1) Photonic crystal nanostructures combine optical tweezers and MEMS resonators to allow trapping and precise mass measurements of cells. 2) MEMS resonators detect resonant frequency changes to measure cell mass, while photonic tweezers fix cell position with low light intensity, enabling study of biophysical properties. 3) A detection system using a split photodiode and detection circuitry was built to measure resonant frequencies by converting the output current from vibrating resonators hitting the photodiode into a voltage for viewing and measuring frequencies.

1. Optical Resonant Frequency Detection Systemfor Mass-
Sensing MEMS Resonators
NNIN REU Intern: Kasia Gibson, Bioengineering, Northeastern University
NNIN Principal Investigator: Lih Y. Lin, Electrical Engineering, University of Washington-Seattle
NNIN Mentors:
 Ethan Keeler,Electrical Engineering, University of Washington-Seattle
 Peifeng Jing, Electrical Engineering, University of Washington-Seattle
 Conner Ballew, Electrical Engineering, University of Washington-Seattle
 Jingda Wu, Electrical Engineering, University of Washington-Seattle
Contacts:Gibson.kasia@gmail.com, lylin@uw.edu, e.keeler@live.com, peifengjing@gmail.com,
ckballew@uw.edu, albuswu@gmail.com
Abstract
Photonic crystal nanostructures are essential in combining two important technologies: optical
tweezers and MEMS resonators to allow effective trapping and enhanced-precision
measurements of cell mass. MEMS resonators measures the cell mass by detecting the resonant
frequency change of the resonant beam. Photonic crystal optical tweezers are applied to improve
the mass sensing capability of MEMS resonators by fixing the cell position with low light
intensity. This enables the investigation of a cell’s biophysical properties. A detection system
consists of a split photodiode and detection circuitry was built to measure the resonant
frequency of a micro-machined resonator. A laser beam incidents onto the vibrating resonator
and produces an optical deflection signal (ideally resembling a sinusoidal wave) upon hitting the
split photodiode. By using the circuit design software, Multisim, an effective circuit schematic
was created that would convert the output current of both photodiodes to an adequate voltage to
effectively view and measure the resonant frequency. During this process, simulations were
conducted, so that the behavior of the circuit could be predicted, before actual assembly. With
the usage of an Arduino microcontroller and programming software, the frequency of the
circuit’s sinusoidal wave could then be measured.