Force trapping gradient using diffractive optical elements

We discuss a new technique to generate force gradient in arrays of optical traps. The arrays can be configured in two or three dimensions by means of phase diffractive optical elements displayed on a spatial light modulator. The design of the diffractive optical elements is based on the approach of spherical wave propagation and superposition, which enables to individually control the strength of each optical trap. Computer simulation and experimental results are discussed for two and three dimensional arrays of traps. An example with silica micro-beads trapped with different forces in two different planes is presented to demonstrate the validity of our approach.</p

Sorting of mesoporous silica derivatives by random optical fields

Mesoporous silica particles are promising candidates for drug delivery applications. In this paper, we first synthesize mesoporous silica MCM-41 and its derivative MCM-41GA with anchored glutaraldehyde bridges, and characterize them using a variety of techniques, including nitrogen adsorption/desorption, X-ray diffraction, NMR spectroscopy, scanning electron microscopy, and thermogravimetric analysis. Then, we employ random optical fields to sort mesoporous silica particles. Random optical fields by containing local intensity gradients throughout a wide range of field of view provide an elegant, easy-to-implement, and low-cost variant of multiple optical tweezers, which is known as speckle tweezers (ST). ST, similar to multiple optical tweezers, for manipulation tasks, such as trapping, sorting, and guiding of collection of micro and sub-micro objects in several disciplines including statistical physics, chemistry, microfluidics and material science. We show that ST can restrict, sieve, and sort MCM-41 and MCM-41GA particles. The different interaction of mesoporous silica variations with the applied ST may be attributed to the pre-applied modification and the differences in the porosity structure and distribution. Therefore, the results provide insight into the textural and chemical characteristics of mesoporous materials, contributing to a deeper understanding of their potential applications