Two papers in the September 8 Science are a testament to the speed at which biological chip formats and standards are evolving. Taton et al. expand on their established method for detecting DNA hybridization using gold nanoparticles attached to a probe (Science 2000, 289:1757-1760). The previous system took advantage of a color change induced upon nanoparticle aggregation, but a new method of nanoparticle-promoted reduction of a silver(I) substrate allows for signal amplification and detection using a conventional flatbed scanner. Compared to a standard fluorescence-based system, the nanoparticle probes show over threefold greater selectivity (thanks to a sharper melting profile) and 100-fold greater sensitivity, making this system particularly suited to analysis of single-nucleotide polymorphisms. Protein arrays, meanwhile, are still in the proof-of-concept stage, and that is what MacBeath and Schreiber provide in the same issue of Science (Science 2000, 289:1760-1763). They use a contact-printing robot,...

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