Extraction of Nile red dye from samples with various particle concentrations. Digital camera image of glass capillary filled with silica solution (left). Bright field (center) and fluorescent images of the capillary tube (right). The droplets are not visible in bright field but are clearly shown in the fluorescent image due to extraction of Nile red dye.

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... This range of nanoparticles concentration is similar to the solid contents in sewage sludge (10 mg/kg ∼ 1000 mg/kg). 65 When the particle suspension was loaded into the capillary tube coated with preformed surface nanodroplets, it was difficult to observe the droplets in bright-field microscope images due to scattering of light by the particles (Fig. 3). However, in fluorescent images, the droplets were clearly visible as the model analyte was readily extracted from the suspension into the droplets. The strong fluorescence intensity in the droplets indicates successful extraction of the dye (the target analyte) by the surface nanodroplets even in the presence of solid particles. In ...

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... detection depends on factors such as the partition coefficient and the quantum efficiency of the fluorescent dyes. We compared to another model compound -Rhodamine B, which has a lower partition coefficient as compared to Nile red (lgP ∼ 2.3 vs lgP ∼ 5). 58 With Rhodamine B, the limit of detection was lower (i.e. 10 −9 M) as compared to Nile red (Fig. S3), possibly due to its comparatively higher quantum efficiency. 71 In the same way, the limit of detection for a suspension sample with 12.5 mg/mL of 150 nm silica particles was tested using Nile red as model compound. The initial concentration of Nile red in the silica solutions varied from 10 −6 M to 10 −9 M. Fig. 5d shows fluorescent ...