Interaction of acridine-calix[4]arene with DNA at the electrified liquid|liquid interface

The behaviour of an acridine-functionalised calix[4]arene at the interface between two immiscible electrolyte solutions (ITIES) is reported. Molecular modelling showed that the acridine-calix[4]arene has regions of significant net positive charge spread throughout the protonated acridine moieties, consistent with it being able to function as an anion ionophore. The presence of this compound in the organic phase facilitated the transfer of aqueous phase electrolyte ions. Upon addition of double stranded DNA to the aqueous phase, the transfer of electrolyte anions was diminished, due to DNA binding to the acridine moiety at the ITIES. The behaviour provides a basis for DNA hybridization detection using electrochemistry at the ITIES

Integration of a 3D hydrogel matrix within a hollow core photonic crystal fibre for DNA probe immobilization

In this paper, we demonstrate the integration of a 3D hydrogel matrix within a hollow core photonic crystal fibre (HC-PCF). In addition, we also show the fluorescence of Cy5-labelled DNA molecules immobilized within the hydrogel formed in two different types of HC-PCF. The 3D hydrogel matrix is designed to bind with the amino groups of biomolecules using an appropriate cross-linker, providing higher sensitivity and selectivity than the standard 2D coverage, enabling a greater number of probe molecules to be available per unit area. The HC-PCFs, on the other hand, can be designed to maximize the capture of fluorescence to improve sensitivity and provide longer interaction lengths. This could enable the development of fibre-based point-of-care and remote systems, where the enhanced sensitivity would relax the constraints placed on sources and detectors. In this paper, we will discuss the formation of such polyethylene glycol diacrylate (PEGDA) hydrogels within a HC-PCF, including their optical properties such as light propagation and auto-fluorescence

Electrochemical Study of Insulin at the Polarized Liquid-Liquid Interface

Insulin is a small protein (RMM ~5700) composed of two polypeptide chains A and B and containing three disulphide bonds, two of which are interchain between A and B, while the third is an intrachain bond within chain A.1,2 Insulin regulates blood glucose by signaling when high levels of blood glucoseare present in the body.3 It stimulates the uptake of glucose by muscle tissue and works together with another hormone, glucagon, to maintain a controlled level of blood glucose. Diabetes mellitus is caused by a deficiency in the secretion (type 1 diabetes) or action (type 2 diabetes) of insulin. According to one study, the prevalence of diabetes for all age groups worldwide is estimated at 2.8% for 2000 rising to 4.4% in 2030.4 The total number of people with diabetes is projected to rise from 171 million in 2000 to 366 million in 2030. Furthermore, the American Diabetes Association (ADA) estimated the national cost of diabetes in the U.S. for 2002 to be $132 billion, increasing to$192 billion in 2020,5 so clearly insulin monitoring is an important subject for medical and physiological studies of this disease

Potentiometric evaluation of calix[4]arene anion receptors in membrane electrodes: Phosphate detection

Ion-selective electrodes (ISEs) allowthe potentiometric sensing of the activity of specific ions in the presence of other ions. They belong to the oldest established group of chemical sensors and their behaviour is generally well understood, founded on basic thermodynamic and kinetic processes [1–5]. ISEs containing polymeric membranes, such as poly(vinyl chloride) (PVC), which are assumed to behave as organic liquids of high viscosity, are by far the most versatile and widely studied class of ISEs. In order to obtain highly selective ISEs on the basis of PVC membranes, suitable ionophores must be doped into these membrane

Study of electrochemical phosphate sensing systems: Spectrometric, potentiometric and voltammetric evaluation

Characterization of the interaction of a urea-functionalized calix[4]arene ionophore and phosphate wasundertaken by combination of nuclear magnetic resonance (NMR) spectrometry, potentiometric selectivity coefficient evaluation and voltammetric ion transfer at the interface between two immiscibleelectrolyte solutions (ITIES). NMR revealed that the urea protons were involved in complexation withthe target anion and potentiometric separate solution selectivity data indicated selectivity for phosphateover chloride and sulphate. Voltammetry at the ITIES confirmed that the ionophore-facilitated transfer ofmonohydrogen phosphate occurred in preference to dihydrogen phosphate transfer. The results correlatewith previously reported data on the potentiometric evaluation of this calixarene as an anionophore inPVC-membrane electrodes. The data provide the basis for development of amperometric monohydrogenphosphate sensors based on the ion-transfer principle

Three-dimensional hydrogel structures as optical sensor arrays, for the detection of specific DNA sequences

The fabrication and characterization of surface-attached PEG-diacrylate hydrogel structures and their application as sensing platforms for the detection of specific target sequences are reported. Hydrogel structures were formed by a photopolymerization process, using substrate-bound Eosin Y molecules for the production of free radicals. We have demonstrated that this fabrication process allows for control over hydrogel growth down to the micrometer scale. Confocal imaging revealed relatively large pore structures for 25% (v/v) PEG-diacrylate hydrogels, which appear to lie in tightly packed layers. Our data suggest that these pore structures decrease in size for hydrogels with increasing levels of PEG-diacrylate. Surface coverage values calculated for hydrogels immobilized with 21-mer DNA probe sequences were significantly higher compared to those previously reported for 2- and 3-dimensional sensing platforms, on the order of 10 16 molecules cm -2. Used as sensing platforms in DNA hybridization assays, a detection limit of 3.9 nM was achieved for hybridization reactions between 21-mer probe and target sequences. The ability of these hydrogel sensing platforms to discriminate between wild-type and mutant allele sequences was also demonstrated, down to target concentrations of 1-2 nM. A reduction in the hybridization time down to a period of 15 min was also achieved, while still maintaining confident results, demonstrating the potential for future integration of these sensing platforms within Lab-on-Chip or diagnostic devices. © 2011 Elsevier Inc. All rights reserved