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Functionalized magnetic microspheres are widely used for cell separations, isolation of proteins and other biomolecules, in vitro diagnostics, tissue engineering, and microscale force spectroscopy. We present here the synthesis and characterization of a silicone magnetic microsphere which can be produced in diameters ranging from 0.5 to 50 μm via emulsion polymerization of a silicone ferrofluid precursor. This bottom-up approach to synthesis ensures a uniform magnetic concentration across all sizes, leading to significant advances in magnetic force generation. We demonstrate that in a size range of 5–20 μm, these spheres supply a full order of magnitude greater magnetic force than leading commercial products. In addition, the unique silicone matrix exhibits autofluorescence two orders of magnitude lower than polystyrene microspheres. Finally, we demonstrate the ability to chemically functionalize our silicone microspheres using a standard EDC reaction, and show that our folate-functionalized silicone microspheres specifically bind to targeted HeLa and Jurkat cells. These spheres show tremendous potential for replacing magnetic polystyrene spheres in applications which require either large magnetic forces or minimal autofluorescence, since they represent order-of-magnitude improvements in each. In addition, the unique silicone matrix and proven biocompatibility suggest that they may be useful for encapsulation and targeted delivery of lipophilic pharmaceuticals.

This paper describes light transmission spectroscopy (LTS), a technique for eliminating spectral noise and systematic effects in real-time spectroscopic measurements. In our work, we combine LTS with spectral inversion for the purpose of nanoparticle analysis. This work employs a wideband multi-wavelength light source and grating spectrometers coupled to CCD detectors. The light source ranges from 210 to 2000 nm, the wavelength-dependent light detection system ranges from 200 to 1100 nm with ≤1  nm resolution, and the nanoparticle diameters range from 1 to 3000 nm. The nanoparticles are suspended in pure water or water-based buffer solutions. For testing and calibration purposes, results are presented for nanoparticles composed of polystyrene and gold. Mie theory is used to model the total extinction cross section, and spectral inversion is employed to obtain quantitative particle size distributions, from which information on the size, shape, and number of nanoparticles can be derived. Discussed are the precision, accuracy, resolution, and sensitivity of our results. The LTS technique is quite versatile and can be applied to spectroscopic investigations where wideband, accurate, low-noise, real-time spectra are desired.

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