Abstract: In this study we report on the spectral properties and G-quadruplex folding ability of fluorescent oligonucleotide probes modified by the attachment of a cholesterol moiety. These probes were designed and studied in order to verify their potential as potassium-sensing devices that can be incorporated into the cellular membrane. The 19-meric guanine-rich deoxyoligonucleotide was labeled with reporter fluorescent FRET groups (FAM and TAMRA) and a cholesterol anchor was attached using different approaches. The probes exhibited abilities to fold into a quadruplex structure and to bind metal cations (Na+ and K+). In an unbound state, both termini of the oligonucleotide are separated, thus fluorophores do not interact with each other and the probe exhibits an unperturbed fluorescence spectrum. In the presence of K+, the quadruplex structure is developed such that it enables fluorophores to be arranged in close proximity, causing generation of a different fluorescence spectrum (FRET signal). Folding properties of probes and their spectral behavior were examined by recording the UV-Vis, fluorescence emission, and excitation spectra (FRET efficiency), and the temperature stability of G-quadruplex structures adopted by probes (melting profiles). Fluorescence energy transfer efficiency increased with increases in sodium or potassium ion concentrations in an aqueous solution, which indicated that the probes retained their cation-binding properties and could be promising candidates for potassium sensing at the cell membrane interface.
Abstract: We report the fabrication of a voltammetric electronic tongue for the detection and discrimination of harmful substances intentionally added to milk to increase its shelf life or imitate protein content. The electronic tongue consisted of three working electrodes composed of platinum, gold, and copper. The measurement principles involved the extraction of information from cyclic voltammograms recorded in unadulterated and adulterated milk. The extracted data were analysed using principal component analysis and the contaminants were successfully differentiated from one another in a score plot. Electrochemical quartz crystal microbalance analysis was used to investigate the electrode response in order to understand the mechanism by which the tongue could discriminate between the samples. It was found that the electrochemical formation and dissolution of platinum and gold oxides, and the reduction of a copper-melamine ionic pair formed at the surface of the copper electrode were the main factors responsible for discrimination. In addition, the electronic tongue was capable of identifying adulterations in different types of milk (whole, skimmed, and semi-skimmed) and milk from different brands. The lowest concentration of adulterant that resulted in a good discrimination was 10.0, 4.16, and 0.95 mmol·L−1 for formaldehyde, urea, and melamine, respectively.
Abstract: The development of sensing systems that can detect ultra-trace amounts of hydrogen peroxide (H2O2) remains a key challenge in biological and biomedical fields. In the present study, we introduce a simple and highly sensitive enzymeless H2O2 biosensor based on a three-dimensional open pore nickel (Ni) foam electrode functionalized with hemoglobin (Hb). Our findings revealed that the Hb maintained its biological functions and effective electronic connection even after immobilization process. The exceptional physical and intrinsic catalytic properties of the Ni foam combined with the bio-functionality and electron transport facility of the Hb robustly construct a H2O2 biosensor. The enzymeless H2O2 biosensor showed high selectivity, a quick response time, high sensitivity, a wide linear range and a low limit of detection (0.83 μM at a signal-to-noise ratio of three). Such an electrode composition with safe immobilization processes offers viability for engineering new biosensors.
Abstract: We fabricated silica nanotubes with hexagonally ordered mesopores (6 nm) inside a membrane disc with a uniform channel neck size of 200 nm and a longitudinal thickness of 60 μm to design an optical sensor membrane (OSM) for the screening and sensing of extremely toxic Hg(II) ions. The optical detection and quantitative recognition of Hg(II) ions in water were conducted even at trace concentrations without the need for sophisticated instruments. The OSM design was based on the physical interaction of a responsive organic probewith silica pore surfacesfollowed by strong and selective binding Hg(II)–probe interactions under specific sensing conditions, particularly at pH 5. Ultra-trace concentrations of Hg(II) ions were easily detected with the naked eye using the OSM. The remarkable ion spectral response of Hg(II) ion–OSM ensured the excellent quantification of the OSM for Hg(II) ion sensing over a wide range of concentrations with a detection limit of 1.75 × 10−9 M. This result indicated that low concentrations of Hg(II) ions can be detected with a high sensitivity. One of the key issues of OSM is the Hg(II) ion-selective workability even in the presence of high doses of competitive matrices and species. The OSM design showed significant Hg(II) ion-sensing capability despite the number of reuse/recycles using simple decomplexation. Given its high selectivity, fast response, and sensitivity, the OSM could be developed into a specific Hg(II) ion-sensing kit in aqueous solutions.
Abstract: We report on a method for selective optical sensing and imaging of potassium ions using a sandwich assembly composed of layers of photonic crystals and an ion-selective membrane. This represents a new scheme for sensing ions in that an ionic strength-sensitive photonic crystal hydrogel layer is combined with a K+-selective membrane. The latter consists of plasticized poly(vinyl chloride) doped with the K+-selective ion carrier, valinomycin. The film has a red color if immersed into plain water, but is green in 5 mM KCl and purple at KCl concentrations of 100 mM or higher. This 3D photonic crystal sensor responds to K+ ions in the 1 to 50 mM concentration range (which includes the K+ concentration range encountered in blood) and shows high selectivity over ammonium and sodium ions. Sensor films were also imaged with a digital camera by exploiting the RGB technique.
Abstract: Single nucleotide polymorphisms (SNPs) are single nucleotide variations which comprise the most wide spread source of genetic diversity in the genome. Currently, SNPs serve as markers for genetic predispositions, clinically evident disorders and diverse drug responses. Present SNP diagnostics are primarily based on enzymatic reactions in different formats including sequencing, polymerase-chain reaction (PCR) and microarrays. In these assays, the enzymes are applied to address the required sensitivity and specificity when detecting SNP. On the other hand, the development of enzyme-free, simple and robust SNP sensing methods is in a constant focus in research and industry as such assays allow rapid and reproducible SNP diagnostics without the need for expensive equipment and reagents. An ideal method for detection of SNP would entail mixing a DNA or RNA target with a probe to directly obtain a signal. Current assays are still not fulfilling these requirements, although remarkable progress has been achieved in recent years. In this review, current SNP sensing approaches are described with a main focus on recently introduced direct, enzyme-free and ultrasensitive SNP sensing by optical methods.