Single cancer cell detection with optofluidic intracavity spectroscopy
Date
2012
Authors
Wang, Weina, author
Lear, Kevin, advisor
Chandrasekar, V., committee member
Krapf, Diego, committee member
Reardon, Kenneth, committee member
Journal Title
Journal ISSN
Volume Title
Abstract
The detection of cancer cells is the basis for cancer diagnostics, cancer screening and cancer treatment monitoring. Non-destructive and non-chemical optical methods may help reduce the complexity and cost of related test, making them more available to the public. The label-free technique of optofluidic intracavity spectroscopy (OFIS) uses light transmitted through a cellular body in a microfluidic optical resonator to distinguish different types of cells by their spectral signatures. The OFIS chips are fabricated in the CSU semiconductor clean room and the fabrication process was reported by a previous Ph.D student, Hua Shao. She also did some initial exploration on combining dielectrophoresis (DEP) with the OFIS technique. Since then, some revisions to the fabrication technique have been made to improve the alignment, bonding and sealing of this microfluidic chip. In addition, new DEP electrode designs have been designed and fabricated to further improve the trapping performance of the traps and facilitate automated cell trapping and analysis. Viability tests were carried out to investigate the effect of heating (induced by DEP electrodes) on cells in chips built with borosilicate and sapphire substrates. These experiments used specially designed DEP electrodes that help more accurately control the DEP exposure time and strength. The survival rate of cells out of DEP enabled OFIS system is greatly affected by the substrate type and DEP exposure dose. The OFIS technique has differentiated red and white human blood cells, as well as canine lymphoma and lymphocytes based on their distinctive transmission spectra. Using OFIS chips fabricated with the modified process, OFIS spectra of settled cells from canine hemangiosarcoma (HSA) cell lines and monocytes in peripheral blood mononuclear cells (PBMCs) were collected and analyzed. To quantify the strength of transverse modes in their spectra, a single characteristic parameter was determined for each cell by forming a linear combination of the mean and standard deviation of the transmission spectra over one free spectral range excluding the residual longitudinal peaks of the bare Fabry-PĂ©rot (F-P) cavities filled with cell suspending medium only. The difference in the characteristic parameters of HSA and monocyte samples was highly statistically significant with a p-value as low as 10-6. A receiver operating characteristic (ROC) curve constructed from t-distributions fit to the HSA and monocytes spectra indicates that the cell classification based on their characteristic parameters can achieve 95% sensitivity and 98% specificity simultaneously. Furthermore, some features observed in the spectra of HSA cells motivated a new optical model of the cell loaded F-P cavity. The OFIS spectra of individual cells from canine HSA and canine lymphoma cancer cell lines exhibit relatively uniformly spaced multiple transverse modes repeated in each free spectral range of a microfluidic F-P cavity while similar spectra of healthy canine monocytes and lymphocytes only have up to 2 or no transverse mode peaks. Modeling of the cells as thin lenses allows paraxial Gaussian beam resonator analysis that produces spectral features that quantitatively match the frequencies of transverse modes and qualitatively agree with the trends in maximum transmission of the modes when aperture losses are included. The extracted experimental focal lengths are significantly larger for cancerous cells than for noncancerous cells and can be used as a potential cell malignancy indicator. Furthermore, a thick lens model was developed, allowing manipulation of more parameters related to cell morphology and its location in the cavity. This model was used to interpret experimental results acquired from settled and suspended cells.
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Subject
biophotonics
optofluidic intracavity spectroscopy
optical cancer diagnostics
cell refractometry