Fingerprint identification is a widely used biometric technique. However, current systems are vulnerable to attacks using fake fingerprints. Existing liveness detection methods typically rely on sophisticated computer algorithms to analyze fingerprint images. This research proposes a novel approach: material-based liveness detection. The core idea is to develop a material that intrinsically distinguishes between live and fake fingerprints during the collection process itself, eliminating the need for complex post-processing algorithms. The key difference exploited is the ability of live fingers to secrete sweat, which is absent in fake fingerprints. This study focuses on designing a sweat-responsive material that would directly reveal the fingerprint pattern only when interacting with live fingers.

The paper reviews existing fingerprint liveness detection methods, which primarily rely on computer algorithms to analyze image data for patterns and level 3 features like sweat pore distributions. The limitations of these methods, such as vulnerability to sophisticated fake fingerprints, are highlighted. The authors then introduce the concept of material-based liveness detection, offering a novel strategy to address the security challenges of traditional methods by shifting the focus from software-based analysis to material-based fingerprint collection.

The researchers synthesized a sweat-responsive COF, COFTPDA-TTFy, using a solvothermal method. The synthesis involved the use of N,N,N',N'-tetrakis(4-aminophenyl)-1,4-benzenediamine (TPDA) and 1,3,6,8-tetrakis(4-formylphenyl)pyrene (TFPy) as building blocks. The resulting COF powders were characterized using various techniques such as powder X-ray diffraction (PXRD), Fourier-transform infrared spectroscopy (FTIR), ¹H nuclear magnetic resonance (NMR), and Brunauer-Emmett-Teller (BET) analysis to confirm its structure and properties. COFTPDA-TTFy films were grown on transparent glass substrates using the same solvothermal method. The morphology of the films was examined using scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM). The sweat responsiveness was investigated by exposing the film to human sweat and analyzing the resulting color change using UV-Vis spectroscopy. Fingerprint collection involved gently touching the film with a finger for a specified duration. The resulting fingerprint patterns were analyzed using image processing techniques. Sweat pore analysis involved reducing the contact time to 1-5 seconds, allowing for visualization of sweat pore distribution. The reusability of the film was evaluated by washing it with ethanol.

The synthesized COFTPDA-TTFy film exhibited a clear color change from yellow to red upon exposure to sweat, creating a visible fingerprint pattern. This color change is attributed to the interaction of sweat components with the COF material and is not simply due to hydration. Artificial fingerprints, lacking sweat, did not produce any visible pattern. The method demonstrated 100% accuracy in distinguishing between live and fake fingerprints. Furthermore, by adjusting the contact time, the researchers successfully collected and analyzed sweat pore distribution images. The COF film exhibited excellent reusability, maintaining clear image quality after 50 cycles of use and washing with ethanol. Fingerprint patterns collected on the COF film were compatible with existing fingerprint recognition software, with high similarity scores observed between multiple prints from the same individual. The sweat pore analysis revealed distinctive patterns, potentially offering insights for clinical research and personal identification. The ease of use and low cost ($0.02 per sample) are major advantages of the method.

The results demonstrate the effectiveness of the proposed material-based liveness detection approach, offering a simple, accurate, and cost-effective alternative to existing methods. The use of a sweat-responsive COF material eliminates the need for complex computer algorithms, simplifying the process while enhancing security. The ability to simultaneously collect fingerprint and sweat pore information provides additional biometric data, potentially improving identification accuracy and offering new opportunities for clinical research related to sweat secretion behavior and chronic diseases. The compatibility of the collected data with existing fingerprint recognition systems enables seamless integration into current personal identification systems.

This study successfully demonstrated a novel material-based liveness detection method using a sweat-responsive COF film. The method offers several advantages, including high accuracy, simplicity, low cost, and reusability. Future research directions could involve exploring other COFs with different properties and investigating the potential applications of the technology in various clinical and forensic settings. Furthermore, exploring the sensitivity of sweat pore distribution patterns to various physiological conditions could offer valuable insights into health diagnostics.

While the study demonstrated high accuracy in distinguishing live from fake fingerprints, the generalizability of the findings to a broader population and diverse environmental conditions warrants further investigation. The current study focused on a specific COF material; further research is needed to investigate the performance of other materials. The effect of different sweat compositions on the sensitivity and reliability of the method should also be carefully studied.