Abstract: The invention provides an electrophoresis apparatus comprising an electrophoretic chamber containing at least on two-plate housing for a sieving matrix, each said at least one two-plate housing consisting of a cover plate and a plate for housing said sieving matrix, wherein said plate includes an optical waveguide array which is characterized by being aligned with respect to a reference direction such as to enable one or more light beams incident on the sieving matrix along said reference direction to be maintained well-confined along said reference direction within any desired length of interaction along the width of said sieving matrix.