Vaishnavi Srinivasaraghavan

Microfluidic chip bio-sensor for detection of cancer cells

Mechanical properties of single cells are associated with their disease status. Thus, cell biomechanics can serve as a reliable biomarker to distinguish cancerous cells from normal ones. Previously, it has been shown that the average deformability of cancerous cells is significantly larger than that of normal cells. In this paper, to compare the deformability of benign and tumor cells, we designed a microfluidic device with a narrow constriction straight channel and two reservoirs. We expect that softer cells will travel faster through the channel than stiffer cells. Hence, we can correlate the measured transit times for the cells to their stiffness. The results show that the average transit time of non-malignant breast cells (MCF 10A) through the channel is 1.9-fold larger than malignant breast cells (MDA-MB-231) and the average transit time of benign early stage mouse ovarian cancer cells is 1.8-fold larger than aggressive late stage ones.

Microelectrode bioimpedance analysis distinguishes basal and claudin-low subtypes of triple negative breast cancer cells

Triple negative breast cancer (TNBC) is highly aggressive and has a poor prognosis when compared to other molecular subtypes. In particular, the claudin-low subtype of TNBC exhibits tumor-initiating/cancer stem cell like properties. Here, we seek to find new biomarkers to discriminate different forms of TNBC by characterizing their bioimpedance. A customized bioimpedance sensor with four identical branched microelectrodes with branch widths adjusted to accommodate spreading of individual cells was fabricated on silicon and pyrex/glass substrates. Cell analyses were performed on the silicon devices which showed somewhat improved inter-electrode and intra-device reliability. We performed detailed analysis of the bioimpedance spectra of four TNBC cell lines, comparing the peak magnitude, peak frequency and peak phase angle between claudin-low TNBC subtype represented by MDA-MB-231 and Hs578T with that of two basal cells types, the TNBC MDA-MB-468, and an immortalized non-malignant basal breast cell line, MCF-10A. The claudin-low TNBC cell lines showed significantly higher peak frequencies and peak phase angles than the properties might be useful in distinguishing the clinically significant claudin-low subtype of TNBC.

A comparative study of nano-scale coatings on gold electrodes for bioimpedance studies of breast cancer cells

The relative sensitivity of standard gold microelectrodes for electric cell-substrate impedance sensing was compared with that of gold microelectrodes coated with gold nanoparticles, carbon nanotubes, or electroplated gold to introduce nano-scale roughness on the surface of the electrodes. For biological solutions, the electroplated gold coated electrodes had significantly higher sensitivity to changes in conductivity than electrodes with other coatings. In contrast, the carbon nanotube coated electrodes displayed the highest sensitivity to MDA-MB-231 metastatic breast cancer cells. There was also a significant shift in the peak frequency of the cancer cell bioimpedance signal based on the type of electrode coating. The results indicate that nano-scale coatings which introduce varying degrees of surface roughness can be used to modulate the frequency dependent sensitivity of the electrodes and optimize electrode sensitivity for different bioimpedance sensing applications.

Isotropically Etched Silicon Microarrays for Rapid Breast Cancer Cell Capture

In this paper, we describe design and fabrication of 3-D silicon microarrays consisting of a wide range of isotropically-etched concave cavities for cell-capturing applications. The microarrays supported rapid and efficient capture of metastatic human breast cancer cells (MDA-MB-231) from single-cell suspensions. Furthermore, the captured cells adhered and were retained within the etched cavities for at least 72 h. Cavity spacing of 30-50 μm was most suitable for capture of the cells within microwells. Cell capture was evident within 1 min and was essentially complete by 20-30 min. Capture of 10 μm beads proceeded with a similar time frame and efficiency. Cell capture was 80%-90% efficient and was independent of cavity diameters tested: 35, 60, 70, and 100 μm. The depth of the microwells ranged from 28 to 54 μm. For single-cell capture, the 35 μm diameter cavity was optimal. The larger cavities contained 3-10 cells and were better suited for applications sensing cell proliferation, cell-cell interactions, stem cell differentiation, and drug responsiveness. The proposed silicon microarrays did not require any chemical coating or surface modification to support micro co-cultures of normal human breast epithelial cells (MCF10A) and MDA-MB-231 after cell trapping. This paper demonstrates that the silicon microarrays efficiently capture individual human breast cancer cells from a mono-culture suspension and in a mixture of excess MCF10A. Therefore the developed silicon platform is suitable for efficient detection and sensing of individual human breast cancer cells.

Chemical induced impedance spectroscopy for single cancer cell detection

This paper reports a MEMS-based impedance spectrometer capable of detecting a single MDA-MB-231 human breast cancer cell in a background of normal MCF10A breast epithelial cells. This has been achieved by 1) stimulating a selective increase in the cancer cell area using the FDA-approved anti-cancer drug SAHA which resulted in a cancer-specific rise in bioimpedance and 2) utilizing a unique thin multi-branched electrode configuration that induced linear cell alignment along the electrode resulting in increased sensitivity. A 5% rise in bioimpedance in response to only 550nM of SAHA was a reliable biomarker for the presence of one or more cancer cells on the electrode. The bioimpedance response to SAHA was rapid and detectable as early as 30min.

Miniature self-calibrated fiber optic tip temperature and pressure sensor

This paper reports a miniaturized fiber optic (FO) sensor developed using microfabrication technology. In this device, the temperature and pressure measurements are incorporated into a single point fiber tip sensor. The temperature-pressure cross sensing issue, a common problem in air gap pressure sensors, is addressed by self-calibrating with the integrated temperature sensor. The sensing element is approximately 300 μm. Signal demodulation was based on an optical white light interferometry algorithm.

Mammary cancer cell manipulation with embedded passivated-electrode insulator-based dielctrophoresis (EπDEP)

In this paper, we introduce a new embedded passivated-electrode insulator-based dielectrophoresis (EπDEP) device for cell manipulation. This device maximizes the electric field strength in the microfluidic channel by reducing the thickness of the passivation layer to 5μm. The devices are made by polymer molding using 3D glass molds fabricated by melting glass into features created by the RIE-lag technique on silicon. This paper demonstrates the trapping of MDA-MB-468 mammary cancer cells using EπDEP technology with very high efficiency (97%).