Digital microfluidics and delivery of molecular payloads with magnetic porous silicon chaperones

Abstract

Digital microfluidics involves the manipulation of molecules and materials in discrete packages. This paper reviews our work using amphiphilic magnetic microparticles constructed from porous silicon. An individual porous particle can be used to carry a nanomole or smaller quantities of a reagent, and assemblies of the particles can encapsulate and transport microliter droplets of liquid containing inorganic, organic, or biological molecules. The tracking and identification of each particle can be accomplished with spectral labels that are encoded into the particles during their synthesis. When used to chaperone liquid droplets, the labels can identify the separate droplets prior to mixing and also the combined droplets after mixing. Magnetic iron oxide nanoparticles encapsulated in the porous matrix allow the manipulation of the particles or whole droplet assemblies with a magnetic field, and they also allow heating of the particle's payload by means of an externally applied RF field. Examples of organic, inorganic, and biomolecular addition reactions, catalytic reactions, and thermolysis reactions are described.

Porous silicon in drug delivery devices and materials☆

“…Oxidation produces a volume expansion (Si to SiO 2 ) that shrinks the pores, locking the payload in place. After [124] Trapping of a positively charged drug payload in a porous SiO 2 layer by ionic adsorption. Porous SiO 2 (oxidized porous Si) has a negative surface charge; molecules with positive charges will spontaneously adsorb to the inner pore walls and surface.…”

Liquid marbles: principles and applications

“…50 They also 10 used the same principle with magnetic porous silicon chaperones and demonstrated the transport of a range of precursors required for droplet based assays and a thermal cycling of a DNA duplex. 51 Whilst their main focus was on the transport of a droplet within another liquid they did demonstrate transport of a magnetic liquid marble through air. 51 Zhao et al studied liquid marbles in air created using hydrophobic Fe3C>4 nanoparticles and observed that a magnet could be used to clear part of the upper surface of the liquid marble of any particles, thus exposing the liquid.…”

“…51 Whilst their main focus was on the transport of a droplet within another liquid they did demonstrate transport of a magnetic liquid marble through air. 51 Zhao et al studied liquid marbles in air created using hydrophobic Fe3C>4 nanoparticles and observed that a magnet could be used to clear part of the upper surface of the liquid marble of any particles, thus exposing the liquid. When the magnet was removed the particulate layer re-covered in a similar manner to the self-coating process described in section 3.3.…”

Particles in Microfluidic Systems

“…33 Another example of hybrid magnetic bead/inert support particles is microporous silicon particles impregnated with the magnetic nanoparticles. 34 These particles are useful when the reaction chemistry in the droplet-based microfluidic system is reactive with the Fe 2 O 3 particles. The porous silicon particles are synthesized via electrochemical corrosion of a Si wafer with hydrofluoric acid.…”