Electrophoretic Versus Dielectrophoretic Nanoparticle Patterning Using Optoelectronic Tweezers

Abstract

Currently, there is increasing interest from many scientific disciplines in the development of systems that are able to sort and arrange many objects in parallel at the nano-and micrometric scale. Among others, photovoltaic tweezers (PVT) are an optoelectronic technique for trapping and patterning nano-and microobjects in accordance with an arbitrary light profile. In this work, the differential features of electro-and dielectrophoretic (EP and DEP) nanoparticle (NP) patterning using PVT are deeply investigated. The study is carried out through theory and experiments. The developed theory extends the applicability of a previously reported model to be able to compute EP potentials and to obtain numerical values for the EP and DEP potential energies. Two-dimensional patterns of charged and neutral aluminum NPs are fabricated on top of Fe∶LiNbO 3 crystals, and different light distributions and other experimental parameters (crystal thickness and NP concentration) are compared. Patterns of charged and neutral NPs show remarkable differences in both particle density distribution and fidelity to the original light profile. The observed different features between EP and DEP trapping are satisfactorily explained by the theoretical analysis. The results provide routes for the optimization of the NP arrangements for both regimes.

Recent Achievements on Photovoltaic Optoelectronic Tweezers Based on Lithium Niobate

“…They used charged particles because they assumed that dielectrophoretic (DEP) forces acting on neutral particles were too weak in this configuration. Nevertheless, using highly doped crystals our group has demonstrated in a number of recent papers an excellent performance for 2D trapping with neutral inorganic micro-and nano-particles [19,29] and biological objects [22]. As previously mentioned, the experimental results have been accompanied with the development of a simple theoretical model for this configuration [28,29] that satisfactorily explains the experimental patterns.…”

“…Then, these experiments essentially operate under electrophoretic forces. This problem is, indeed, relevant and has been only recently addressed [19] by comparing on a quantitative basis the DEP and EP potentials at close distances from either the x-cut or z-cut crystal surfaces. The study shows clear differences in the expected particle density profiles obtained for the two cases and in both, x-and z-cut configurations.…”

“…As previously mentioned, the experimental results have been accompanied with the development of a simple theoretical model for this configuration [28,29] that satisfactorily explains the experimental patterns. The comparison between electrophoretic and dielectrophoretic patterning which deals with charged and neutral particles respectively, is deeply investigated in reference [19] by theory and z-cut experiments. In that work significant differences in both particle density distribution and fidelity to the original light profile have been found.…”

“…As it happens with optical tweezers, the PV forces can be combined with hydrodynamical or additional electrical forces to achieve similar effects to those obtained with optical tweezers. Another relevant difference has to do with the capability of PV tweezers to manipulate electrically charged as well as neutral particles [17][18][19]. In the first case, one uses the dragging effect of the PV electric fields (electrophoretic forces) whereas for neutral particles one uses the dielectrophoretic (gradient) forces as in standard optical tweezers.…”

Real‐Time Operation of Photovoltaic Optoelectronic Tweezers: New Strategies for Massive Nano‐object Manipulation and Reconfigurable Patterning

“…The main objective of the work is to investigate these new scenarios involving real‐time operation under static or moving illumination on z ‐cut LiNbO 3 :Fe substrates. These substrates are particularly suitable because its active surface presents an axially symmetric PV field pattern which has been recently simulated . Different situations of practical interest are investigated by studying in real time the dynamical response of the manipulation process: 1) real‐time action on particles for static laser beam illumination, 2) response to moving light beams, and 3) response to arbitrary combinations of light and dark intervals.…”