Lab on fiber: A 3D-printed fiber-tip microprobe for synchronous detection of doxorubicin concentration and...

Accurate monitoring of doxorubicin (DOX) is important for individualized chemotherapy, yet conventional fiber-optic surface plasmon resonance (SPR) sensors are often limited by large probe dimensions and temperature cross-sensitivity. In this paper, a compact fiber-tip microprobe that integrates SPR and Fabry-Perot interference (FPI) for synchronous detection of DOX concentration and temperature is reported. The microprobe is composed of a square frustum-similar structure, which is directly printed on the end face of a single-mode fiber by femtosecond laser-induced two-photon polymerization. By optimizing the structural parameters, SPR and FPI are simultaneously excited within the 24 μm-high microprobe. The sensing surface is further functionalized with the DOX-specific aptamer to enable selective molecular recognition. In the range of 0-100 μM DOX, the SPR and FPI channels exhibit sensitivities of 0.075 and 0.060 nm/μM, respectively, with corresponding limits of detection of 8.8 and 19.1 μM. Over 28-40 °C, the SPR and FPI temperature sensitivities are -0.66 and -0.61 nm/°C, respectively. A dual-parameter decoupling matrix enabled simultaneous determination of DOX concentration and temperature. The microprobe also showed satisfactory stability and selectivity, demonstrating its potential for miniaturized therapeutic drug monitoring.