Measuring Binding of Protein to Gel-Bound Ligands Using Magnetic Levitation

Shapiro, Nathan D.; Mirica, Katherine A.; Soh, Siowling; Phillips, Scott T.; Taran, Olga; Mace, Charles R.; Shevkoplyas, Sergey S.; Whitesides, George M.

doi:10.1021/ja211788e

Cited by 61 publications

(112 citation statements)

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“…iii) MagLev can be used to perform a range of important, density-based bioanalyses. [13][14][15][16][17] iv) The simplicityof-use, portability, and low cost of MagLev make it particularly attractive for use in resource-limited settings (e.g., schools, mines, archeological sites, field operations, and laboratories in the developing countries).…”

Section: Introductionmentioning

confidence: 99%

Tilted Magnetic Levitation Enables Measurement of the Complete Range of Densities of Materials with Low Magnetic Permeability

et al. 2016

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Magnetic levitation (MagLev) of diamagnetic or weakly paramagnetic materials suspended in a paramagnetic solution in a magnetic field gradient provides a simple method to measure the density of small samples of solids or liquids. One major limitation of this method, thus far, has been an inability to measure or manipulate materials outside of a narrow range of densities (0.8 g/cm 3 <  < 2.3 g/cm 3 ) that are close in density to the suspending, aqueous medium. This paper explores a simple method-"tilted MagLev"-to increase the range of densities that can be levitated magnetically. Tilting the MagLev device relative to the gravitational vector enables the magnetic force to be decreased (relative to the magnetic force) along the axis of measurement. This approach enables many practical measurements over the entire range of densities observed in matter at ambient conditions-from air bubbles ( ≈ 0) to osmium and iridium ( ≈ 23 g/cm 3 ). The ability to levitate, simultaneously, objects with a broad range of different densities provides an operationally simple method that may find application to forensic science (e.g., for identifying the composition of miscellaneous objects or powders), industrial manufacturing (e.g., for quality control of parts), or resource-limited settings (e.g., for identifying and separating small particles of metals and alloys). INTRODUCTIONMagnetic levitation (MagLev) of diamagnetic or weakly paramagnetic materials suspended in a paramagnetic solution in a magnetic field gradient provides a simple method to measure density. [1][2][3][4] Based the balance of gravitational and magnetic forces, this method has four important capabilities and types of applications that make it attractive for use in a variety of settings. i) MagLev offers the ability to resolve small differences in the densities of samples (e.g., pastes, gels, heterogeneous solids, small particles, crystal polymorphs) 1,2,4-7 with physical properties that make them difficult or impossible to analyze by other instruments (e.g., density gradient columns, pycnometers, oscillating-tube densometers). 8 ii) MagLev can be used for complex, shape-based tasks, such as noncontact, three-dimensional self-assembly, 9,10 orientation control 11 , and quality control 12 of a wide variety of polymeric components. iii) MagLev can be used to perform a range of important, density-based bioanalyses. [13][14][15][16][17] iv) The simplicityof-use, portability, and low cost of MagLev make it particularly attractive for use in resource-limited settings (e.g., schools, mines, archeological sites, field operations, and laboratories in the developing countries).Despite these advantages, one major limitation, thus far, has been an inability to measure or manipulate materials outside of

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Section: Introductionmentioning

confidence: 99%

Tilted Magnetic Levitation Enables Measurement of the Complete Range of Densities of Materials with Low Magnetic Permeability

et al. 2016

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“…For instance, [BMIM] 3 [DyCl 6 ] has a magnetic susceptibility (χ = 12.4 × 10 −4 ) that is about three times greater than that of saturated aqueous MnCl 2 solution (∼4.5 M, χ = 4.2 × 10 −4 ). This PIL, therefore, enables the levitation of analytes across a wider range of densities (0.80 < ρ < 2.00 g/cm 3 ) than that accessible (1.20 < ρ < 1.50 g/cm 3 ) at the highest concentration of aqueous MnCl 2 solution (∼4.5 M) having no additives. We have extrapolated the linear plots of levitation height (0−45 mm) against density, and the density range that can be measured practically may be smaller.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…23,24 The magnetic susceptibility of paramagnetic ions increases with decreasing temperature according to the equation: χ = C/(T − T c ) where χ is the magnetic susceptibility, T is the temperature (K), C is the Curie constant, and T c is the Curie−Weiss temperature (K). 10 We illustrate, for example, that lowering the temperature of [Aliq] 3 [HoBr 6 ] PIL to −20°C increases its magnetic susceptibility (χ r.t. = 6.30 × 10 −4 ; χ −20°C = 6.95 × 10 −4 ); this increase enables the levitation of denser beads (e.g., 1.25 g/ cm 3 ) than could be levitated using the same PIL at room temperature ( Figure S2, Supporting Information). The temperature-dependent magnetic susceptibility and density of PILs broaden the range of densities that can be measured using the same paramagnetic medium ( Figure S2, Supporting Information).…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…The temperature-dependent magnetic susceptibility and density of PILs broaden the range of densities that can be measured using the same paramagnetic medium ( Figure S2, Supporting Information). The density of the [Aliq] 3 [HoBr 6 ] PIL increased (ρ r.t. = 1.10 g/cm 3 ; ρ −20°C = 1.15 g/cm 3 ); this increase reduces the need to use additives (e.g., diamagnetic cosolutes, diamagnetic ionic liquids) to adjust the density of the medium.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…(v) To allow for measurement of water-soluble analytes, the paramagnetic metal ion must be converted into an organic-soluble chelate to give useful solubility; this transformation requires additional synthesis steps. (vi) Measurement of very low (ρ < 1.00 g/cm 3 ) and high (ρ > 3.00 g/cm 3 ) densities is complicated or difficult using simple techniques (although possible with newer versions of MagLev).…”

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Paramagnetic Ionic Liquids for Measurements of Density Using Magnetic Levitation

et al. 2013

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Paramagnetic ionic liquids (PILs) provide new capabilities to measurements of density using magnetic levitation (MagLev). In a typical measurement, a diamagnetic object of unknown density is placed in a container containing a PIL. The container is placed between two magnets (typically NdFeB, oriented with like poles facing). The density of the diamagnetic object can be determined by measuring its position in the magnetic field along the vertical axis (levitation height, h), either as an absolute value or relative to internal standards of known density. For density measurements by MagLev, PILs have three advantages over solutions of paramagnetic salts in aqueous or organic solutions: (i) negligible vapor pressures; (ii) low melting points; (iii) high thermal stabilities. In addition, the densities, magnetic susceptibilities, glass transition temperatures, thermal decomposition temperatures, viscosities, and hydrophobicities of PILs can be tuned over broad ranges by choosing the cation−anion pair. The low melting points and high thermal stabilities of PILs provide large liquidus windows for density measurements. This paper demonstrates applications and advantages of PILs in density-based analyses using MagLev.M agnetic levitation (MagLev) is a useful new method for measuring the density of a diamagnetic object. 1−9 MagLev, as developed in our laboratory, relies on paramagnetic solutions (typically generated by dissolving a paramagnetic salt, alone or as a chelate, in water or an organic solvent), placed in a magnetic field gradient, to suspend a diamagnetic object against gravity. 1 This procedure has broad generality but also six limitations: (i) Evaporation of the solvent from a solution of paramagnetic salt will increase the concentration of the paramagnetic species and, thus, the magnetic susceptibility of the solution. This evaporation of solvent complicates the use and storage of paramagnetic solutions and, in some applications, requires calibration or the use of internal standards. (ii) Aqueous solutions of paramagnetic salts cannot be used for density-based measurement of water-miscible or water-soluble analytes. (iii) Paramagnetic salts have high but ultimately finite solubility in water (the limiting solubility of MnCl 2 is ∼4.5 M) and even more limited solubility in organic solvents. Water has limited ability to dissolve the paramagnetic salts at subzero temperatures (<0°C). These limits to solubility constrain the range of densities that can be measured using these solutions. (iv) Some organic solvents used for watermiscible analytes in MagLev (especially CHBr 3 for high-density samples) are toxic and/or flammable. (v) To allow for measurement of water-soluble analytes, the paramagnetic metal ion must be converted into an organic-soluble chelate to give useful solubility; this transformation requires additional synthesis steps. (vi) Measurement of very low (ρ < 1.00 g/cm 3 ) and high (ρ > 3.00 g/cm 3 ) densities is complicated or difficult using simple techniques (although possible with newer...

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