Nanomaterials for Sensing Applications

The field of sensors encompasses a wide variety of materials and devices used for capturing physical, chemical or biological stimuli converting them to measurable output signals. Nanomaterials may be used as active sensing elements or receptors, as transducing components (e.g. electro- or chemo-mechanical actuators), and even as electrodes in electronic circuitry and power systems (e.g. nanowires)^1,2.

The Center for Nanomaterials and Sensor Development at the State University of New York at Stony Brook which the author established in 2003 and she still directs, specializes on the synthesis and use of nanomaterials: metal oxides, electro-active polymers, their composites, and their hybrids with biomolecules (enzymes, peptides), primarily as active elements of bio-/chemical sensor systems. Nanomaterials are very important to resistive chemosensing², a key transduction mode in which chemical or biochemical signal inputs induce changes in the electrical resistance of the active element.

Since gas adsorption on the sensor materials' surfaces is fundamental to the resistive gas detection process, reducing the dimensionality of the sensor materials to the nanoscale, thus increasing their surface to volume ratio, has the obvious effect of improving gas sensitivity^a. Numerous reports in the literature have documented several orders of magnitude increases in the gas response of nanomaterials compared to their bulk(ier) counterparts^1,3. The response and recovery time of nanomaterials-based chemiresistors may be impressively as low as milliseconds^1-3.

Professor Gouma's research group has made unique contributions to establishing and explaining the gas specificity observed in functional metal oxide nanomaterials, such as TiO₂, MoO₃ and WO₃. Using a crystallo-chemical approach, it is shown that the phase of the nanomaterial (crystallographic polymorph) rather than it's chemical composition, is the critical parameter controlling the affinity of a stoichiometric metal oxide to a specific gaseous analyte^4,5. For example, both the â-phase of MoO₃ and the ã-phase of WO₃ are selective to nitric oxide (NO), because both share the cubic rhenium trioxide structure⁶. This is not the case with the a-phase of MoO₃- having a unique, open orthorhombic crystal structure- that serves as a highly selective ammonia detector⁷.

Interestingly, there is a little-known phase of the WO₃ material that is ferroelectric and makes an excellent acetone detector⁸. This phase is thermodynamically stable below -40°C⁹. Thanks to the availability of nanomanufacturing processes¹⁰, Professor Gouma's research group was able to stabilize this nanophase to RT and to use it for sensing¹¹. This "novel" nanomaterial, å-phase WO₃, interacts with polar gases through a dielectric poling sensing mechanism^8,11, a true breakthrough in gas sensing.

As nanoscale synthesis of metal oxides favors metastability¹², there is a toolbox of "rare" phases now available to gas detection and monitoring, including hexagonal WO₃, anatase and brookite TiO₂, to name a few. Furthemore, processing these "gas-selective" oxide phases in 1D nanowire configurations^b adds improved sensitivity to gas specificity¹³, thus detection limits of only a few gas molecules (ppb levels) of signaling metabolites have been achieved recently^1-3. This finding has important implications for nanomedicine^c applications of nanomaterials.

Among the successful nanotechnologies that The Center for Nanomaterials and Sensor Development at the State University of New York at Stony Brook has pioneered, single breath analysis diagnostics stand out. Electronic Olfaction¹⁴ (whether it is electronic nose or tongue technologies), has been limited by the lack of selective sensors to discriminate gases in a complex gas environment (such as breath odor).

Figure 1. Ceramic oxide nanoparticles that are used as sensing elements in a breathanalysis device prototype (shown above) that monitors selectively the concentration of a gaseous biomarker for diabetes monitoring in a non-invasive manner (Copyright: P. Gouma, CNSD).

The nanomaterials-based sensors described above offer inexpensive alternatives to costly and bulky optical detectors, the main competing selective gas sensing technology under development¹⁵. On/off nanosensor devices have been demonstrated that may detect from bacterial infection to diabetes, and even lung cancer¹⁶. Using bio-doped nanostructured oxides (urease in MoO₃)¹⁷ or bio-nanocomposites (PANI/CAionophores/ peptides)¹⁸ as sensing elements, further expands the scope of using nanomaterials as resistive biosensors in non-invasive diagnostic tools.

In summary, nanomaterials are having a tremendous impact in sensing applications as they offer improved selectivity, sensitivity, and rapid response to the bio-/chemical analytes of interest. Resistive chemosensors using nanomaterials have enabled novel inexpensive and non-invasive applications for health and safety, such as breath analyzers, sweat test diagnostics, and other personalized medicine and protection tools. Selfpowered nanosensor devices relying completely on hybrid nanowire technology are envisioned for the near future.

References

1. P. Gouma, Nanomaterials for Chemical Sensors and Biotechnology, Pan Stanford Publishing, 2009.
2. P. Gouma, D. Kubinski, E. Comini, and V. Guidi, eds, "Nanostructured Materials and Hybrid Composites for Gas Sensors and Biomedical Applications", Materials Research Society, Warrendale, PA, Spring 2006.
3. G. Shen, P-C. Chen, K. Ryu, and C. Zhou, "Devices and Chemical Sensing Applications of Metal Oxide Nanowires, Journal of Materials Chemistry, 19, pp. 828-839, 2009.
4. P.I. Gouma, A. K. Prasad, and K.K. Iyer, "Selective Nanoprobes for Signaling Gases", Nanotechnology, 17, pp. S48-S53, 2006.
5. P. I. Gouma, "Nanostructured Polymorphic Oxides for Advanced Chemosensors", Rev.Adv. Mater. Sci., 5, pp. 123-138, 2003.
6. P.I Gouma and K. Kalyanasundaram, "A Selective Nanosensing Probe for Nitric Oxide", Appl. Phys. Lett., 93, 244102, 2008.
7. A.K. Prasad, D. Kubinski, and P. I. Gouma, "Comparison of Sol-Gel and RF Sputtered MoO₃ Thin Film Gas Sensors for Selective Ammonia Detection", Sensors & Actuators B, 9, pp.25-30, 2003.
8. Lisheng Wang, "Tailored Synthesis and Characterization of Selective Metabolitedetecting Nanoprobes for Handheld Breath Analysis", Ph.D. thesis, SUNY Stony Brook, Dec 2008.
9. B.T. Matthias and E.A. Wood, "Low temperature polymorphic transformation in WO₃". Phys. Rev., 84(6), pp. 1255-1255, 1951.
10. K. Wegner and S.E. Pratsinis, "Nozzle-quenching process for controlled flame synthesis of titania nanoparticles", AICHE J., 15, pp. 432-436, 2003.
11. L. Wang, A. Teleki, S.E. Pratsinis, and P.I. Gouma, "Ferroelectric WO₃ Nanoparticles for Acetone Selective Detection", Chem. Mater., 20(15), pp. 4794- 4796, 2008.
12. H. Zhang, H. and J.F. Banfield, "Understanding polymorphic phase transformation behavior during growth of nanocrystalline aggregates: Insights from TiO₂", Journal of Physical Chemistry B, 104, pp. 3481-3487 2000.
13. P. Gouma, K. Kalyanasundaram, and A. Bishop, "Electrospun Single Crystal MoO₃ Nanowires for Bio-Chem sensing probes", Journal of Materials Research, Nanowires and Nanotubes special issue, 21(11), pp. 2904-2910, 2006.
14. P. Gouma and G. Sberveglieri, "Novel Materials and Applications of Electronic Noses and Tongues", MRS Bulletin, 29 (10), pp. 697-700, 2004.
15. M.R. McCurdy, Y. Bakhirkin, G. Wysocki, R. Lewicki, and F.K. Tittel, "Recent Advances in Laser-spectroscopy-based Techniques for Applications in Breath Analysis", J. Breath Res., 1, 014001, pp. R1-R12, 2007.
16. P. Gouma, K. Kalyanasundaram, X. Yun, M. Stanacevic and L. Wang, "Chemical Sensor and Breath Analyzer for Ammonia Detection in Exhaled Human Breath", IEEE Sensors, Special Issue on Breath Analysis, 10 (1), pp. 49-53, 2010.
17. S.Y. Gadre and P. Gouma, "Biodoped Ceramics: Synthesis, Properties And Applications", J. Amer. Ceram. Soc. - Invited Feature Article, 89 (10), pp. 2987- 3002, 2006.
18. A. S. Haynes and P.I. Gouma, "Electrospun Conducting Polymer-based Sensors for Advanced Pathogen Detection", IEEE Sensors Journal, 8(6), pp. 701-70, June 2008.