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In this work, we report the design, fabrication and characterization of novel biochemical sensors consisting of nanoscale grooves and slits milled in a metal film to form planar plasmonic interferometry. By integrating thousands of plasmonic interferometers per square millimeter with a microfluidic system, we demonstrate a sensor able to detect physiological concentrations of glucose in water over a broad wavelength range (400–800 nm). A wavelength sensitivity between 370–630 nm/RIU (RIU, Refractive Index Units), a relative intensity change between ∼103–106 %/RIU, and a resolution of ∼3×10−7 in refractive index change were experimentally measured using typical sensing volumes as low as 20 femtoliters. These results show that multispectral plasmonic interferometry is a promising approach for the development of high-throughput, real-time and extremely compact biochemical sensors.