Modification of ultrasmall gold nanoparticles (AuNPs) with the lipoic acid derivative of folic acid was found to enhance their accumulation in the cancer cell, as compared to AuNPs without addressing units. The application of lipoic acid enabled the control of the gold nanoparticle functionalities leading to enhanced solubility and allowing for attachment of both the folic acid and the cytotoxic drug, doxorubicin. More robust attachment of doxorubicin to the nanoparticle through the amide bond resulted in toxicity comparable with that of the drug alone, opening a new perspective for designing more potent, but less toxic nanopharmaceuticals. The increased uptake was accompanied by pronounced nuclear accumulation and observable cytotoxicity. Doxorubicin binding via covalent amide bonds enhanced stability of the whole drug vehicle and provided much better control over doxorubicin release in the cell environment, as compared to physical adsorption or pH sensitive bonding commonly used for anthracycline carriers. Confocal microscopy revealed that the bond was stable in the cytoplasm for 22 h. The ability to slow down the rate of drug release may be crucial for the application in sustained anticancer drug delivery. Biological analyses performed using MTT assay and confocal microscopy confirmed that the ultrasmall AuNPs with the lipoic acid derivative of folic acid exhibit relatively low cytotoxicity, however when loaded with a chemotherapeutic, they cause a significant reduction in the cell viability.

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A significant problem still exists with the low power output and durability of the bioelectrochemical fuel cells. We constructed a fuel cell with an enzymatic cascade at the anode for efficient energy conversion. The construction involved fabrication of the flow-through cell by three-dimensional printing. Gold nanoparticles with covalently bound naphthoquinone moieties deposited on cellulose/polypyrrole (CPPy) paper allowed us to significantly improve the catalysis rate, both at the anode and cathode of the fuel cell. The enzymatic cascade on the anode consisted of invertase, mutarotase, Flavine Adenine Dinucleotide (FAD)-dependent glucose dehydrogenase and fructose dehydrogenase. The multi-substrate anode utilized glucose, fructose, sucrose, or a combination of them, as the anode fuel and molecular oxygen were the oxidant at the laccase-based cathode. Laccase was adsorbed on the same type of naphthoquinone modified gold nanoparticles. Interestingly, the naphthoquinone modified gold nanoparticles acted as the enzyme orienting units and not as mediators since the catalyzed oxygen reduction occurred at the potential where direct electron transfer takes place. Thanks to the good catalytic and capacitive properties of the modified electrodes, the power density of the sucrose/oxygen enzymatic fuel cells (EFC) reached 0.81 mW cm−2, which is beneficial for a cell composed of a single cathode and anode.

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Metal nanostructures are often used in bioelectrocatalytic systems to increase the electrode surfacea rea or to improve the conductivity of biofilms.W ed emonstrate, that decreasing the size of gold nanoparticles below 2nmm ay result in ac hange of the mechanism of electron transfer (ET) between the enzyme active site and the electrode from direct to mediated ET.C lustersw ith diameters smaller than 2nme xhibited molecule-likeb ehavior reflected in the appearance of oxidation and reduction peaks separated by ac learly developed HOMO-LUMO gap. The redox activity of the nanoparticles was found to contributet ot he ET mechanism of fructosed ehydrogenase switching it to gold cluster mediated electron transfer instead of direct ET.I nt he presence of gold clusters at the electrode, the overpotential of the catalyzed fructose oxidation reaction was 100 mV lower andt he catalytic reaction rate constant was 2.5 times larger confirming the unique mediating role of the Au clusters.Gold nanoparticles (AuNPs)a nd their applicationsi nb ioelectrocatalysis, have raised as ignificant interest in the last few years. [1] Owing to their high affinity to thiols they are an excellent platform for introducing functional moieties and for the surfacea ttachment of biological speciesi nacontrolled manner.A uNPs provide variability of chemical and physical properties whicha re strongly dependent on the nanoparticle's size. Optical effects, such as surface plasmon bands due to collective excitation of conduction electrons, are observed for nanoparticles with diameters above % 2nm. For diameters below this value, the plasmon bands diminish andn ew bands are developedc orresponding to electronic transitions. [2] The electrochemical properties of AuNPs also vary with size and three types of behavior are observed:b ulk gold exhibits continuum behavior, small nanoparticles show quantum doublelayer charging, while the smallest-clusters, exhibit "moleculelike" behavior.V oltammograms of AuNPs, with diameters lower than 2nm, give voltammetry current peaks corresponding to a single electron transfer processes to or from the nanoparticle's metallicc ore, [3] whereas molecule-like processes are reflected in the oxidationa nd reduction signals, separated by ac learly developed HOMO-LUMOg ap. [4] Gold nanoparticles (AuNPs) are successfully utilized for nanostructuring electrode surfaces in protein-based electronics. In most cases, "planar" electrode surfaces withoutp orous nanostructure, show insufficiento rn oe lectron transfer (ET) between the immobilizede nzyme actives ites and the electrode. The commonly offered explanation for "enzyme nanowiring"i s ad esirable orientation of the proteins on the surface to shorten the ET distance. An increase in the catalytic current, originating from nanostructuration of the electrode surface, is typically observed. However,i ts houldb ee mphasized that the observede ffect is often related to an expansion of the real electrode surface, and is not ar esult of thermodynamics; such as a decreaseinthe overpotential ...