I am trying to develop electrochemical biosensor using screen printed electrode. The sensor gives good response in blank solutions. However, in presence of proteins, such as albumin, the signal completely disappears. I want to understand if there is a way to prevent protein adsorption, which I believe is distorting the signal.
Adding a protective layer such as polyurethane sometimes helps maintain signal in enzymatic biosensors. Signal definitely does drop in the presence of protein, but it shouldn't disappear. Are you using albumin as a matrix for your enzyme?
The proteins are in body fluid such as serum. I am not using any enzyme in the system. I have attempted to cover the electrode with a simple Whatman filter to prevent albumin from reaching the electrode surface. However, it did not bring any difference.
Dear Pallavi Dasgupta
By changing the pH and creating an electrostatic repulsion,( depending on used modifier) proteins can be far away from the electrode surface. Moreover, the solubility of protein depends on, among other things, the pH of the solution. Similar to the amino acids that comprise protein, protein itself can be either positively or negatively charged overall due to the terminal amine -NH2 and carboxyl (-COOH) groups and the groups on the side chain. It is positively charged at low pH and negatively charged at high pH. The intermediate pH at which a protein molecule has a net charge of zero is called the isoelectric point of that protein. In general, the net charge on the protein, either positive or negative, can interact with water molecules, meaning that it is more likely for a protein molecule to dissociate itself from other protein molecules, thus, more soluble. As a result, protein is the least soluble when the pH of the solution is at its isoelectric point.
Thank you sir for your valuable input. But can you guide me regarding what modifiers can be used to induce electrostatic repulsion? Or should I change the potential that I use on the electrode for carrying out the analysis. At present, I keep potential in the range of 0.5V to -1.5V
By mixing your modifier with charged polymers (such as Nafion and chitosan) you can increase the chances of electrostatic repulsion. Nafion is negatively charged polymer (sulfonate); it will electrostatically repel other anions or negatively charged species , like ascorbate, urate. Moreover,chitosan is a positively charged biopolymer that can be used for your work.
Hi,
As commented before, a protective layer, a membrane could be appropriate. In this case, the thickness of the layer is important in order to allow the diffusion of the analyte to get the electrode surface. In order to avoid leaking of enzymes (also proteins) from a modified electrode (just the opposite of your case) we have employed Nafion, but is also an ion exchanger and this should be considered.
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