IDBR: TYPE A: Mass-Sensing Nanostructure-Enhanced Laser Tweezers

University Of Washington, Seattle WA

Investigators

Abstract

Non-Technical Decscription: Understanding how cell size is controlled is a fundamental area of cell biology that has not been well understood. The size and mass of a cell convey important physiological properties that are closely regulated by various environmental and genetic factors. Characterizing the dependence of cell growth rate on cell mass for individual cells can elucidate the mechanisms underlying cell cycle progression, and there are also examples of human diseases characterized by increased cell size (hypertrophy) such as cardiac hypertrophy that can lead to heart failure and sudden death. In general, being able to monitor size and mass of single cells over time can provide important physiological information and has potential impact in cell biology, tissue engineering, cancer, and disease research. A barrier to studying size control in mammalian cells is the inaccuracy in measuring size, mass, growth rate, and the dynamics of pathways controlling growth and proliferation. Often the cell mass is estimated indirectly by measuring cell size, however, it has been shown that the mass density of a cell is not constant through its cell cycle. Recently, there has been research on using mechanical resonators to measure the cell mass directly. These approaches either require exquisite microfluidic structures and setup or are restricted to adherent cells. The locations of the cells on the mechanical resonators also cannot be accurately controlled, which limits the sensing accuracy. This project aims to develop a precise cell mass sensing and monitoring system that can work with both adherent and suspension cells by combining nanostructure-enhanced laser tweezers (NELT) with an array of MEMS resonators. This multi-disciplinary project will provide training opportunities for two graduate students, one postdoc, and NSF REU program will be pursued to provide research experience for undergraduate students. The PI and her group will continue participating in education outreach activities through UW College of Engineering Discovery Days for K-12 students. New education materials resulting from the research will be incorporated in the outreach demo activities. Technical Decscription: The proposed approach utilizes high efficiency optical trapping on a photonic crystal (PhC) platform that has been demonstrated by the PI's group. The system integrates PhC nanostructures on the surface of an array of MEMS resonators to achieve precise placement of live cells on the resonators with low optical intensity. The MEMS resonator consists of a suspended micro-disk structure whose resonant frequency depends on its mass. Cell mass will be measured by characterizing the resonant frequencies of the MEMS resonators. The platform will be placed under a fluorescence microscope for optical imaging and analysis. This system does not require exquisite microfluidic setup and can simultaneously achieve the following functions: (1) Suitable for both adherent and suspension cells. (2) High-precision measurement of a cell mass versus time, or single-point mass measurement in time with high throughput. (3) Optical imaging of an array of cells as a function of time to obtain size and other information on cell status. This project seeks to achieve the following aims: (A) Design and fabricate PhC nanostructures to achieve optical trapping with low intensity for live cells. Finite-difference time domain (FDTD) simulations will be used to design and optimize the PhC nanostructures to achieve highest trapping enhancement for the specific size of cells or particles. The PhC will be fabricated on a regular Si substrate first then integrated with the MEMS resonators. Optical trapping will be performed for polystyrene beads with various sizes to confirm that enhanced trapping efficiency can be achieved. (B) Design and fabricate PhC-integrated MEMS resonators to achieve mass-sensing with high accuracy. The same particle will be released and re-trapped on the MEMS resonator, and frequency response re-measured. The process will be repeated to allow assessing mass-sensing accuracy. (C) Perform mass sensing and monitoring of adherent and suspension cells. Cells will be synchronized in their cell cycle using serum starvation, thymidine-nocodazole block and double thymidine block for cell mass measurement. An array of reconfigurable optical traps will be set up using a spatial light modulator for the study. A dissemination plan for the proposed instrument will be implemented with the project. The plan involves disseminating the research results and the capability of the instrument through technical conferences, publications, and the PI's research group website; working with UW Center for Commercialization to seek licensing and commercialization of the proposed technology.