ABH-Glycan Microarray Characterizes ABO Subtype Antibodies: Fine Specificity of Immune Tolerance After ABO-Incompatible Transplantation.

Organ transplantation from ABO blood group-incompatible (ABOi) donors requires accurate detection, effective removal and subsequent surveillance of antidonor antibodies. Because ABH antigen subtypes are expressed differently in various cells and organs, measurement of antibodies specific for the antigen subtypes in the graft is essential. Erythrocyte agglutination, the century-old assay used clinically, does not discriminate subtype-specific ABO antibodies and provides limited information on antibody isotypes. We designed and created an ABO-glycan microarray and demonstrated the precise assessment of both the presence and, importantly, the absence of donor-specific antibodies in an international study of pediatric heart transplant patients. Specific IgM, IgG, and IgA isotype antibodies to nonself ABH subtypes were detected in control participants and recipients of ABO-compatible transplants. Conversely, in children who received ABOi transplants, antibodies specific for A subtype II and/or B subtype II antigens-the only ABH antigen subtypes expressed in heart tissue-were absent, demonstrating the fine specificity of B cell tolerance to donor/graft blood group antigens. In contrast to the hemagglutination assay, the ABO-glycan microarray allows detailed characterization of donor-specific antibodies necessary for effective transplant management, representing a major step forward in precise ABO antibody detection.

Specific detection of proteins using photonic crystal waveguides.

Specific detection of proteins is demonstrated using planar photonic crystal waveguides. Using immobilized biotin as probe, streptavidin was captured, causing the waveguide mode cut-off to red-shift. The device was shown to detect a 2.5 nm streptavidin film with a 0.86 nm cut-off red-shift. An improved photonic crystal waveguide sensor design is also described and shown to have a 40% improved bulk refractive index response.

Exciton-mediated hydrosilylation on photoluminescent nanocrystalline silicon.

A novel white light-promoted reaction using photoluminescent nanocrystalline silicon enables the hydrosilylation of alkenes and alkynes, providing stabilization of the porous silicon without significant loss of the photoemissive qualities of the material. Photopatterning and lithographic fabrication of isolated porous silicon structures are made possible. Experiments and observations are presented which indicate that the light promoted hydrosilylation reaction is unique to photoluminescent silicon, and does not function on nonemissive material. Hydrosilylation using a reactive center generated from a surface-localized exciton is proposed based upon experimental evidence, explaining the photoluminescence requirement. Indirect excitons formed by light absorption mediate the formation of localized electrophilic surface states which are attacked by incoming alkene or alkyne nucleophiles. Supra-band gap charge carriers have sufficient energy to react with nucleophilic alkenes and alkynes, thereupon causing Si-C bond formation, an irreversible event. The light-promoted hydrosilylation reaction is quenched by reagents that quench the light emission from porous silicon, via both charge transfer and energy transfer pathways.

Positive and negative photopatterning of metal oxides on silicon via bipolar electrochemical deposition.

Negative and positive microscale patterning of metal oxides is efficiently and rapidly carried out on flat Si(100) surfaces via a simple white light assisted bipolar electrochemical process.

Desorption-ionization mass spectrometry on porous silicon.

Desorption mass spectrometry has undergone significant improvements since the original experiments were performed more than 90 years ago. The most dramatic change occurred in the early 1980s with the introduction of an organic matrix to transfer energy to the analyte. This reduces ion fragmentation but also introduces background ions from the matrix. Here we describe a matrix-free strategy for biomolecular mass spectrometry based on pulsed-laser desorption-ionization from a porous silicon surface. Our method uses porous silicon to trap analytes deposited on the surface, and laser irradiation to vaporize and ionize them. We show that the method works at femtomole and attomole levels of analyte, and induces little or no fragmentation, in contrast to what is typically observed with other such approaches. The ability to perform these measurements without a matrix also makes it more amenable to small-molecule analysis. Chemical and structural modification of the porous silicon has enabled optimization of the ionization characteristics of the surface. Our technique offers good sensitivity as well as compatibility with silicon-based microfluidics and microchip technologies.