standard Carbon Quantum Dots for dsRNA Delivery

http://medent.usyd.edu.au/photos/aedes_aegypti_larvae.jpg

Aedes aegypti larva. Image credit: Richard C. Russell

Das et al. (2015) in Applied Materials & Interfaces compare chitosan, silica and carbon quantum dot nanoparticles as dsRNA delivery platforms for silencing genes in larval mosquitoes.

Direct injection of dsRNA into the hemocoel of insects has  been somewhat effective for silencing genes in some insects but the half life of dsRNA in hemolymph is probably fairly short and massive amounts of dsRNA are usually injected to deal with its short half life.  It is estimated that the half life of siRNA in serum, for example, is from a few minutes to about an hour.

Feeding insects dsRNA is certainly convenient but this mode of delivery also shows variable efficacy depending on the species of  insect.

Chitosan chemical structural formula.svg

Chemical structure of chitosan. Chitosan is obtained from shrimp and crab shells.

The use of nanoparticles has, in some cases, improved the efficacy of dsRNA gene silencing through feeding.  Chitosan nanoparticles have been used to delivery dsRNA to mosquito larvae through feeding and in this paper Das et al.  explore two other nanoparticles- carbon quantum dots and silica nanoparticles- for delivering dsRNA to mosquito (Aedes aegypti) larvae.

The authors target two genes, SNF7 and SRC, and use GFP as their negative control.

The design of the study is fairly simple.  Make nanoparticles using carbon quantum dots, silica and chitosan; load an equal amount of dsRNA for each of the target and control genes and feed these loaded nanoparticles to mosquito larvae once a day for 3 days and on the fifth day determine transcript levels.  The authors also measured lethality during the course of the experiment.

 

The basic findings showed that carbon quantum dots (CQDs)loaded with dsRNA were most effective in silencing the two target genes used in this study suggesting that CQDs might be a reasonable alternative to chitosan-based nanoparticles.

What are carbon quantum dots and are they difficult to make?

Carbon quantum dots (CQDs, C-dots or CDs), which are generally small carbon nanoparticles (less than 10 nm in size) with various unique properties, have found wide use in more and more fields during the last few years.  quoted in doi: 10.1039/C4TC00988F

carbon quantum dots.jpg

Carbon quantum dots

Das et al. make carbon quantum dots using a simple method involving the use of a microwave oven.  An aqueous mixture of polyethylene glycol and polyethyleneimine was heated in a microwave for a few minutes resulting in functionalized carbon quantum dots.  These were then loaded with dsRNA that had been suspended in sodium sulfate by simply mixing at 4 degrees C.  Easy.

The authors report their CQDs to be on average 3.5nm.

Functionalized CQDs had a positive charge and readily associated with dsRNA.

The authors speculate about why CQDs were more effective than chitosan and silica and think that it is because they were able to retain dsRNA after extended incubation at very basic pH conditions to a much greater extend than chitosan and silica nanoparticles.  The gut of mosquito larvae is variably alkaline and therefore CQDs may have resulted in better bioavailability of dsRNA.  Interesting.  Nonetheless, CQDs seemed to perform better under the conditions tested and might be worth considering for other insect systems.

Take a look at this paper for more of the details.

Das, S., Debnath, N., Cui, Y., Unrine, J., Palli, S. R., 2015  Chitosan, Carbon Quantum Dot, and Silica Nanoparticle Mediated dsRNA Delivery for Gene Silencing in Aedes aegypti: A Comparative Analysis. ACS Appl Mater Interfaces 7:  19530-19535doi: 10.1021/acsami.5b05232.

 

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