Fig. 4
An MDC for droplet dilution and SERS detection. a A 10-fold droplet dilution MDC assembled by 15 modules, including 1:4 droplets splitting modules (No.1 and No.4), 1:1 droplets splitting modules (No.9 and No.12), moving-track control modules (No.6 and No.14), droplets merging modules (No.3 and No.11), oscillatory shaking modules (No.7 and No.8), droplets collector (No.2, No.5, No.10, No.13 and No.15). The red dotted lines are the tracks of R6G droplet. The white dotted lines are the tracks of water droplets. b The video screenshots of 10-fold dilution process of 44.0 L 10− 1 mol/L R6G droplet, which is gradually fading, indicating it is diluted. Detail explanations are shown in Supplementary. c Accuracy analysis of 10-, 102-, 103-fold dilution of 10− 1 mol/L R6G droplets. The inserted error bars represent the concentration deviations among ten droplets at each dilution fold. d SERS spectra of R6G droplets at four different concentrations that are diluted from 10− 5 mol/L R6G droplets. Before SERS detections, R6G molecular are enriched on MDC by hydrophobic enrichment effect. The inserted images are 44.0 L R6G droplets before and after enrichment