Organic
nanosheets peeled from porous polymer show potential as imaging and transport
agents in biological applications
Two-dimensional (2D) nanomaterials known as
nanosheets have attracted a great deal of attention in recent years because of
their large surface-to-volume ratio and unconventional properties. Graphene,
for example, has found use in a wide range of applications in electronics as it
displays both insulating and semiconducting properties.
Scientists have developed a variety of techniques
for making nanosheets, but the fabrication of freestanding organic nanosheets
remains a challenge. The current technology could either build small 2D
fragments from small molecular units in solution or confine molecules or
fragments in 2D geometries. Sometimes the 2D fragments might even aggregate
into three-dimensional (3D) frameworks.
Yugen Zhang, Jackie Ying and co-workers at the
A*STAR Institute of Bioengineering and Nanotechnology have now discovered an
easy way of making organic nanosheets — by peeling layers off a porous
polymer1. They used a porous polyisocyanurate, which contains many highly
reactive, terminal isocyanate groups within its outer layers. These terminal
groups can react with amine-functionalised small molecules under relatively
mild conditions to give nanosheets that are subsequently isolated by
filtration.
“Conventional methods for making organic nanosheets
involve the deposition of thin layers of materials onto a solid support,” says
Zhang. “Our method does not require the use of a support and is the first of
its kind for making organic nanosheets.”
A range of amine-containing molecules can be used to
make differently functionalised nanosheets — for example, aminopropanol and
D-glucosamine. The latter creates blue fluorescent nanosheets that show good
water solubility. The thickness of the amorphous nanosheets is around three
nanometres, and the longer the reaction time, the thinner the sheets and the
smaller the dimensions of the sheets. The researchers have obtained nanosheets
with thicknesses ranging from 40 to 150 nanometres.
The researchers tested how the fluorescent
nanosheets perform as bioimaging materials. They found that the nanosheets had
very low cytotoxicity and remained stable in water for up to four months. In
addition, the fluorescent nanosheets gave off a blue light after they entered
the cytoplasm of biological cells. Furthermore, the nanosheets could act as carriers
for delivering hydrophobic molecules, such as the dye molecule known as 'Nile
red', into the cytoplasm of cells.
In the future, the researchers aim to make various
nanostructured materials using this method and study the materials’ properties.
“The nanosheets could also potentially be used in sensing and conducting
materials,” says Zhang.
The A*STAR-affiliated researchers contributing to
this research are from the Institute
of Bioengineering and Nanotechnology
References
- Zhang, Y. et al. Mesoscopic organic nanosheets peeled
from stacked 2D covalent frameworks. Chemical Communications 47,
7365–7367 (2011). | article
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