title: Integrated measurement of the mass and surface charge of discrete microparticles using a suspended microchannel resonator.
abstract: Measurements of the mass and surface charge of microparticles are employed in the characterization of many types of colloidal dispersions. The suspended microchannel resonator (SMR) is capable of measuring individual particle masses with femtogram resolution. Here, we employ the high sensitivity of the SMR resonance frequency to changes in particle position, relative to the cantilever tip, to determine the electrophoretic mobility of discrete particles in an applied electric field. When a sinusoidal electric field is applied to the suspended microchannel, the transient resonance frequency shift corresponding to a particle transit can be analyzed by digital signal processing to extract both the buoyant mass and electrophoretic mobility of each particle. These parameters, together with the mean particle density, can be used to compute the size, absolute mass, and surface charge of discrete microspheres, leading to a true representation of the mean and polydispersity of these quantities for a population. We have applied this technique to an aqueous suspension of two types of polystyrene microspheres, to differentiate them based on their absolute mass and their surface charge. The integrated measurement of electrophoretic mobility using the SMR is determined to be quantitative, based on comparison with commercial instruments, and exhibits favorable scaling properties that will ultimately enable measurements from mammalian cells.
authors.affiliation: Department of Biological Engineering, Massachusetts Institute of Technology, 20 Ames Street, Cambridge, Massachusetts 02139, USA.
authors.forename: Philip
authors.initials: P
authors.lastname: Dextras
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Burg
authors.forename: Scott R
authors.initials: SR
authors.lastname: Manalis
mesh_terms: D004867:Equipment Design; D046210:Microfluidic Analytical Techniques / Q000295:instrumentation*; D008863:Microspheres; D008970:Molecular Weight; D010316:Particle Size; D011137:Polystyrenes / Q000737:chemistry*; D055672:Static Electricity; D013499:Surface Properties
chemical_list: D011137:Polystyrenes