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Bio-inspired sensors are sensors which detect and quantify physical and chemical aspects of their surroundings in the same functioning manner as a purely biological system in nature would do.

Sensors in animals
Animals rely on sensors to detect stimuli through the five “traditional” senses like sight, which detects photons or light, hearing which senses acoustic waves, the touch which comprises several signals such as mechanical and thermal ones, and finally, the chemical sensors of taste and smell. However, there are several examples of advanced sensing in nature that go beyond these “traditional” senses, some examples are the infrared sensing capabilities of snakes and jewel beetles, the electromagnetic sensing capabilities of the platypus, sharks and  ray fish or the magnetic field sensing capabilities of pigeons and sea turtles.

Sensors in plants
Due to their sedentary nature, plants have had to evolve sophisticated sensing systems in order to adapt to environmental changes and react to this information. Stimuli arrive in a heterogeneous manner and local signal perception triggers the systemic transmission of information using a range of factors like small molecules, hormones, RNAs, proteins, volatile chemicals, hydraulic and electrical signals. For example the temperature sensing mechanisms have to do with the Ca2+, temperature elevation activates Ca2+ channels, triggering a transient Ca2+ influx. The temperature increase also increases peroxide (H2O2) levels that might activate a similar pathway.

Examples of Bio-inspired sensors
Bio-inspired sensors are man-made devices inspired by nature, e.g., sensors changing color when in contact with liquid or vapor just like bird feathers, insect cuticles or butterfly wings do.

Optical sensors
In nature, the iridescence resulting from the periodic structure of photonic crystals, is used for species recognition and mate selection by many species. This microstructure brings about special superhydrophobicity, which shields them from rainfall, and structural colors like those found in butterfly wings or on peacock feathers. The use of colloidal photonic crystals has been proposed as a sensor to monitor changes in the environment of the system based on color changes.

Gas sensors

In nature the wing structure of blue Morpho butterfly is composed of chitin-and-air multilayers whose colour changes when exposed to different vapours. When vapour replaces the air in the cavities, there is a change in refractive index difference between two materials, which causes the colour to redshift in the optical wavelength. Colour change in the wings can be attributed to absorption of different vapours and/or different concentrations and outperform response of existing engineered photonic sensors. Another example is iridescent blue colour in scales of Hoplia coerulea beetle. The scales are are made of periodic porous multilayers and the colour changes from blue to green when in contact with water.

Production methods of bio-inspired multilayered polymer or metal-oxide sensors include self-assembly, coextrusion, or spin-coating, which makes them high-sensitivity and low-cost sensors. Available 'classic' gas and vapor sensors have a single-output and are used when response selectivity is not required. Photonic crystal sensors colour change is related to their photonic band structure, which depends on a refractive index and thickness of multilayers. The smallest change in one of the parameters will notably change reflected colour.

Metal-oxide gas-sensors are based on the change of the refractive index difference between two materials as the vapor or liquid enters the pores of the layers. Polymer-based gas sensors are devices made of polymer multilayers, sensitive to certain vapour (e.g. ethanol, acetone). Absorption of vapour causes swelling of the polymer layer. The change of layers thickness will induce the colour change in the multilayers.

Light Sensors

Light Sensors, also called photodetectors or photosensors, are devices or systems which convert light or other electromagnetic radiation into another form of signal, either chemical or electrical. In year 2004 photosynthetic purple bacteria served as a source of bio-inspiration, due to their antennae like complexes, which are able to convert sunlight into chemical potentials and thus able to generate electric current. . Artificial biological photosynthesis is a challenge which was pursued for a long time by chemists and biologists.

Tactile sensors
Human fingers are a suitable source of bio-inspiration for the sense of touch, since many engineers are trying to mimic this sensation and apply it to machines in both domestic and industrial use. For this task scientists employ tactile sensors, which are usually formed by an array of force sensors such as MEMS,Piezoresistors,Capacitive sensors or strain gauges. The combination of these sensors allows for sophisticated ways of enabling machines to experience the sense of touch.