Geometry of Structurally Non-Rigid Pyridinium Cations in an Excited State.

Quantum-chemical calculations of phenyl-substituted pyridinium cations established the formation of two non-rigid equilibrium structures in a singlet excited S state. These two structures are characterized by a significant torsion of the methyl group and flattened geometry of the phenyl rings relative to the plane of the heteroaromatic ring, as well as sp hybridization of a nitrogen atom. Structural features of the S equilibrium structures and their deviation from the pyridinium cation geometry in the ground state explain the experimentally detected abnormally large Stokes shift.

Design and optimisation of Photochrome Aptamer Switch Assay (PHASA).

Photochrome Aptamer Switch Assay (PHASA) is our unique and recently developed fluorescent biosensing platform that exploits the combination of aptamer adaptive binding and photoisomerisation kinetics of stilbenes. The PHASA is based on converting any suitable stilbene-ligand-aptamer complex into a reversible biosensor. Binding affinity, aptamer concentration, and stilbene molecular structure determine the PHASA performance criteria.

New Photochrome Probe Allows Simultaneous pH and Microviscosity Sensing.

4-N,N'-dimethylamino-4'-N'-stilbenemaleamic acid (DASMA), a unique molecular photochrome probe that exhibits solubility and retains trans-cis photoisomerisation in a wide range of organic solvents and aqueous pH environments, was prepared, purified and chemically characterised. Absorption, fluorescence excitation and emission spectra and constant-illumination fluorescence decay were measured in acetonitrile, dimethyl sulfoxide, ethanol, propylene carbonate, and aqueous glycerol mixtures. The pseudo-first-order fluorescence decay rates were found to be strongly dependent on the medium viscosity.

Recent advances in aptasensors based on graphene and graphene-like nanomaterials.

Graphene and graphene-like two-dimensional nanomaterials have aroused tremendous research interest in recent years due to their unique electronic, optical, and mechanical properties associated with their planar structure. Aptamers have exhibited many advantages as molecular recognition elements for sensing devices compared to traditional antibodies. The marriage of two-dimensional nanomaterials and aptamers has emerged many ingenious aptasensing strategies for applications in the fields of clinical diagnosis and food safety.

Novel Photochrome Aptamer Switch Assay (PHASA) for adaptive binding to aptamers.

A novel Photochrome-Aptamer Switch Assay (PHASA) for the detection and quantification of small environmentally important molecules such as toxins, explosives, drugs and pollutants, which are difficult to detect using antibodies-based assays with high sensitivity and specificity, has been developed. The assay is based on the conjugation of a particular stilbene-analyte derivative to any aptamer of interest. A unique feature of the stilbene molecule is its reporting power via trans-cis photoisomerisation (from fluorescent trans-isomer to non-fluorescent cis-isomer) upon irradiation with the excitation light.