1. Dhumpa, R.; Truong, T. M.; Wang, X.; Bertram, R.; Roper, M. G. “Negative feedback synchronizes islets of Langerhans” Biophys J. 2014, 106, 2275-2282. PMCID: PMC4052280.

2. Wang, X.; Roper, M. G. “Measurement of DCF fluorescence as a measure of reactive oxygen species in murine islets of Langerhans” Anal. Methods 2014, 6, 3019-3024. PMCID: PMC4061712.

3. Schrell, A. M.; Roper, M. G. “Frequency-encoded laser-induced fluorescence for multiplexed detection in infrared-mediated quantitative PCR” Analyst 2014, 139, 2695-2701. PMCID: PMC4013171.

4. Lomasney, A. R.; Lian, Y.; Roper, M. G. “Simultaneous monitoring of insulin and islet amyloid polypeptide secretion from islets of Langerhans on a microfluidic device” Anal. Chem. 2013, 85, 7919-7925. PMCID: PMC3770151.

5. Zhang, X.; Dhumpa, R.; Roper, M. G. “Maintaining stimulant waveforms in large volume microfluidic cell chambers” Microfluid. Nanofluid. 2013, 15, 65-71. PMCID: PMC3828119.

6. Dhumpa, R.; Roper, M. G. “Temporal gradients in microfluidic systems to probe cellular dynamics: A review.” Anal. Chim. Acta 2012, 743, 9-18. PMCID: PMC3428035.

7. Baker, C. A.; Roper, M. G. “Online coupling of digital microfluidic devices with mass spectrometry detection using an eductor with electrospray ionization” Anal. Chem. 2012, 84, 2955-2960. PMCID: PMC3310327.

8. Yu, Y.; Li, B.; Baker, C. A.; Zhang, X.; Roper, M. G. “Quantitative polymerase chain reaction using infrared heating on a microfluidic chip” Anal. Chem. 2012, 84, 2825-2829. PMCID: PMC3310344.

9. Duong, C. T.; Roper, M. G. “A microfluidic device for the automated derivatization of free fatty acids to fatty acid methyl esters” Analyst 2012, 137, 840-846.

10. Zhang, X.; Daou, A.; Truong, T. M.; Bertram, R.; Roper, M. G. “Synchronization of islets of Langerhans by glucose waveforms” Am. J. Physiol. Endocrinol. Metab. 2011, 301, E742-E747. PMCID: PMC3191549.

11. Guillo, C.; Truong, T. M.; Roper, M. G. “Simultaneous capillary electrophoresis competitive immunoassay for insulin, glucagon, and islet amyloid polypeptide secretion from mouse islets of Langerhans” J. Chromatogr. A, 2011, 1218, 4059-4064. PMCID: PMC3109176.

12. Baker, C. A.; Bulloch, R.; Roper, M. G. “Comparison of separation performance of laser-ablated and wet-etched microfluidic systems” Anal. Bioanal. Chem. 2011, 399, 1473-1479. PMCID: PMC3026912.

13. Zhang, X.; Grimley, A.; Bertram, R.; Roper, M. G. “Microfluidic system for generation of sinusoidal glucose waveforms for entrainment of islets of Langerhans” Anal. Chem. 2010, 82, 6704-6711. PMCID: PMC2921651.

14. Cao, L.; Zhang, X.; Grimley, A.; Lomasney, A. R.; Roper, M. G. “Microfluidic multi-analyte gradient generator” Anal. Bioanal. Chem. 2010, 398, 1985-1991. PMCID: PMC2998889.

15. Baker, C.; Roper, M. G. “A continuous-flow, microfluidic fraction collection device” J. Chromatogr. A 2010, 1217, 4743-4748. PMCID: PMC2923460.

16. Lomasney, A. R.; Guillo, C.; Sidebottom, A. M.; Roper, M. G. “Optimization of capillary electrophoresis conditions for a glucagon competitive immunoassay using response surface methodology” Anal. Bioanal. Chem. 2009, 394, 313-319. PMCID: PMC2667558.

17. Zhang, X.; Roper, M. G. “Microfluidic perfusion system for automated delivery of temporal gradients to biological cells” Anal. Chem. 2009, 81, 1162-1168. PMCID: PMC2921651.

18. Baker, C. A.; Duong, C. T.; Grimley, A.; Roper, M. G. “Recent advances in microfluidic detection systems” Bioanalysis, 2009, 1, 967-975. PMCID: PMC2856342.

19. Roper, M. G.; Guillo, C. “New technologies in affinity assays to explore cellular communication” Anal. Bioanal. Chem. 2009, 393, 459-465. PMCID: PMC2605775.

20. Guillo, C.; Roper, M. G. “Affinity assays for detection of cellular communication and biomarkers” Analyst 2008, 133, 1481-1485. PMCID: PMC2597362.

21. Tierno, P.; Reddy, S. V.; Roper, M. G.; Jofansen, T. H.; Fischer, T. M. “Transport and separation of biomolecular cargo on paramagnetic colloidal particles in a magnetic ratchet” J. Phys. Chem. B 2008, 112, 3833-3837.

22. Guillo, C.; Roper, M. G. “Two-color electrophoretic immunoassay for simultaneous measurement of insulin and glucagon content in islets of Langerhans” Electrophoresis, 2008, 29, 410-416.

23. Roper, M. G.; Easley, C. J.; Legendre, L. A.; Humphrey, J. A. C.; Landers, J. P. "Completely non-contact temperature control and sensing on a microfluidic chip" Anal. Chem. 2007, 79, 1294-1300.

24. Easley, C. J.; Karlinsey, J. M.; Bienvenue, J. M.; Legendre, L. A.; Roper, M. G.; Feldman, S. H.; Hughes, M. A.; Hewlett, E. L.; Merkel, T. J.; Ferrance, J. P.; Landers, J. P. "A fully-integrated microfludidic genetic analysis system with sample in-answer out capability" Proc. Natl. Acad. Sci., USA 2006, 103, 19272-19277.

25. Roper, M. G.; Frisk, M. L.; Oberlander, J. P.; Ferrance, J. P.; McGrory, B. J.; Landers, J. P. "Extraction of C-reactive protein from serum on a microfluidic chip" Anal. Chim. Acta 2006, 569, 195-202.

26. Yue, G. E.; Roper, M. G.; Balchunas, C.; Pulsipher, A.; Coon, J. J.; Shabanowitz, J.; Hunt, D. F.; Landers, J. P.; Ferrance, J. P. "Protein digestion and phosphopeptide enrichment on a glass microchip" Anal. Chim. Acta 2006, 564, 116-122.

27. Legendre, L. A.; Bienvenue, J. M.; Roper, M. G.; Ferrance, J. P.; Landers, J. P. "A simple, valveless microfluidic sample preparation device for extraction and amplification of DNA from nanoliter-volume samples" Anal. Chem. 2006, 78, 1444-1451.

28. Yue, G. E.; Roper, M. G.; Jeffery, E. D.; Easley, C. J.; Balchunas, C.; Landers, J. P.; Ferrance, J. P. "Glass microfluidic devices with thin membrane voltage junctions for electrospray mass spectrometry" Lab Chip 2005, 5, 619-627.

29. Easley, C. J.; Legendre, L. A.; Roper, M. G.; Wavering, T. A.; Ferrance, J. P.; Landers, J. P. "Extrinsic Fabry-Perot interferometry for noncontact temperature control of nanoliter-volume enzymatic reactions in glass microchips" Anal. Chem. 2005, 77, 1038-1045.

30. Roper, M. G.; Easley, C. J.; Landers, J. P. “Advances in polymerase chain reaction on microfluidic chips” Anal. Chem. 2005, 77, 3887-3894.

31. Kulkarni, R. N.; Roper, M. G.; Dahlgren, G. M.; Kauri, L. M.; Kahn, C. R.; Kennedy, R. T. "Islet secretory defect in insulin receptor substrate 1 null mice is linked with reduced calcium signaling and expression of sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA)-2B and -3" Diabetes 2004, 53, 1517-1525.

32. Roper, M. G.; Shackman, J. G.; Dahlgren, G. M.; Kennedy, R. T. "Microfluidic chip for continuous monitoring of hormone secretion from live cells using an electrophoresis-based immunoassasy" Anal. Chem. 2003, 75, 4711-4717.

33. Roper, M. G.; Qian, W-J.; Zhang, B. B.; Kulkarni, R. N.; Kahn, C. R.; Kennedy, R. T. “Effect of the insulin mimetic L-783,281 on intracellular [Ca2+] and insulin secretion from pancreatic b-cells” Diabetes 2002, 51, S43-S49.

34. German, I.; Roper, M. G.; Kalra, S. P.; Rhinehart, E.; Kennedy, R. T. "Capillary liquid chromatography of multiple peptides with on-line capillary electrophoresis immunoassay detection" Electrophoresis 2001, 22, 3659-3667.

35. Aspinwall, C. A.; Qian, W-J.; Roper, M. G.; Kulkarni, R. N.; Kahn, C. R.; Kennedy, R. T. "Roles of insulin receptor substrate-1, phosphatidylinositol 3-kinase, and release of intracellular Ca2+ stores in insulin-stimulated insulin secretion in β-cells" J. Biol. Chem. 2000, 275, 22331-22338.

Technologies

Frequency-Modulated Continuous Flow Analysis

Professor Roper and collaborators have developped a new method to multiplex mass spectrometric sample analysis. The purpose of this invention is to be able to analyze multiple samples simultaneously using mass spectrometry. The operation of this method is to pulse the flow of individual samples to the mass spectrometer at unique frequencies. The flow from the individual samples are combined together with a make-up flow that is used to ensure the total flow rate to the mass spectrometer is constant. After mixing of all the streams from the samples and the make-up flow, pulses of each sample are delivered to the mass spectrometer with the pulse frequencies being unique to that particular sample. The mass spectrometer collects the m/z data vs. time. At each m/z there is a time-dependent signal that is the sum of all the pulses from the different samples. For any one particular m/z, a Fourier transform is used to convert the time-based mass spectrometry signal intensity to the frequency domain resulting in a series of peaks at particular frequencies. Each of these frequency peaks corresponding to the different samples. The height of the peaks in the frequency domain is proportional to the concentrations of the samples in the syringes.

The benefit of this new method over the labeling strategy is that the frequency modulated approach allows multiplexing of a theoretically wide number of samples without the need for chemical labeling. Therefore, any problems with chemical labeling (inefficiencies, side products, etc.) are avoided. Also, more than 4-5 samples can be used simultaneously as Jong as their frequencies can be resolved in the frequency domain and the analytes are within the dynamic range of the mass spectrometer. A final advantage is that since all the samples are combined together, any samples that may have different levels of salts (detrimental to mass spectrometry) experience the same salt concentration. This means that they are all affected in the same manner and are much less susceptible to salt effects which hurt mass spectrometry experiments.

This technology was developed in collaboration with Jim Edwards at Saint Louis University

Microfluidic Sample Preparation Device for Electron Microscopy

Cryogenic electron microscopy (cryoEM) is quickly becoming a routine method in the determination of high-resolution structures of biological molecules. However, for most samples before cryoEM data can be collected, the sample quality and heterogeneity must first be characterized using negative staining. Conventionally, EM grids are prepared by hand and, as such, variability is introduced due to user-to-user differences. The variability of the staining can have large effects on the final stained sample, ultimately hindering the resolution, image processing, and data analysis.

A microfluidic platform is presented for preparing negatively stained grids for use in transmission electron microscopy (EM). The microfluidic device is composed of glass etched with readily fabricated features that facilitate the extraction of the grid post staining and maintains the integrity of the sample. The device allows for sealing of an electron microscopy grid, facile and reproducible delivery of a sample, followed by delivery of subsequent solutions that could be negative stains or other biological samples. The device houses the EM grid in an outlined chamber with an access point below the grid for gentle and easy recovery of the EM grid. The fluid is directed to the grid using the integrated channels of the microfluidic system.

Utilization of this device simultaneously reduced environmental contamination on the grids and improved the homogeneity of the heavy metal stain needed to enhance visualization of biological specimens as compared to conventionally prepared EM grids.

High-magnification images from grids prepared by the microfluidic system showed similar image qualities as those prepared by hand. With this methodology for housing the grid, opportunities are abound for more integrated systems using elastomeric materials for incorporation of valving and other microfluidic features. For example, this system can subsequently be complemented with gradient generators or multianalyte perfusion and reaction timers to study both multivariable interactions as well as reaction kinetics. This proof of principle paves the way for future added layers of complexity that can be used to uniquely investigate structural biology dynamics.

Results have been published in Analytical Chemistry (Roper, 2016, American Chemical Society Publications) and led to multiple requests by research groups offering to beta test the prototype.