| Abstract
| - This paper describes a method for local heating of discrete microliter-scale liquid droplets. Thedroplets are covered with magnetic porous Si microparticles, and heating is achieved by application of anexternal alternating electromagnetic field. The magnetic porous Si microparticles consist of two layers.The top layer contains a photonic code and it is hydrophobic, with surface-grafted dodecyl moieties. Thebottom layer consists of a hydrophilic silicon oxide host layer that is infused with Fe3O4 nanoparticles. Theamphiphilic microparticles spontaneously align at the interface of a water droplet immersed in mineral oil,allowing manipulation of the droplets by application of a magnetic field. Application of an oscillating magneticfield (338 kHz, 18 A rms current in a coil surrounding the experiment) generates heat in the superparamagnetic particles that can raise the temperature of the enclosed water droplet to >80 °C within 5 min. Asimple microfluidics application is demonstrated: combining complementary DNA strands contained inseparate droplets and then thermally inducing dehybridization of the conjugate. The complementaryoligonucleotides were conjugated with the cyanine dye fluorophores Cy3 and Cy5 to quantify the melting/rebinding reaction by fluorescence resonance energy transfer (FRET). The magnetic porous Si microparticleswere prepared as photonic crystals, containing spectral codes that allowed the identification of the dropletsby reflectivity spectroscopy. The technique demonstrates the feasibility of tagging, manipulating, and heatingsmall volumes of liquids without the use of conventional microfluidic channel and heating systems.
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