Highly aligned multi-wall carbon nanotube arrays up to 4 mm tall were synthesized on Si wafers using a chemical vapor deposition process with water delivery. Based on the long nanotube arrays, several prototype smart materials were developed including a biosensor, electrochemical actuator, and nanotube probes. The biosensor was formed by casting epoxy into a nanotube array and polishing the ends of the nanotubes. This electrode produced a near ideal sigmoidal cyclic voltammogram. Nanotube electrodes were then used to form a label-free immunosensor based on electrochemical impedance spectroscopy. The nanotube array immunosensor has good sensitivity, but decreasing the array size and improving the biofunctionalization is expected to dramatically increase the reproducibility and sensitivity. The electrochemical actuator was formed by bonding an electrode to a 1mm square by 4 mm long as-grown nanotube array post. The nanotube array actuator operated up to 10 Hz in a 2 M NaCl solution. With a driving voltage of 2 volts, the actuator produced 0.15% strain. Finally, nanotube bundles are being welded to tungsten tips and put inside glass needles for use as probes for biosensors and electrophysiology applications. All the smart materials applications discussed are recent, and further development is expected to yield improved performance and commodity level practical devices.