Magnetic barcoded hydrogel microparticles for multiplexed detection

Abstract

Magnetic polymer particles have been used in a wide variety of applications ranging from targeting and separation to diagnostics and imaging. Current synthesis methods have limited these particles to spherical or deformations of spherical morphologies. In this paper, we report the use of stop flow lithography to produce magnetic hydrogel microparticles with a graphical code region, a probe region, and a magnetic tail region. These anisotropic multifunctional magnetic polymer particles are an enhanced version of previously synthesized "barcoded" particles (Science, 2007, 315, 1393-1396) developed for the sensitive and rapid multiplexed sensing of nucleic acids. The newly added magnetic region has acquired dipole moments in the presence of weak homogeneous magnetic fields, allowing the particles to align along the applied field direction. The novel magnetic properties have led to practical applications in the efficient orientation and separation of the barcoded microparticles during biological assays without disrupting detection capabilities.

Figure 1

Production of magnetic barcoded particles. (A) Synthesis process of magnetic barcoded particles. Stop flow lithography (SFL) is used to generate particles with three distinct chemical regions. The top stream is comprised of PEG-DA with food coloring and rhodamine A, while the other streams consist of PEG-DA with probe oligonucleotide and magnetic beads, respectively. Downstream of the synthesis site, a PEG-DA perfusion stream is used to move un-incorporated magnetic beads into a waste outlet. (B) An experimental bright field image of the three phases flowing in the channel. The magnetic beads in the bottom flow are seen to be well-dispersed. The scale bar is 50 μm. (C) Dimensions of a magnetic barcoded particle. Coding holes are designed with the following dimensions: ‘1’ (12 × 15 μm), ‘2’ (12 × 27.5 μm), and ‘3’ (12 × 40 μm). The code in this illustration is ‘2333’.

Figure 2

Magnetic barcoded particles. (A) A bright field image (20× objective) of magnetic barcoded particles with code ‘2333’. (B) A fluorescent image of (A). (C) The side view of a magnetic barcoded particle in a bright field image (20× objective). (D) A fluorescent image of (C). (E) A bright field image (5× objective) of magnetic barcoded particles with code ‘0013’. Scale bars are 50 μm (A and B), 25 μm (C and D) and 100 μm (E).

Figure 3

Response of magnetic barcoded particles. (A) Response of magnetic barcoded particles to out-of-plane (21.1±0.1mT) magnetic field. (B) Response of magnetic barcoded particles to in-plane (14.7±0.1mT) magnetic field. (C) Reorientation of a magnetic barcoded particle in a microfluidic channel using a hand magnet. (D) Snapshots of magnetic transportation of a magnetic barcoded particle using a hand magnet. The particle was transported towards a narrow region in the microfluidic channel used for single-particle scanning analysis. (E) Image of reoriented magnetic barcoded particles moving towards a hand magnet. (F) Bulk separation of magnetic barcoded particles using a hand magnet. Scale bars are 50 μm (C and D), 100 μm (A and B), and 200 μm (E).

Figure 4

Incubation matrix. Particles with a fluorescent code region, an internal probe region, and a tail region were synthesized and incubated with either 0 or 200 amol of two different biotinylated target oligonucleotides at 50 °C for 90 min. Following incubation, probe-target complexes were labeled with streptavidin-phycoerythrin (SAPE) at 21.5 °C for 45 min. Particle type 1 featured no probe, a magnetic tail, and code ‘2333’; type 2 featured probe 1, a magnetic tail, and code ‘2003’; type 3 featured probe 2, a magnetic tail, and code ‘0013’; type 4 featured probe 1, a non-magnetic tail, and code ‘2013.’ Each plot shows the average of 5 scans of each particle type at the specified incubation condition. Horizontal axis is axial (lengthwise) position in pixels, and vertical axis is mean fluorescent intensity in arbitrary units. The mean signal across the width of the particle has been computed and plotted at each axial position. The red numbers above each scan indicate the mean fluorescent intensity measured in the probe region and in the tail region. The red bars in the first plot indicate the windows over which the averages were taken. Quoted numbers represent the mean of five separate scans.