Parallel, Non-Contact Trapping and Translation of Yersenia Pestis Bacteria with Optoelectronic Tweezers

Abstract

Studies of host-pathogen (HP) interactions at the single cell level are critical for understanding the often elaborate, dynamical processes involved in pathogen invasion of hosts and disease initiation and progression. In order to monitor the pathogen invasion process, most often one mixes a solution containing pathogens into a culture of host cells, and then hopes the host cell being monitored is invaded by a pathogen. These chance encounters have been monitored using fluorescence microscopy, allowing for example fluorescent effector proteins to be monitored as they are injected into a host cell (Enninga, Mounier et al. 2005; Schlumberger, Muller et al. 2005). Such “mix and hope” strategies are simple, direct, and necessary for initial studies. However, they do not provide a path to obtain large sample sizes, control of timing of pathogen invasion, or a way to determine how many bacteria are required to defeat host defenses. We present recent results from using optoelectronic tweezers (OET) (Chiou, et al. 2005) as a tool for manipulating single pathogenic bacteria, opening a promising route for controlled initiation of HP interactions. Optoelectronic trapping uses laser-excited carriers inside a thin film of amorphous or crystalline Si to create a non-uniform electric field. These carriers, coupled with an electric field modulated in the MHz range produces strong field gradients. The object being trapped is polarized by the electric field, and gradients in the electric field create a potential well which traps the object. This trapping is obtained at extremely low optical intensities (<1W/cm∧2) and does not require functionalization of the pathogen in order to facilitate delivery to the host, opening up novel possibilities for massively parallel studies of HP interactions.