IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 41, NO. 3, MARCH2006 651 A 0.18- m CMOS Bioluminescence Detection Lab-on-Chip Helmy Eltoukhy, Khaled Salama, Member, IEEE, and Abbas El Gamal, Fellow, IEEE Abstract—The paper describes a bioluminescence detection lab-on-chip consisting of a fiber-optic faceplate with immobilized luminescent reporters/probes that is directly coupled to an optical detection and processing CMOS system-on-chip (SoC) fabricated in a 0.18- m process. The lab-on-chip is customized for such applications as determining gene expression using reporter gene assays, determining intracellular ATP, and sequencing DNA. The CMOS detection SoC integrates an 8 16 pixel array having the same pitch as the assay site array, a 128-channel 13-bit ADC, and column-level DSP, and is fabricated in a 0.18- m image sensor process. The chip is capable of detecting emission rates below lux over 30 s of integration time at room temperature. In addition to directly coupling and matching the assay site array to the photodetector array, this low light detection is achieved by a number of techniques, including the use of very low dark current photodetectors, low-noise differential circuits, high-resolution analog-to-digital conversion, background subtraction, correlated multiple sampling, and multiple digitizations and averaging to reduce read noise. Electrical and optical characterization results as well as preliminary biological testing results are reported. Index Terms—Biosensor, CMOS imager, lab-on-chip, lumines- cence detection. I. INTRODUCTION T HERE is a growing need to perform biological testing such as DNA sequencing, immunoassays, and gene expression analyses for point-of-care and on-site environmental, medical, forensics, and biohazard studies [1]–[3]. Clinical platforms for performing such testing today are bulky, high-power, and re- quire large amounts of reagents, making them ill-suited for such applications. Moreover, the complexity of biological systems makes testing expensive, labor intensive, and time consuming, often requiring the experiments to be repeated several times to achieve the required level of reliability. Consequently, there is a need for developing hand-held, miniaturized, and highly auto- mated testing platforms to enable robust, low-cost point-of-care analysis. To address this need, there have been recent efforts to develop lab-on-chip solutions in which sampling, preparation, analysis and reporting of a wide range of chemical compounds are integrated and automated [4]–[8]. In addition to reducing system size, cost, and power consumption, such lab-on-chips can increase system throughput, thus reducing testing time and labor. Manuscript received July 7, 2005; revised November 28, 2005. This work was supported in part by the National Institute of Health under Grant 5 PO1 HG000205 and the Defense Advanced Research Projects Agency under Grant N66001-02-1-8940. The authors are with the Department of Electrical Engineering, Stan- ford University, Stanford, CA 94305 USA (e-mail: eltoukhy@stanford.edu; ksalama@stanford.edu; abbas@ee.stanford.edu). Digital Object Identifier 10.1109/JSSC.2006.869785 Because of the size and cost constraints of a lab-on-chip, it is also necessary to reduce the amounts of reagents used. Such reduction, however, decreases the levels of the biochemical sig- nals generated, and special efforts must be devoted to enhancing detection sensitivity [9]–[11]. Of the many methods developed for biological testing and molecular detection, optical detec- tion methods such as luminometry and fluorometry generally achieve the highest sensitivity and as a result are the most widely used. In this paper, we are mainly concerned with lab-on-chip design for luminometry. Luminometric methods, such as luciferase-based assays, involve the detection and quantifica- tion of light emission as a result of a chemical reaction [3]. Such methods have been used to detect pathogens and proteins, perform gene expression and regulation studies, and sequence DNA. They are also becoming increasingly popular due to their high sensitivity, low background, wide dynamic range, and relatively inexpensive instrumentation. Luminometry is also more amenable to lab-on-chip in- tegration than the more widely used fluorometric methods. Signal photoemission is triggered simply upon the addition of the final chemical required to precipitate the luminescence reaction, without much associated background emission. In contrast, fluorometric methods require an excitation source to stimulate photoemission of the fluorescent-tagged species and extremely sharp interference filters to reliably discern the generated photoemission amidst the high background. As such, cost-effective lab-on-chip integration for luminometry is much simpler than for fluorometry, since no interference filters or excitation sources are required. Most luminescence detection systems used in the biological field today perform detection using cooled CCD-based camera systems. Cooling, which is used to reduce detector dark current to enhance its sensitivity, is costly and consumes too much power, making miniaturization of these systems difficult. The use of intermediary optics also makes miniaturization difficult. More specifically, lower-end CCD-based systems employ fairly simple optics, incurring significant optical loss in the imaging system and hence large amounts of reagents are needed for ad- equate detection. In contrast, high-end imaging systems avoid this loss by using multi-piece optical systems or custom-fitted fiberoptic components, which makes them quite costly and bulky. Another approach to reducing optical loss, which is well- suited to lab-on-chip miniaturization, is to forgo intermediary optics altogether and directly couple the chemiluminescence assay to the imaging device [12], [13]. The main drawback of this approach is the stringent design constraints arising from the 0018-9200/$20.00 © 2006 IEEE