To coat the gold nanoparticles with DNA, take 400 microliters of commercially obtained gold nanoparticle solution and centrifuge it at 3, 500G at room temperature for five minutes. Using a pipette, remove the supernatant and resolubilize the pellet in 25 microliters of UltraPure water. Next, add four microliters of commercially obtained 100 micromolar thiol modified DNA.
Add one microliter of 100 millimolar TCEP solution. Incubate the mixture for 10 minutes at room temperature. Following incubation, add five microliters of the mixture to the previously concentrated gold nanoparticle solution.
Vortex the resulting mixture for five seconds and freeze for at least two hours at minus 20 degrees Celsius. After thawing the frozen mixture at room temperature, centrifuge the same at 3, 500G for five minutes at room temperature to remove excess added DNA coating. Using a pipette, remove the supernatant and resolubilize the pellet in 10 microliters of water.
The changing color of the solution at each step indicated proper coating of the gold nanoparticle. The deep red color of the gold nanoparticles changed to dark purplish red as soon as the DNA was added. Freezing changed the color to purple, and thawing returned it to deep red.
The absorbance spectra of the 60 nanometer DNA coated gold nanoparticles showed a shift in absorbance peak compared to that of the bare gold nanoparticles.
