Smartphone-assisted upconversion nanoparticles-aptamer-based probe functionalized hydrogel microneedles for rapid interstitial fluid lactate profiling.

Rapid assessment of lactate dynamics is important for evaluating tissue hypoxia, metabolic stress, and exercise-induced physiological responses. However, conventional lactate measurements predominantly rely on blood sampling and enzyme-based assays, making them poorly suited for rapid and minimally invasive assessment of localized lactate dynamics in interstitial fluid (ISF). Here, we developed a rare-earth nanomaterial-aptamer probe-functionalized composite hydrogel microneedle patch for rapid ISF lactate profiling. The sensing system integrates fluorescence resonance energy transfer (FRET)-based signal modulation with smartphone-assisted imaging, enabling portable lactate quantification within 20 min. The hydrogel microneedles facilitate minimally invasive ISF access while providing an integrated interface for analyte recognition and optical signal transduction. In vitro, the patch exhibited a concentration-dependent fluorescence response over a lactate range of 2-20 mM (R2 = 0.961), with a limit of detection (LOD) of 0.47 mM. In a rat model with elevated lactate levels, ISF lactate concentrations measured using the microneedle patch showed a strong correlation with simultaneously determined blood lactate concentrations obtained using a commercial assay kit, supporting reliable in vivo lactate assessment. Collectively, this work presents an integrated, minimally invasive, and portable strategy for rapid ISF lactate profiling and provides a versatile platform for the timely evaluation of exertion-related metabolic biomarkers and personalized physiological assessment.