C-BER - Centre for BIOMEDICAL ENGINEERING RESEARCH CAP - Centre for APPLIED PHOTONICS Computational Modelling of Bioparticles Trapping using Optical Fiber Tweezers Joana S. Paiva1,2, Rita S. R. Ribeiro1,2, Pedro A. S. Jorge1,2, Carla C. Rosa1,2, Joao P. S. Cunha1,3 1INESC Technology and Science, Portugal; 2Physics and Astronomy Department, Faculty of Sciences, University of Porto; 3Faculty of Engineering, University of Porto The Optical Fiber Tweezers (OFTs) Optical Tweezers (OT) are optical devices that, based on the forces exerted by a strongly focused optical beam on a dielectric particle with few microns, are able to trap and manipulate it [1-2]. The optical forces exerted on the particle are resultant of the momentum transfer between radiation field and the scattering particle [2]. Conventional Optical Tweezers (COTs): (A) (B) Composed by a set of bulk elements incorporated in an inverted microscope (small working distances; limited degree of portability; hard handling; difficulties in focusing). Optical Fiber Tweezers (OFTs): Based on optical fibers. Flexible, small. Their tips could be machined for generating specific optical effects [1]. Applications Figure 1: (A) Microscopic image of a polymeric Optical Fiber Tweezer tip fabricated in our laboratory using the method described in [1]. (B) Microscopic snapshot showing the simultaneous trapping phenomena of four yeast cells using this tip. Biology, Medicine and Applied Photonics, for mechanical characterization of particular biological processes, cells (e.g., Red Blood Cells elasticity quantification) [1-3] or intracellular structures (e.g., DNA molecules manipulation) [1-2]. OFT trapping forces computational model The method proposed by Barnett and Loudon was used to calculate OFT trapping forces in theory [2]. This method considers that the optical forces exerted on particles could be modelled as Lorentz forces exerted on microscopic dipoles which compose each particle. Electromagnetic Field propagation was performed using the Finite Differences Time Domain (FDTD) method implemented on the MEEP software [2]. Forces were calculated using custom-made Matlab and Python scripts. εr (A) (C) (B) Figure 2: (A) Simulation environment graphical representation (including the waveguide – fiber tip - and a 4μm curvature radius circular particle), showing components’ relative permittivity (εr) 2D spatial distribution. (B) Normalized propagated electromagnetic field intensity resultant from the FDTD method. (C) Trapping map forces (normalized) for a round particle located in several different positions (each point represents a particle position). An application case: Healthy vs. Malaria-infected Red Blood Cells (RBCs) OFT forces Computational simulations using the above method showed that, theoretically, it is possible to trap RBCs in different Malaria-infection degrees and that there is a relation between RBC infection degree and the maximum force magnitude that is possible to exert on it. (A) (B) Figure 3: (A) Magnitude force according to infection degree. (B) Maximum magnitude force vs. infection degree (Spearman; r=-1.00, p < 0.01). [1] R. Ribeiro, O. Soppera, A. Oliva, A. Guerreiro, and P. Jorge, “New trends on optical fiber tweezers,” Journal of Lightwave Technology, vol. 33, no. 16, pp. 3394–3405, 2015. [2] J. Paiva, R. Ribeiro, P. Jorge, C. Rosa, J. Cunha, “Computational modeling of red blood cells trapping using Optical Fiber Tweezers”, in: Bioengineering (ENBENG), 2017 IEEE 5th Portuguese Meeting on, IEEE, 2017, pp. 1-4. [3] J. Paiva, R. Ribeiro, P. Jorge, C. Rosa, A. Guerreiro, J. Cunha, “2D Computational Modeling of Optical Trapping Effects on Malaria-infected Red Blood Cells”, in: OSA Frontiers in Optics, OSA, 2017 [submitted]. Grant: PD/BD/135023/2017