Sensors are made to detect any changes in electrical, chemical fields, etc. For highly sensitive sensing applications, semiconductors are produced when doping with nanoparticles. Nowadays, the doping process uses nanoparticles with a very high level of precision and accuracy to deliver semiconductor sensors. The interest in them is because of the electrical conductivity that can be tuned and tuning can be done through facile polymerization, properties of soft organic material, and doping. When doping with nanomaterials of unique chemical and physical characteristics, as dopants, helps the conducting polymer in getting new and even enhanced properties, for instance, improved strength, improved conductivity, additional functional groups, and large surface area. When the conducting polymers are being doped with nanomaterials, the properties of nanomaterials and conducting polymers are combined, which has found a vast amount of applications in different fields, such as solar cells, catalysis, fuel cells, supercapacitors, thermoelectricity, and sensors. Theoretical and experimental evidence assured doping importance for the advancement in nanoscience and nanotechnology of new functional materials. This article mainly focuses on recent improvements in biosensors and electrochemical sensors, based on conducting polymers doped with different nanomaterials. In addition, there is a discussion on, selective NO2 gas sensors, using gold nanoparticles to create tunable sensors, Polystyrene nanoparticles, and biosensors, Nanoparticle doping, Hydrogen sensors based on ZnO nanoparticles.
Sensors detect changes properties in the chemical, electrical, mechanical, radiant, magnetic, or thermal way. To date, semiconductor materials can be used to manufacture most sensors, for creating a 3-D final product. In the manufacturing of a semiconductor, doping is a foremost step. When nanoparticles are being used as a dopant, semiconductors can be used for applications in highly sensitive sensing. For introducing the impurities into the material, including the required properties that a material needs, doping is the process. Semiconductor materials manufacture highly sensitive sensors by using the semiconductors’ electromagnetic properties with a high level of precision and accuracy. Since the last decade, the manufacturing of semiconductors has improved due to advancements in the field of nanotechnology. Many researchers are now finding the use of nanoparticles in doping for different sensor applications. Few are mentioned in this article.
Selective NO2 gas sensors
The sol-gel method is used by the researchers for synthesizing nickel-oxide (NiO) that’s doped with cerium (Ce), which when applied for sensing gas, works better in sensing nitrogen dioxide(NO2) than other traditional materials.
Creating tunable sensors using gold nanoparticles
Doping tunable nature gives the manufacturers ability to accurately control impurities level in a volatile-organic-compound (VOC) and in the semiconductor materials sensing application. Molybdenum disulfide (MoS2) is doped with gold (Au) nanoparticles only a size of 10 nanometers. The charge was transferred in between Au and MoS2 because nanoparticles allowed, enabling the production of the sensors.
Biosensors and nanoparticles of polystyrene
In biosensing world, specific mechanical sensors are used for monitoring of bodily processes like pulse, swallowing, and back posture in real-time. Recently, it was showed how nanoparticles of polystyrene doping graphene oxide could act as a highly responsive piezoelectric, flexible sensor for this application.
Electrochemiluminescence and Nanoparticle doping
It’s proved that for the manufacturing of sensitive sensing devices, semiconductor materials are used which are produced by combining nanoparticles’ doping with the electrochemiluminescence (ECL) transduction method. For applications in biosensing, this method is specifically interesting because if the mechanical and chemical events can be sensed beforehand, we would be able to differentiate between life-saving diagnoses, deadly uncertainty, and early diagnoses.
Hydrogen sensors based on ZnO nanoparticles
H2, ethanol, and CO are the gases that can be sensed by ZnO. As the bulk material has not sufficient sensitivity, Wang et al. employed Pd coated ZnO nanorods for detecting H2 down to 10 ppm, with a 2.6% relative response and a recovery time of less than 20 s at 25.8C. When the nanoparticles were impregnated with 1% Pt, Pt beneficial effects were added, which improved ZnO gas sensing characteristics. Further impregnation of Pt improves the recovery and response times. At low temperatures, Pt and Co doping ZnO nanoparticles represent very good sensitivity for H2. For long periods, over several cycles, ZnO nanoparticle sensors are stable, displaying their practical use as H2 sensors. In ZnO: Ag nanocolumnar films, the response and the recovery times are greatly lessened for the fully modified nanocolumnar thin films. Ag-doped ZnO columnar films improved the properties of sensing gases like acetone, ethanol, methanol, and 2-propanol vapours.
Nanomaterial-doped conducting polymers for biosensors and electrochemical sensors
In 1977, polyacetylene, an organic polymer displayed a very high electronic conductivity when doped with iodine. Now, a huge amount of attention is gained by conducting polymers in fields like biomedical applications, bioelectronics, anti-corrosion, and storage of energy. The doping and properties of soft organic material tune the electrical conductivity, which makes this interesting. Dopants modulate extended π-conjugated molecular backbone, therefore, modulating electrical conductivity. Effective applications in biosensors and electrochemical sensors were seen. Due to development, now for polymers’ polymerization, nanomaterials that are carrying negative charges have been used as novel dopants. Improved or even remarkable properties, for instance, enhanced conductivity, large surface area, additional functional groups, and enhanced strength are attained when polymers are doped with nanomaterials because of the properties of nanomaterials and conducting polymers are combined. These have broad applications in different areas.Until now, the development of many conducting polymers has occurred, and the best of them are polyaniline (PANI), polyindole, and poly(3,4-ethylene dioxythiophene) (PEDOT).
Due to the advantage of having high conductivity and super stability, PEDOT, the most widely and representative used derivative of polythiophenes. Combinations of nanomaterials and PEDOT together generate way many potentially promising composites which have witnessed rapid growth recently, in the electrochemical field.
Carbon nanomaterial-doped PEDOT
Recently, carbon nanomaterials like Carbon nanotubes and GR have been implemented in PEDOT as dopants. With that help, different sensors are built up and with which impressive progress in sensing has been achieved.
In electrocatalysis, CNTs doping PEDOT nanocomposites are also of a huge deal. The performance was seen to be improved when nanoparticles were introduced on PEDOT-CNTs. Even in biosensors, CNT-doped PEDOT composites are also attractive materials.
Metal nanoparticle-doped PEDOT
High conductivity and a network of the 3D microporous structure was processed by the prepared nanomaterial. Also, nitrite’s electrochemical sensing can be done by the production of the Au nanoclusters (AuNCs) doped PEDOT.
Other nanomaterial-doped PEDOT
Broad applications are possessed by these materials when it comes to sensing and promising application vistas in the sensors that are in development. For the doping of PEDOT, one good candidate was considered, known as nanocrystalline cellulose; this is because of its low cost, high surface area, and good biocompatibility. The performance of electrochemically polymerized PEDOT-NCC is better when it comes to electrocatalytic activity and charge storage capacity. We realized the sensitive detection for DA while its good electrocatalytic activity was exploited. H2O2 has a remarkable catalyst known as Prussian blue (PB), and it is prepared in nanoparticles form, and it’s used for polymer’s doping. A PB-PEDOT nanocomposite was used for H2O2 electrochemical catalytic reduction, and it was reported by Wang and his co-workers. In nanocomposite, the PEDOT does not only protect PB nanoparticles from realizing its high stability, but it also acts between nanoparticles of PB as the connector to increase its electrochemical performance.
For modifying the electrode, PANI is the best material. PANI is studied in detail as a material that modifies electrode in different fields, like electronic devices, biosensors, batteries, and integrated circuits, due to its easy synthesis, unique electroactivity, good stability in the environment, unusual de-doping/doping chemistry, and high capacity, when different nanocomposites doped PANI, improved and better performance is exhibited by the materials.
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Carbon material-doped PANI
Carbon nanotubes are the best carbon material. Doping of Polymeric nanocomposites of PANI with carbon materials are superior and have more functions and properties as compared to those of the pure component’s nanoparticle dispersion, mechanical stability, selectivity, and detection sensitivity so that they can play significant roles in biosensors and chemical sensors. Few carbon materials, for instance, CNTs and GR, have been used widely.
Other nanomaterial-doped PANI
Based on PANI, a broad range of nanocomposites are applied as dopants.
Another very attractive material for sensor applications is PPy which can be polymerized easily in neutral aqueous solution as compared to that of polythiophene and PANI, which needs acidic media. It is broadly used to fabricate biosensors or electrochemical sensors because of its acceptable stability and high electrical conductivity. For development in both biosensors and electrochemical sensors, composites of polythiophene that are nanomaterial-doped were used broadly. Nandini et al. prepared another H2O2 sensor based on polythiophene that’s doped with AuNP nanotube (AuNPNTs).
It is seen that by doping nanocomposites of Poly(p-phenylene sulfide) PPS with specific nanomaterials, for instance, carbon nanofibers, and CNT, Poly(p-phenylene sulfide) PPS nanocomposites performance was improved effectively. It’s estimated that PPS doped with nanomaterial might find exceptional applications in both biosensing and electrochemical sensing in the future.
The properties and qualities of the dopant when mixed with the properties of nanomaterial, will make it better than ever. Nanoparticle-doped materials considerably enhance the sensing performance, for instance, low limit of detection, rapid response, good selectivity, high repeatability, as well as enabling the preparation of facile. Each dopant has some particular catalytic activity towards various targets, so conducting polymers being doped with more than just one dopant is great as the product will have combined properties of all. An interesting fact is that the electrical conductivity can be tuned by the dopants by modulating the prolonged π-conjugated molecular backbone. Applications in electrochemical sensors and biosensors were noticed. This article also focuses on how to use gold particles to create tunable sensors, and selective NO2 gas sensors are also discussed.