Measurement of adsorption constants of laccase on gold nanoparticles to evaluate the enhancement in enzyme activity of adsorbed laccase.

Adsorption of enzymes to nanoparticles and the mechanisms responsible for enzyme activity modulation of adsorbed enzymes are not well understood. In this work, gold nanoparticles were used for electrostatic adsorption of a plant-derived laccase. Adsorption constants were determined by four independent techniques: dynamic light scattering, electrophoretic light scattering, agarose gel electrophoresis and fluorescence quenching. Stable bionanoconjugates were formed with log K in the range 6.8-8.9. An increase in enzyme activity was detected, in particular at acidic and close to neutral pH values, a feature that expands the useful pH range of the enzyme. A model for the adsorption was developed, based on geometrical considerations and volume increase data from dynamic light scattering. This indicates that enzymes adsorbed to gold nanoparticles are ca. 9 times more active than the free enzyme.

Silver Nanostars-Coated Surfaces with Potent Biocidal Properties.

Bacterial proliferation on certain surfaces is of concern as it tends to lead to infectious health problems. Nanotechnology is offering new options for engineering antimicrobial surfaces. Herein, the antibiofilm and biocidal properties of star-shaped silver nanoparticles (AgNSs) in suspension and as coating surfaces were studied. AgNSs and spherical silver nanoparticles (AgNPs) (used for comparison purposes) were synthesized using reported methods. Glass disks (9 mm diameter) were covered with AgNSs using deposition by centrifugation. Minimum inhibitory concentrations (MICs) of AgNSs and AgNPs were determined against several reference strains and multidrug-resistant isolates and their antibiofilm activity was assessed against preformed biofilms of Pseudomonas aeruginosa and Staphylococcus aureus by both Live/Dead staining and atomic force microscopy (AFM). The antimicrobial properties of AgNSs-coated surfaces were evaluated by the "touch test" method on agar, and also Live/Dead staining and AFM. The MIC values of the AgNSs were 2-4 times lower than those of the AgNPs. Biofilms treated with AgNSs at a concentration equal to the MIC were not significantly affected, although they exhibited more dead cells than the non-treated biofilms. The biocidal activity of AgNSs-coated surfaces was attested, since no growth on agar nor viable cells were observed after contact of the inoculated bacteria with the coated surface for 6 and 24 h. Thus, AgNSs show greater potential as a surface coating with biocidal effects than used as suspension for antimicrobial purposes.

A multiparametric study of gold nanoparticles cytotoxicity, internalization and permeability using an in vitro model of blood-brain barrier. Influence of size, shape and capping agent.

Gold nanoparticles (AuNPs) have biomedical application on imaging and due to increased optical performance, star-shaped AuNPs are of special interest. Because shape, size and capping greatly influence their toxicokinetics and toxicodynamics, a systematic multiparametric comparative study of the influence of these parameters on the cytotoxicity, internalization, and in vitro permeability was conducted in human Cerebral Microvascular Endothelial Cell line (hCMEC/D3), an in vitro model of the human blood-brain barrier (BBB). AuNPs of different size (14 nm and ∼50 nm), shape (spheres and stars), and coating (11-mercaptoundecanoic acid or MUA and sodium citrate) were synthesized and fully characterized. The time- and concentration-dependent cytotoxic profile of the tested AuNPs differed for the different AuNPs. Generally, toxicity was greater for stars relative to sphere-shaped AuNPs, and citrate coating was more toxic than MUA. Regarding the influence of size, smaller-sized AuNPs were more cytotoxic when compared at the same Au concentration. However, when the concentration of AuNPs was expressed as the number of AuNPs/mL, a higher degree of cytotoxicity was noted for the larger ̴50 nm AuNPs. To understand the influence of size, shape and capping, a systematic study design, in which only one of the variables changes, is determinant for correct data interpretation. Considering the results herein presented, for the sake of comparison of differently-sized AuNPs, it is preferable to design the study based upon the number of nanoparticles, since at a fixed Au concentration the number of particles available to promote effect is higher for smaller-sized AuNPs. Cellular internalization also differed among the tested AuNPs; although all were unable to cross the in vitro BBB, the intracellularly accumulated AuNPs can induce cell damage and later compromise BBB integrity and permeability.

Office paper decorated with silver nanostars - an alternative cost effective platform for trace analyte detection by SERS.

For analytical applications in portable sensors to be used in the point-of-need, low-cost SERS substrates using paper as a base, are an alternative. In this work, SERS substrates were produced on two different types of paper: a high porosity paper (Whatman no. 1); and a low porosity paper (commercially available office paper, Portucel Soporcel). Solutions containing spherical silver nanoparticles (AgNPs) and silver nanostars (AgNSs) were separately drop-casted on hydrophilic wells patterned on the papers. The porosity of the paper was found to play a determinant role on the AgNP and AgNS distribution along the paper fibres, with most of the nanoparticles being retained at the illuminated surface of the office paper substrate. The highest SERS enhancements were obtained for the office paper substrate, with deposited AgNSs. A limit of detection for rhodamine-6G as low as 11.4 ± 0.2 pg could be achieved, with an analytical enhancement factor of ≈107 for this specific analyte. The well patterning technique allowed good signal uniformity (RSD of 1.7%). Besides, these SERS substrates remained stable after 5 weeks of storage (RSD of 7.3%). Paper-induced aggregation of AgNPs was found to be a viable alternative to the classical salt-induced aggregation, to obtain a highly sensitive SERS substrates.