A One-Drop Quantitative Concentration Pipette Using Micro- to Centimeter-Scale Fluidics.

The analytical process is typically divided into three stages: pretreatment, assay, and detection. In the assay and detection stages, some analytical platforms require very small sample volumes. Small sample volumes can increase reaction rates. However, reducing the sample volume to a single drop (10 μL) while maintaining the integrity and recovery of the target analyte remains a significant challenge in microanalysis. Common sample pretreatment methods include concentration, liquid exchange, and filtration, but they are prone to sample loss. Liquid-liquid conversion methods, such as heating evaporation, can easily lead to complete evaporation of trace samples, making it difficult to capture the target droplet. Cyclone evaporation can only be performed in large spaces, making it difficult to operate in ordinary microfluidic channels. To address these issues, this study constructs a multiscale fluidic device, with each scale corresponding to a different function: a centimeter-scale space for cyclone concentration and speed control; a millimeter-scale channel for stopping the cyclone concentration process and keeping a single drop of liquid; and a micrometer-scale orifice for ejecting the concentrated sample solution. Based on this, this study designed and developed a novel concentration pipette that integrates concentration and sample ejection functions. This concentration pipette can concentrate 1.0 mL of liquid sample to 10 μL within 1.5 h at temperatures below 30 °C, making it suitable for biological samples. Experimental results demonstrate that this concentration pipette can achieve nearly 100-fold concentration while maintaining a recovery rate of over 95%, effectively addressing the challenge of sample ejection. It offers an economical, efficient, and user-friendly solution for detecting small-volume samples. The concentration pipette can be applied to large molecules (BSA), small molecules (Sunset Yellow), and atoms (Pb2+).