Advanced optical design for biochip scanning system

Abstract

Laboratory-on-a-chip has been interested widely in recent years, where the sample preparation, bio-chemical reaction, separation, detection and analysis, are performed in a small biochip which is only a fingernall dimension. In order to obtain a high detection sensitivity 1 fluors/micrometers <SUP>2</SUP> (one fluorescence molecular per square micrometer) in biochip scanning system, it is required that the scanning objective lens is a big numerical aperture (&gt; 0.5), very small focal spot (&lt; 5 micrometers ) and long back focal length (&gt; 3 mm). In this paper, a combined lens is designed for the scanning objective lens, which is with big numerical aperture NA &gt; 0.7, very small focal spot (&lt; 2 micrometers ) and long back focal length (&gt; 3 mm). The phase aberrations of combined lens, including the aspherical aberration and the chromatic aberration corresponding to wavelength 532 nm, 570 nm, 635 nm, 670 nm, are corrected very well. The encircled energy diagram of the lens is good to the diffraction limit. The focal spot diagram, the optical path difference diagram, the transverse ray fan plot and the modulation transfer function, are studied also. A novel confocal scanning system of biochip with the designed combined lens as the objective lens is developed, some experiment results in a multi-channel biochip are obtained.