Nanosensor

Nanosensors are nanoscle devices that measure physical .quantities and convert those quantities to signals that can be detected and analyzed. There are several ways being proposed today to make nanosensors; these include top-down lithography, bottom-up assembly, and molecular self-assembly. There are different types of nanosensors in the market and in development for various applications. Though all sensors measure different things, sensors share the same basic workflow: a selective binding of an analyte, signal generation from the interaction of the nanosensor with the bio-element, and processing of the signal into useful metrics. Nanosensors are nanoscle devices that measure physical .quantities and convert those quantities to signals that can be detected and analyzed. There are several ways being proposed today to make nanosensors; these include top-down lithography, bottom-up assembly, and molecular self-assembly. There are different types of nanosensors in the market and in development for various applications. Though all sensors measure different things, sensors share the same basic workflow: a selective binding of an analyte, signal generation from the interaction of the nanosensor with the bio-element, and processing of the signal into useful metrics. Nanomaterials-based sensors have several benefits in sensitivity and specificity over sensors made from traditional materials. Nanosensors can have increased specificity because they operate at a similar scale as natural biological processes, allowing functionalization with chemical and biological molecules, with recognition events that cause detectable physical changes. Enhancements in sensitivity stem from the high surface-to-volume ratio of nanomaterials, as well as novel physical properties of nanomaterials that can be used as the basis for detection, including nanophotonics. Nanosensors can also potentially be integrated with nanoelectronics to add native processing capability to the nanosensor.:4–10 In addition to their sensitivity and specificity, nanosensors offer significant advantages in cost and response times, which makes nanosensors suitable for high-throughput applications. Nanosensors provide real-time monitoring compared to traditional detection methods such as chromatography and spectroscopy. These traditional methods may take days to weeks to obtain results and often require investment in capital costs as well as time for sample preparation. One-dimensional nanomaterials such as nanowires and nanotubes are well suited for use in nanosensors, as compared to bulk or thin-film planar devices. They can function both as transducers and wires to transmit the signal. Their high surface area can cause large signal changes upon binding of an analyte. Their small size can enable extensive multiplexing of individually addressable sensor units in a small device. Their operation is also 'label free' in the sense of not requiring fluorescent or radioactive labels on the analytes.:12–26 There are several challenges for nanosensors, including avoiding fouling and drift, developing reproducible calibration methods, applying preconcentration and separation methods to attain a proper analyte concentration that avoids saturation, and integrating the nanosensor with other elements of a sensor package in a reliable manufacturable manner.:4–10 Because nanosensors are a relatively new technology, there are many unanswered questions regarding nanotoxicology which currently limits their application in biological systems. Some nanosensors may impact cell metabolism and homeostasis, changing cellular molecular profiles and making it difficult to separate sensor-induced artifacts from fundamental biological phenomena. Potential applications for nanosensors include medicine, detection of contaminants and pathogens, and monitoring manufacturing processes and transportation systems.:4–10 By measuring changes in physical properties (volume, concentration, displacement and velocity, gravitational, electrical, and magnetic forces, pressure, or temperature) nanosensors may be able to distinguish between and recognize certain cells at the molecular level in order to deliver medicine or monitor development to specific places in the body. The type of signal transduction defines the major classification system for nanosensors. Some of the main types of nanosensor readouts include optical, mechanical, vibrational, or electromagnetic. There are many mechanisms by which a recognition event can be transduced into a measurable signal. Electrochemical nanosensors are based on detecting a resistance change in the nanomaterial upon binding of an analyte, due to changes in scattering or to the depletion or accumulation of charge carriers. One possibility is to use nanowires such as carbon nanotubes, conductive polymers, or metal oxide nanowires as gates in field-effect transistors, although as of 2009 they had not yet been demonstrated in real-world conditions.:12–26 Chemical nanosensors contain a chemical recognition system (receptor) and a physiochemical transducer, in which the receptor interacts with analyte to produce electrical signals. Other examples include electromagnetic or plasmonic nanosensors, spectroscopic nanosensors such as surface-enhanced Raman spectroscopy, magnetoelectronic or spintronic nanosensors, and mechanical nanosensors.:12–26 Photonic devices can also be used as nanosensors to quantify concentrations of clinically relevant samples. A principle of operation of these sensors is based on the chemical modulation of a hydrogel film volume that incorporates a Bragg grating. As the hydrogel swells or shrinks upon chemical stimulation, the Bragg grating changes color and diffracts light at different wavelengths. The diffracted light can be correlated with the concentration of a target analyte. There are currently several hypothesized ways to produce nanosensors. Top-down lithography is the manner in which most integrated circuits are now made. It involves starting out with a larger block of some material and carving out the desired form. These carved out devices, notably put to use in specific microelectromechanical systems used as microsensors, generally only reach the micro size, but the most recent of these have begun to incorporate nanosized components.