This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Penicillin has cured syphilis cases since 1943, but symptoms of the sexually transmitted infection, known as "the great imitator," mimic many other diseases and can come and go without treatment while the infection keeps causing harm. If it remains undetected, it can spread to partners and to babies during pregnancy, causing lifelong effects.
A new rapid test developed by a team led by Penn State researchers detects lower levels of the two types of antibodies the body makes to fight the syphilis bacteria and respond to disease-related cell damage, potentially leading to earlier interventions and fewer appointments for patients. Key to the advancement are the nanoparticles that accumulate and form the visible line for a positive result on most diagnostic tests, according to corresponding author Dipanjan Pan, Penn State's Dorothy Foehr Huck & J. Lloyd Huck Chair Professor in Nanomedicine.
The team's new pilot testing device, presented in a study published in ACS Sensors, swapped the typical gold nanoparticle for one layered in silver and sealed in more gold to produce test lines 19% to 46% stronger than those of comparable devices while reliably detecting lower concentrations of antibodies. "The low-titer range, meaning the range with the lowest concentration of antibodies, is particularly challenging for detecting syphilis," Pan said. He added that nanoparticles accumulate into a visible line as they bind to more and more antibodies in a sample flowing through the device.
"This range is also clinically important, occurring during early infection, later stages of syphilis or after treatment when antibody levels are declining to make sure treatment worked." In the diagnostic pathway established by the U.S. Centers for Disease Control and Prevention (CDC), the first "treponemal" blood test detects antibodies against the syphilis bacteria, Treponema pallidum. These antibodies stay in the body for decades, and a patient who received treatment years ago will still test positive as long as the antibodies remain in their system.
The second "non-treponemal test" looks for separate antibodies created in response to cellular damage, indicating the stage of infection and whether a person needs treatment. Running both tests lessens the chance for false-negative or false-positive results and gives doctors a better sense of whether the disease occurred in the past, is currently active or has been properly treated, according to the CDC. "What is important about our approach is that we are not asking clinicians to abandon this well-established diagnostic pathway," Pan said.
"Instead, we are trying to reproduce the same sequence of diagnostic information in a much faster and potentially point-of-care format." The limitation to this point, he explained, was not the ability to detect the antibodies but the ability of clinicians to see the gold nanoparticles that only become visible to the naked eye when enough of them accumulate. One way to make them "brighter" was to increase their size. However, around 60 nanometers, roughly 100 times smaller than a red blood cell, they start clumping or settling like sand in a river rather than flowing through the device.
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