Issue 22, 2013

Cavity-enhanced optical trapping of bacteria using a silicon photonic crystal

Abstract

On-chip optical trapping and manipulation of cells based on the evanescent field of photonic structures is emerging as a promising technique, both in research and for applications in broader context. Relying on mass fabrication techniques, the involved integration of photonics and microfluidics allows control of both the flow of light and water on the scale of interest in single cell microbiology. In this paper, we demonstrate for the first time optical trapping of single bacteria (B. subtilis and E. coli) using photonic crystal cavities for local enhancement of the evanescent field, as opposed to the synthetic particles used so far. Three types of cavities (H0, H1 and L3) are studied, embedded in a planar photonic crystal and optimized for coupling to two collinear photonic crystal waveguides. The photonic crystals are fabricated on a silicon-on-insulator chip, onto which a fluidic channel is created as well. For each of the cavities, when pumped at the resonance wavelength (around 1550 nm), we clearly demonstrate optical trapping of bacteria, in spite of their low index contrast w.r.t. water. By tracking the confined Brownian motion of B. subtilis spores in the traps using recorded microscope observations, we derive strong in-plane trap stiffnesses of about 7.6 pN nm−1 W−1. The values found agree very well with calculations based on the Maxwell stress tensor for the force and finite-difference time-domain simulations of the fields for the fabricated cavity geometries. We envision that our lab-on-a-chip with photonic crystal traps opens up new application directions, e.g. immobilization of single bio-objects such as mammalian cells and bacteria under controlled conditions for optical microscopy studies.

Graphical abstract: Cavity-enhanced optical trapping of bacteria using a silicon photonic crystal

Supplementary files

Article information

Article type
Paper
Submitted
26 Jul 2013
Accepted
23 Aug 2013
First published
23 Aug 2013
This article is Open Access
Creative Commons BY-NC license

Lab Chip, 2013,13, 4358-4365

Cavity-enhanced optical trapping of bacteria using a silicon photonic crystal

T. van Leest and J. Caro, Lab Chip, 2013, 13, 4358 DOI: 10.1039/C3LC50879J

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