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A biosensor can sense biological elements after interaction with the recognition element. The signal produced due to interaction of the analyte with its biochemical element is transduced by a transducer and detected by appropriate modes. The miniaturization of these biosensors at the nano level using nanostructures as a platform for sensing the analyte or its detection is called a nanobiosensor. Several biological elements can be detected like nucleic acids, enzymes, antibodies, microorganisms, toxins, cells etc. with high specificity. This mini review focuses on the different types of nanobiosensors based on the type of analyte and the type of transducer used for detection. The different types of fluorescence based design of biosensors are also discussed along with the metal enhanced fluorescence based nanobiosensors. The application of biosensors towards the diagnosis of various diseases, targeted drug delivery and imaging is also discussed. [ABSTRACT FROM AUTHOR]

Zinc oxide (ZnO) is a semiconductor metal oxide nanoparticle with inherent optical properties. Among the different zinc oxide nanostructures, nanoflowers have greater surface area. Utilizing this property a reagentless biosensor has been developed for the detection of beta amyloids, a hallmark of neurodegenerative diseases like Alzheimer's disease, Creutzfeldt-Jakob Syndrome, insulin dependent type II diabetes etc. The poor fluorescence quantum yield and photobleaching effect of Thioflavin T (ThT) upon binding to the model insulin amyloid beta sheets in solution can be overcome by the present engineered biosensor where ThT acts as a target as well as a reporter to detect amyloids adsorbed on a solid template based on ZnO nanoflower. ThT was adsorbed on ZnO NFs grown over nano-silver thin film coated glass slide. The in vivo imaging system was used to detect and quantify the fluorescence intensity generated from the substrates upon binding with insulin amyloid. ZnO NFs have the waveguiding property which increases the local field intensity caused by a resonance between the guided fundamental mode and evanescent field associated with high- order modes. This resonance phenomenon reinforces the excitation of the fluorophores in close proximity of the NFs thereby exhibiting enhanced fluorescence like Fabry Pero't Resonator (FPR). Considering the engineering and sensitivity, the reported nanobiosensor developed on ZnO nanoflower can be treated as faster and cost effective amyloid sensor. [ABSTRACT FROM AUTHOR]