project description

The photoacoustic effect describes the conversion of electromagnetic energy to mechanical energy, namely, that an object absorbing non-ionizing laser pulses experiences local thermal expansions, and vibrates with frequencies in the ultrasonic range which may be detected. Imaging based on this effect yields high contrast from the optical component, and high resolution from the acoustic component (1). For biomedical purposes, users of this technique take advantage of endogenous and exogenous contrast agents to obtain physiological information from the biological tissue, endogenous examples including oxy- and deoxy-hemoglobin to determine blood flow speed (2). The bacterial pigment Violacein (Vio) has been reported to be an effective contrast agent under this technique (3). Furthermore, previous iGEM teams have developed and optimized a biosynthesis pathway for this pigment (4, 5). This team seeks to build upon, and move forward from, these past investigations and develop a biosensor in E. coli to produce Violacein in the presence of significant concentrations of biomarkers for disease; naturally, the team’s search for potential biomarkers will be for those which may pass through an animal’s or human’s gastrointestinal tract. This team considers the additional design aspect of logic gates to modulate the specificity for our system. Alongside Violacein, this team will experiment with similar genetic circuits using the fluorescent protein iRFP. For the purposes of testing the resultant system(s), this team has made an arrangement with a group at MD Anderson who can introduce our bacteria into mice, and who have photoacoustic imaging equipment to image the bacteria within the gastrointestinal tracts of the mice.
References Jun X, Junjia Y, and Lihong VW. “Photoacoustic Tomography: Principles and Advances.” Progress in Electromagnetics Research 147:1-22, 2014. Fang H, Maslov K, and Wang LV. “Photoacoustic Doppler Effect from Flowing Small Light-Absorbing Particles.” Physical Review Letters 99:184501, 2007. Yuanyuan J, et al. “Violacein as a Genetically-Controlled, Enzymatically Amplified and Photobleaching-Resistance Chromophore for Optoacoustic Bacterial Imaging.” Nature.com. Nature Publishing Group. 19 June 2015. Web. 18 May 2016. E. Chromi. 2009. (18 May 2016; https://2009.igem.org/Team:Cambridge) USCF iGEM 2012. 2012. (18 May 2016; https://2012.igem.org/Team:UCSF)