It doesn't adsorb by itself? You could try modifying some side groups with -S or -N, those might help binding the gold

The OH groups can be esterified with some small molecule containing an amino or sulfur side group. Or would that interfere with further preparation steps?

Please elaborate the process, or may be you can give some reference articles to modify OH group of dextran. Thanks for the suggestions....

This is from the top of my head so I'm not sure it will work, but you might try doing an esterfication with a simple amino acid (glycine?). The abundant OH groups on the dextran will be available for the acid group to bind, the NH group on the other end will be available to bind to the gold. The ester bond is not that strong in water, but since you have a lot of OHs available the numbers should work in your favor I guess.

At least that is the simplest method I can think of. You can make much more permanent bonds through organic chemistry, but you will need the materials and expertise for that.

I currently don't have access to literature, so I'm afraid I can't give you any references.

Thank you very much for your response.