Abstract: Provided are implantable probes for analyzing biological fluids and related methods of using and making. The probe is formed with an integrated on-chip probe body that provides for collection and storage of analyte from biological fluid and facilitates subsequent analysis, including by a mass spectrometer (MS). The analysis has high spatial accuracy as the probe tip that collects biological fluid sample is small, including less than 100 ?m with an opening less than 10 ?m. Temporal information can be obtained by storing the analyte from the biological fluid as a train of droplets separated by an immiscible fluid. The probe body can be electrically energized to facilitate sample ionization and transfer to a MS analysis device. In this manner, the integrated on-chip probe body facilitates analyte collection, storage and subsequent analysis within a single probe body material, including a doped silicon material.