Hi Tasneem, you could try Proteinase K am/or trypsin tp clean off the biosensor.

Removing Thiol ligands from Au surfaces is quite difficult without using another thiol based agent -> which would render the AuNP useless for further binding studies.

So my elaborate guess would be: use something like a diamine in high concentration and see if it works (ethylendiamine is the weapon of choice id say in this case).