Assessment of terbium (III) as a luminescent probe for the detection of tuberculosis biomarkers

• Nicotinic acid, a specific marker of M. tuberculosis, can be detected via luminescence.
• The detection limit with a commercial phosphorimeter is 0.4 µmol·L-1.
• Other metabolites of M. tuberculosis can interfere via absorbed excitation light.
• The interference can be removed via trapping of the most volatile metabolites.
• A breath analysis procedure's cost is compared with the Xpert TBM/RIF test.

A detection method for nicotinic acid, a specific metabolite marker of Mycobacterium tuberculosis present in cultures and patients' breath, is studied in complex solutions containing other metabolites and in biological media such as urine, saliva and breath condensate. The method is based on the analysis of the luminescence increase of Tb3+ complexes in the presence of nicotinic acid due to the energy transfer from the excited ligand to the lanthanide ion. It is shown that other potential markers found in M. tuberculosis culture supernatant, such as methyl phenylacetate, p-methyl anisate, methyl nicotinate and 2-methoxy biphenyl, can interfere with nicotinic acid via a competitive absorption of the excitation photons. A new strategy to circumvent these interferences is proposed with an upstream trapping of volatile markers preceding the detection of nicotinic acid in the liquid phase via the luminescence of Tb3+ complexes. The cost of the method is evaluated and compared with the Xpert MTB/RIF test endorsed by the World Health Organization.

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