# Label-Free Microdroplet Concentration Detector Based on a Quadruple Resonant Ring Metamaterial

## TL;DR

A new label-free detector uses a metamaterial to measure concentration changes in microdroplets with high precision and speed.

## Contribution

The novel contribution is a quad-resonator metamaterial-based detector that enables label-free, high-sensitivity concentration detection.

## Key findings

- The device achieves a sensitivity of 28.53 GHz/RIU with a linear relationship between resonance frequency shift and concentration.
- The relative deviation between simulation and measurement is less than 3%, confirming model reliability.
- The detector is reusable for over 50 cycles and suitable for high-throughput detection with single measurements under 30 seconds.

## Abstract

This paper proposes and experimentally validates a label-free microdroplet concentration detector based on a quad-resonator metamaterial. The device exploits the linear relationship between the dielectric constant of a binary mixed solution and its concentration, mapping concentration information to absorption frequency shifts with a sensitivity of 28.53 GHz/RIU. System modeling was performed through full-wave simulation. Experimental results demonstrate a highly linear relationship between resonance frequency shift and concentration across ethanol, water, and ethanol–water solutions. The relative deviation between simulation and measurement is less than 3%, validating the model’s reliability and the robustness of the detection principle. This detector supports rapid non-contact sample replacement without requiring chemical labeling or specialized packaging. It can be mass-produced on standard PDMS substrates, with each unit reusable for >50 cycles. With a single measurement time of <30 s, it meets high-throughput detection demands. Featuring low power consumption, high precision, and scalability, this device holds broad application prospects in point-of-care diagnostics, online process monitoring, and resource-constrained scenarios. Future work will focus on achieving simultaneous multi-component detection via multi-resonator arrays and integrating chip-level wireless readout modules to further enhance portability and system integration.