AbstractBACKGROUNDThe synthesis and application of novel Au nanostructures are of increasing importance in modern nanotechnology.RESULTSClosely packed and chemically difficult‐to‐synthesize Au nanohorns (AuNHs) were synthesized in the presence of Escherichia coli cells (ECCs) and hexadecyltrimethylammonium chloride (CTAC) by a microorganism‐mediated, CTAC‐directed (MCD) approach. A proper ECC dosage, ascorbic acid (AA) and CTAC concentrations were essential for the growth of the AuNHs. In the formation mechanism of the AuNHs the ECCs surface acted as a platform for preferential nucleation and initial anisotropic growth of Au nanocrystals. As a result, some of the adjacent nanoparticles over the cell surface connected together via linear fusion to form dendritic nanostructures. Meanwhile, secondary nucleation in the solution gave rise to smaller nanoparticles that were consumed later on via Ostwald ripening during the formation of the AuNHs. Eventually, the two‐dimensional film‐like nanostructures between adjacent cells easily connected to form well‐defined AuNHs with three‐dimensional nanostructures. Interestingly, the AuNH/ECC composites can be used directly as sensitive surface‐enhanced Raman spectroscopy (SERS) substrates for effective detection of 4‐mercaptobenzoic acid (MBA).CONCLUSIONThe MCD strategy was an effective approach to novel AuNHs and AuNH/microorganism nanocomposites as SERS substrate. © 2014 Society of Chemical Industry