Research: Nano-bio Sensors

Single and Nanobundle Chemical and Biological "Touch" Sensors
Bio-memetic Nano-pore "Passage" Sensor for Bio-Medical Applications

Single and Nanobundle Chemical and Biological "Touch" Sensors

WHY

Recent demonstrations of versatile and sensitive nanowire-based "touch" sensors, whose electrical properties respond dramatically to the attachment of chemical and biological molecules, promise to dramatically alter the application space for bio-chemical sensors: their small sizes may make them less intrusive, their enhanced surface-to-volume ratio and size-influenced electrical-mechanical properties could make them more sensitive, and their compatibility with CMOS processing could make them less expensive and easy to integrate. However, like many pioneering works, the available experimental data are broadly scattered, the theoretical basis of the improved sensitivity poorly understood, and the path to further optimization ill-defined. In this research, we are developing a predictive theoretical framework for nano-bio sensors that will help with design and optimization of these systems. Specifically, we plan to (a) define the key functional variables and unifying principles for such sensors for rapid and simple interpretation of experimental data, (b) establish the limits to scalability and sensitivity of these devices, and (c) explore trade-off for sensitivity and response time for optimized performance. In some ways, bio-sensor research today is in similar stage as transistor research was after its invention but before Shockley's seminar work on transistor operation. Shockley's theory explained the measured transistor data consistently using simple principles, differentiated between normal and anomalous responses, and suggested means for further optimization. Our research work, if successful, will provide a similar framework for nano-bio sensors so that their initial promise as a versatile interface and key enabling technology to biomedical and physical systems can actually be realized.

WHO ARE INVOLVED

Pradeep Nair, Graduate Student, Purdue
S. Datta, Professor, ECE Purdue
R. Bashir, Professor, ECE Purdue

Bio-memetic Nano-pore "Passage" Sensor for Bio-Medical Applications

WHY

Single molecule sensors in which nano-scale pores within biological or artificial membranes act as mechanical gating elements are promising devices for the rapid characterization and sequencing of nucleic acid molecules. The two terminal electrical measurements of translocation of polymers through single ion channels and that of ssDNA molecules through protein channels have already been demonstrated, and their sensitivity and selectivity have sparked tremendous interest in such single molecule sensors. The prevailing view regarding the nanopore sensors is that there exists no electrical interaction between the nanopore and the translocating molecule, and that all nanopore sensors reported to-date, whether biological or artificial, operate as a coulter-counter, i.e. the ionic current measured across the pore decreases (is mechanically blocked) when the DNA molecule transverses through the pore. However, recent experiments from Prof. Bashir's group challenge the prevailing view of exclusive mechanical interaction during the translocation of dsDNA molecules through these channels and demonstrate that the ionic current can either increase or decrease due to a combination of mechanical channel blocking and electrical gating of DNA induced surface charge current and if properly designed and correctly operated, the nanopore containing membranes can become the third electrically active element of these single-ion sensors (in addition to anode and cathode), thereby allowing far superior performance of these devices than have been envisioned thus far. Our group is developing transport models for DNA through such nano-pores so that the existing experiments can interpreted, the geometry of the sensors can be optimized, and ultimate limits and responsivity of the sensors can be established.

WHO ARE INVOLVED

Pradeep Nair, Graduate Students, Purdue
R. Bashir, Professor, ECE Purdue

BACKGROUND PAPERS

[1] R. Bashir, H. Chang, F. Kosari, G. Andreadakis, M. Alam, G. Vasmatzis, "DNA Mediated Fluctuation in Ionic Current through Silicon Oxide Nano-Channels," Nanoletters, August, 2004.

[2] Bezrukov, S., Vodyanoy, I., Parsegian, V. A., Counting Polymers Moving through a single Ion Channel, Nature, 370, 279-281 (1994).

[3] Cornell, B. A., et al., A Biosensor Using Ion-Channel Switches, Nature, 387, 580-584 (1997).

[4] Kasianowicz, J. J., Brandin, E., Branton, D., and Deamer, D. W., Characterization of Individual Polynucleotide Molecules using a Membrane Channel, Proc. National Academy of Science, 93, 13770-13773 (1996).

[5] Meller, A., Nivon, L., Brandin, E., Golovchenko, J., and Branton, D., Rapid nanopore discrimination between single polynucleotide molecules, Proc. National Academy of Science, 97, 1079-1084 (2000).

[6] Austin, R. H., The art of sucking spaghetti, Nature Materials, 2, 567-568 (2003).