We experimentally demonstrate thatplasmonic nanoparticles embeddedin the evanescent field of subwavelength optical waveguides (WGs)are highly sensitive to distances normal to the propagation of light,showing an ∼10× increase in spatial resolution comparedto the optical field decay of the WG. The scattering cross-sectionof the Au nanoparticle is increased by the plasmon–dielectriccoupling interaction when the nanoparticle is placed near the dielectricsurface of the WG, and the decay of the scattering signal is enhanced,showing angstrom level distance sensitivity within 10 nm from theWG. Numerical studies with the finite-difference time-domain (FDTD)method correlate well with the experimental results. To demonstratereal-time monitoring of a single molecule stretching in the evanescentfield, we linked individual single-stranded DNA molecules betweenthe WG and plasmonic nanoparticles and pushed on the nanoparticleswith fluidic forces. The simple design and ease of obtaining opticalfeedback on molecular displacements makes our approach ideal for newin situ force sensing devices, imaging technologies, and high-throughputmolecular analysis. [ABSTRACT FROM AUTHOR]