Chromogenic lactate-leukocyte esterase substrates

Self-Immolative Electrochemical Redox Substrates: Emerging Artificial Receptors in Sensing and Biosensing

The development of artificial receptors has great significance in measurement science and technology. The need for a robust version of natural receptors is getting increased attention because the cost of natural receptors is still high along with storage difficulties. Aptamers, imprinted polymers, and nanozymes are some of the matured artificial receptors in analytical chemistry. Recently, a new direction has been discovered by organic chemists, who can synthesize robust, activity-based, self-immolative organic molecules that have artificial receptor properties for the targeted analytes. Specifically designed trigger moieties implant selectivity and sensitivity. These latent electrochemical redox substrates are highly stable, mass-producible, inexpensive, and eco-friendly. Combining redox substrates with the merits of electrochemical techniques is a good opportunity to establish a new direction in artificial receptors. This Review provides an overview of electrochemical redox substrate design, anatomy, benefits, and biosensing potential. A proper understanding of molecular design can lead to the development of a library of novel self-immolative redox molecules that would have huge implications for measurement science and technology.

Synthesis and Characterization of Pyridine Compounds for Amperometric Measurements of Leukocyte Esterase

We introduce a new class of substrates (compounds I-III) for leukocyte esterase (LE) that react with LE yielding anodic current in direct proportion to LE activity. The kinetic constants K_m and k_cat for the enzymatic reactions were determined by amperometry at a glassy carbon electrode. The binding affinity of I-III for LE was two orders of magnitude better than that of existing optical LE substrates. The specificity constant k_cat /K_m was equal to 2.7, 3.8, and 5.8×10⁵  m^-1  s^-1 for compounds containing the pyridine (I), methoxypyridine (II), and (methoxycarbonyl)pyridine (III), respectively, thus showing an increase in catalytic efficiency in this order. Compound III had the lowest octanol/water partition coefficient (log p=0.33) along with the highest topological surface area (tPSA=222 Ų ) and the best aqueous solubility (4.0 mg mL^-1 ). The average enzymatic activity of LE released from a single leukocyte was equal to 4.5 nU when measured with compound III.

Spectrophotometric determination of leukocytes in urine

A spectrophotometric method based on myeloperoxidase activity for the determination of leukocytes in urine is described. Red cells that may be found in urine samples were lysed by an ammonium chloride method. Leukocytes were then sedimented by centrifugation and lysed using Triton X-100 (Sigma Chemicals Co., St. Louis, MO). Myeloperoxidase-catalyzed oxidation of o-dianisidine was carried out at 37 degrees C, pH 7. The reaction was stopped with the addition of 2 M H2SO4, and a stable form of oxidized o-dianisidine in acidic solution was obtained. Solid particles that may be found in urine samples were removed by centrifugation to avoid turbidity, and absorbance values of the supernatants were recorded at 400 nm. An Average number of leukocytes were noted per number of fields by microscopic examination and were related with the absorbance values of the supernatants at 400 nm. Pearson correlation (r) between our presented spectrophotometric analysis results and visual microscopic analysis was 0.877. Roche Combur 10-test M strips (Roche, Mannheim, Germany) and Multistix 10 SG Bayer test strips (Bayer Diagnostics, UK) were 0.645 and 0.648, respectively (P < 0.0001).

Spectrophotometric determination of leukocytes in blood

The determination of leukocyte concentration in human blood depending on the detection of oxidized o-dianisidine in acidic solution is studied. The oxidation of o-dianisidine was carried out by peroxidase enzymes found in leukocytes. The reaction was stopped by the addition of 4N H(2)SO(4) to the solution, and a very stable, colored o-dianisidine derivative was obtained. The calibration graph was plotted with the recorded absorbance values at 400 nm assigned to the y-axis, and leukocyte counts in 1-mL blood samples to the x-axis. The equation of the calibration graph was y=0.0025 x +0.0904, with a correlation coefficient of R=0.994. The coefficient of variation and P-value of the method were 4.00% and 0.05%, respectively.