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In this paper, gold nanorods' (GNRs) interaction with different proteins (i.e. carbonic anhydrase, lysozyme, ovalbumin and bovine serum albumin (BSA)) at physiological pH is investigated using localized surface plasmon resonance (LSPR) spectroscopy. We observe that the incubation of these proteins at different concentrations with cetyltrimethylammonium bromide-capped GNRs of three aspect ratios induces dramatic changes in the extinction spectra of the nanoparticles. In particular, we correlate the position and shape of the longitudinal LSPR peaks to the ability of the proteins to specifically interact with GNRs' surface. The different types of behaviour observed are explained by the exposed molecular surface area of the proteins' cysteine residues as modelled on the basis of their respective X-ray crystallographic data structures. Cysteine is the only amino acid that exhibits an SH group that is well known to have a strong affinity to gold. The presence and the accessibility of such a residue may explain the protein binding to GNRs. The isoelectric point of the proteins is also an important characteristic to take into account, as the electrostatic strength between GNRs and protein explains some of the cases where aggregates are formed. Keywords Proteins. LSPR. Gold nanorods (GNRs). isoelectric point. Solvant accessible area, Introduction During the last decades when nanosciences have made their revolution, gold nanoparticles (GNPs) have attracted particular interests for many reasons. Among them, two have drawn our attention in the [...]