Nano-Biosensors

    A biosensor is a device that combines a biological recognition element with a physical or chemical transducer to detect a biological product. In other words, it is a probe that integrates a biological one with an electronic component to yield a measurable signal. Several biosensors are being developed for different applications. Typically a biosensor consists of three components: the biological recognition element, the transducer and the signal processing electronics and functions at five different levels:

•        Bioreceptor that bind the specific form to the sample
•       Electrochemical interface where specific biological processes occur giving rise to a         signal
•       A transducer that converts the specific biochemical reaction in an electrical signal
•       A signal processor for converting the electronic signal into a meaningful physical            parameter 
•       A proper interface to display the results to the operator

    Various nanomaterials have been used in biosensors technology to produce nanobiosensors. Various nanomaterials are implemented either into transducers or receptors operation parts, so as to enhance their multidetection capability and sensitivity. These nanomaterials are nanoparticles, nanotubes, quantum dots (QDs) or other biological nanomaterials. These nanomaterials can contribute to either the bio-recognition element or the transducer or both, of a biosensor. Nanoparticles-based biosensor are particularly attractive because they can be easily synthesized in bulk using standard chemical techniques. Biosensors may be classified according to the mechanism of biological selectivity (bioreceptor) otherwise, on the mode of physiochemical signal transduction (transducer). Bioreceptor is a molecular species that exploits a biochemical mechanism of recognition. They are accountable for binding the concerned analyte to the sensor for measurement. Bioreceptor can broadly be classified into five distinct classes. These classes comprise antibody-antigen bioreceptor, enzymatic bioreceptor, nucleic acids (DNA) bioreceptor, cellular bioreceptor, biometric bioreceptor and bactriophage bioreactor. The transducer plays a crucial part in the detection and identification process of a biosensor. The transduction methods such as optical, electrochemical and mass based are the most favored and universal method.

Surface plasmon resonance (SPR) is a robust tool that can measure the binding kinetics of two molecules without the help of any fluorescent tag. Thus, this technique can be said as peculiarity that appears during optical illumination of a metal surface and can be adopted for biomolecular interaction analysis. The advantages affiliated with this are that it takes less time to detect binding events since it is label-free, it excluded additional reagents, assays and steps. Aptamers are those which work with the principle of target specific binding with high affinity, they are single stranded nucleic acid, they fit for the target in all the way forming three dimensional with strict bonding can be produced in vitro.  This kind of nanosensors gives more specific and effective detecting plant diseases, crop resistance and yield production.

Smart dusts are the devices made up of micro sized electro chemical sensors contained in it.  It works on three principles, sensing, processing and computing. This technology gains popularity in a way of its operations. It can be monitored with wireless radios, transducer irrespective of location of sensor, its size is very small due to which it can be undetectable. Major power of sensing itself to the environmental changes, automation and computing has made it come to greater extent. Smart dust technology could be used for monitoring various parameters such as temperature, humidity, insect and disease infestation, but still there are major drawbacks faced by this technology like the impact on environment, toxicity.

             Electronic nose (E-nose) consists of an array of gas sensors  which are composed of NPs e.g. ZnO nanowires with a broad and partly overlapping selectivity and an electronic pattern recognition system with multivariate statistical data processing tools. Their resistance changes with the passage of the certain gas and generate a change in electrical signal that form the fingerprint pattern for gas detection. This pattern is used to determine the type, quality, and quantity of the volatile organic compounds being detected. Plants release volatile organic compounds as a byproduct of everyday physiological processes and these specific compounds and the quantities release are indicative of both the crop and field conditions.