Fractionation by shape in deterministic lateral displacement microfluidic devices

The ability to use microfluidic systems to fractionate a mixture of suspended particles based on their shape could lead to important applications. In the case of bioparticles, for example, shape is an important factor used to identify and characterize them. In fact, cell morphology has long been used in clinical diagnosis and it is also a marker of cell cycle (Sugaya et al. 2011; Beech et al. 2012; DuBose et al. 2014). At the nanoscale, nanoparticles exhibit shape-dependent properties (Burda et al. 2005), including mechanical (Park et al. 2008), optical (Jin et al. 2001) and catalytic properties (Narayanan and El-Sayed 2004). In addition, nanoparticles are sometimes the building blocks of larger assemblies, and shape could determine the emerging structures (Kowalczyk et al. 2011). At even smaller, molecular scales, the potential separation of enantiomers using microdevices was recently investigated (Bogunovic et al. 2012). A number of different methods have recently been investigated to separate microparticles and nanoparticles by shape (Sharma et al. 2009; Sugaya et al. 2011; Riahifar et al. 2011; Beech et al. 2012; Akbulut et al. 2012; Shin et al. 2013; DuBose et al. 2014). In microfluidics, a promising separation method is deterministic lateral displacement (DLD), which offers continuous two-dimensional separation of suspended particles (Huang et al. 2004; Balvin et al. 2009; Koplik and Drazer 2010; Bowman et al. 2012). DLD has been particularly successful in the separation of biological samples (Zheng et al. 2005; Davis et al. 2006; Li et al. 2007; Huang et al. 2008; Inglis et al. 2008, 2010, 2011; Morton et al. 2008a, b; Green et al. 2009; Joensson et al. 2011; Holm et al. 2011; Beech et al. 2012; Zhang et al. 2012; Loutherback et al. 2012). However, only a few studies have investigated the role of shape in DLD separation Abstract We investigate the migration of particles of different geometrical shapes and sizes in a scaled-up model of a gravity-driven deterministic lateral displacement (g-DLD) device. Specifically, particles move through a square array of cylindrical posts as they settle in a quiescent fluid under the action of gravity. We performed experiments that cover a broad range of orientations of the driving force (gravity) with respect to the columns (or rows) in the square array of posts. We observe that as the forcing angle increases, particles initially locked to move parallel to the columns in the array begin to move across the columns of obstacles and migrate at angles different from zero. We measure the probability that a particle would move across a column of obstacles, and define the critical angle θc as the forcing angle at which this probability is 1/2. We show that critical angle depends on both particle size and shape, thus enabling both sizeand shape-based separations. Finally, we show that using the diameter of the inscribed sphere as the characteristic size of the particles, the corresponding critical angle becomes independent of particle shape and the relationship between them is linear. This linear and possibly universal behavior of the critical angle as a function of the diameter of the inscribed sphere of the particles could provide guidance in the design and optimization of g-DLD devices used for shape-based separation.