Optimum Combined Lenses for Confocal Biochip Scanning System

Laboratory-on-a-chip technology has attracted wide interest in recent years, where the sample preparation, bio-chemical reaction, separation, detection and analysis are performed in a small biochip of the size of a fingernail. To obtain a high detection sensitivity of 1 fluors/μm2 (one fluorescence molecule per square micrometer) in biochip scanning systems, the scanning objective lens is required to have a high numerical aperture (>0.5), very small focal spot (<5 μm), and long back focal length (>3 mm). This study presents the design of optimum combined lenses including scanning objective and fluorescence focal lenses. The scanning objective had a high numerical aperture (NA) of 0.72, a very small focal spot of 1.67 μm, a long back focal length of 3.2 mm, and a high resolving power of 760 lines/mm. The fluorescence focal lenses had an NA of 0.3, a fluorescence focal spot of 16 μm, a long back focal length of 16.7 mm and a resolving power of 590 lines/mm. The phase aberrations of the combined lenses, including the aspherical aberration and the chromatic aberration corresponding to wavelengths of 532, 570, 635, and 670 nm, were well-corrected. The encircled energy diagram of the lenses was within the diffraction limit. The study also included the focal spot diagram, the optical path difference diagram, the transverse ray fan plot, and the modulation transfer function. A confocal biochip scanning system with designed combined lenses was developed and some experiments were conducted on a multi-channel biochip.