Stereoselective detection of amino acids with protein-modified single asymmetric nanopores

We demonstrate here facile approach to immobilize bovine serum albumin (BSA) protein molecules on the surface and inner walls of single asymmetric nanopores through mussel-inspired chemistry. Firstly, dopamine (DA) is allowed to self-polymerize under alkaline conditions, leading to the deposition of a thin and surface-adhered polydopamine (PDA) film on to the pore surface. Then, the BSA immobilization on PDA-coated pore surface is achieved via exploiting the amine groups on protein molecules and o-benzoquinone moieties through Michael addition reaction. The success of the chemical functionalization reactions is monitored through the changes in the corresponding current-voltage (I-V) curve. The immobilized BSA molecules serve as chiral receptor on the pore surface and have the ability to selectively bind l-enantiomer of tryptophan (l-Trp) amino acid. The specific BSA-tryptophan interactions inside the confined geometries lead to measurable changes in the electronic readout resulting from the modulation of ion current passing through the nanopore. The method permits l-Trp concentration detection in the range 100 μM to 1.5 mM. On the contrary, we did not notice any significant change in ion flux when the BSA-modified pore is exposed to phenylalanine (d-/l-Phe), d-tyrosine and d-tryptophan amino acids, separately. In this context, we believe that such nanoporous system can be extended for the detection and recognition of a variety of pharmaceutical molecules based on specific protein-drug interactions.

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