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Multiple microRNAs (miRNAs) are detected in a microarray format using a novel approach that combines a surface enzyme reaction with nanoparticle-amplified SPR imaging (SPRI). The surface reaction of poly(A) polymerase creates poly(A) tails on miRNAs hybridized onto locked nucleic acid (LNA) microarrays. DNA-modified nanoparticles are then adsorbed onto the poly(A) tails and detected with SPRI. This ultrasensitive nanoparticle-amplified SPRI methodology can be used for miRNA profiling at attomole levels. MicroRNAs (miRNAs) are small RNA molecules (19 to 23mers) that can regulate the expression of genes in plants and animals by binding to the 3′-untranslated region of messenger RNAs.1 Several research groups have studied miRNA gene regulation in processes as diverse as cell proliferation, fat metabolism, and cell differentiation.2,3 The recent surge of interest in miRNAs and the related small interfering RNA (siRNA) gene silencing methodology3 has led to an increased need for the ultrasensitive detection and quantitation of small miRNAs in both solution and surface microarray formats.4-