A microfabricated analysis chip with integrated waveguides for evanescent field absorption detection is provided. Fabrication of the microfluidic device may be performed by micropatterning a layer of photoresist or other suitable material using a single step photoresist process to produce a microchannel and an optical structure (e.g., a U-bend waveguide) in the microfluidic device. The microfluidic device couples a micro-channel network with a waveguide in a collinear fashion to maintain higher path length and incurring little or no scattering, dispersion, and divergence losses. A sample can be passed through the microchannel while light is transmitted through the waveguide. Any change in refractive index as well as change in optical absorbance property of fluid flowing in the microchannel can be detected by detecting changes in light output power (e.g., changes in absorbance). A change in concentration of solution in the microchannel can be determined by detecting a change in light absorbance output.