Microdevices dedicated to monitor metabolite levels have recently enabled many applications in the field of cell analysis, to monitor cell growth and development of numerous cell lines. By combining the traditional technology used for electrochemical biosensors with nanoscale materials, it is possible to develop miniaturized metabolite biosensors with unique properties of sensitivity and detection limit. In particular, enzymes tend to adsorb onto carbon nanotubes and their optical or electrical activity can perturb the electronic properties. In the present work we propose multi-walled carbon nanotube-based biosensors to monitor a cell line highly sensitive to metabolic alterations, in order to evaluate lactate production and glucose uptake during different cell states. We achieve sensors for both lactate and glucose, with sensitivities of 40.1 mu A mM(-1) cm(-2) and 27.7 mu A mM(-1) cm(-2), and detection limits of 28 mu M and 73 mu M, respectively. This nano-biosensing technology is used to provide new information on cell line metabolism during proliferation and differentiation, which are unprecedented in cell biology. (C) 2011 Elsevier B.V. All rights reserved.