Dear friend Goh Dirong

The pretreatment of thiolated ssDNA aptamers before immobilization on gold or silver nanoparticles can have a significant impact on the immobilization efficiency and stability of the resulting conjugates. Here are some points to consider:

1. Disulfide reduction: Thiol-modified oligos are typically supplied in the oxidized disulfide form, and reducing the disulfide bonds to thiol groups is often necessary before immobilization. This can be achieved using reducing agents such as tris(2-carboxyethyl)phosphine (TCEP) or dithiothreitol (DTT). The reduction step helps convert the disulfide-linked oligos into free thiol groups, which are more reactive for conjugation with gold or silver nanoparticles.

2. Immobilization efficiency: Pretreating the thiolated ssDNA aptamers by reducing the disulfide bonds to thiol groups can enhance the immobilization efficiency on gold or silver nanoparticles. The presence of free thiol groups allows for stronger and more stable binding to the nanoparticle surface, promoting efficient conjugation.

3. Stability and functionality: The pretreatment step can also improve the stability and functionality of the immobilized aptamers. Thiol groups provide a more robust and reliable attachment to the metal nanoparticle surface, reducing the risk of detachment or degradation over time. This ensures the long-term stability and functionality of the aptamer-nanoparticle conjugates.

While it is generally recommended to pretreat the thiolated ssDNA aptamers before immobilization, it is important to note that the necessity and effectiveness of this step can vary depending on the specific experimental conditions and the nature of the thiolated oligos. Different immobilization strategies or nanoparticle surfaces may have different requirements.