Development of Liquid Handling Technology for Single Blood Drop Analysis

The precise dispensing of droplets is a crucial step for acquiring reliable diagnostic results. When a source sample volume is limited, the need for precise dispensing of submicroliter and nanoliter quantities is especially important. In this study, we developed a positive-displacement high-precision dispensing technique using a nickel electroformed tube with an inner diameter accuracy of ±0.7 μm. The dispensing variation of 0.1 μL was evaluated using a photometric method. To reduce liquid retention on the edge of the electroformed tube, the outside surfaces of the tube were hydrophobically treated with self-assembled monolayers on a gold surface. Regarding the results, the most stable coefficients of variation (CV) was 0.70 %, i.e. 0.70 nL. Furthermore, the glucose and cholesterol concentrations in 0.2 μL of animal-based control serum were colorimetrically measured with enzymatic reactions. The CV value of the analysis was approximately 2.38 % and 1.45 %, respectively, suggesting that several biochemical panels can be precisely measured even from one drop of whole blood (∼10 μL). The present positive-displacement dispenser ensures zero contamination and an almost-zero dead volume, and therefore would be useful for multi-panel clinical blood diagnosis.