An attachable work tray assembly includes a work tray, having a bottom and a wall encircling the bottom, a swingable arm pivotally connected to a side of the work tray and a fastening set for holding the swingable arm and the work tray in position. A light source 1 and a lens 11 for generating parallel light are provided on an inner surface of a housing 5. A multi-channel sensor including collections of SPR elements which are commonly functionalized to one of several targets is also described.