As with any reagent, it’s important to know what you’re dealing with. The size of the gold nanoparticles at the centre of a SmartFlare will dictate the number of oligonucleotides that can be bound to the surface. Likewise, if the GNPs are aggregated, that will affect the way they interact with cells. In order to visualise the SmartFlares, lab member Joan Comenge took a sample of the uptake control to the Transmission Electron Microscope (TEM).
10 μl droplets of the sample were drop casted onto a formvar/carbon filmed 200-mesh copper grid (ordered from TAAB) and left to dry in air. Gold nanoparticles were visualized using a Tecnai G3 spirit TEM at 120 KeV.
From the fields imaged (totalling 251 discrete particles), it’s possible to geometrically characterise the particles.
The Major and Minor Axis of a fitted ellipse tell you both about the aspect ratio of the particles but also serve as an estimate of particle diameter.
The Circularity is calculated as (4π*area)/(perimeter2) where a perfect circle will have a value of one and values less than this describe a more elongated shape.
Authors: Dave Mason & Joan Comenge