Invented by Prabhu Soundarrajan, James P. Novak, Applied Nanotech Holdings Inc
The Applied Nanotech Holdings Inc invention works as followsThe present invention relates to systems and method for detecting chemical and biological species in liquid phase. The systems and method use carbon nanotubes in order to increase sensitivity and selectivity by decreasing interference, and detecting wide concentrations.
Background for Nanobiosensors and carbon nanotube thin-film transistors
Biosensors are devices that incorporate a biological component (e.g. enzyme, antibody) in order to detect chemical species, biological species, and organic substances. Biosensors are useful in a variety of applications, including but not limited, to extreme environments (Dong, et. al., Electroanalysis 15, 157,2003), the detection of pathogenic bacteria and food (Ivnitski, et. al. Electroanalysis 12, 317 2000), glucose monitoring and food industry.
The conventional sensing electrodes used to immobilize enzymes in biological systems have shown limited selectivity and sensitivity. Sensor performance is also limited by possible interfering substances.
Most electrochemical sensors operate in liquid phase. In some cases, the analyte can be gaseous and the electrochemical sensor will not be able to detect it. The performance of liquid electrolyte sensor is limited by electrode corrosion, saturation of analyte during liquid phase and other operational problems such as the requirement to continuously stir the analyte into the sensing element.
Aligned carbon nanotubes are useful for electrochemical biosensing, but their reproducibility is a major problem. The high manufacturing costs of aligned nanotubes limit their commercialization.
There have been previous reports of electrochemical gas biosensors using ionic conducting films like nafion and tetrabutylammonium toluene-4-sulphonate (TBATS) for the detection of hydrogen peroxide and phenol vapors (Saini et al., Biosensors and Bioelectronics 10, 945, 1995; EP0585113A2), which use specific enzymatic reactions. However, these sensors used an enzyme (horseradish peroxidase) and a mediator (potassium hexacyanoferrate (II)) for sensing hydrogen peroxide with enzyme mediator gels. The ?drop and dry? process of the mediator, gel and enzymes did not yield a high sensitive and selective detection. There have been reports about biosensors using a thick film electrochemical device with an insulating substrate for the determination of ethanol vapors using alcohol dehydrogenase enzyme which also involved the ?drop and dry? process (EP634488A2).
Chemical sensors are devices which detect chemical and biological species by detecting the interaction of two molecules. These sensors are capable of detecting a variety of analytes, in liquid, gas and solid phases. Sensors are available for ambient and extreme environmental conditions. Chemical sensors are capable of detecting very low levels of analytes when optimized. However, they require a lot of equipment to support them. The equipment prevents the sensors being portable.
Conventional sensor can be manufactured using a variety of techniques. Each technique is specific to the analyte that you want to detect. The interaction between molecules would be the best technique. Signals could be produced by light emission, electron transfers or any other physical change. “Every sensor requires a transduction method, which converts the chemical event into a measurable signal.
Current methods of detection are limited in their selectivity at the limit of detection. Separating a signal and the noise around it becomes very difficult at these extremes. Internal amplification can be used to increase the signal-to-noise ratio. The internal amplification of the desired signal prevents noise from being introduced to a detection system by outside electronics. The detector can be built using transistor architecture to easily achieve amplification. This architecture can benefit from the inherent gain of a semi-conducting material.
Carbon nanotube transistors (CNTs) have been around for several years. (Tan et al., Nature, 1998 (393) 49, Martel et al., Appl. Phys. Lett. 1998 (73) 2447). In many examples, a CNT is placed between the electrodes. The preparation of these devices is difficult, as it requires tedious placements of electrodes in relation to the CNT. These advanced techniques require specialized instruments such as electron microscopes and electronic beam writing. This is because the instrumentation needed for fabrication and characterization prevents it from being a fabricated technique.
An embodiment is a sensor that detects an analyte and comprises: a nanotube of carbon; a polymer attached to the nanotube of carbon; and a detection element immobilized on the nanotube of carbon.
Another embodiment of the invention comprises a sensor to detect an analyte that includes: a carbon-nanotube, a polymer attached to the carbon-nanotube and a detection element immobilized on the polymer.
Another embodiment is a sensor that contains a sensing component for detecting analytes embedded in a matrix of polymer intermixed with carbon nanotubes.
Another embodiment is a sensor that includes a sensing component for detecting analytes, and the sensor is attached to a carbon-nanotube.
Yet another embodiment is a method for detecting analyte, comprising: immobilizing polymer and a sensing component to a nanotube of carbon; and using a transduction element with the sensing component to detect the analyte.
BRIEF DESCRIPTION DES DRAWINGS
Referring to the drawings and descriptions in conjunction, it is possible to gain a better understanding of the invention.
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