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We gratefully acknowledge partial support by the OfÞce of Naval Research (I.G.K.

and H.H.R.), NSF, Air Force OfÞce of ScientiÞc Research, and the Humboldt Foundation (I.G.K.), and by a Marie Curie Fellowship (A.G.P.) under contract HPMFCT-2000-00685.

We thank M.

Pollmann for the measurement of Fig.

1C and S.

Shvartsman for many discussions. 19 June 2001; accepted 28 August 2001 Submicrometer Metallic Barcodes Sheila R.

Nicewarner-Pen ÷a, 1R.

GrifÞth Freeman, 2 Brian D.

Reiss, 1Lin He, 2David J.

Pen÷a, 1Ian D.

Walton, 2 Remy Cromer, 2Christine D.

Keating, 1* Michael J.

Natan 2* We synthesized multimetal microrods intrinsically encoded with submicrome- ter stripes.

Complex striping patterns are readily prepared by sequential elec- trochemical deposition of metal ions into templates with uniformly sized pores. The differential reßectivity of adjacent stripes enables identiÞcation of the striping patterns by conventional light microscopy.

This readout mechanism does not interfere with the use of ßuorescence for detection of analytes bound to particles by afÞnity capture, as demonstrated by DNA and protein bioassays. Multiplexing and miniaturization are becom- ing pervasive themes in bioanalysis.

The push to measure ever-increasing numbers of species from smaller and smaller sample vol- umes has led to innovative devices for sample manipulation [e.g., chip-based microfluidics (1)] and ingenious approaches to simulta- neous measurement capabilities (e.g., mi- Fig.

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