UTMB Department of Pathology

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Since its invention shortly after the turn of the century by Mikhail Twett, chromatography has found applications in all branches of science. My research interest is in developing clinical assays on capillary electrophoresis (CE), one of the latest and rapidly expanding branches of chromatography. CE has become a powerful analytical technique for the separation of a variety of analytes ranging from inorganic icons to large biomolecules such as proteins and nucleic acids. Presently an important area of research in CE is in the development of new instrumentally simple on-column detectors which allow the detection of separated analytes at low concentrations. The main goal of my research endeavor is to develop a detection system that can directly (i.e., with no prior preconcentration or derivatization) detect analytes occurring at picomolar concentrations in body fluids. Two fundamentally different techniques are being developed in this laboratory.

The first technique involves laser-induced resonance energy transfer (RET) from analytes to lanthanides such as terbium and europium. Typically it involves the separation of analyte molecules by CE which is followed by their excitation to triplet level via a high-powered laser. The excited triplet returns to the ground level by transferring its energy to lanthanide ions present in an electrophoresis buffer. The long-lived luminescence of lanthanides post RET is then monitored. This detection mode is currently used to develop simple and sensitive assays for clinically important analytes such as steroids, proteins, aromatic like-tones, hydroxy-indoleacetic acid derivatives and tetracyclines. Its application in simultane-ous detection of RNA and DNA fragments in CE is also under investigation.

The second technique measures chemiluminescence resulting from the ozone mediated oxidation of nitrogen containing molecules post CE separation. The detector prototype if under development in this laboratory and will facilitate a sensitive and direct detection of nitrogen-containing molecules, e.g., proteins, amino acids, nucleic acid, and therapeutic drugs with no prior derivitization.

1. Mohammad AA, Elefano EC, Leigh D, Stredler D, Okorodudu AO, Petersen JR. Using computer simulation to study the impact of increasing test volume on turn around times of STAT samples on ci8000intergrated chemistry and immunoassay analyzer. Clin Chem 2004 (accepted)
2. Petersen JR, Okorodudu AO, Mohammad AA, Payne DA. Capillary Electrophoresis and its application in the clinical laboratory. Clin Chim Acta.330:1-30; 2003
3. Wu J, Petersen JR, Mohammad AA, Okorodudu AO. Point-of-Care hemoglobin measurement by Stat-Site MHgb reflectance meter. Point of Care, J Near-Patient Testing Tech 2:8-11;2003
4. DeHoyos DR, Mann P, Okorodudu AO, Mohammad AA, Petersen JR. Development of a website for a decentralized point of care testing program. Point of Care, J Near-Patient Testing Tech 1:63-70; 2002
5. Youh C, Elghetany MT, Petersen JR, Mohammad A, Okorodudu AO. Accuracy and precision of point-of-care testing for glucose and prothrombin time at the critical care units. Clin. Chim. Acta. 307:119-123, 2001
6. Chance JJ, Lio DJ, Sokoll LJ, Silberman MA, Engelstad ME, Nichols JH, Liu X, Mohammad AA, Petersen JR, Okorodudu AO. Multi-site analytical evaluation of the SenDx 100TM blood gas/electrolyte analyzer for point of care testing. Crit. Care Med. 28:2081-5, 2000.
7. Okorodudu AO, Youh C, Elghetany MT, Mohammad AA, Petersen JR. POCT accuracy and precision. Adv. Admin. Lab. 9:8-10, 2000
8. Liu X, Turner B, Mohammad AA, Reisner B, Okorodudu AO, Petersen JR. Evaluation of assay specificity for IgM to T. gondii on the Sanofi Access immunoassay system. Diag. Microbiol. Infect. Dis. 36:237-39, 2000
9. Rao LV, Okorodudu AO, Elghetany MT, Mohammad AA, Petersen JR. Stability of prothrombin time and activated partial thromboplastin time tests under different storage conditions. Clin. Chim. Acta. 300:13-21, 2000
10. Fujinari E, Petersen JR, Okorodudu AO, Mohammad AA. Apparatus and method for interfacing an open capillary and CLND detector for conducting of- column analysis. J.Chromatogr. A. 868:121-25, 2000
11. Rao LV, Petersen JR, Mohammad AA, Bissell MG, Okorodudu AO. Cost-effective utilization of CK-MB, mass and activity assays. Lab. Med. 30:271-75, 1999.
12. L.V. Rao, J.R. Petersen, M.G. Bissell, A. O. Okorodudu, Mohammad AA. Development of urinary free cortisol assay using solid phase extraction capillary electrophoresis. J.Chromatogr., B. 730:123-28, 1999
13. Rao LV, Petersen JR, Bissell MG, Okorodudu AO and Mohammad AA. Specific Determination of urinary free cortisol by solid phase microparticle extraction capillary electrophoresis with fused silica capillaries. Clin. Chem. 43: 1801-1803, 1997
14. Valbuena GA., Petersen JR, Bissell MG and Mohammad AA, Anionic- zwitterionic mixed micelles in micellar electrokinetic separation of clinically relevant steroids on fused silica capillary. J. Chromatogr. A. 781: 467-474, 1997
15. Mohammad AA, Okorodudu AO, Bissell MG, Dow P, Regger G, Meier A, Guodagno P, Petersen JR. Clinical application of capillary isoelectric focussing on fused silica capillary for determination of hemoglobin variants. Clin. Chem. 43: 1798 - 1799, 1997.
16. Rao LV., James OA, Mann LM, Mohammad AA, Okorodudu AO, Bissell MG, Petersen JR. Evaluation of Immuno-1 Toxoplasma IgG Assay in the prenatal screening of toxoplasmosis. Diagn. Microbiol. Infect. Dis.27: 13-15, 1997
17. Bissell MG, Okorodudu AO, Petersen JR, Mohammad AA. Laser induced resonance energy transfer - a novel approach towards achieving high sensitivity in capillary electrophoresis. II. Applications for environmental testing. J. Chromatogr. A. 767:217 - 221, 1997
18. Olapade AJ, Petersen JR Bissell MG, Okorodudu AO, Harris PL, Clayton SS, Mohammad AA. Improved sample retrieval and turnaround time in the clinical laboratory with a spreadsheet template for sample storage. Clin. Chem. 42:1571- 1573, 1996
19. Mohammad AA, Helen Summers, Bissell MG A.O. Okorodudu. STAT turnaround time satellite and point-to-point testing. Lab. Med. 27: 684-688, 1996
20. Petersen JR, Bissell MG, Mohammad AA, Laser induced resonance energy transfer - a novel approach towards achieving high sensitivity in capillary electrophoresis. I. Clinical diagnostic application. J. Chromatogr. A. 744: 37-44, 1996
21. Petersen JR Mohammad AA, Bissell MG Application of capillary electrophoresis in the separation of steroids of clinical relevance. Am. Clin. Lab. 14-15, 1996
22. Mohammad AA, Bissell MG, Petersen JR. Rapid determination of clinically relevant steroids by micellar electrokinetic capillary electrophoresis. J. Cap. Electrophor. 2:105-10, 1995
23. Mohammad AA, Filos D, Petersen JR. Evaluation of automated random access immunoassay analyzer for thyroids. Clin. Chem. 41:1538 - 1540, 1995
24. Mohammad AA, Bissell MG, and Petersen JR. Detection of steroids that are elevated in congenital adrenal hyperplasia by micellar electrokinectic chromatography. Clin. Chem. 41:1369 - 1370, 1995
25. Mohammad AA, Petersen JR, Bissell MG. Micellar electrokinectic capillary chromatography separation of steroids in urine by trioctylphosphine oxide and Cationic surfactant. J. Chromatogr. B 674:31-38, 1995.
26. Mohammad AA, Harrington K, Wandruszka RV. Fluorescence sensitization of aqueous terbium and europium ions without aromatic donors or synergistic agents. Anal. Lett. 26:1681 – 1690, 1993
27. Mohammad AA, Harrington K, Wandruszka RV. Determinations of steroids in urine by micellar HPLC with detection by sensitized terbium fluorescence. Anal. Chem. 65: 2346 – 2351, 1993
28. Mohammad AA,Wandruszka RV. A new fluorescent cholesterol derivative: Structure and blood plasma analysis. Photochem. Photobiol, 56:163 – 170, 1992.
29. Mohammad AA, Wandruszka RV. Determination of phenolic herbicides in soil by peroxyoxalate chemiluminescence. Anal. Lett. 24:93 – 102, 1991

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