Molecular selectivity and autonomous controllability are the key aspects for biological vascular, olfactory and gustatory units. In the past decade, nanotechnology for these units based on monolithic integration has come close in the geometrical form factor, but is lack of both intelligence for selectivity and direct control schemes to meet the autonomous power budget. For example, microfluidic capillary channels are presently a common practice, but selective valves lag far behind from functional plant vascular units. Ions can cause significant characteristics shift in MOS capacitors [Sze81] and CHEMFET [Steiner95], long-term control, power efficiency and ion selectivity are vastly inferior to biological olfactory and gustatory sensors.
Expanded from our previous work in chemoreceptive neuron MOS (CnMOS) sensors [Liu02, Shen03], we will present a new unified silicon technology platform for constructing the necessary components in an autonomous sensor node. This includes chemical sensors and microfluidic valves with high selectivity, high sensitivity, large dynamic range, long lifetime, low power consumption, field reconfigurability and simple calibration/reset protocols. Fabrication process is a minor modification of conventional CMOS Flash nonvolatile memory, where the CMOS sensing circuits are reliably isolated from the extended floating gate in the fluidic areas for long-term void of contamination. Sensor selectivity and valve actuation are derived from the surface electrochemistry [Bard01] of the polymer coating and the nonvolatile charge condition. Our preliminary measurement results have successfully demonstrated the targeted characteristics of chemical sensing and electrowetting actuation [Lee00]. The floating-gate CMOS circuits can also implement a micropower neuromorphic electronic interface for such sensor node whose architecture is based on what is known about the olfactory and gustatory sensory systems of animals. This electronic interface can provide a distilled set of informative features for a recognition system to perform analysis and risk assessment, and further direct the valve/vascular units for high-fidelity confirmation testing. The complete monolithic system including sensing, actuation, computing and control is expected to dissipate only a few hundred microwatts of power in total for field operations. Such devices could be manufactured in large numbers very inexpensively and deployed rapidly as environmental sensors, running autonomously for long periods of time on either solar power or miniature chemical batteries.
 A. J. Bard and L. R. Faulkner, "Double-layer structure and adsorption," Chap. 13, Electrochemical Methods: Fundamentals and Applications, Wiley, 2001.
 J. Lee and C. -J. Kim, "Surface-Tension-Driven Microactuation Based on Continuous Electrowetting," J. MEMS 9, 171 (2000).
 Z. Liu, G. Pei, Y. N. Shen and E. C. Kan, "Interaction between CMOS nonvolatile charges and molecules in solution", Tenth Foresight Conference on Molecular Nanotechnology, 2002.
 N. Y. Shen, Z. Liu, B. A. Minch, and E. C. Kan, "The Chemoreceptive Neuron MOS Transistors (CnMOS): A Novel Floating-Gate Device for Molecular and Chemical Sensing," Proc. Transducers'03, 2003.
 F. -P. Steiner, A. Hierlemann, C. Cornila, G. Noetzel, M. Bachtold, J. G. Korvink, W. Gopel and H. Baltes, "Polymer coated capacitive microintegrated gas sensor," Proc. Transducers, 1995.
 S. M. Sze, Physics of Semiconductor Devices, 2nd Ed., Wiley, 1981.
Fig. 1. Change of liquid equilibrium length before and after electron tunneling operation at the control gate: (a) Image of the initial equilibrium condition after fluid is delivered to the microfluidic channel, which has a width of 20µm. (b) The liquid contact angle changes and the front advances about 10µm after injecting electrons to the extended floating gate due to electrowetting effects. Notice that the injection electrons are nonvolatile and control gate voltage is not needed to maintain the new liquid-solid interface.
Eqs. 1 and 2. Young's equation describes the balance of three interfacial tensions in a capillary system at the equilibrium. Lippman's equation indicates the solid-liquid surface tension can be modified by the combination of the electrical double layer capacitance and the coupling voltage across the capacitance.
Fig. 10. The illustration of the contact angle θ in a capillary system. The contact angle is determined by the balance between the solid-gas (air in our case), liquid-gas, and solid-liquid interfacial tensions at the equilibrium, and is described by the Young's equation.