Coupling stimuli-responsive magnetic nanoparticles with antibody-antigen detection in immunoassays.

Because current homogeneous immunoassays show some limitations, particularly low sensitivity, we developed a new immunoassay to overcome these limitations. The approach was based on magnetic nanoparticles with a thermoresponsive polymer layer, a negatively charged polymer, and streptavidin-biotin-based antibody-antigen detection and yielded higher sensitivity than commonly used heterogeneous immunoassays. Because no special equipment is needed, it can be applied to currently available absorbance-based systems for high-throughput assays.

DNA detection on a power-free microchip with laminar flow-assisted dendritic amplification.

In this paper, we describe DNA detection experiments using our two original technologies, power-free microchip and laminar flow-assisted dendritic amplification (LFDA), which were previously applied to immunoassays. A microchip was fabricated by combining a poly(dimethylsiloxane) (PDMS) part having microchannel patterns and a glass plate modified with probe DNA. We carried out two kinds of experiments: the detection of 21-base biotinylated target DNA and the detection of single-nucleotide polymorphism (SNP) in 56-base unlabeled target DNA by sandwich hybridization with biotinylated probe DNA.

Detection of non-cross-linking interaction between DNA-modified gold nanoparticles and a DNA-modified flat gold surface using surface plasmon resonance imaging on a microchip.

Gold nanoparticles (GNPs) with fully matched DNA duplexes on their surfaces aggregate together without molecular cross-linking at high salt concentrations. The mechanism of this non-cross-linking (NCL) interaction has been elusive. In this paper, NCL interaction between duplex-modified GNPs and a duplex-modified flat gold surface is presented for the first time.

Surface plasmon resonance imaging on a microchip for detection of DNA-modified gold nanoparticles deposited onto the surface in a non-cross-linking configuration.

Recently we reported that gold nanoparticles (GNPs) with fully matched duplexes on their surfaces are selectively deposited onto walls of poly(dimethylsiloxane) (PDMS) microchannels at high salt concentrations. In this study, the surface plasmon resonance (SPR) imaging technique was applied to monitor this phenomenon for improvement of detection sensitivity and elucidation of the phenomenon. The microchip was fabricated by bonding a surface-patterned PDMS plate and a gold thin film-deposited glass substrate.

Point mutation detection with the sandwich method employing hydrogel nanospheres by the surface plasmon resonance imaging technique.

We propose a surface modification procedure to construct DNA arrays for use in surface plasmon resonance (SPR) imaging studies for the highly sensitive detection of a K-ras point mutation, enhanced with hydrogel nanospheres. A homobifunctional alkane dithiol was adsorbed on Au film to obtain the thiol surface, and ethyleneglycol diglycidylether (EGDE) was reacted to insert the ethyleneglycol moiety, which can suppress nonspecific adsorption during SPR analysis. Then streptavidin (SA) was immobilized on EGDE using tosyl chloride activation.

Flow-stress-induced discrimination of a K-ras point mutation by sandwiched polymer microsphere-enhanced surface plasmon resonance.

The highly sensitive detection of a K-ras point mutation with the aid of DNA-carrying microspheres as a flow-stress receptor is proposed at the surface of a surface plasmon resonance (SPR) biosensor. Single-stranded DNAs were immobilized onto epoxy-group-derivatized gold surfaces and the hybridization of DNA targets was monitored. The subsequent interaction with DNA-carrying micospheres enhanced the SPR response.

Hydrogel-microsphere-enhanced surface plasmon resonance for the detection of a K-ras point mutation employing peptide nucleic acid.

Highly-sensitive detection of a K-ras point mutation in codon 12, frequently found in pancreatic cancer, based on DNA-carrying hydrogel microspheres as a response enhancer for surface plasmon resonance (SPR), is described. Acrylamide-based microspheres with carboxyl groups were conjugated with DNA probes. Use of the DNA-carrying microsphere in the sandwich method, that is, binding of the microspheres with target DNAs at the sensor surface, enhanced the SPR response as a combined result of increased dielectric constant by the DNA-carrying microspheres.