We demonstrate a highly sensitive approach for concentration measurements by Michelson interferometry with twisted helical light beams. When superimposing two helical light beams with opposing topological charge, a characteristic daisy flower interference pattern is generated which rotates when a phase shift is introduced in one of the interferometer arms. By analyzing the change in the interference pattern caused by a microfluidic sample, we can determine the refractive index and therefore the concentration of aqueous samples such as glucose and NaCl minimally invasive and label-free with a sensitivity on the order of 10e-6 refractive index units.
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