Abstract: DNA-templated few-atom silver nanoclusters (DNA/Ag NCs) are a new class of organic/inorganic composite nanomaterials whose fluorescence emission can be tuned throughout the visible and near-IR range by simply programming the template sequences. Compared to organic dyes, DNA/Ag NCs can be brighter and more photostable. Compared to quantum dots, DNA/Ag NCs are smaller, less prone to blinking on long timescales, and do not have a toxic core. The preparation of DNA/Ag NCs is simple and there is no need to remove excess precursors as these precursors are non-fluorescent. Our recent discovery of the fluorogenic and color switching properties of DNA/Ag NCs have led to the invention of new molecular probes, termed NanoCluster Beacons (NCBs), for DNA detection, with the capability to differentiate single-nucleotide polymorphisms by emission colors. NCBs are inexpensive, easy to prepare, and compatible with commercial DNA synthesizers. Many other groups have also explored and taken advantage of the environment sensitivities of DNA/Ag NCs in creating new tools for DNA/RNA detection and single-nucleotide polymorphism identification. In this review, we summarize the recent trends in the use of DNA/Ag NCs for developing DNA/RNA sensors.
Abstract: The mechanosensitive channel of large conductance, MscL, has been proposed as a triggered nanovalve to be used in drug release and other nanodevices. It is a small homopentameric bacterial protein that has the largest gated pore known: greater than 30 Å. Large molecules, even small proteins can be released through MscL. Although MscL normally gates in response to membrane tension, early studies found that hydrophilic or charged residue substitutions near the constriction of the channel leads to pore opening. Researchers have successfully changed the modality of MscL to open to stimuli such as light by chemically modifying a single residue, G22, within the MscL pore. Here, by utilizing in vivo, liposome efflux, and patch clamp assays we compared modification of G22 with that of another neighboring residue, G26, and demonstrate that modifying G26 may be a better choice for triggered nanovalves used for triggered vesicular release of compounds.
Abstract: An immobilization protocol was developed to attach receptors on smooth silver thin films. Dense and packed 11-mercaptoundecanoic acid (11-MUA) was used to avoid uncontrolled sulfidization and harmful oxidation of silver nanolayers. N,N'-dicyclohexylcarbodiimide (DCC) and N-hydroxysuccinimide (NHS) were added to make the silver surfaces reactive. A comparative study was carried out with different immersion times of silver samples in 11-MUA solutions with different concentrations to find the optimum conditions for immobilization. The signals, during each step of the protocol, were analyzed with a refractometer based on the surface plasmon resonance (SPR) effect and luminescence techniques. Molecular interactions at the surfaces between the probe and target at the surface nanolayer shift the SPR signal, thus indicating the presence of the substance. To demonstrate specific biosensing, rabbit anti-estrone polyclonal immunoglobulin G (IgG) antibody was immobilized through a linker on 47 nm silver layer deposited on SF11 glass. At the final stage, the representative endocrine disruptor—estrone—was attached and detected in deionized water with a diverging beam SPR imaging sensor.
Abstract: The use of label-free technologies based on electrical impedance is becoming more and more popular in drug discovery. Indeed, such a methodology allows the continuous monitoring of diverse cellular processes, including proliferation, migration, cytotoxicity and receptor-mediated signaling. The objective of the present study was to further assess the usefulness of the real-time cell analyzer (RTCA) and, in particular, the xCELLigence platform, in the context of early drug development for pharmacology and toxicology investigations. In the present manuscript, four cellular models were exposed to 50 compounds to compare the cell index generated by RTCA and cell viability measured with a traditional viability assay. The data revealed an acceptable correlation (ca. 80%) for both cell lines (i.e., HepG2 and HepaRG), but a lack of correlation (ca. 55%) for the primary human and rat hepatocytes. In addition, specific RTCA profiles (signatures) were generated when HepG2 and HepaRG cells were exposed to calcium modulators, antimitotics, DNA damaging and nuclear receptor agents, with a percentage of prediction close to 80% for both cellular models. In a subsequent experiment, HepG2 cells were exposed to 81 proprietary UCB compounds known to be genotoxic or not. Based on the DNA damaging signatures, the RTCA technology allowed the detection of ca. 50% of the genotoxic compounds (n = 29) and nearly 100% of the non-genotoxic compounds (n = 52). Overall, despite some limitations, the xCELLigence platform is a powerful and reliable tool that can be used in drug discovery for toxicity and pharmacology studies.
Abstract: Dynamic fluoroimmunoassay with a flow-through system using optical fiber probes consisting of polystyrene was developed and applied to a quantitative detection of E. coli O157:H7. The system measures E. coli as fluorescence of sandwich-type immune complexes formed by capture antibodies immobilized on the surface of the probe, E. coli cells, and fluorescently labeled detection antibodies. Excitation was carried out using an evanescent wave from the probe. Resulting fluorescence recoupled into the probe was detected by a photodiode. The assay system was constructed with a flow cell which was available for sequential injection of experimental reagents. In vitro characterization was performed using the flow cell, and the calibration range of E. coli O157:H7 was from 103 to 107 cells/mL. The measurement for each sample was completed within 12 min. Furthermore, it was also possible to estimate the concentrations of E. coli O157:H7 by the increasing rate of fluorescence during binding reaction of detection antibodies to antigens. This minimized the time for measurement down to 6 min. The system is suitable for rapid and direct determination for microorganisms or bacteria in food, clinical, and environmental sources.
Abstract: The aim of the present editorial is to briefly summarize the current scientific and technological accomplishments in the field of organic electronic biosensors as described in the articles published in this Special Issue. By definition, a biosensor is a robust analytical device that combines a biological recognition element (e.g., antibodies, enzymes, cells) with a transducer. Organic electronic bio-devices are considered as potentially reliable substitutes of conventional and rather expensive analytical techniques employed for several applications such as medical diagnosis, food safety and environment pollution monitoring. Some insights into the selection and immobilization of recognition elements, signal amplification, fabrication techniques and analytical performance of biosensing devices will be presented.