Isolation of circulating fetal trophoblasts by a four-stage inertial microfluidic device for single-cell analysis and noninvasive prenatal testing.

Noninvasive detection of circulating fetal cells carrying the entire fetal genome is a promising way for prenatal testing of genetic diseases. However, ideal approaches for efficient separation of these valuable cells are not available. Here, a novel inertial microfluidic chip (CelutriateChip 1) is developed for ultra-fast, label-free enrichment of circulating trophoblasts (CTBs) from the whole blood samples of pregnant women. The unique structural design of the four-stage curved channel in CelutriateChip 1 enables CTBs with larger size to be efficiently separated from the blood samples under the effect of inertial and Dean drag forces. The transition of the target cells among the stages enables CelutriateChip 1 to achieve one or two orders of magnitude higher throughput compared to single channel inertial microfluidic chips. After optimization of conditions, CTBs can be recovered from 2 mL of whole blood within 5 min with an average recovery efficiency ranging from 52.3% to 65.8% and high white blood cell depletion (99.95%). CTBs collected from the chip can be isolated at the single-cell level and used for downstream immunofluorescence staining and genetic genotyping. Clinical tests are performed on 30 pregnant women and the results demonstrate that CTBs are obtainable in 86.67% of pregnancy cases. A single-base variant in the HBB gene can be accurately detected by sequencing of rare CTBs. This simple, antibody-free and low-cost approach holds promise for obtaining rare CTBs for prenatal detection of various genetic diseases.

Spiral microchannel with rectangular and trapezoidal cross-sections for size based particle separation.

The paper reports a new method for three-dimensional observation of the location of focused particle streams along both the depth and width of the channel cross-section in spiral inertial microfluidic systems. The results confirm that particles are focused near the top and bottom walls of the microchannel cross-section, revealing clear insights on the focusing and separation mechanism. Based on this detailed understanding of the force balance, we introduce a novel spiral microchannel with a trapezoidal cross-section that generates stronger Dean vortices at the outer half of the channel. Experiments show that particles focusing in such device are sensitive to particle size and flow rate, and exhibits a sharp transition from the inner half to the outer half equilibrium positions at a size-dependent critical flow rate. As particle equilibration positions are well segregated based on different focusing mechanisms, a higher separation resolution is achieved over conventional spiral microchannels with rectangular cross-section.