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Michael Sepaniak BS: Northern Illinois University (1974) 420 Dabney/Buehler Hall |
Keywords:
Analytical chemistry, microscale separations, optical spectroscopy, capillary-scale separations, applied laser spectroscopy and detection, chemical sensors, molecular modeling
Research Area:
Fundamental and practical development of capillary LC and electrokinetic separation techniques; microscale bioanalysis and environmental analysis; laser-based optical detectors; fiberoptic-based chemical and separations-based sensors; cantilever sensors.
Description of Research:
Separations: Our separations research program is dedicated to the development of capillary electrokinetic separation techniques for chemical analysis. Fundamental work focuses on studies involving highly ordered assemblies as selective reagents for capillary electrophoresis (CE) separations. These additives include macrocyclic compounds such as cyclodextrins (CDs) and calixarenes, micelles, and soluble (entangled) polymers and are employed in electrophoretic (e.g., CE) or electrochromatographic (e.g., micellar electrokinetic capillary electrochromatography (MEKC), cyclodextrin distribution capillary electrochromatography, CDCE) modes of separation. Since the CDs used in the CDCE technique effect solute retention independently, it is possible to develop "designer" CDCE separation systems (simple- to-complex combinations of commercially available CDs) that meet many separation challenges. A principal goal of our work is to study molecular recognition as it applies to CE separations using molecular mechanics modeling techniques. Computationally determined interaction strengths have aided in predicting and explaining elution characteristics. More recently, these techniques have facilitated a more in depth look at the types of intermolecular interactions that are responsible for CDCE separations and have guided the synthesis of new reagents. The mechanisms by which DNA restriction fragments migrate, disperse, and interact with proteins in size-selective CE separations employing entangled polymers as running buffer additives are also being studied. The size selective CE technique is being developed as a method of determining the genetic complexity of samples of environmental significance.
Optical Detection: Sensitive methods of detection for CE are being developed based on two novel methods. In the first sheath flow cells are being employed for ultra sensitive laser induced fluorescence detection and as reaction chambers for post column derivatization. The second method involves the microfluidic transfer of CE effluent from a capillary to a planar format. Electrospray techniques are used to deposit spatially focused CE effluent and separated analyte bands onto planar substrates. Subsequently, optical methods of detection may be performed without the time constraints of on-line detection and with the possibility of lower limits of detection. We are focusing initially on laser induced fluorescence detection (native and based on derivatization) and surface enhanced Raman spectroscopy (SERS) detection. SERS detection is also being perform directly on-colum using CE running buffers that contain nano-scale silver particles.
Micro-sensors: A prominent area of research involves the development of separation- based fiberoptic sensors (SBFOSs). Basically, the SBFOS is a single fiberoptic, single buffer reservoir (the sample constitutes the other reservoir) device that is usually operated in a frontal mode of separation. The introduction of CE methodologies into sensing provides a unique and powerful element of selectivity for remote analyses and should offer unparalleled versatility and reusability. Several prototype SBFOSs have been fabricated and evaluated for measurements of fluorescent dyes and toxins in CE and MECC modes of separation, respectively. Methods to impart selectivity to micro-electro-mechanical sensors (MEMS) are also being developed. Methods of depositing and immobilizing polysiloxane phases, chelating resins and imprinted sol gels, and macrocylic reagents on micron dimension cantilever-based MEMS are being developed. The macrocycle compounds developed and characterized through molecular recognition studies should serve as tunably selective sequestering phases when immobilized on the planar substrate. These various phases will be used to increase response factors and add chemical specificity to gravimetric, photo induced stress, and photothermal measurements with the cantilever-based MEMS. Methods of developing nano-structured surface features are being developed with the goals of enhancing the response characteristics of the sensors.
Selected Publications:
- Surface enhanced Raman scattering under liquid nitrogen. R.J. Hinde, M.J. Sepaniak, R.N. Compton, N.V. Lavrik and J. Nordling, Chem. Phys. Lett. 339, 167 (2001).
- Spatially focused deposition of electrophoresis effluent onto SERS substrates for off-column spectroscopy. G.L. Devault and M.J. Sepaniak, Electrophoresis 22, 2303 (2001).
- Nanostuctured microcantilevers with functionalized cyclodextrin receptor phases: self assembled monolayers and vapor deposited films. C.A. Tipple, N.V. Lavrik, M. Culha, J. Headrick, P.G. Datskos, and M.J. Sepaniak, Anal. Chem. 74, 3118 (2002).
- The development of a substrate translation technique to minimize the adverse effect of laser irradiation effects on surface enhanced Raman scattering spectra. M.A. De Jesus, K. S. Giesfeldt, and M.J. Sepaniak, Appl. Spectrosc. 57, 428 (2003).
- Enantioselective sensors based on antibody-mediated nanomechanics. P. Dutta, C.A. Tipple, N.V. Lavrik, P.G. Datskos, O. Hofstetter, and M.J. Sepaniak, Anal. Chem. 75, 2342 (2003).