Diamond, because of its electrical and chemical properties, may be a suitable material for integrated sensing and signal processing. But methods to control chemical or biological modifications on diamond surfaces have not been established. Here, we show that nanocrystalline diamond thin-films covalently modified with DNA oligonucleotides provide an extremely stable, highly selective platform in subsequent surface hybridization processes. We used a photochemical modification scheme to chemically modify clean, H-terminated nanocrystalline diamond surfaces grown on silicon substrates, producing a homogeneous layer of amine groups that serve as sites for DNA attachment. After linking DNA to the amine groups, hybridization reactions with fluorescently tagged complementary and non-complementary oligonucleotides showed no detectable non-specific adsorption, with extremely good selectivity between matched and mismatched sequences. Comparison of DNA-modified ultra-nanocrystalline diamond films with other commonly used surfaces for biological modification, such as gold, silicon, glass and glassy carbon, showed that diamond is unique in its ability to achieve very high stability and sensitivity while also being compatible with microelectronics processing technologies. These results suggest that diamond thin-films may be a nearly ideal substrate for integration of microelectronics with biological modification and sensing.

We report a new scheme for attachment of functionalized organic molecules to polycrystalline diamond films. In this scheme, ultraviolet light is used to cause a local reaction between a hydrogen-terminated diamond surface and organic molecules present as a thin overlayer liquid film. Comparison of functionalized alkenes and alkanes shows that alkenes attach more efficiently. By attaching organic molecules with suitable protecting groups and then deprotecting after attachment to the surface, it is possible to prepare diamond surfaces terminated with carboxylic acid groups or with primary amine groups. These functional groups may serve as an attractive starting point for further chemical modification of diamond surfaces.

Preparation and hybridization of DNA-modified polycrystalline diamond substrates with fluorescently labeled complementary and noncomplementary oligonucleotide sequences were investigated. Hydrogen-terminated, free-standing diamond substrates were photochemically modified to produce amine-terminated surfaces. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy were used to characterize the initial attachment of a protected amine and the subsequent deprotection chemistry. Thiol-terminated DNA oligonucleotides were then linked to the amine-terminated diamond surfaces using a heterobifunctional linker. It is shown that hybridization on DNA-modified polycrystalline diamond is specific, with strong binding of perfectly matched 16-mer complements and little or no binding to 16-mers with 4 mismatched nucleotides. A direct comparison of DNA hybridization on DNA-modified diamond and DNA-modified surfaces of crystalline silicon shows that the diamond surfaces exhibit superior chemical stability under the conditions employed to hybridize and denature the DNA-modified surfaces.

Recently developed DNA-modified diamond surfaces exhibit excellent chemical stability to high-temperature incubations in biological buffers. The stability of these surfaces is substantially greater than that of gold or silicon surfaces, using similar surface attachment chemistry. The DNA molecules attached to the diamond surfaces are accessible to enzymes and can be modified in surface enzymatic reactions. An important application of these surfaces is for surface invasive cleavage reactions, in which target DNA strands added to the solution may result in specific cleavage of surface-bound probe oligonucleotides, permitting analysis of single nucleotide polymorphisms (SNPs). Our previous work demonstrated the feasibility of performing such cleavage reactions on planar gold surfaces using PCR-amplified human genomic DNA as target. The sensitivity of detection in this earlier work was substantially limited by a lack of stability of the gold surface employed. In the present work, detection sensitivity is improved by a factor of approximately 100 (100 amole of DNA target compared with 10 fmole in the earlier work) by replacing the DNA-modified gold surface with a more stable DNA-modified diamond surface.

CommunicationsTipping large arrays of micrometer-scale dominos onto their side generates complex 3D topographies and arrays of nanoscale electrodes. These microdominos collapse in parallel when a shearing force is applied uniformly to an array of free-standing pillars. For more information, see the Communication by G. M. Whitesides and coworkers on the following pages.

Nanocrystalline diamond thin films of sub-micron thickness have been covalently modified with DNA oligonucleotides. Quantitative studies of hybridization of surface-bound oligonucleotides with fluorescently tagged complementary and non-complementary oligonucleotides were performed. The results show no detectable nonspecific adsorption, with extremely good selectivity between matched and mismatched sequences. Impedance spectroscopy measurements were made of DNA-modified boron-doped nanocrystalline diamond films. The results show that exposure to non-complementary sequences induce only small changes in impedance, while complementary DNA sequences produce a pronounced decrease in impedance. The combination of high stability, selectivity, and the ability to directly detect DNA hybridization via electrical means suggest that diamond may be an ideal substrate for continuously-monitoring biological sensors.

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Over the past several years, multivariate approaches have been developed that address the problem of disease diagnosis. Here, we report an integrated approach to the problem of prognosis that uses protein microarrays to measure a focused set of molecular markers and non-parametric methods to reveal non-linear relationships among these markers, clinical variables, and patient outcome. As proof-of-concept, we applied our approach to the prediction of early mortality in patients initiating kidney dialysis. We found that molecular markers are not uniformly prognostic, but instead vary in their value depending on a combination of clinical variables. This may explain why reports in this area aiming to identify prognostic markers, without taking into account clinical variables, are either conflicting or show that markers have marginal prognostic value. Just as treatments are now being tailored to specific subsets of patients, our results show that prognosis can also benefit from a 'personalized' approach.