A new approach to ultrasensitive detection of DNA hybridization based on nanoparticle-amplified surface plasmon resonance (SPR) is described. Use of the Au nanoparticle tags leads to a greater than 10-fold increase in angle shift, corresponding to a more than 1000-fold improvement in sensitivity for the target oligonucleotide as compared to the unamplified binding event. This enhanced shift in SPR reflectivity is a combined result of greatly increased surface mass, high dielectric constant of Au particles, and electromagnetic coupling between An nanoparticles and the Au film. DNA melting and digestion experiments further supported the feasibility of this approach in DNA hybridization studies; The extremely large angle shifts observed in particle-amplified SPR make it possible to conduct SPR imaging experiments on DNA arrays.:ln the present work, macroscopic 4 x 4 arrays; were employed, and a similar to 10 pM limit of quantitation. was achieved for 24-mer oligonucleotides (surface density less than or equal to 8 x 10(8) molecules/cm(2)). Even without further optimization, the sensitivity of this technique begins to approach that of traditional fluorescence-based methods for DNA hybridization. These results illustrate the potential of particle-amplified SPR for array-based DNA analysis and ultrasensitive detection of oligonucleotides.