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

Abstract

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 100μM to 1.5mM. 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.