Application of an optically induced electrokinetic manipulation technique on live bacteria

In this paper, we apply a recently demonstrated rapid electrokinetic patterning (REP) technique to Shewanella oneidensis MR-1 and confirm the application possibility of the technique on bio-materials. This technique utilizes a simple microfluidic chip with two indium tin oxide (ITO) coated parallel electrodes and requires the simultaneous application of AC electric field and the hologram provided from an infrared (1064 nm) laser, in order to control and aggregate particles onto electrodes. For the experimentation in this paper, Shewanella oneidensis MR-1 are cultured by green fluorescent protein (GFP) on Luria-Bertani (LB) agar plate and through sample pretreatment process, mid-log phase samples of the bacteria finally are obtained. As a result of applying REP technique to this bacteria sample, we could collect a lot of the bacteria onto ITO electrode surfaces rapidly and the bacteria cluster could be translated with the movement of laser focus position under uniform electric field. Also it was confirmed that there exists a particular frequency range, i.e. critical frequency for REP based bacteria cluster. We could find that under the application of REP technique, the ellipsoidal bacteria are reoriented with respect to electric field lines as electrical frequency increases up. Also the change in the vertical distance between the bacteria and the electrode surface with electrical voltages could be observed. These results show that the REP technique can be used to separate, sort and manipulate bioparticles like bacteria.