Overview of Chemical and Biological Nanosensors
Nanosensors are crucial tools for applications in environmental monitoring, chemical processes, diagnostics, clinical practices as well as personal safety. Nanowire sensors have the potential to be smaller, more sensitive, demand less power and react faster than their macroscopic counterparts. The increased sensitivity and faster response time of semiconductor nanowires is a direct result of their large surface-to- volume ratio and the small cross-section available for conduction channels.
Various mechanisms have been proposed for the fabrication of chemical and biological sensors using nanowires (NWs), nanorods (NRs) and nanocrystals/quantum dots (NCs/QDs). Most are based on creating electrical circuits on substrates followed by exposure to the agent to be sensed. Nanosensors can also be fabricated using microelectromechanical system (MEMS) technology (1) or made from nanoscale field effect transistors (FETs) (2). The presence of the target analyte can be tracked by changes in conductance, resistance and potentials.
Low dimensionality of nanomaterials along with well defined atomic precision will lead to opportunities for the miniaturization of chemical and biological sensors. Semiconducting CdSe nanostructures have gained interest due to their unique and flexible electrical and optical properties, which can be useful in sensing applications. One way of tuning its properties is a core-shell modification, where a ‘core’ is coated with a ‘shell’ from another material. Sensors and electronics are merely two applications of these very useful materials.
Advantages of Nanowires for Nanosensors
Nanowires are 1D nanomaterials which makes their length useful for effective electrical conduction. (3) Electrical transport in the long direction is faster than hopping from dot to dot, while tunneling probably takes place at very short distances. In addition to tunable properties, nanowires display high sensitivity to surface phenomena due to their high surface-to-volume ratio. Some of the material parameters can be independently controlled, such as their thermal conductivity, which is not the case for their bulk counterparts. (3)
Core-shell geometry of semiconductor nanowires can increase the efficiency of charge collection by shortening the path travelled by minority carriers in an electrical system.(4) Currently, this plays a role in photovoltaics, but extension to sensors and electronics is a possibility.
Selected Literature about Nanomaterial Based Nanosensors
Various procedures for fabricating chemical and biological sensors using different nanomaterials have been published.
Using CdSe nanostructures, a novel method with enhanced selectivity for detecting DNA sequences has been presented by H. Fan et al.(5) This method is based on the change in the electrochemical signal, indicated by Methylene blue (MB), due to the hybridization of DNA on the large surface area of the nanostructures (composed of CdSe Nanowires/Nanorods) modified glassy carbon electrode.
Core(shell): matrix CdSe(ZnS): SiO2 luminescence-based high temperature sensor has been fabricated. This can be applied in combination with other luminescent indicators, which are probably also temperature dependent, for multi-sensing applications. (6)
Numerous chemical sensors for applications in gas phase detection have been published. Ethanol sensing using ZnO nanowire sensors has been proposed by Wan et al. These nanosensors have been successful in terms of high sensitivity and fast response time at a working temperature of 300 °C, with an increase in sensitivity (ratio of the measured resistance in air and ethanol-air) from 1.9 to 47 when the ethanol exposure is increased from 1 ppm to 200 ppm. (1) Core-shell ZnO/CdS nanocables based NH3 sensors have also displayed superior results as compared to pure ZnO nanocables sensor, due to the increased surface-to-volume ratios of these core-shell nanocables, resulting from CdS coating. In fact, at 30 ppm NH3 a pure ZnO nanorod displayed a sensitivity of only 40 while the ZnO/CdS coaxial nanocable exhibited a higher sensitivity of 3800. (7)
In addition to ZnO nanowires, semiconducting Si nanowires have also been used to fabricate NO2 sensors, with excellent results. The electrical characteristics of such a sensor have been useful in detecting NO2 down to a few ppb (parts per billion). Along with this, the fabrication costs of the gas sensor are low. (8)
Enable your Nanosensor research with US Nanotechnology
US Nano has intellectual property relating to the industrial scale synthesis of both nanowires and core/shell nanowires available for licensing or joint development opportunities. The core/shell nanowires posses a morphology with higher surface area than conventional nanowires. US Nano’s methods can be applied to produce ZnO nanowires, a popular choice for nanosensor applications. Additionally, US Nano has developed methods to inkjet print nanowires, allowing for the rapid production of fast, cheap, and rugged printed electronic devices such as nanosensors. For an overview of US Nano’s competencies across the entire nanosensor fabrication process, please visit our Technology page.
Contact us to discuss how we can advance your chemical or biological nanosensor research through licensing or joint development projects.
Selected References on Nanomaterial Based Nanosensors
(1) Wan, Q.; Li, Q. H.; Chen, Y. J.; Wang, T. H.; He, X. L.; Li, J. P.; Lin, C. L. Fabrication and ethanol sensing characteristics of ZnO nanowire gas sensors. Applied Physics Letters 2004, 84, 3654.
(2) Cui, Y.; Wei, Q.; Park, H.; Lieber, C. M. Nanowire nanosensors for highly sensitive and selective detection of biological and chemical species. Science (New York, N.Y.) 2001, 293, 1289–92.
(3) M. S. Dresselhaus, Y.-M. Lin, O. Rabin, M. R. Black, Jing Kong, G. D. Springer Handbook of Nanotechnology; Bhushan, B., Ed.; Springer Berlin Heidelberg: Berlin, Heidelberg, 2010; pp. 113–160.
(4) Tang, J.; Huo, Z.; Brittman, S.; Gao, H.; Yang, P. Solution-processed core-shell nanowires for efficient photovoltaic cells. Nature nanotechnology 2011, 6, 568–72.
(5) Fan, H.; Ju, P.; Ai, S. Controllable synthesis of CdSe nanostructures with tunable morphology and their application in DNA biosensor of Avian Influenza Virus. Sensors and Actuators B: Chemical 2010, 149, 98–104.
(6) Pugh-Thomas, D.; Walsh, B. M.; Gupta, M. C. CdSe(ZnS) nanocomposite luminescent high temperature sensor. Nanotechnology 2011, 22, 185503.
(7) Du, N.; Zhang, H.; Chen, B.; Wu, J.; Yang, D. Low-temperature chemical solution route for ZnO based sulfide coaxial nanocables: general synthesis and gas sensor application. Nanotechnology 2007, 18, 115619.
(8) Cuscunà, M.; Convertino, A.; Zampetti, E.; Macagnano, A.; Pecora, A.; Fortunato, G.; Felisari, L.; Nicotra, G.; Spinella, C.; Martelli, F. On-chip fabrication of ultrasensitive NO2 sensors based on silicon nanowires. Applied Physics Letters 2012, 101, 103101.