We report the preparation of free-standing flexible conductive reduced graphene oxide/Nafion (RGON) hybrid films by a solution chemistry that utilizes self-assembly and directional convective-assembly. The hydrophobic backbone of Nafion provided well-defined integrated structures, on micro- and macroscales, for the construction of hybrid materials through self-assembly, while the hydrophilic sulfonate groups enabled highly stable dispersibility ( approximately 0.5 mg/mL) and long-term stability (2 months) for graphene. The geometrically interlocked morphology of RGON produced a high degree of mechanical integrity in the hybrid films, while the interpenetrating network constructed favorable conduction pathways for charge transport. Importantly, the synergistic electrochemical characteristics of RGON were attributed to high conductivity (1176 S/m), facilitated electron transfer (ET), and low interfacial resistance. Consequently, RGON films obtained the excellent figure of merit as electrochemical biosensing platforms for organophosphate (OP) detection, that is, a sensitivity of 10.7 nA/microM, detection limit of 1.37 x 10(-7) M, and response time of <3 s. In addition, the reliability of RGON biosensors was confirmed by a fatigue test of 100 bending cycles. The strategy described here provides insight into the fabrication of graphene and hybrid nanomaterials from a material perspective, as well as the design of biosensor platforms for practical device applications.

Nanometer-scale metal particles are finding many applications in the fields of biology and nanotechnology owing to their unique optical and magnetic properties. Phytochelatin (PC) and other metal-binding proteins have an ability to bind heavy metals and have been used for heavy-metal removal. Thus, we reasoned that they might be employed for the synthesis of metal nanoparticles (NPs). Herein, we report the in vivo biosynthesis of diverse NPs by recombinant Escherichia coli expressing phytochelatin synthase (PCS) and/or metallothionein (MT). NPs of various metal elements, including semiconducting, alkali-earth, magnetic, and noble metals and rare-earth fluorides, could be synthesized in E. coli. The size of NPs could be tuned on the nanoscale by changing the concentration of metal ions in the medium. Thus, the controlled synthesis of NPs with desirable characteristics for in vitro assays and cellular imaging was possible. Paramagnetic NPs could also be synthesized by using the same system. The strategy of employing recombinant E. coli as an NP factory is generally applicable for the combinatorial synthesis of diverse NPs with a wide range of characteristics.Metal NPs exhibit unique optical, electronic, and magnetic properties, which depend on their composition, size, and structure, and have therefore been explored extensively for various applications in bio-and nanotechnology.

A non-labeled, portable plasmonic biosensor-based device was developed to enable the ultra-sensitive and selective detection of Salmonella typhimurium in pork meat samples. Specifically, a plasmonic sensor, using the self-assembly of gold nanoparticles (AuNPs) to achieve a regulated diameter of 20 nm for the AuNP monolayers, was used to conduct high-density deposition on a transparent substrate, which produced longitudinal wavelength extinction shifts via a localized surface plasmon resonance (LSPR) signal. The developed aptamers conjugated to the LSPR sensing chips revealed an ultra-sensitive upper limit of detection (LOD) of approximately 104 cfu/mL for S. typhimurium in pure culture under the optimal assay conditions, with a total analysis time of 30–35 min. When the LSPR sensing chips were applied on artificially contaminated pork meat samples, S. typhimurium in the spiked pork meat samples was also detected at an LOD of 1.0 × 104 cfu/mL. The developed method could detect S. typhimurium in spiked pork meat samples without a pre-enrichment step. Additionally, the LSPR sensing chips developed against S. typhimurium were not susceptible to any effect of the food matrix or background contaminant microflora. These findings confirmed that the developed gold nanoparticle-aptamer-based LSPR sensing chips could facilitate sensitive detection of S. typhimurium in food samples.