Hi,

I am doing aptamer based electrochemical biosensor.

First, I cleaned screen printed gold electrode using 0.5M H2SO4. Then, immobilized aptamer followed by blocking using 2mM MCH. I use redox solution (potassium ferro ferric solution).

Problem:

For detection, I use 1X PBS (as control), target protein and non-target proteins.

The measured current for all (control, target and non-target protein) are same. From the blocking (MCH) to detection, the current changes is ~30-40uA.

Even though, the current drop more but cannot differentiate control to target protein.

Questions

1. Should I considered protein did not bind to aptamer/ligand? However, previously when I run ELISA there is signal.

2. Is this due to inadequate of washing? I just flow through 1ml of deionized water above the working electrode (not directly on top of working electrode).

3. Is this due to inadequate blocking?

4. Or any other possible reasons?