Evaluation of optical biosensing techniques towards point-of-care diagnosis of active TB.

Abstract

Tuberculosis (TB) remains one of the leading causes of mortality and morbidity globally even though it is a treatable disease. South Africa is one of 22 countries with a high TB burden that accounts for 83% of worldwide TB cases. Recent innovations in "near-patient" or point-of-care (POC) diagnostic technologies for TB have resulted in early treatment initiation. For instance, the roll-out of GeneXpert MTB/RIF devices in resource-limited countries has resulted in improved rapid and accurate diagnosis of TB and rifampicin resistance testing. Regardless, these devices also have limitations, for example, requirements for specialized infrastructure, operation by highly trained personnel, and high costs per test. This is a significant setback, especially in developing countries. Thus, a rapid and effective diagnosis of TB is a crucial intervention strategy for reducing the burden of TB. As a result, there is a need for a cost-effective, userfriendly, and robust POC TB diagnostic device with high sensitivity and specificity. Hence, this study focuses on the evaluation of optical biosensing techniques for the development of a POC device for TB diagnosis. Biosensors offer great advantages over conventional analytical techniques. Specifically, they can provide multiple capabilities such as user-friendly operation, real-time analysis, rapid response, high sensitivity and specificity, portability, label-free detection, and cost-effectiveness. This diagnostic approach possesses suitable features to develop POC diagnostics and monitoring technologies. A novel optical biosensor chip was developed to monitor biomolecular interactions between mycolic acid antigens and antimycobacterium tuberculosis antibodies. Mycolic acid was successfully immobilized on a goldcoated surface and a photonic crystal-based surface and allowed to react with antimycobacterium tuberculosis antibody as an analyte. The biosensor chip surface was characterized using various tests, including atomic force microscopy (AFM), scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) spectroscopy. To enhance the detection signal from biomolecular binding events, gold nanoparticles (AuNPs) were bioconjugated with goat anti-rabbit IgG H&L secondary antibody and introduced on the biosensing surface. Characterization of the AuNPs before and after bioconjugation was performed using ultravioletvisible (UV-vis) absorption spectroscopy, dynamic light scattering (DLS), transmission electron microscopy (TEM), and further analyzed using Fourier-transform infrared (FTIR) spectroscopy. The gold-coated biosensor chip was analyzed using a custom-built nanoplasmonic biosensing setup to differentiate the experiment from control groups, and the photonic crystal-based biosensor chip was analyzed using a similar setup using a white light source. The obtained results showed that mycolic acid was successfully immobilized on the biosensing surface and made it possible to capture anti-mycobacterium tuberculosis antibodies. The nanoplasmonic optical biosensing technique was indeed successful in the detection of anti-mycobacterium tuberculosis antibodies.