Detection of biomolecules using nano-scale electronic devices.

    Our objective is to use carbon nanotube filed effect transistors to monitor different biological processes in physiological buffers under both static conditions and when external parameters such as temperature, pH, and buffer composition are varied.

    Currently we are using CVD (chemical vapor deposition) grown carbon nanotube network field effect transistors (NTFETs) for real time monitoring of biological processes. The transistors are fabricated by Nanomix, Inc, a company specializing in fabricating nano-scale electronic devices.  There Professor Gruner has been involved in the fabrication and exploration of the interactions of gases and chemicals with NTFETs both in air and in buffer environments. This research has established the possibility of electronic detection of chemical species in a gaseous environment or in vacuum and has led to the first demonstration of chemical sensing in a buffer environment, including different transistor operation configurations. Both conventional bottom gating [1], and gating through the liquid [2] have been employed to evaluate transistor characteristics. These experiments also led to the identification of the sensing mechanism in NTFETs. The current research is partly based on these experiments and on the extension of the device sensing capabilities to bio-molecules [3].

Figure 1. Source-drain current Isd is measured as a function of gate voltage Vg at fixed source-drain bias Vsd (transistor transfer characteristic). Gate current Ig is constantly monitored  to ensure there are no parasitic electrochemical currents between the electrolyte and the nanotube network. During the experiment, the setup accumulates transfer characteristics and stores them in the computer memory for future analysis. This approach can be used, for example, for real time monitoring of non-specific protein binding to nanotubes.

Figure 2. NTFET is placed in 150mM phosphate buffered saline (PBS) solution and later exposed to 50nM streptavidin. Conduction through nanotube network (source-drain contacts separated by 10 microns) at Vg=-0.3 V is represented by the black line. As seen in the insert, exposure to streptavidin leads the device transfer characteristic to shift to the left, indicating that proteins donate electrons to nanotubes from its amine groups.

 References:

1. Star A, Gabriel JCP, Bradley K, Gruner G, “Electronic detection of specific protein binding using nanotube FET devices”, NANO LETTERS 3 (4): 459-463 APR 2003.

2. Bradley K, Gabriel JCP, Briman M, Star A, Gruner G, “Charge transfer from ammonia physisorbed on nanotubes ”, PHYSICAL REVIEW LETTERS 91 (21), 2003.

3. Bradley K, Briman M, Star A, Gruner G, “Charge transfer from adsorbed proteins”, NANO LETTERS 4 (2): 253-256 FEB 2004.