Nanoliter-scale biological fluid conductivity detection via a laser-printed functionalized fiber probe

The development of micro-detectors capable of detecting conductivity in trace biological fluids is crucial for physiological signal monitoring and personal healthcare. To date, widely used conductivity detectors face challenges such as large probe size, complex detection systems, and difficulty in achieving trace and invasive detection. Here, we present a laser-printing fiber probe functionalized with customized Fabry-Perot cavities for conductivity detection in ultra-trace biological fluids. This probe demonstrates an actual detection capacity of 50 nL, the lowest volume required among known micro detectors. It achieves a high sensitivity of 232.77 pm·(mS·cm⁻¹)⁻¹ and offers micron-level spatial resolution suitable for invasive detection. Furthermore, the capillary combination and good anti-interference performance of temperature and pH prove the feasibility of invasive and complex environment detection, respectively. Our work provides a new paradigm for nanoliter-scale biological fluid detection and can be reconfigured to detect other biomarkers via the customization of structures and materials, enhancing the potential of fiber probes in bio-diagnosis and health monitoring. © 2026 The Author(s).