Nanosensors are sensing devices with at least one of their sensing dimensions being up to100 nm. In the field of nanotechnology, nanosensors are instrumental for (a) detecting physical and chemical changes, (b) monitoring biomolecules and biochemical changes in cells, and (c) measuring toxic and polluting materials presented in the industry and environment. Nanosensors can be classified according to their energy source, structure and applications. The nanostructured materials used in manufacturing of nanosensors are such as: nanoscale wires (capability of high detection sensitivity), carbon nanotubes (very high surface area and high electron conductivity), thin films, metal and metal oxides nanoparticles, polymer and biomaterials. The aim of this review is to provide an overview of all classifications of nanosensors, showing the characteristcs and functioning mechanisms among the various categories.

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Ni-Mo nanocrystalline deposits (7–43 nm) with a nodular morphology were prepared by electrodeposition using direct current from citrate-ammonia solutions. They exhibited a single Ni-Mo solid solution phase. The size of the nodules increased as electroplating current density increased. The molybdenum content—estimated using EDX analysis—in the deposits decreased from about 31 to 11 wt% as the current density increased from 5 to 80 mA·cm−2. The highest microhardness value (285 Hv) corresponded to nanodeposits with 23% Mo. The highest corrosion resistance accompanied by relatively high hardness was detected for electrodeposits containing 15% Mo. Mo content values between 11 and 15% are recommended for obtaining better electrocatalytic activity for HER.

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Nanocrystalline Ni-Fe deposits with different composition and grain sizes were fabricated by electrodeposition. Deposits with iron contents in the range from 7 to 31% were obtained by changing the Ni2+/Fe2+mass ratio in the electrolyte. The deposits were found to be nanocrystalline with average grain size in the range 20–30 nm. The surface morphology was found to be dependent on Ni2+/Fe2+mass ratio as well as electroplating time. The grains size decreased with increasing the iron content, especially in case of short time electroplating. Increasing the electroplating time had no significant effect on grain size. The microhardness of the materials followed the regular Hall-Petch relationship with a maximum value (762 Hv) when applying Ni2+/Fe2+mass ratio equal to 9.8.