# Recent Development of Morphology Controlled Conducting Polymer Nanomaterial-Based Biosensor
## 2 Polypyrrole-Based Electrodes
### 0D Nanostructures  
As stated earlier, the popularity of PPy nanoparticles as biosensor sensing materials is due to the ability to incorporate various diverse receptors for analyte detection thanks to the large surface to volume ratio of these polymers. In particular, spherical PPy, which are most commonly used for producing biosensors, can be prepared via numerous methods, namely, microemulsion polymerization, self-assembly, and dispersion polymerization. Of the three methods listed, microemulsion polymerization is the most extensively utilized means of fabricating diverse nanometer-sized conducting polymer particles at low temperatures [73; 74]. In contrast, the self-assembly approach takes advantage of the evaporation processes occurring in the liquid reaction medium [75]. Dispersion polymerization features the synthesis of sterically stabilized PPy colloids using a tailor-made reactive polymeric stabilizer [76; 77]. [PERSON] et al. described the preparation of PPy nanoparticles with a diameter range of 20-100 nm using FeCl\({}_{3}\) in aqueous solutions containing PVA as a stabilizer [78]. Moreover, the generation of uniformly sized PPy nanoparticlesfor biosensor transducers was best conducted when the carboxylated polypyrrole (CPPy) chain was synthesized via the co-polymerization of pyrrole and 3-carboxyl pyrrole monomers [79].  
[PERSON] et al. reported introducing uniformly sized nanoparticles to the electrode's surface using the spin coating technique to solve the issues of limited surface area caused by nanoparticle aggregation. Additionally, amide coupling between the particle of interest and the electrode's surface induces greater electrode stability (Figure 1a) [79]. In [PERSON]'s study, the human parathyroid hormone receptor (PTH), which is vital for maintaining calcium homeostasis in mammals, was incorporated into the close-packed CPPy nanoparticle-based electrode. Irregularities associated with internal PTH levels result in potentially fatal diseases such as adenoma, hyperplasia, osteoporosis, and cancer. Here, the sensor electrode was extremely sensitive to human PTH and exhibited high stability because of amide formation reactions between the nanoparticle and the electrode. [PERSON] et al. incorporated platinum particles onto the surface of CPPy to fabricate nonenzymatic biosensors capable of detecting the neurotransmitter, dopamine (Figure 1b) [80]. In conjunction with platinum catalysts, this biosensor consistently detected dopamine at concentrations as low as 100 fM without the involvement of other biomaterials. [PERSON] et al. recently manufactured a biosensor electrode that could detect the odor molecule, cadaverine, in the gas phase using nickel-attached PPy nanoparticles (Figure 1c) [81]. Here, the strong binding interaction between the olfactory receptor embedded nanoparticles, namely, TAAR13c-embedded nanodisk, and nickel was vital for cadaverine detection. In this study, the TAAR13c-embedded nanodisk was introduced stably onto the electrode coated with the nanoparticles of interest. This artificial olfactory biosensor was capable of detecting low concentrations of cadaverine in both liquid (100 aM) and gaseous (10 ppb) phases.