Infection Screening in Biofluids with Glucose Test Strips

The four glucosyl esters were synthesized and tested for the determination of infection enzyme leukocyte esterase (LE) in human synovial (joint) fluid and urine. The esters acted as LE substrates releasing glucose in a direct proportion to the activity of LE in a sample. The freed glucose was then detected by a coupled-enzyme assay at either a nitrogen-doped carbon nanotube (N-CNT) electrode or a commercial glucose test strip. The assays at the N-CNT electrode detected LE down to 0.81 nM (25 μg L^-1) and showed the fastest kinetics (2.1 × 10⁵ M^-1 s^-1) for esters with the least crowded space around their carbonyl group. When used with glucose strips, the esters discerned clinically relevant levels of LE up to at least 26 nM (800 μg L^-1) in the microliter-sized samples of bodily fluids. The reading of glucose strips with a potentiostat, instead of a personal glucose meter (blood glucometer), shortened the time of required sample incubation from 3 h to 5 min. Correcting the signal of incubated sample for that of original sample eliminated matrix effects and accounted for the presence of native glucose. The new esters have a potential to extend the use of glucose strips (already used by millions for diabetes monitoring) to the quantification of the severity of urinary tract and periprosthetic joint infections.