title: Monitoring cell secretions on microfluidic chips using solid-phase extraction with mass spectrometry.
abstract: Microfluidics is an enabling technology for both cell biology and chemical analysis. We combine these attributes with a microfluidic device for on-line solid-phase extraction (SPE) and mass spectrometry (MS) analysis of secreted metabolites from living cells in culture on the chip. The device was constructed with polydimethylsiloxane (PDMS) and contains a reversibly sealed chamber for perfusing cells. A multilayer design allowed a series of valves to control an on-chip 7.5 μL injection loop downstream of the cell chamber with operation similar to a six-port valve. The valve collects sample and then diverts it to a packed SPE bed that was connected in-line to treat samples prior to MS analysis. The valve allows samples to be collected and injected onto the SPE bed while preventing exposure of cells to added back pressure from the SPE bed and organic solvents needed to elute collected chemicals. Here, cultured murine 3T3-L1 adipocytes were loaded into the cell chamber and non-esterified fatty acids (NEFAs) that were secreted by the cells were monitored by SPE-MS at 30 min intervals. The limit of detection for a palmitoleic acid standard was 1.4 μM. Due to the multiplexed detection capabilities of MS, a variety of NEFAs were detected. Upon stimulation with isoproterenol and forskolin, secretion of select NEFAs was elevated an average of 1.5-fold compared to basal levels. Despite the 30-min delay between sample injections, this device is a step towards a miniaturized system that allows automated monitoring and identification of a variety of molecules in the extracellular environment.
authors.affiliation: Department of Chemistry, University of Michigan, Ann Arbor, MI, 48109, USA.
authors.forename: Colleen E
authors.initials: CE
authors.lastname: Dugan
authors.affiliation: Department of Chemistry, University of Michigan, Ann Arbor, MI, 48109, USA.
authors.forename: James P
authors.initials: JP
authors.lastname: Grinias
authors.affiliation: Department of Molecular & Integrative Physiology, University of Michigan, Ann Arbor, MI, 48109, USA.
authors.forename: Sebastian D
authors.initials: SD
authors.lastname: Parlee
authors.affiliation: Department of Internal Medicine, University of Michigan, Ann Arbor, MI, 48109, USA.
authors.forename: Mahmoud
authors.initials: M
authors.lastname: El-Azzouny
authors.affiliation: Department of Internal Medicine, University of Michigan, Ann Arbor, MI, 48109, USA.
authors.forename: Charles R
authors.initials: CR
authors.lastname: Evans
authors.affiliation: Department of Chemistry, University of Michigan, Ann Arbor, MI, 48109, USA. rtkenn@umich.edu.|Department of Pharmacology, University of Michigan, Ann Arbor, MI, 48109, USA. rtkenn@umich.edu.
authors.forename: Robert T
authors.initials: RT
authors.lastname: Kennedy
mesh_terms: D041721:3T3-L1 Cells; D017667:Adipocytes / Q000737:chemistry*; D000818:Animals; D004867:Equipment Design; D005230:Fatty Acids, Nonesterified / Q000032:analysis*; D056656:Lab-On-A-Chip Devices; D013058:Mass Spectrometry / Q000295:instrumentation*; D051379:Mice; D046210:Microfluidic Analytical Techniques / Q000295:instrumentation*; D052616:Solid Phase Extraction / Q000295:instrumentation*
chemical_list: D005230:Fatty Acids, Nonesterified
keywords: Adipocyte; Automation; Integration; Mass spectrometry; Microfluidic; Solid-phase extraction