Multiplexed Colorimetric Capillary-Driven Microfluidic Sensor for Detecting Bacterial STIs

Chlamydia, syphilis, and gonorrhea are three of the most common bacterial sexually transmitted illnesses (STIs) with over 2.4 million cases diagnosed and reported in the United States in 2023. While a large portion of these cases are curable, many cases go undiagnosed and therefore hinders effective disease control. STIs can have serious consequences such as pelvic inflammation, infertility, increased risk of HIV acquisition, and neonatal death. Routine, accessible testing is urgently needed to improve early diagnosis and intervention. This work proposes a multiplexed, rapid colorimetric test for chlamydia, syphilis, and gonorrhea that offers the user a visual output in less than 20 minutes. A microfluidic device is constructed of laser-cut polyethylene terephthalate (PET) and double-sided adhesive (DSA) sheets to form hollow channels that allow rapid capillary-driven flow. Nitrocellulose strips are pretreated to immobilize target-specific antibodies each for chlamydia, syphilis, and gonorrhea. Horseradish peroxidase (HRP)-labeled antibody and 3,3’,5,5’-tetramethylbenzidine (TMB) are dried onto a conjugate release pad to be placed inside the hollow channels. Upon the addition of a liquid sample that contains the bacterial STI antigen, fluid travels through and fills the microfluidic channels, rehydrating and transporting the colorimetric reagents in a carefully engineered order to yield color formation on the modified nitrocellulose strips. End users can be informed of the presence of three different types of STI antigens in their genital samples. Initial single-pathogen prototypes showed detection limits of 5.29 ng/mL for chlamydia major outer membrane protein and 2.69 ng/mL for syphilis p47 protein. Developing the gonorrhea assay further and integrating the three assays into a multiplexed microfluidic device will benefit many sexually active personnels by providing a rapid, sensitive, affordable at-home assay that could test for three prevalent bacterial STIs.