Amid the rapid evolution of technologies in precise detection, intelligent monitoring, and personalized medicine, chemical sensors—core devices for obtaining information on material composition and concentration—are advancing toward miniaturization, flexibility, array integration, and low-cost manufacturing. Leveraging its unique advantages of non-contact precision deposition, digital pattern control, and high material utilization, inkjet printing technology has overcome the limitations of traditional sensor fabrication methods that rely on masks, complex processes, and high costs. It has thus emerged as an innovative technological pathway for constructing high-performance chemical sensors. From flexible wearable biomarker detection to industrial environmental pollutant monitoring, inkjet-printed chemical sensors are demonstrating tremendous research value and application potential.
I. Core Adaptation Logic Between Inkjet Printing Technology and Chemical Sensors
The performance of chemical sensors fundamentally depends on the selectivity, response speed, and stability of sensitive materials, while device miniaturization and integration directly determine the expansion of application scenarios. Through precise regulation and deposition of functional inks, inkjet printing technology enables a high degree of matching among “material–structure–performance” in sensor design. Its adaptability is mainly reflected in three aspects:
(1) Precise Loading and Structural Regulation of Sensitive Materials
Inkjet printing enables precise deposition of inks containing nanoscale sensitive materials (such as MXene, polyaniline, and molecularly imprinted polymers) in droplets ranging from picoliters to nanoliters, with droplet volume deviation less than 5%. This allows quantitative control over the thickness (100 nm–10 μm) and microstructure of the sensitive layer.
For example, in humidity sensor fabrication, by controlling the number of printed layers of MXene/sodium alginate composite ink, the porosity and specific surface area of the sensitive layer can be precisely adjusted, resulting in more than a threefold increase in humidity response sensitivity. This precise controllability addresses the pain points of uneven material distribution and difficult dosage control inherent in traditional coating processes.
(2) Digital Customization of Multidimensional Structures
Based on CAD-designed digital printing systems, microelectrode patterns and sensor arrays with line widths below 10 μm can be fabricated directly without additional mask processing.
A research team at Donghua University optimized a two-dimensional polyaniline ink formulation to achieve patterned electrode printing with a resolution of 50 μm. The electrochromic response speed improved by 40% compared to traditional processes. This flexibility enables single-chip integration of multi-parameter detection systems. For instance, by printing inks containing different molecularly imprinted nanoparticles, sensor arrays capable of simultaneously detecting vitamin C, tryptophan, and creatinine can be constructed.
(3) Compatibility with Flexible Substrates and Integrated Systems
The non-contact nature of inkjet printing enables stable film formation on flexible substrates such as PET, PI, and chitosan, with a minimum bending radius of 5 mm without performance degradation.
A team from the Chinese Academy of Sciences simultaneously printed micro-supercapacitors and temperature sensors using aqueous MXene ink on flexible substrates, constructing a fully flexible self-powered sensing system. This overcomes the limitation of traditional sensors that rely on external power supplies. Such integration capability provides critical technical support for the development of wearable and implantable sensors.
II. Core Fabrication Technologies and Application Scenarios of Inkjet-Printed Chemical Sensors
(1) Design and Optimization of Key Ink Systems
Ink formulation is the core determinant of inkjet-printed chemical sensor performance. It must simultaneously meet printing compatibility requirements (viscosity 5–25 mPa·s, surface tension 25–40 mN/m) and sensing functionality. Three typical ink systems have been developed:
1. Conductive Polymer-Based Inks
These are based on polyaniline (PANI), polypyrrole, and similar materials, with dispersion stability achieved through solvent engineering.
The Donghua University team, based on Hansen solubility parameter theory, selected formic acid as a dispersant and prepared a two-dimensional layered PANI ink without surfactants. After 15 days of standing, no sedimentation occurred. The printed electrodes achieved 76% optical transmittance modulation at 720 nm and are suitable for electrochemical gas sensors.
2. Two-Dimensional Nanomaterial-Based Inks
Materials such as MXene and graphene are preferred due to their high specific surface area and conductivity.
A team from Xihua University modified MXene with polyelectrolyte sodium alginate (SA), forming a composite ink used to print humidity sensors with a response time of only 0.3 seconds to human breath and a recovery time of 2.0 seconds. The temperature sensitivity coefficient (TCR) reached 1.08% ℃⁻¹, representing a 103% improvement over unmodified systems.
A research team from the Chinese Academy of Sciences developed aqueous MXene/PH1000 hybrid ink with multifunctionality as electrode, current collector, and interconnect. The printed micro-supercapacitor directly powered an integrated temperature sensor.
3. Functionalized Nanoparticle Inks
Core-shell nanoparticle design enables specific detection.
A team at the California Institute of Technology developed core-shell cubic nanoparticle ink, with nickel hexacyanoferrate as the core for stability and molecularly imprinted polymer as the shell for target recognition. The printed sweat sensor enables real-time monitoring of vitamins, hormones, and other biomarkers, showing application potential in personalized cancer drug dosage regulation.
(2) Technological Breakthroughs in Typical Application Scenarios
1. Flexible Wearable Health Monitoring
Inkjet-printed sweat sensors enable non-invasive health monitoring.
Flexible sensors printed with MXene/SA composite ink, combined with the biocompatibility and antibacterial properties of chitosan substrates, can adhere to skin to monitor body temperature and sweat humidity, achieving a response amplitude of 357%.
Molecularly imprinted nanoparticle sensors can track anticancer drug levels in vivo, supporting precision medicine. These devices exhibit less than 10% performance degradation after 1000 bending cycles, meeting long-term wearable requirements.
2. Environmental and Industrial Detection
In gas and humidity monitoring, inkjet printing enables the combination of high sensitivity and miniaturization.
Gas sensors printed with two-dimensional PANI electrodes respond to harmful gases through changes in protonation degree, with coloration and bleaching response times of only 1.8 seconds and 2.4 seconds, respectively.
Matching-layer inks printed for ultrasonic probes allow acoustic impedance tuning from 2.7 to 42 MRayl and acoustic attenuation of 5–9.3 dB/cm, enabling precise detection of fluid composition changes in industrial environments.
3. Self-Powered Integrated Sensing Systems
Through collaborative printing of multifunctional inks, “sensing–power supply” integration can be achieved.
The Chinese Academy of Sciences team simultaneously printed MXene-based micro-supercapacitors (volumetric capacitance 754 F/cm³) and temperature sensors on flexible substrates. Combined with flexible silicon thin-film solar cells, the system enables real-time temperature monitoring and data transmission without external power supply, offering a new solution for IoT node monitoring.
III. Technical Advantages and Existing Core Challenges
(1) Breakthrough Advantages Compared with Traditional Processes
1. Dual Optimization of Cost and Efficiency
Traditional photolithography processes have material utilization rates below 50%, whereas inkjet printing exceeds 95%, significantly saving expensive materials such as MXene and precious metals.
Digital pattern design eliminates the need for remanufacturing molds when switching products, shortening development cycles from months to days and making it suitable for small-batch, multi-variety sensor production.
2. Precise Regulation of Performance and Function
By adjusting the number of printed layers, sensitive layer thickness can be linearly controlled. For example, a five-layer PANI printed electrode achieved a coloration efficiency of 259.1 cm²C⁻¹, a 2.3-fold increase compared to a single layer.
Multi-nozzle array printing enables synchronous deposition of different sensitive materials to construct multi-parameter detection arrays, which is difficult to achieve using traditional coating processes.
3. Deep Integration of Flexibility and Functionality
Low-temperature film formation (60–120 ℃ drying) prevents thermal damage to flexible substrates, enabling integration with textiles and skin patches.
Integrated printing with micro-energy devices overcomes power supply limitations in wearable systems.
(2) Major Bottlenecks in Industrialization
1. Balancing Ink Stability and Functionality
Nanoparticles such as MXene and PANI tend to agglomerate at high concentrations, requiring dispersants or modifiers, which may compromise sensing performance.
For example, surfactants reduce electrode conductivity, while binders may block active sites of sensitive materials. Although solutions such as formic acid protonation and polyelectrolyte modification exist, universally applicable ink formulation theories are still lacking.
2. Insufficient Printing Consistency and Long-Term Reliability
Nozzle clogging causing droplet deviation (error exceeding 2 μm) may result in sensor response deviation greater than 15%.
Thermal expansion and contraction of flexible substrates can cause cracking of sensitive layers. Although real-time monitoring technology can partially correct errors, quality control costs remain high in mass production.
3. Performance Degradation in Complex Environments
Wearable sensors exposed to sweat and temperature fluctuations may experience dissolution or oxidation of sensitive materials.
For instance, MXene-based sensors exhibit significantly reduced stability in environments with pH > 8. Although chitosan encapsulation can mitigate degradation, response sensitivity still declines by more than 20% after long-term use (over 30 days).
Inkjet printing technology is thus redefining the fabrication paradigm of chemical sensors. By integrating materials science, digital manufacturing, and flexible electronics, it is accelerating the transition from laboratory research to industrial applications. However, overcoming challenges in ink formulation theory, reliability control, and environmental stability remains critical to unlocking its full industrial potential.