Tuberculosis (TB) is the world’s second deadliest infectious disease, after HIV/AIDS. Culture is still the gold standard in TB diagnostics, but is slow (~2 weeks), costly, and requires biosafety level 2+ infrastructure. TB can be cured if promptly detected, which places the dearth of early diagnostic tests and poor clinical infrastructure at the forefront of barriers to the successful identification and treatment of infected individuals and to the mitigation of secondary transmission. Our platform is predicated on surface enhanced Raman spectroscopy (SERS) technology. The assay uses selective recognition elements to capture antigenic biomarkers of TB from serum, where they are present at concentrations of ~1 nM in early-stage infection. Furthermore, the SERS platform is amendable to use in resource limited settings.
A SERS Immunoassay with Raman readout was designed to detect lipoarabinomannan (LAM) as a marker of active TB infection, with limits of detection (LOD) in serum of ≤1ng/mL. . A proof of principal study conducted with specimens collected from a small 34 patient cohort with culture confirmed (smear positive, HIV negative) for TB. Serum samples were acidified, centrifuged and the supernatant was neutralized prior to application to the SERS substrate.
An evaluation of assay effectiveness was performed using 24 TB-positive and 10 TB-negative patient serum specimens. Of the TB-positive specimens, 21 had measureable levels of LAM; LAM was not detectable in 3 of these specimens or in the 10 TB-negative specimens. Moreover, 17 of the TB-positive specimens contained LAM at levels below that which would be detectable by ELISA.
LAM as a sole serum based marker had a clinical sensitivity of 91% and specificity of 100%, a positive predictive value of 100%, and a negative predictive value of 76.9%. Three samples were considered false negatives as the detected level of LAM was at the analytical LOD of the assay. All 10 TB negative patient samples tested well below the LOD. From these preliminary results, we believe that our platform has the potential to provide clinicians with a new diagnostic tool to reliably detect markers of TB at levels below that of ELISA. Furthermore, serum testing has an added advantage of detecting TB antigen in patients without a cough as well as for non-pulmonary forms of the disease.
A. Crawford, None
R. Robinson, None
D. Chatterjee, None
K. Hanson, None
M. Porter, None