Microneedle Patch for In Situ Neutrophil Monitoring.

Monitoring neutrophil levels plays an essential role in diagnosing infections and various diseases, as well as for managing specific treatments such as chemotherapy and radiotherapy. However, the traditional complete blood count technique is invasive and challenging for quick and frequent monitoring of neutrophil. Herein, a button-like microneedle patch for rapid and convenient detection of neutrophil levels is reported without vascular invasion. This patch consists of a hollow microneedle array with a vacuum chamber for extraction of interstitial fluid, a hydrogel sheet for colorimetric detection of neutrophil level based on neutrophil-specific enzyme (myeloperoxidase), and a mobile phone application for data recording and quantification. The detection ability is validated both in vitro and in vivo in a chemotherapy-induced neutropenic rat model. Moreover, this button patch achieves precise measurement of the neutrophil levels in patients' urine and abdominal drainage fluid. This minimally invasive colorimetric patch can potentiate in situ neutrophil monitoring without blood sampling procedures or in-lab apparatus, which can serve as a substitution for routine blood counts especially for patients in less developed areas.