Aluminum nanocrystals have emerged as an earth-abundant material for plasmonics applications. Al nanocrystals readily oxidize in aqueous-based solutions, however, transforming into highly stratified γ-AlOOH nanoparticles with a 700% increase in surface area in a matter of minutes. Here we show that by functionalizing Al nanocrystals with the bioinspired polymer polydopamine, their stability in aqueous media is dramatically increased, maintaining their integrity in aqueous solution for over 2 weeks with no discernible structural changes. Polydopamine functionalization also provides a molecular capture layer that enables the capture of polycyclic aromatic hydrocarbon pollutants in H2O samples and their detection by surface-enhanced Raman spectroscopy, when polydopamine-stabilized Al nanocrystal aggregates are used as substrates. This approach was used to detect a prime carcinogenic H2O pollutant, benzo[a]pyrene with a sensitivity in the sub part-per-billion range.