Self-organized patterning through the dynamic segregation of DNA and silica nanoparticles

Abstract

Exotic pattern formation as a result of drying of an aqueous solution containing DNA and silica nanoparticles is reported. The pattern due to segregation was found to critically depend on the relative ratio of nanoparticles and DNA, as revealed by polarization microscopy, scanning electron microscopy, and fluorescence microscopy. The blurred radial pattern that is usually observed in the drying of a colloidal solution was shown to be vividly sharpened in the presence of DNA. Uniquely curved, crescent-shaped micrometer-scale domains are generated in regions that are rich in nanoparticles. The characteristic segregated patterns observed in the present study are interpreted in terms of a large aspect ratio between the persistence length (∼ 50 nm) and the diameter (∼ 2 nm) of double-stranded DNA, and the relatively small silica nanoparticles (radius: 5 nm).

Figure 1. PM images obtained after the complete drying of droplets containing (a) nanoparticles only (7.8% wt.) and (b) nanoparticles (NP) at the same concentration with DNA at 20.8 mg · mL⁻¹ corresponding to a NP/dsDNA ratio of 1∶0.5 (2 nanoparticles per double-strand DNA).

The scale bar is 1 mm.

Figure 2. HR-SEM images of dried drops for a NP/dsDNA ratio of 1∶0.5.

The scaling bar corresponds to (a) 10 μm and (b) 2 μm.

Figure 3. HR-SEM images of dried droplets for NP/dsDNA ratios of (a) 1∶0.25 and (b) 1∶0.167.

The scaling bar is 10 μm and 7 μm respectively.

Figure 4. Fluorescence microscopic observation.

(a) Image obtained by staining DNA with the dye YOYO-I for the NP/dsDNA ratio 1∶0.5. (b) Control sample without DNA at the same dye concentration as in (a). The scaling bar is 10 μm.

Figure 5. HR-SEM observation.

Intersection between a radial crack (wider) and a lateral crack (narrower) for a NP/dsDNA ratio of 1∶0.5. The distribution of segregation domains does not seem to be affected by the cracks, which suggests that they are formed before the latter. The scale bar is 4 μm.

Figure 6. Schematic representation of the kinetic process of segregation between nanoparticles and DNA.

(a) Initially, DNA strands are randomly oriented, but tend to align in a parallel fashion as they are separated from the particles. (b): Schematic of the transition from a round-shaped segregation domain to a crescent-shaped domain. I): initial round shape with relatively disordered DNA molecules. II): intermediate state. III): final crescent shape with aligned DNA molecules.