Due to the unique optical properties of CNC, they have been used as photonic humidity sensors [488], but their maximum water uptake was limited by the dissolution and decomposition of the CNC structure. Recently, Lu and Pan [26] developed a novel humidity sensor by the chemical bonding induced between CNC and polyacrylamide, using glutaraldehyde as a bridging agent. Itwas found that when the humidity increases, the polyacrylamide swells enlarging the pitch of the chiral nematic structure of CNC. That causes a change in color which can be measured by reflectance spectra (Fig. 5.17).In addition, this composite can be used in several cycles of humidity without suffering degradation.With the objective of being used as biological and chemical sensors, where biocompatibility and electrical conductivity are required, Jasim and Ullah [489] developed electrically conductive BC membranes through oxidative polymerization with polyaniline (PAni). Then, single-walled carbon nanotubes (SWCNTs) were uniformly distributed in the composites. Both degradation resistance and electrical conductivity were enhanced with the implementation of both components. Degradationtemperature was increased from 232C to 310C, and electrical conductivity was improved to 1.4131022 S/cm with BC-PAni/SWCNTs at the dose of 0.1 mg/mL.A smart fluorescence biosensor was developed by [490], through the biosynthesis of BC with nitrogendoped carbon dots, previously synthesized by a hydrothermal method with citric acid and ethanediamine. The prepared biosensor exhibited a blue emission under the excitation wavelength of 350 nm. Results of spectroscopy showed that the prepared material presented a sensitiveresponse to Fe31 (Fig. 5.18) in a wide range (from 0.5 to 600 μM) with an ultralow detection limit of 84 nM.