Rapid, highly sensitive troponin assays for the analysis of serum at the point-of-care are particularly desirable for the effective treatment of myocardial infarction (MYI). TiO(2) nanotube arrays constitute a low cost, high surface area, semiconducting architecture with great promise for biosensing applications due to their compatibility with multiple detection techniques. Using TiO(2) nanotube arrays functionalized with highly robust and ordered carboxyalkylphosphonic acid self-assembled monolayers, we have developed a simple and highly sensitive fluorescence immunoassay which can detect concentrations of human cardiac troponin I as low as 0.1 pg ml(-1) without the use of enzymatic amplification. Varying the morphological parameters of the nanotube arrays allows tuning the detection range over 6 orders of magnitude of the troponin concentration from 0.1 pg ml(-1)-100 ng ml(-1).