Rapid Colorimetric Quantita2tive Portable Platform for Detection of Brucella melitensis Based on a Fluorescence Resonance Energy Transfer Assay and Nanomagnetic Particles.

Brucellosis is a bacterial zoonotic disease that requires major attention for both health and financial facilities in many parts of the world including the Mediterranean and the Middle East. The existing gold standard diagnosis relies on the culturing technique, which is costly and time-consuming with a duration of up to 45 days. The Brucella protease biosensor represents a new detection approach that will lead to low-cost point-of-care devices for sensitive Brucella detection. In addition, the described diagnostic device is portable and simple to operate by a nurse or non-skilled clinician making it appropriate for the low-resource setting. In this study, we rely on the total extracellular protease proteolytic activity on specific peptide sequences identified using the FRET assay by high-throughput screening from the library of peptide (96 short peptides such as dipeptides and tripeptides) substrates for Brucella melitensis (B. melitensis). The B. melitensis-specific protease substrate was utilized in the development of the paper-based colorimetric assay. Two specific and highly active dipeptide substrates were identified (FITC-Ahx-K-r-K-Ahx-DABCYL and FITC-Ahx-R-r-K-Ahx-DABCYL). The peptide-magnetic bead nanoprobe sensors developed based on these substrates were able to detect the Brucella with LOD as low as 1.5 × 102 and 1.5 × 103 CFU/mL using K-r dipeptide and R-r dipeptide substrates, respectively, as the recognition element. The samples were tested using this sensor in few minutes. Cross-reactivity studies confirmed that the other proteases extracted from closely related pathogens have no significant effect on the sensor. To the best of our knowledge, this assay is the first assay that can be used with low-cost, rapid, direct, and visual detection of B. melitensis.