Abstract
Large arrays of femtoliter-sized chambers are important tools for single molecule research as well as bioanalytical applications. We have optimized the design and fabrication of two array types consisting of 250 × 250 (62 500) femtoliter chambers either by surface etching of fused silica slides or by polydimethylsiloxane (PDMS) molding. Highly diluted solutions of β-galactosidase were enclosed in such arrays to monitor the fluorogenic reactions of hundreds of individual enzyme molecules in parallel by wide-field fluorescence microscopy. An efficient mechanical sealing procedure was developed to prevent diffusion of the fluorescent reaction product out of the chambers. Different approaches for minimizing non-specific surface adsorption were explored. The signal acquisition was optimized to grant both a large field of view and an efficient signal acquisition from each femtoliter chamber. The optimized femtoliter array has enabled a three-in-one enzyme assay system: First, the concentration of active enzyme can be determined in a digital way by counting fluorescent chambers in the array. Second, the activity of the enzyme bulk solution is given by averaging many individual substrate turnover rates without the need for knowing the exact enzyme concentration. Third—unlike conventional enzyme assays—the distribution of individual substrate turnover rates yields insight into the conformational heterogeneity in an enzyme population. The substrate turnover rates of single β-galactosidase molecules were found to be broadly distributed and independent of the type of femtoliter array. In general, both types of femtoliter arrays are highly sensitive platforms for enzyme analysis at the single molecule level and yield consistent results.
Similar content being viewed by others
References
Liebherr RB, Gorris HH (2014) Enzyme molecules in solitary confinement. Molecules 19(9):14417–14445
Gorris HH, Walt DR (2010) Analytical chemistry on the femtoliter scale. Angew Chem Int Ed 49(23):3880–3895
Tan WH, Yeung ES (1997) Monitoring the reactions of single enzyme molecules and single metal ions. Anal Chem 69(20):4242–4248
Rondelez Y, Tresset G, Tabata KV, Arata H, Fujita H, Takeuchi S, Noji H (2005) Microfabricated arrays of femtoliter chambers allow single molecule enzymology. Nat Biotechnol 23(3):361–365
Rissin DM, Gorris HH, Walt DR (2008) Distinct and long-lived activity states of single enzyme molecules. J Am Chem Soc 130(15):5349–5353
Liebherr RB, Renner M, Gorris HH (2014) A single molecule perspective on the functional diversity of in vitro evolved beta-glucuronidase. J Am Chem Soc 136(16):5949–5955
Gorris HH, Rissin DM, Walt DR (2007) Stochastic inhibitor release and binding from single-enzyme molecules. Proc Natl Acad Sci U S A 104(45):17680–17685
Mogalisetti P, Gorris HH, Rojek MJ, Walt DR (2014) Elucidating the relationship between substrate and inhibitor binding to the active sites of tetrameric beta-galactosidase. Chem Sci 5(11):4467–4473
Rissin DM, Kan CW, Campbell TG, Howes SC, Fournier DR, Song L, Piech T, Patel PP, Chang L, Rivnak AJ, Ferrell EP, Randall JD, Provuncher GK, Walt DR, Duffy DC (2010) Single-molecule enzyme-linked immunosorbent assay detects serum proteins at subfemtomolar concentrations. Nat Biotechnol 28(6):595–599
Kim SH, Iwai S, Araki S, Sakakihara S, Iino R, Noji H (2012) Large-scale femtoliter droplet array for digital counting of single biomolecules. Lab Chip 12(23):4986–4991
Rotman B (1961) Measurement of activity of single molecules of beta-D-galactosidase. Proc Natl Acad Sci U S A 47(12):1981–1991
Boukobza E, Sonnenfeld A, Haran G (2001) Immobilization in surface-tethered lipid vesicles as a new tool for single biomolecule spectroscopy. J Phys Chem B 105(48):12165–12170
Hsin TM, Yeung ES (2007) Single-molecule reactions in liposomes. Angew Chem Int Ed 46(42):8032–8035
Bolinger PY, Stamou D, Vogel H (2008) An integrated self-assembled nanofluidic system for controlled biological chemistries. Angew Chem Int Ed 47(30):5544–5549
Piwonski HM, Goomanovsky M, Bensimon D, Horovitz A, Haran G (2012) Allosteric inhibition of individual enzyme molecules trapped in lipid vesicles. Proc Natl Acad Sci U S A 109(22):E1437–E1443
Comellas-Aragones M, Engelkamp H, Claessen VI, Sommerdijk NAJM, Rowan AE, Christianen PCM, Maan JC, Verduin BJM, Cornelissen JJLM, Nolte RJM (2007) A virus-based single-enzyme nanoreactor. Nat Nanotechnol 2(10):635–639
Gorris HH, Blicharz TM, Walt DR (2007) Optical-fiber bundles. FEBS J 274(21):5462–5470
Rissin DM, Walt DR (2006) Digital readout of target binding with attomole detection limits via enzyme amplification in femtoliter arrays. J Am Chem Soc 128(19):6286–6287
Ehrl BN, Liebherr RB, Gorris HH (2013) Single molecule kinetics of horseradish peroxidase exposed in large arrays of femtoliter-sized fused silica chambers. Analyst 138(15):4260–4265
Shon MJ, Cohen AE (2012) Mass action at the single-molecule level. J Am Chem Soc 134(35):14618–14623
Zhang HB, Nie S, Etson CM, Wang RM, Walt DR (2012) Oil-sealed femtoliter fiber-optic arrays for single molecule analysis. Lab Chip 12(12):2229–2239
Witters D, Knez K, Ceyssens F, Puers R, Lammertyn J (2013) Digital microfluidics-enabled single-molecule detection by printing and sealing single magnetic beads in femtoliter droplets. Lab Chip 13(11):2047–2054
Ge S, Liu W, Schlappi T, Ismagilov RF (2014) Digital, ultrasensitive, end-point protein measurements with large dynamic range via Brownian trapping with drift. J Am Chem Soc 136(42):14662–14665
Henley WH, Dennis PJ, Ramsey JM (2012) Fabrication of microfluidic devices containing patterned microwell arrays. Anal Chem 84(3):1776–1780
Jekauc I, Watt M, Hornsmith T, Tiffany J (2004) Necessity of chemical edge bead removal in modern day lithographic processing. In: Sturtevant JL (ed) Advances in resist technology and processing XXI. Bellingham, WA, USA. SPIE Proceedings, pp 1255–1263. doi:10.1117/12.535268
Juers DH, Matthews BW, Huber RE (2012) LacZ beta-galactosidase: structure and function of an enzyme of historical and molecular biological importance. Protein Sci 21(12):1792–1807
English BP, Min W, van Oijen AM, Lee KT, Luo G, Sun H, Cherayil BJ, Kou SC, Xie XS (2006) Ever-fluctuating single enzyme molecules: Michaelis-Menten equation revisited. Nat Chem Biol 2(2):87–94
Shoemaker GK, Juers DH, Coombs JML, Matthews BW, Craig DB (2003) Crystallization of beta-galactosidase does not reduce the range of activity of individual molecules. Biochemistry 42(6):1707–1710
Sui G, Wang J, Lee CC, Lu W, Lee SP, Leyton JV, Wu AM, Tseng HR (2006) Solution-phase surface modification in intact poly(dimethylsiloxane) microfluidic channels. Anal Chem 78(15):5543–5551
Rissin DM, Walt DR (2006) Digital concentration readout of single enzyme molecules using femtoliter arrays and Poisson statistics. Nano Lett 6(3):520–523
Brocklehurst K, Resmini M, Topham CM (2001) Kinetic and titration methods for determination of active site contents of enzyme and catalytic antibody preparations. Methods 24(2):153–167
Xue Q, Yeung ES (1995) Differences in the chemical reactivity of individual molecules of an enzyme. Nature 373(6516):681–683
Obayashi Y, Iino R, Noji H (2015) A single-molecule digital enzyme assay using alkaline phosphatase with a cumarin-based fluorogenic substrate. Analyst 140(15):5065–5073
Gorris HH, Walt DR (2009) Mechanistic aspects of horseradish peroxidase elucidated through single-molecule studies. J Am Chem Soc 131(17):6277–6282
Acknowledgments
We thank Florian Götz (University of Applied Sciences Regensburg) for preparing the first generation of femtoliter arrays, the precision mechanical workshop (University of Regensburg) for the fabrication of the array holder, and the Center for Sensor Applications (SAPPZ, University of Applied Sciences Regensburg) for 3D printing. We also acknowledge funding from the German Research Council (DFG grant GO 1968/3-1).
Author information
Authors and Affiliations
Corresponding author
Additional information
Raphaela B. Liebherr and Albert Hutterer contributed equally to this work.
Electronic supplementary material
Below is the link to the electronic supplementary material.
ESM 1
(PDF 740 kb)
Rights and permissions
About this article
Cite this article
Liebherr, R.B., Hutterer, A., Mickert, M.J. et al. Three-in-one enzyme assay based on single molecule detection in femtoliter arrays. Anal Bioanal Chem 407, 7443–7452 (2015). https://doi.org/10.1007/s00216-015-8910-0
Received:
Revised:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s00216-015-8910-0