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Chemosensors, Volume 2, Issue 3 (September 2014), Pages 182-218

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Research

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Open AccessArticle Immobilization of Tyrosinase from Avocado Crude Extract in Polypyrrole Films for Inhibitive Detection of Benzoic Acid
Chemosensors 2014, 2(3), 182-192; doi:10.3390/chemosensors2030182
Received: 14 March 2014 / Revised: 11 June 2014 / Accepted: 27 June 2014 / Published: 3 July 2014
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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 [...] Read more.
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. Full article
Open AccessArticle Photonic Crystal-Based Sensing and Imaging of Potassium Ions
Chemosensors 2014, 2(3), 207-218; doi:10.3390/chemosensors2030207
Received: 28 April 2014 / Revised: 4 August 2014 / Accepted: 9 September 2014 / Published: 18 September 2014
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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 [...] Read more.
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. Full article
(This article belongs to the Special Issue Photonic Sensors for Biological and Chemical Measurements)
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Review

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Open AccessReview Toward Non-Enzymatic Ultrasensitive Identification of Single Nucleotide Polymorphisms by Optical Methods
Chemosensors 2014, 2(3), 193-206; doi:10.3390/chemosensors2030193
Received: 2 February 2014 / Revised: 7 July 2014 / Accepted: 8 July 2014 / Published: 22 July 2014
Cited by 1 | PDF Full-text (582 KB) | HTML Full-text | XML Full-text
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 [...] Read more.
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. Full article
(This article belongs to the Special Issue Nucleic Acid Probes)

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