In this paper, non-contact microplastic concentration monitoring is enabled using a sensitivity-enhanced planar microwave sensor. The sensing platform is a tag-reader structure that consists of a dual-resonator tag and a passive microwave reader. The dual-tag structure is combined with a silicon reservoir as a sample container and is energized through the electromagnetic (EM) coupling with the reader. The extremely sensitive area of the tag resonators is exposed to the sample under the test; it creates an exceptional microplastic deposition monitoring with the concentration of the microplastic in the liquid under the test as low as 400K particles/L. The sensor monitors the deposition of microplastic particles in the mixed liquid in a real-time manner and reflects it as the frequency resonance variation in the transmission response.