Development of plasmonic thin-layer chromatography for size-selective and optical-property-dependent separation of quantum dots

Nano-objects, such as quantum dots (QDs), are essential units for the construction of functional materials and devices in current technologies. The establishment of a versatile scheme to sort desired components from a crude product is crucial for bringing out the full potential of the original materials. However, it is still challenging to separate QDs with the same composition on the basis of size and to sort QDs with the same size but different optical properties. Here, we demonstrate such sorting for the first time by combining plasmonic optical trapping with thin-layer chromatography (TLC), which is a widely used tool. LED photoexcitation of the localized surface plasmon resonance of Au nanoparticles immobilized on a TLC plate affected the distance QDs traveled depending on the wavelength and intensity of irradiated light, which led to clear separation according to the size and/or optical properties of the QDs. Since optical property-based separation cannot be achieved by conventional chromatography, in which the interactions between stationary phases of chromatographs and QDs are simply based on differences in the size or surface functionality of the QDs, the present strategy will be a key solution for the establishment of a versatile scheme for sorting nano-objects. Optical traps: Capillary action boosts quantum dot sorting Researchers have adapted a classical technique known as thin-layer chromatography (TLC) to improve size- and shape-selective separation of semiconductor nanoparticles known as quantum dots. Chemists typically use TLC to separate molecules by how quickly they travel up silica gel-coated glass plates by capillary action. A Japanese team led by Tsukasa Torimoto from Nagoya University and Yasuyuki Tsuboi at Osaka City University report that TLC plates modified with gold nanoparticles can serve as optical traps. Their experiments showed that the nanoparticles can produce the optical force which halts the migration of quantum dots larger than 8 nanometers up the plate, while smaller dots pass by. Tuning the wavelength and intensity of light used to generate the optical force enabled sorting of quantum dots with similar sizes but distinct shapes and optical properties. Plasmonic thin-layer chromatography was developed for the separation of quantum dots (QDs) by combining plasmonic optical trapping with thin-layer chromatography (TLC). Photoexcitation of the localized surface plasmon resonance of Au nanoparticles immobilized on a TLC plat