Yusuke Kitamura

Template-directed formation of luminescent lanthanide complexes: versatile tools for colorimetric identification of single nucleotide polymorphism.

We present the facile technique of colorimetric SNP (single nucleotide polymorphism) analysis through DNA-templated cooperative complexation between a luminescent lanthanide ion (Ln(III): Tb(III) or Eu(III)) and two ODN (oligodeoxyribonucleotide) conjugates carrying a metal chelator. Families of complexane-type chelators and heterocyclic aromatic ligands were covalently attached to ODNs to form conjugates for application as capture and sensitizer probes. The sequences of the conjugates were designed so as to form a ternary tandem duplex with the target, where their auxiliary units face each other, providing a microenvironment to accommodate Ln(III). Only the combination of EDTA (ethylenediaminetetraacetic acid) conjugates and phen (1,10-phenanthroline) conjugates provided significant emissions with quantum yields of 3.3% and 1.5% for Tb(III) and Eu(III), respectively, in the presence of the target. Biallelic polymorphism in the TPMT (thiopurine S-methyltransferase) gene, wt/wt (G/G), mut/mut (C/C), and wt/mut (G/C), were distinguished as emissions in green, red, and yellow, respectively; the colors were identified even by the naked eye.

DNA analysis based on toehold-mediated strand displacement on graphene oxide

Fluorescent dye-labeled probe DNA was immobilized on fluorescence-quenching graphene oxide (GO) through a capture DNA. When targets were added, the probes were released from the GO through toehold-mediated strand exchange. Higher emission recovery and more signal contrast were achieved relative to conventional methods that are based on direct adsorption of probes.

In situ oxygenous functionalization of a graphite electrode for enhanced affinity towards charged species and a reduced graphene oxide mediator

The weak affinity of bare carbon based electrodes for biological molecules or charged species is a major drawback for their direct application in analytical electrochemistry. We observed that the surfaces of graphite rods and glassy carbon (GC) ring electrodes can be modified by oxygenated functional groups through controlled electrochemical oxidation in aqueous media. Study of their cyclic voltammetry, surface conductivity, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, infrared spectroscopy (IR) and powder X-ray diffraction (PXRD) spectroscopy confirmed the chemical change. In the electrodynamics study, the modified GC ring in a rotating ring-disk electrode (RRDE) assembly showed better electron transfer efficiency than the virgin electrode when evaluated using a Ru(bpy)32+/3+ couple. In comparison to the virgin electrode, the modified graphite rod exhibited better affinity toward polyvinylpyrrolidone protected reduced graphene oxide (PVP-rGO) attached to glucose oxidase enzymes (GOx), and showed the direct attachment of mediators to the oxygenated electrode surface. These observations imply that a small oxygenated layer on the carbon electrode surface can significantly increase its activity. The present evidence indicates the possibility for the oxygenous functionalization of carbon based electrodes for applications in areas like electrokinetics studies and biosensing, where strong analyte–electrode interactions are useful.

Metal ion-directed dynamic splicing of DNA through global conformational change by intramolecular complexation

Chemically engineered DNAs—in which global conformation can be modulated in response to specific stimuli—could be allosteric functional DNAs themselves or work as a modulator of the functional nucleic acids such as DNAzymes and aptamers. Here, we show that two terpyridines built in the DNA backbone form a stable intramolecular 1:2 complex, [M(terpy)2](2+), with divalent transition metal ions. Upon complexation, the DNA conjugates adopt a Ω-shape structure, in which two distal sequences located outside the terpyridines connect with each other to form a continuous segment with a specific structure or sequence. Such a DNA structure is globally controlled by local metal complexation events that can be rationally designed based on general coordination chemistry. This method is regarded as metal ion-directed dynamic sequence edition or DNA splicing. DNAzymes with peroxidase-like activity can thus be regulated by several transition metal ions through sequence edition techniques based on the Ω-motif.

Graphene oxide: A fertile nanosheet for various applications

Graphene oxide (GO) is chemically exfoliated graphene with various oxygen functional groups bound to its sp2 basal plane. GO is not only a precursor for graphene in large-scale production but provides a fertile platform for applications from electronics to biology owing to its outstanding characteristics. In this review, we introduce the preparation and reduction methods and discuss recent application examples on electrochemistry and biological sensors.

Electrochemical Sensing of Neurotoxic Agents Based on Their Electron Transfer Promotion Effect on an Au Electrode

An electrochemical molecular sensor based on a new principle is reported. Nereistoxin (NRT, 4-N,N-dimethylamino-1,2-dithiolane), a naturally occurring neurotoxin (nicotinic acetylcholine receptor agonist), was adsorbed on an Au electrode via Au-S covalent bonding and accelerated the electron transfer between the electrode and the marker, ferricyanide anion. The contrast between the electrochemical responses obtained with the bare and NRT-modified Au electrodes was more pronounced at a low ionic strength of the supporting electrolyte, KCl. In the presence of 1 mM KCl, almost a 0/1 contrast between the signals was obtained through electrostatic interaction between the protonated tertiary amino group of NRT and the anionic ferricyanide ion. No current was observed with an electrode modified with mercaptopropionic acid. An unusually low ionic strength thickened the electric double layer to the degree where current was not observed with the bare electrode. The effect of the electrostatic concentration of the marker ion becomes obvious under such conditions. Commercially available NRT-related pesticides such as Cartap and Bensultap were also detected using the same format after pretreatments by hydrolysis/reduction. The present sensing method was successfully applied to human serum with satisfactory sensitivity.