Rapid enrichment of biomolecules using simultaneous liquid and particulate dielectrophoresis

Abstract

Here we show that dielectrophoretic (DEP) liquid actuation can be used to dispense arrays of nanoliter-sized droplets loaded with biomolecules. Size-based enrichment of these biomolecules occurs rapidly and simultaneously with the droplet dispensing. The physical mechanism responsible for the effect is the positive DEP force directed toward the electrodes that is imposed by the non-uniform electric field during the very rapid DEP actuated flow before droplet formation. Experiments conducted with a suspension of lambda DNA (molecular weight: 31.5 x 10(3) kDa) and lectin protein (120 kDa) containing identical molar concentration shows separation of DNA and protein within the nanolitre sized droplets formed along the electrode. The density ratio of protein to DNA varies smoothly from 1 : 1 in the parent droplet to approximately 3 : 1, favoring the smaller sized protein in the daughter droplet dispensed furthest from the parent droplet, approximately 2.4 mm from the parent droplet. Experiments conducted with binary protein solutions containing identical molar concentrations of bovine serum albumin (66 kDa) and fibrinogen (340 kDa) reveal that enrichment is enhanced as the length of the electrodes is increased. The density ratio of BSA to fibrinogen varied from 1 : 1 in the parent droplet to approximately 1.97 : 1 at the last (tenth) droplet, located approximately 4.2 mm from the parent droplet. The entire process, consisting of droplet dispensing and particle separation, occurs in less than one second.

Insulator-based dielectrophoresis with β-galactosidase in nanostructured devices

“…Theoretically, DEP manipulation of nm- sized proteins is challenging since extremely high electric field gradients are required in order to generate DEP forces large enough to compete with molecular diffusion, electrokinetic and electrothermal forces. Regardless, nearly 20 groups have investigated protein DEP experimentally employing metal electrodes 8,10,11,30 , nanopipettes 31 , carbon nanotubes 32 , and in droplets 33 . For instance, Hölzel demonstrated single molecule DEP trapping 3 with eDEP 8 .…”

Tuning direct current streaming dielectrophoresis of proteins

“…However, the manipulation of proteins by DEP has recently been demonstrated. 14,[26][27][28][29][30][31] As anticipated, high field strengths and gradients are required while DEP under DC and AC conditions was reported. Interestingly, proteins with molecular weight smaller than 100 kDa were successfully accumulated on electrodes, 14,26 carbon nanotubes, 27 within droplets, 28 and using nanopipettes.…”

“…14,[26][27][28][29][30][31] As anticipated, high field strengths and gradients are required while DEP under DC and AC conditions was reported. Interestingly, proteins with molecular weight smaller than 100 kDa were successfully accumulated on electrodes, 14,26 carbon nanotubes, 27 within droplets, 28 and using nanopipettes. 19 H€ olzel et al showed the DEP induced trapping of the large multimeric protein R-phycoerythrin at metal electrode gaps; 30 whereas Bakewell et al investigated frequency dependent DEP behavior of avidin.…”

“…19,[26][27][28][29][30][31][32] This is not only due to the particular special arrangements at the microscale used to generate high electric field gradients, but also a consequence of the solvent conditions and intrinsic protein properties. Moreover, a generic theoretical model predicting protein polarizability and accounting for the large protein variety has not been developed yet.…”

A bead-based fluorescence immunosensing technique enabled by the integration of Förster resonance energy transfer and optoelectrokinetic concentration

“…Alternatively, some research efforts turn to focus on developing techniques for maneuvering micro-/nano-sized particles. [20][21][22][23][24][25][26][27] However, only few of them are capable of harnessing particles programmably, i.e., addressable manipulation. Among the technologies, optoelectronic tweezers were first incorporated into a bead-based immunoassay for a surface-enhanced Raman scattering (SERS) detection.…”