A paper-based loop-mediated isothermal amplification assay coupled with a portable heating device for point-of-care detection of syphilis in low-resource settings

Syphilis, a sexually transmitted disease caused by the spirochete bacterium <i>Treponema pallidum</i>, remains a significant global health concern. Serological methods are widely used but have limitations in early-stage infections and immunocompromised patients. This highlights the need for rapid, accurate, and cost-effective diagnostic tools to aid in syphilis management and outbreak prevention. Paper-based analytical devices have gained considerable attention in recent years for point-of-care applications due to their simplicity, low cost, and minimal equipment requirements. In this study, we have developed a paper-based loop-mediated isothermal amplification (LAMP) assay for the detection of <i>T. pallidum</i> DNA in clinical samples, targeting the <i>Pol A</i> and <i>RNase P</i> genes. The platform utilized a paper substrate integrated with hydroxy naphthol blue dye for visual colorimetric detection. A portable heating platform was designed to maintain the isothermal conditions necessary for amplification. The device demonstrated excellent stability when stored at 4 °C and 25 °C, with reproducibility significantly reduced at 37 °C. Sensitivity tests revealed a detection limit of 6.4 × 10^-4 ng μL^-1. Clinical evaluation of the paper-based LAMP assay was conducted using 52 suspected syphilis cases and 25 healthy volunteers. The assay achieved a sensitivity of 96.15% and a specificity of 100% in detecting syphilis. This portable, cost-effective device offers a promising lab-on-a-chip diagnostic solution for syphilis and can be adapted for detecting other infectious diseases.