Recent developments in polynorepinephrine: an innovative material for bioinspired coatings and colloids.

While applications of polydopamine (PDA) are exponentially growing, research concerning the closely related neurotransmitter derivative polynorepinephrine (PNE) is in paucity, even though norepinephrine shares dopamine's ability to self-polymerize and form a coating film that is nearly substrate-agnostic. In this review, we demonstrate that PNE can be used as an alternative to PDA with equal or ever superior performance. PNE offers a thinner and smoother coating surface and thus is capable of more effectively resisting fouling by biofoulants, enhancing cell adhesion capability, surface hydrophilicity and biomolecule immobilisation. With the abundance of catechol, amino and hydroxyl groups in PNE's structure, PNE can perform as an electron donor and receiver at the same time and initiate ring opening and redox reactions. It has also been shown that PNE has the potential to be used as a biosensor due to its bioconjugation and molecular recognition ability. Here, we summarise the applications of PNE to date and discuss its potential research directions in the near future.