Design and development of lab-on-a-centrifuge based on liquid-core waveguide enhancement technology for colorimetric...

Rapid and sensitive detection of Cr(VI) in soil is crucial for environmental monitoring and human health risk assessment. Portable, highly integrated detection devices have widely demand for on-site Cr(VI) analysis. In this work, a highly sensitive detection system based on a centrifugal liquid-core waveguide (LCW) was successfully designed. Driven by centrifugal force, the system achieved the entire process automation, including filtration of soil Cr(VI) extracts, sample introduction, colorimetric reaction, signal detection, and waste liquid discharge. A Teflon AF 2400 LCW was used as the long optical path sample cell to increase sensitivity, while centrifugal force was used to remove air bubbles from the detection fluid path, significantly enhancing detection stability for 6.75 times. A π-shaped detection liquid structure was designed to avoid the use of pumps and valves, minimizing dead volume. Innovatively, a rotation maximum detection method was used to reduce measurement errors with continuous operation. After optimizing the operating conditions, the detection of a single sample could be completed in 10 min (excluding extraction time). The system achieved a limit of detection (LOD) of 3 μg/L for water Cr(VI) and a linear range from 10 to 150 μg/L (R² = 0.9987). The theoretical LOD of soil Cr(VI) is 0.3 mg/kg. The reliability and practicality of the system were confirmed through the accurate analysis of certified reference materials and real soil samples. This work provides a precise solution for the on-site, rapid, and highly sensitive quantification of Cr(VI) in soil.