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.
Abstract: Inhibition-based biosensors were developed by immobilizing tyrosinase (Tyr, polyphenol oxidase) from the crude extract of avocado fruit on electrochemically prepared polypyrrole (PPy) films. The biosensors were prepared during the electropolymerization of pyrrole in a solution containing a fixed volume of the crude extract of avocado. The dependence of the biosensor responses on the volume used from the crude extract, values of pH and temperature was studied, and a substrate, catechol, at different concentrations, was amperometrically detected by these biosensors. Benzoic acid, a competitive inhibitor of Try, was added to the catechol solutions at specific concentrations aimed at obtaining the inhibition constant, K’m, which ranged from 1.7 to 4.6 mmol∙L−1 for 0.0 and 60 µmol∙L−1 of benzoic acid, respectively. Studies on the inhibition caused by benzoic acid by using PPy/Try films, and catechol as a substrate, allowed us propose how to develop, under optimized conditions, simple and low-cost biosensors based on the use of avocado fruit.
Abstract: An innovative and low-cost method is proposed for the detection and discrimination of indole-positive pathogen bacteria. The method allows the non-invasive detection of gaseous indole, released by bacteria, with nanoporous colorimetric sensors. The innovation comes from the use of nanoporous matrices doped with 4-(dimethylamino)-cinnamaldehyde, which act as sponges to trap and concentrate the targeted analyte and turn from transparent to dark green, long before the colonies get visible with naked eyes. With such sensors, it was possible to discriminate E. coli from H. alvei, two indole-positive and negative bacteria after seven hours of incubation.
Abstract: Thin films of analyte-specific hydrogels were combined with microfabricated piezoresistive pressure transducers to obtain chemomechanical sensors that can serve as selective biochemical sensors for a continuous monitoring of metabolites. The gel swelling pressure has been monitored in simulated physiological solutions by means of the output signal of piezoresistive sensors.The interference by fructose, human serum albumin, pH, and ionic concentration on glucose sensing was studied. With the help of a database containing the calibration curves of the hydrogel-based sensors at different values of pH and ionic strength, the corrected values of pH and glucose concentration were determined using a novel calibration algorithm.