Local Heating of Discrete Droplets Using Magnetic Porous Silicon-Based Photonic Crystals

Abstract

This paper describes a method for local heating of discrete micro-liter scale liquid droplets. The droplets are covered with magnetic porous Si microparticles, and heating is achieved by application of an external alternating electromagnetic field. The magnetic porous Si microparticles consist of two layers: the top layer contains a photonic code and it is hydrophobic, with surfacegrafted dodecyl moieties. The bottom layer consists of a hydrophilic Si oxide host layer that is infused with Fe 3 O 4 nanoparticles. The amphiphilic 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 magnetic field (338 kHz, 18A 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.A simple microfluidics application is demonstrated: combining complementary DNA strands contained in separate droplets and then thermally inducing dehybridization of the conjugate. The complementary oligonucleotides were conjugated with the cyanine dye fluorophores Cy3 and Cy5 to quantify the melting/re-binding reaction by fluorescence resonance energy transfer (FRET). The magnetic porous Si microparticles were prepared as photonic crystals, containing spectral codes that allowed the identification of the droplets by reflectivity spectroscopy. The technique demonstrates the feasibility of tagging, manipulating, and heating small volumes of liquids without the use of conventional microfluidic channel and heating systems.

Photoluminescence‐Based Sensing With Porous Silicon Films, Microparticles, and Nanoparticles

“…Recent advances in microfluidics, inkjet technologies, and the like have made great strides in reducing sample processing and analysis times, and porous Si systems have also made contributions to this area. For example, stratified ''nanoreactors'' in which enzyme compartmentalization, [75] reagent delivery, [196] protein separation, [32,56,76] and reactant heating, [197] have been fabricated. The electrochemistry of porous Si allows one to incorporate sample and signal processing tasks at the materials level.…”

Porous silicon in drug delivery devices and materials☆

“…The oral administration of porous Si to provide a dietary supplement of silicon [182] has also been assessed [183]. Porous Si drug delivery devices have taken the form of particles [25,184,185], films [16], chip implants [186,187], composite materials [146,150], and microneedles [188,189]. Much work has focused on microparticle systems [21,25,30,31,[106][107][108][190][191][192][193] due to their relative ease of fabrication, administration, and their compatibility with existing drug delivery concepts.…”

“…The latter workers have investigated the interactions between various drugs with the different porous Si surface chemistries in detail [20]. The incorporation of superparamagnetic iron oxide nanoparticles, of interest for Magnetic Resonance Imaging (MRI) has been demonstrated [25,121], and remote RF heating (by Néel relaxation) of such structures has been reported [185]. The amount of drug that can be loaded into a porous Si microparticle is large due to its relatively large free volume.…”

Particles in Microfluidic Systems

“…34 In addition, the magnetic beads can be simultaneously used for localized heating of the droplets using an AC radiofrequency electromagnetic field. 34,35 The magnetic Si particles described previously were used for thermal cycling of PCR amplification of DNA. The particles achieved reproducible melting and dehybridization (35-55 C) of the DNA strands using a 338 kHz 18 amp rms RF signal.…”