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The interaction of light propagating in the wave-guiding structures with the surrounding media through its evanescent field has been used to detect biochemical activities without labeling the target molecules. By introducing multiple slots in a dielectric waveguide, we found that a much stronger evanescent field could be achieved in the surrounding media while still maintaining good optical confinement. The experimental demonstration of microring resonator sensors using single-mode waveguides having three slots indicates a 5-fold increase in sensitivity for homogeneous sensing and more than 3-fold increase in sensitivity for surface sensing in comparison to those of a waveguide without slots. Numerical simulations suggest an even higher sensitivity enhancement (as high as 100 times) as more slots and larger waveguide widths are used.