A High-Sensitivity and Low-Cost Turbidimeter Based on Metal Capillary Cavity

Clean water is important for human health, but commercial turbidimeter with high sensitivity (detection limit < 0.01 NTU) is still lacking. Herein, a high-sensitivity and low-cost turbidimeter based on a metal capillary cavity (MCC), which consists of a metal capillary and two apertured mirrors, was proposed. In order to improve the detection limit, the signal-to-noise ratio (SNR) needs to be improved by optimizing the aperture size of MCC, since there is a trade-off between optical path and light intensity received by the detector, e.g., a smaller aperture can increase optical path, but it would reduce light intensity received by the detector. The optimal aperture radius of 0.15 mm was obtained by experiments. The turbidimeter was used to measure formazine turbidity solution, and a detection limit of 0.001 NTU was realized, which is more than 3.6-fold lower than that of previous reports and commercial turbidimeters. The turbidimeter features a compact structure, high sensitivity, and low cost.