Local protein detection with lateral flow assay read through tissue using X-ray excited luminescence chemical imaging.

Significance: Implant-associated infections can be difficult to detect at early stages. Noninvasively measuring inflammatory biomarkers such as C-reactive protein (CRP) in synovial fluid can improve early diagnosis and patient outcomes. Aim: We aim to show proof of principle for an implantable immunoassay device combined with an optical readout method to detect extracellular proteins through tissue. The system integrates lateral flow assay (LFA) strips with X-ray scintillators in a sealed implantable casing. Approach: An LFA strip is placed above a scintillator layer inside the implant. An X-ray beam excites the scintillator, generating luminescence that passes through the LFA. Test and control lines alter the transmitted light, and a fluorescent layer shifts the luminescence to red wavelengths to improve tissue penetration. External activation is enabled via high-intensity focused ultrasound to melt a wax seal. Results: We demonstrated protein detection using LFA strips for CRP and human chorionic gonadotropin through 6 mm of porcine muscle. Optical images clearly resolved 0.5-mm-wide test and control lines, with a strong correlation between signals measured with and without tissue. The device remained functional after extended fluid immersion. Conclusions: We show that LFA-based immunoassays can be integrated with X-ray excited luminescence imaging for through-tissue protein detection, advancing the development of implantable biosensors.