It depends on the end group of your peptide.If it has Cysteine , you can use  reducing agent like DTT to attach the peptide to the gold surface. If your peptide is amine terminated, you can use EDC/NHS

Dear Chandrasekaran,

Thanks very much. Your answer is quite relevant to my problem. Just in case, what could be the alternative if both the conditions you mentioned are not met by the peptide? 

What is the functional group of your peptide? And what is on the surface of your gold? Usually gold NPs will be coated with surfactants like Citrate, CTAB etc when chemically synthesized. As you have used green chemistry, you need to find out what is surrounding the gold. 

Dear Chandrasekaran,

Thanks very much for the reply. The sequence of my peptide is THRPPMWSPVWP. Perhaps proline would be important for binding with gold particles? As for the coating on gold particles, we have used the fractions containing alkaloids so they would be the ones surrounding the gold surface. 

Thats right. The end group of peptide is the key in conjugation. The best and easiest way is to either amine terminate or thiol terminate your peptide. Now that Proline has NH group, you have to check if it can react with alkaloids. Otherwise you  have to replace the alkaloids with other stabilizers that can react with Proline. 

Thank you very much for the guidance. Your reply is quite helpful and eliminated my confusion. Best regards.

You are most welcome. Good luck with your research!