Biocompatible and label-free separation of cancer cells from cell culture lines from white blood cells in ferrofluids

Abstract

This paper reports a biocompatible and label-free cell separation method using ferrofluids that can separate a variety of low-concentration cancer cells from cell culture lines (~100 cancer cells/mL) from undiluted white blood cells, with a throughput of 1.2 mL/h and an average separation efficiency of 82.2%. The separation is based on size difference from cancer cells and white blood cells, and is conducted in a custom-made biocompatible ferrofluid that retains not only excellent short-term viabilities, but also normal proliferations of 7 commonly used cancer cell lines. A microfluidic device is designed and optimized specifically to shorten the exposure time of live cells in ferrofluids from hours to seconds, by eliminating time-consuming off-chip sample preparation and extraction steps and integrating them on-chip to achieve one-step process. As a proof-of-concept demonstration, a ferrofluid with 0.26% volume fraction was used in this microfluidic device to separate spiked cancer cells from cell lines at a concentration of ~100 cells/mL from white blood cells with a 1.2 mL/h throughput. The separation efficiencies were 80±3%, 81±5%, 82±5%, 82±4%, and 86±6% for A549 lung cancer, H1299 lung cancer, MCF-7 breast cancer, MDA-MB-231 breast cancer, and PC-3 prostate cancer cell lines, respectively. Separated cancer cells purity was between 25.3% and 28.8%. In addition, separated cancer cells from this strategy showed an average short-term viability of 94.4±1.3% and separated cells were cultured and demonstrated normal proliferation to the confluence even after the separation process. Owning to its excellent biocompatibility and label-free operation, and its ability to recover low concentration of cancer cells from white blood cells, this method could lead to a promising tool for rare cell separation.

Label-free ferrohydrodynamic cell separation of circulating tumor cells

“…Previous ferrohydrodynamic cell sorting devices were developed to process cells at low throughput and high spike ratios, 45, 47–49 therefore cannot be realistically used to separate CTCs from blood. CTCs are extremely rare in the blood circulation, occurring usually at a concentration of less than 100 CTCs per mL of blood.…”

“…Therefore, its pH value, tonicity, materials and surfactants of nanoparticles need to be optimized as a biocompatible medium for cells, while at the same time the overall colloidal stability of the ferrofluid will have to be well maintained. Based on our previous work, 48, 49 we have developed a water-based ferrofluid with maghemite nanoparticles in it that was tested to be biocompatible for cancer cells from cultured cells lines. The particles had a mean diameter of 11.24 nm with a standard deviation of 2.52 nm (ESI,† Fig.…”

“…48, 49 Details of the ferrofluid synthesis and functionalization are listed in ESI†. Size and morphology of the maghemite nanoparticles were characterized via transmission electron microscopy (TEM; FEI Corp., Eindhoven, the Netherlands).…”

“…After entering the channel region that was on top of a permanent magnet, large cells including CTCs and some WBCs experienced more size-dependent magnetic buoyance force than smaller WBCs, resulting in a spatial separation between them at the outlets of the device. Although ferrohydrodynamic cell separation was demonstrated before, 45–49 its application in CTCs was challenging in the past for the following reasons. First, rarity of CTC necessitates a blood-processing throughput of close to 7.5 mL h −1 and recovery rate of at least 80% in low concentration (<100 cell mL −1 ) conditions.…”

“…8 Previous applications of ferrohydrodynamic cell separation mostly focused on sorting of bacteria and yeast cells, 45, 46 bacteria and red blood cells, 47 and cancer cells of cultured cell lines from blood. 48, 49 The throughputs of these studies were lower than what was required of CTC separation, and the target cells were mostly spiked at a much higher concentration (e.g., 10 5 -10 6 cells mL −1 ) than CTCs. 45–48 Second, ferrofluids, as a colloidal suspension of magnetic nanoparticles with diameters of approximately 10 nm, need to be rendered biocompatible for CTC separation.…”