Rapid differential diagnosis of periprosthetic joint infection by microdroplet reaction on portable biochip and indicator

Periprosthetic joint infection (PJI) is a catastrophic complication after joint arthroplasty. A key step to treat PJI is accurate diagnosis. However, according to the existing guidelines, no biomarker has been used to diagnose PJI alone and autoimmune diseases such as rheumatoid arthritis (RA) often interfere with the diagnosis. Patients with PJI often still face issues such as misdiagnosis and delayed treatment after a comprehensive scoring diagnosis. Thus, a rapid quantitative detection method based on excellent biomarker is needed. Here, an all-printed photonic crystal (PC) biochip is reported. Through the fluorescence enhancement effect of the photonic crystals and the design of the hydrophilic and hydrophobic patterning structure, trace detection of lactoferrin (LTF) in a drop of viscous synovial fluid can be achieved within 10 min by the biochip. The detection limit is as low as 4.6 ng/mL. For more intuitive results, portable testing equipment is developed with indicator light displays of three colors (green = NPJI, yellow = RA, and red = PJI) to indicate the diagnosis depending on the biochip's fluorescence intensity. Furthermore, 79 clinical synovial fluid samples are tested with PC biochips, and the PC results are in good agreement with the ELISA results. Due to the microdroplet reaction on PCs, biochips are suitable for the detection of the selected markers in the synovial fluid. The use of the three-color portable testing equipment avoids the need for professional testing devices. Overall, this strategy provides a new paradigm for the early and differential diagnoses of PJI.