependent glucose dehydrogenase, GDH, and Au nanoparticles (NPs) is assembled on a Au surface using an electropolymerization process. The bis-aniline-cross-linked GDH/Au NPs composite reveals effective electrical contact with the electrode (ket=1100 s(-1)), and the effective bioelectrocatalyzed oxidation is driven by the enzyme/NPs matrix. The GDH/Au NPs-functionalized electrode is implemented as an amperometric glucose sensor, and it reveals superior functions when compared to an analogous glucose oxidase/Au NPs system. The O2-insensitive GDH/Au NPs composite electrode was further used as an anode in a membraneless glucose/O2 biofuel cell. The cathode in this system was composed of bilirubin oxidase cross-linked onto a carbon nanotube-modified glassy carbon electrode. The power output of the cell was 32 μW cm(-2).

Integrated, electrically contacted beta-nicotinamide adenine dinucleotide- (NAD(+)) or beta-nicotinamide adenine dinucleotide phosphate- (NADP(+)) dependent enzyme electrodes were prepared on single-walled carbon nanotube (SWCNT) supports. The SWCNTs were functionalized with Nile Blue (1), and the cofactors NADP(+) and NAD(+) were linked to 1 through a phenyl boronic acid ligand. The affinity complexes of glucose dehydrogenase (GDH) with the NADP(+) cofactor or alcohol dehydrogenase (AlcDH) with the NAD(+) cofactor were crosslinked with glutaric dialdehyde and the biomolecule-functionalized SWCNT materials were deposited on glassy carbon electrodes. The integrated enzyme electrodes revealed bioelectrocatalytic activities, and they acted as amperometric electrodes for the analysis of glucose or ethanol. The bioelectrocatalytic response of the systems originated from the biocatalyzed oxidation of the respective substrates by the enzyme with the concomitant generation of NAD(P)H cofactors. The electrocatalytically mediated oxidation of NAD(P)H by 1 led to amperometric responses in the system. Similarly, an electrically contacted bilirubin oxidase (BOD)-SWCNT electrode was prepared by the deposition of BOD onto the SWCNTs and the subsequent crosslinking of the BOD units using glutaric dialdehyde. The BOD-SWCNT electrode revealed bioelectrocatalytic functions for the reduction of O(2) to H(2)O. The different electrically contacted SWCNT-based enzyme electrodes were used to construct biofuel cell elements. The electrically contacted GDH-SWCNT electrode was used as the anode for the oxidation of the glucose fuel in conjunction with the BOD-SWCNT electrode in the presence of O(2), which acted as an oxidizer in the system. The power output of the cell was 23 muW cm(-2). Similarly, the AlcDH-SWCNT electrode was used as the anode for the oxidation of ethanol, which was acting as the fuel, with the BOD-SWCNT electrode as the cathode for the reduction of O(2). The power output of the system was 48 microW cm(-2).