Mkit: A cell migration assay based on microfluidic device and smartphone

Abstract

Mobile sensing based on the integration of microfluidic device and smartphone, so-called MS² technology, has enabled many applications over recent years, and continues to stimulate growing interest in both research communities and industries. In particular, it has been envisioned that MS² technology can be developed for various cell functional assays to enable basic research and clinical applications. Toward this direction, in this paper, we describe the development of a MS²-based cell functional assay for testing cell migration (the M_kit). The system is constructed as an integrated test kit, which includes microfluidic chips, a smartphone-based imaging platform, the phone apps for image capturing and data analysis, and a set of reagent and accessories for performing the cell migration assay. We demonstrated that the M_kit can effectively measure purified neutrophil and cancer cell chemotaxis. Furthermore, neutrophil chemotaxis can be tested from a drop of whole blood using the M_kit with red blood cell (RBC) lysis. The effects of chemoattractant dose and gradient profile on neutrophil chemotaxis were also tested using the M_kit. In addition to research applications, we demonstrated the effective use of the M_kit for on-site test at the hospital and for testing clinical samples from chronic obstructive pulmonary disease patient. Thus, this developed M_kit provides an easy and integrated experimental platform for cell migration related research and potential medical diagnostic applications.

Keywords: Cell functional assay; Cell migration; Chemotaxis; Microfluidic device; Smartphone.

Fig. 1. Illustration of the M_kit

(A) Components of the M_kit; (B) Operation flow of the M_kit. CF indicates chemotactic factor.

Fig. 2. Illustration of the smartphone imaging platform

(A) Expanded view of the imaging platform. The system is 260 (L) × 180 (W) × 100 (H) mm; The illustration and a picture of the real assembled imaging platform are shown on the right; (B) Optical configuration of the imaging platform; (C) Smartphone app interface showing the cell migration distance analysis. The green line denotes the edge of the gradient channel next to the docking structure. The final result is presented as the average migration distance of all cells ± standard error of the mean (s.e.m.) in μm.

Fig. 3. Illustration of the microfluidic device for cell migration test

(A) Microfluidic device illustration to test purified cells or directly from whole blood with RBC lysis. (B–C) Enlarged view of the microfluidic channel with cell docking. The red spheres indicate the cells, which were initially aligned by the thin barrier channel because the cell size is larger than the height of the barrier channel. Upon chemoattractant stimulation, cells will change their morphology to crawl through the barrier channel into the gradient channel. (D) Illustration of a cell migration experiment for parallel chemotaxis test and medium control. CF indicates chemotactic factor. Blue color indicates the channel walls and green color reflects the glass surface.

Fig. 4. Gradient measurements by the smartphone imaging system

(A) Gradient of FITC-Dextran in the two gradient channels captured by the smartphone system; (B) Gradient profile at different time points in one gradient channel; (C) Gradient profiles in two gradient channels.

Fig. 5. Chemotaxis test of neutrophils and cancer cells using the M_kit

(A) Final distribution of purified neutrophils and cancer cells in the gradient channels in response to a 100 nM fMLP gradient or a 30 nM EGF gradient respectively. The experiment was done in duplicate on each device for purified neutrophils or cancer cells. (B) Cell migration distance analysis of chemotaxis experiments using purified neutrophil and cancer cells. (C) Final distribution of neutrophils from whole blood to a 100 nM fMLP gradient or in the medium control; (D) Cell migration distance analysis of neutrophil from whole blood in 3 different devices. The bars show the average migration distance of all cells to the fMLP gradient for each device and the error bars are the standard error of the mean (s.e.m.). The migration distance of the medium control shown in the graph is the average of all cells from one device and it is similar in all three devices.

Fig. 6. Chemotaxis test of neutrophils to fMLP gradients of different doses and profiles using the M_kit

(A) Cell migration distance of neutrophils to fMLP gradients of different doses; (B) Cell tracking analysis by calculating CI and cell speed to different fMLP gradient doses; (C–D) Rhodamine 6 G gradient images and the corresponding final cell distribution images at the upstream and downstream of the gradient channel; (E) Plot of gradient profiles at the upstream and downstream (normalized to the upstream gradient) of the gradient channel; (F) Cell migration distance analysis of neutrophil in upstream and downstream to a 100 nM fMLP gradient. The bars show the average value of the parameter of all cells for each condition and the error bars are the standard error of the mean (s.e.m.). The data shown are from a set of representative experiments (one experiment for each condition)