Since their inception in 2012, triboelectric nanogenerators (TENGs) have revolutionized energy harvesting and active sensing, finding applications in diverse fields such as green energy, molecular detection, healthcare, and gesture recognition [1,2,3,4,5,6]. With their potential to function as both power sources and smart sensors, TENGs offer a promising avenue for sustainable and personalized healthcare solutions. Conductive polymers play a crucial role in the design of TENG-based biosensors and enhancing their applicability in health monitoring, environmental sensing, and point-of-care diagnostics.

TENGs can be seamlessly integrated into intelligent systems for scavenging energy from ambient environments or the human body, providing sustainability, wearability, and portability [7,8,9,10]. In the realm of healthcare, bio-friendly TENGs can be directly worn or implanted into the body to monitor physiological parameters, metabolic status, and even treat diseases with the aid of advanced information technologies. Their simple operation, easy miniaturization, and ability to detect physiological signals make TENGs ideal for clinical devices with predictive, personalized, and participatory characteristics [11,12,13].

Conductive polymer-based TENGs (CPNGs) have shown immense promise in healthcare applications, particularly in connected healthcare and long-term personalized treatments. These innovative devices enable high-quality, real-time monitoring of personal health parameters while providing sustainable and long-lasting power sources [14,15,16]. The integration of CPNGs with conductive polymers enhances their performance by serving as contact layers, amplifying electrical signals, ensuring biocompatibility, and offering flexibility and stretchability. This, in turn, allows for the development of comfortable and unobtrusive wearable devices with improved wearability and user compliance. Furthermore, the functionalization of conductive polymers with specific recognition elements, such as enzymes, antibodies, or aptamers, enables selective and sensitive detection of target analytes in TENG-based biosensors.

However, despite the remarkable advancements in this field, challenges persist concerning power output, device stability, biocompatibility, and integration with other cutting-edge technologies such as flexible electronics and advanced data processing systems [17,18,19,20,21,22,23]. To fully realize the potential of CPNGs in healthcare applications, future research must address these limitations and explore novel strategies for enhancing the performance and capabilities of these versatile devices.

TENGs leverage the triboelectric phenomenon and electrostatic induction to convert biomechanical energy into electrical energy [24,25,26,27,28,29,30,31]. When materials with different electronegativities come into contact, electron transfer occurs between them [32,33,34,35,36,37]. As they separate, electrostatic induction prompts electron flow towards the external load, generating an alternating current through repeated contact–separation cycles.

TENGs can be categorized into four primary types: the vertical contact–separation mode, lateral sliding mode, single-electrode mode, and free-standing triboelectric layer mode.

Vertical Contact–Separation Mode: In this mode, two triboelectric materials with opposing polarities are positioned closely together. They are periodically brought into contact and separated along a vertical axis. When the materials touch, triboelectric charges generate at their interface. As they separate, the charges redistribute, creating an electric potential difference that drives the electron flow through an external load, producing electric power.

Lateral Sliding Mode: In this mode, two triboelectric materials with opposing polarities slide against each other horizontally. When the materials slide, they generate triboelectric charges at their interface, similar to the vertical contact–separation mode. However, the materials’ relative motion is parallel to their interface, resulting in a continuous change in the overlapping area. This change generates an electric potential difference, which drives the electron flow through an external load.

Single-Electrode Mode: In this mode, only one triboelectric material has an attached electrode, while the other material remains electrically isolated. The isolated material is periodically brought into contact and separated from the material with the attached electrode. Triboelectric charges generated at the interface induce charges on the single electrode during contact and separation. A ground electrode connects to the single electrode through an external load, and the electric potential difference between the ground and the single electrode causes electrons to flow through the load, generating electric power.

Freestanding Triboelectric Layer Mode: In this mode, a freestanding triboelectric layer is sandwiched between two electrodes. The freestanding layer has opposite triboelectric polarities on its two sides. The electrodes are periodically brought into contact and separated from the freestanding layer, causing it to deform. This deformation generates triboelectric charges at the interfaces between the freestanding layer and the electrodes. The resulting electric potential difference between the two electrodes drives the electron flow through an external load.

Strategies for improving energy collection efficiency by introducing conductive polymers have gained traction in recent years (Table 1). One such strategy involves doping conductive polymers into the friction layer of a TENG, which leads to a better charge transfer, increased surface area, and tunable work function. The integration of conductive polymers with TENGs via the following strategies has expanded their potential applications in various wearable devices and sensors.

Ahmad et al. developed a novel TENG with an enhanced performance by incorporating conductive polyaniline (PANI) and tribonegative graphene oxide (GO) into the tribopositive material [39]. The unique combination of PANI and GO in the tribopositive layer introduces a new mechanism for performance enhancement, wherein the electron-accepting ability of GO and the conductivity of PANI facilitate the electron flow under an external impact force, thus increasing the surface charge density and overall TENG performance. The resulting TENG device comprises a polymer with 700 µL PANI and 4 mg mL⁻¹ GO as the tribopositive layer, while polydimethylsiloxane (PDMS) serves as the tribonegative layer in a 1 × 2 cm² configuration. This innovative TENG design generates an open-circuit voltage of 314.92 V and a current density of 37.81 mA m⁻², achieving a peak power density of 10.43 W m⁻², which is sufficient to power over 175 white light-emitting diodes directly. The proposed tribopositive material, combining PANI and GO, offers a low-cost, easy-to-fabricate solution for creating highly stable and efficient TENGs with a significantly improved performance, paving the way for future developments in sustainable energy harvesting.

In the study by Jelmy et al., conductive polymers such as polyaniline (PANI) play a significant role in improving the performance of TENG based on polydimethylsiloxane (PDMS) [40]. The researchers incorporated binary hybrids of graphene oxide (GO) and conducting polymers (CPs) such as PANI into the PDMS via an ultrasonication-assisted dispersion technique at room temperature. The dielectric properties of the PDMS composite were enhanced through various phenomena, such as electronic, vibrational, orientation, ionic, and interfacial polarization. The electron donating–accepting process between PDMS and the GO/CP filler increased the surface charge density of the PDMS composite, boosting the overall TENG performance. The presence of electron-trapping GO in the filler further contributed to the improvement of the composite material’s charge density. The study demonstrated that the PANI nanofiber intercalated GO morphology of the GO/PANI hybrid in the PDMS composite yielded a superior current generation compared to the PPy nanosphere intercalated GO incorporated PDMS system. These findings suggest the potential for utilizing the proposed material in mechanical energy harvesting applications through simple body movements, such as finger tapping and foot stamping.

Another strategy involves incorporating conductive polymers into gels to create more flexible and adaptable TENGs. In a pioneering study by Khan et al. [41]., a fully supramolecular gel-based TENG was developed, incorporating the conductive polymer poly(3,4-ethylenedioxythiophene) poly-styrene sulfonate (PEDOT:PSS) into an electrode gel. The gel-based TENG, called FSASG-TENG (fully self-healable anti-freezing supramolecular gel-triboelectric nanogenerator), displayed an exceptional performance, maintaining its stability even after 5000 cycles and multiple cut/self-healing processes. The supramolecular gel networks offered remarkable stretchability, reaching up to 50 times strain, and rapid self-healing (4 min for electrode gel and 24 h for tribolayer gel). Notably, the FSASG-TENG showcased a wide working temperature range of −40 to 80 °C, with an energy-harvesting capability verified at these temperatures. Moreover, the energy collected by the gel-based TENG was demonstrated to power commercial electronics, highlighting its potential as a versatile and deformable power source for flexible electronics. This innovative, self-healable, stretchable, and anti-freezing TENG offers a promising solution for energy harvesting in autonomous flexible electronics across a broad temperature range.

In their research, Yu et al. developed a novel strategy to fabricate a large-scale polyaniline (PANI)/PVDF-TrFE porous aerogel bulk piezoelectric/triboelectric nanogenerator (PTNG) using in-situ doping and liquid nitrogen quenching [42]. The composite aerogel, prepared with a PVDF-TrFE copolymer as the main substrate, sodium carboxymethyl cellulose (SCMC) as a thickener, and PANI as a conductive filler, undergoes rapid cooling with liquid nitrogen after thermoforming to induce the β-phase. Conductive polymers, such as PANI, play a critical role in enhancing the electrical properties of the composite piezoelectric polymer, allowing for an improved performance. The optimal output of the PANI/PVDF-TrFE PTNG, which contains up to 71% β-phase, achieves 246 V and 122 μA at a frequency of 30 Hz and pressure of 0.31 MPa, with a power density of 6.69 W/m². This innovative strategy facilitates the direct use of the PANI/PVDF-TrFE porous aerogel bulk without the need for subsequent electric field polarization, ultimately reducing energy consumption and shortening the preparation time. Yu et al.’s work addresses the challenge of polarizing PVDF bulk material, paving the way for three-dimensional manufacturing and practical applications of PVDF-based nanogenerators.

Overall, these strategies highlight the significant potential of conductive polymers for improving energy collection efficiency in TENGs. With continued research and development, these strategies will likely lead to further advancements in sustainable energy harvesting technologies.

Conductive polymers play a vital role in TENG biochemical sensing applications, such as ammonia sensing and sweat sensing. These polymers, including polyaniline (PANI), polypyrrole (PPy), and poly(3,4-ethylenedioxythiophene) (PEDOT), improve the sensitivity, selectivity, flexibility, biocompatibility, and environmental stability of TENG-based sensors [48] (Table 2). They enhance the sensitivity of sensors by providing efficient charge transport pathways and such polymers can be chemically modified to achieve selective recognition of target analytes [49]. Their inherent flexibility enables the integration with wearable or flexible devices, while their biocompatibility and environmental stability make them suitable for applications involving direct contact with the human body or exposure to challenging conditions. Overall, conductive polymers are essential for the development of advanced, self-powered, wearable, or implantable sensors in TENG-based biochemical sensing applications.

Conductive polymers are vital in TENG ammonia sensing as they enhance the sensitivity, selectivity, and stability of the sensors. For instance, Liu et al. have developed self-powered triboelectric gas sensors that use polyaniline (PANI) film for both the electrode and positive triboelectric layer [47]. These sensors measure triboelectric output signal variations without external power and exhibit high sensitivity to low ammonia concentrations due to limited active adsorption sites on the triboelectric layers. Conductive polymer nanofibers and composite materials further improve the TENG performance and expand potential applications, including wearable or flexible devices.

The integration of conductive polymers as nanofibers or conductive composite materials into TENGs not only enhances their performance but also expands their potential applications, such as wearable or flexible TENG devices [50,51,52,53,54,55,56,57]. This is due to the improved mechanical properties, such as flexibility, strength, and durability, which result from creating nanofibers or composite materials.

In a related development, Wang et al. introduced a novel approach to design a selective NH₃ sensor utilizing polyaniline (PANI) nanofiber-supported Nb2CTx nanosheets, which is directly driven by a TENG at room temperature [43]. This unique combination of PANI nanofibers and Nb₂CTx nanosheets, together with the TENG implementation, enhances the NH₃-sensing response and provides a broad sensing range of 1–100 ppm NH₃ at approximately 25 °C under 87.1% relative humidity (RH). This study showcases the potential of integrating TENGs and conductive polymers for the development of high-performance gas sensors.

The high surface area-to-volume ratio of conductive polymer nanofibers is crucial for increasing triboelectric charge generation efficiency. Furthermore, combining conductive polymers with other materials, such as sponge or metal nanoparticles, enables the creation of composites with tunable electrical properties. This, in turn, optimizes TENG performance.

Expanding on these advancements, Liu et al. have designed a conductive and elastic sponge-based triboelectric nanogenerator (ES-TENG) that employs conductive polymers such as polyaniline (PANI) for harvesting random mechanical energy and ammonia sensing [44]. By growing PANI nanowires on the sponge’s surface, the researchers developed a conductive elastic sponge that can harvest kinetic energy from irregular motion with various amplitudes and directions. The porous sponge and its PANI nanowires, serving as the ES-TENG’s triboelectric layer, offer a large contact area that enhances triboelectric efficiency. Moreover, the conductive PANI coating functions as the ES-TENG’s electrode, generating an output of 540 V and 6 μA. This innovative ES-TENG design demonstrates potential applications in irregular and random mechanical energy harvesting and self-powered NH₃ sensors, owing to its microporous and nanowire structures, elasticity, conductivity, and ease of fabrication.

Conductive polymer composites offer lightweight and cost-effective alternatives to traditional materials, and their compatibility with various fabrication techniques makes them versatile for different processes and substrates [58,59,60,61,62,63]. These properties render conductive polymer nanofibers and composites suitable for a wide range of TENG applications, including energy harvesting, sensing, and actuation.

One notable example is Wang et al.’s innovative self-powered ammonia (NH₃) sensor, which utilizes polyaniline (PANI)/MXene (V2C) composites as building blocks for a supercapacitor powered by an electromagnetic-triboelectric hybrid generator [45]. The MXene’s large accessible surface area enhances the electrochemical activity of PANI, resulting in an improved performance for both the NH₃ sensor and the supercapacitor. This integrated self-power system demonstrates the potential for creating self-powered gas sensing solutions in industrial and agricultural settings, with applications ranging from mine ammonia leakage alarms to food safety monitoring for remote seniors.

Further building on the potential of conductive polymers, Chang et al. developed a highly sensitive and efficient biosensor based on conductive polyaniline (PANI) and reduced graphene oxide (rGO) nanosheets [46]. The PANI-rGO heterostructure exhibits a remarkable sensing performance for ammonia detection, offering linear sensibility, a low limit of detection (46 ppb), and a rapid response time (approximately 75 s). The unique properties of conductive polymers, such as PANI, make them ideal for high-sensitivity sensing materials, while the in-situ growth of monomers on the graphene surface allows for the fabrication of homogeneous PANI-rGO heterostructures without the need for additives.

This innovative, cost-effective, and environmentally friendly biosensor can be integrated with a TENG to create a wearable, self-powered ammonia sensor for early warning systems. The advancements in self-powered sensing systems, as demonstrated by Wang et al. and Chang et al., hold great potential for practical applications and expand the scope of self-powered devices across various industries.

The combination of conductive polymers with TENGs has shown promise in the development of self-powered and highly sensitive sensors for various biochemical sensing applications [64]. The unique properties of various conductive polymers, such as PANI, make them suitable candidates for the development of sensors for detecting various biomarkers, including creatinine or other components in sweat.

PANI can significantly improve the sensitivity of TENG-based sensors by providing efficient charge transport pathways [65,66,67,68,69,70]. Additionally, PANI can be chemically modified to achieve selective recognition of target analytes. The inherent flexibility of PANI enables the seamless integration of PANI-integrated TENG sensors with wearable or flexible devices, making them suitable for the on-body or non-invasive monitoring of creatinine levels. Furthermore, the biocompatibility of PANI makes it an ideal choice for applications involving direct contact with the human body.

In a pioneering study by Luo et al., a cutting-edge, flexible creatinine nanosensor was developed utilizing polyaniline (PANI) and polydimethylsiloxane (PDMS) [71]. The sensor’s operation relies on the synergy between the TENG and the creatinine enzymatic reaction. The enzyme-modified TENG, composed of PANI and PDMS, exhibits changes in electroconductivity due to the enzymatic reactions. These changes, in turn, affect the triboelectric output and provide information about the ambient creatinine concentration.

The nanosensor demonstrates remarkable sensitivity at room temperature, with a 51.42% response when the creatinine concentration is 10⁻³ mol/L, and impressive selectivity compared to NaCl, glucose, and urea. Furthermore, the sensor supports a wide range of flexibility in bending angle measurements (10°–40°), making it suitable for wearable sensing applications. Experimental results indicate that this flexible nanosensor enables continuous, non-invasive detection of creatinine, opening new avenues for electronic skin and self-powered healthcare systems.

In conclusion, the unique properties of PANI, such as its flexibility, biocompatibility, and ability to be chemically modified, make it an ideal material for enhancing the performance of TENG-based sensors. The development of wearable, non-invasive sensors such as the one designed by Luo et al. showcases the potential for real-time monitoring of biomarkers such as creatinine. This advancement paves the way for innovative electronic skin and self-powered healthcare systems, revolutionizing personal health tracking and management. As researchers continue to explore the capabilities of PANI, we can expect to see more breakthroughs in the field of non-invasive, real-time health monitoring and personalized medicine.

PANI has the potential to greatly enhance the environmental stability and durability of TENG-based sensors, making them suitable for the long-term monitoring of sweat components under various conditions [77,78,79,80,81,82,83,84]. The unique electrical properties of PANI can be fine-tuned to optimize the performance of these sensors. Moreover, by combining PANI with other materials, researchers can create composites with tailored electrical properties that further enhance the overall performance of the sensor.

In a study conducted by Qin et al., a highly flexible and self-powered biosensor was developed for the real-time analysis and wireless transmission of Na+, K+, and Ca²⁺ levels in sweat [72]. This cutting-edge sensor incorporates polyaniline (PANI) as a conductive polymer, which is combined with cellulose nanocomposites to create a hydrogel electrode. The resulting electrode boasts remarkable tensile and electrical self-healing efficiencies of over 95% within 10 s, as well as stretchability up to 1530% and conductivity of 0.6 S/m.

The integration of PANI within the hydrogel electrode greatly enhances the sensor’s performance, enabling the detection of Na+, K+, and Ca²⁺ ions with sensitivities of 0.039, 0.082, and 0.069 mmol⁻¹, respectively. By leveraging the triboelectric effect for real-time monitoring, the sensor can wirelessly transmit data to a user interface, providing easy access to the information. The self-powered sweat sensor designed by Qin et al., with PANI as a crucial component, showcases extraordinary flexibility, stability, sensitivity, and selectivity, setting the stage for advanced health monitoring applications.

In conclusion, the unique properties of conductive polymers such as PANI suggest that they can play a significant role in enhancing the performance of TENG-based sensors for various applications. By harnessing the advantages of PANI, researchers can develop highly sensitive, flexible, biocompatible, and stable TENG-based sensors for creatinine or sweat detection. This, in turn, paves the way for the development of wearable, non-invasive, and real-time monitoring of these biomarkers, revolutionizing personal health tracking and management.

In the future, the integration of PANI with other advanced materials and techniques will enable researchers to develop even more sophisticated TENG-based sensors. This will result in expanded applications in various fields such as sports performance monitoring, disease detection and management, and environmental monitoring. The ongoing advancements in PANI-based TENG sensors illustrate the potential for transformative breakthroughs in non-invasive, real-time health monitoring and personalized medicine.