I am troubleshooting a biosensor with gold nanoparticles with and without various small chain thiol coating molecules. We are trying to assess the efficacy of the coatings, but have primarily been using BSA, which binds very strongly to AuNPs, even with coatings. Following the literature, we are using mixtures of OH- and COO- terminated alkanethiols, and soon will transition to PEG-thiols of the same headgroups.
I'm very interested in finding another protein, ideally similar in size to BSA (66kDA) that has been shown to be less promiscuous in terms of non-specific AuNP binding. I imagine this would be a protein that is less electrostatically charged than BSA, does not have active surface thiols (through cysteine) and has few hydrophobics regions. My current candidates are actin and glutamate hydrogenase (although I think both have surface thiols, not sure how active they are), and protein A; although its generic IgG binding capacity makes it unfavorable for followup antibody-antigen experiments.
BSA is commonly used. Other proteins about that size and widely available would be Avidin (67 kDa), NeutraAvidin (60 kDa), Garden pea (Pisum sativum) agglutinin (PSA, 50 kDa), Ovalbumin (45 kDa), or Horse radish peroxidase (44 kDa)
Dear Adam
I presume you want to irreversibly block all non specific binding sites after you have your interrogating ligand bound to the particles. BSA is not a good one. You can use casein 1-2%. Please note, casein is soluble only at high pH [around 11] and you have to bring down the pH slowly/gradually. All pH adjustments in the case of nano gold will have to be with acids like phosphoric acid . Lots of literature available in this subject
Thanks guys.
Ravi, why is BSA not a good choice for this?
Also, for this task in particular, we aren't too concerned with blocking; rather, want to actually measure the non-specific adsorption. Since BSA is very strongly adsorbing onto our surface, we want a protein of similar mass that is less likely to adsorb non-specifically as a control.
Hm, so right now NeutraAvidin seems like the best front runner! Thanks.
Sorry I misunderstood the question
If you are only interested in binding characteristics, and want to use a control protein, then you should select However, most proteins bind to some extent onto gold nano particles. You may want to test streptokinase [reported not to have any cystein residues]. You may also try other proteins from bactetria or yeast (see attachments). You may already know the way one can test binding capacity of various proteins to nano gold. The most common one is NaCl flocculation test
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