Improving the limit of detection in portable luminescent assay readers through smart optical design

• Published in: Journal of biophotonics Vol. 13; no. 1; pp. e201900241 - n/a
• Main Authors: Li, Yaning, Ma, Xiangui, Wang, Wenhe, Yan, Shaojie, Liu, Fangshuo, Chu, Kaiqin, Xu, Guobao, Smith, Zachary J.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY‐VCH Verlag GmbH & Co. KGaA 01.01.2020; Wiley Subscription Services, Inc
• Subjects: Apertures; Assaying; Biomarkers; Cell phones; Chemiluminescence; Design; Electrochemiluminescence; Light sources; Optical design; Optics; Organic chemistry; Performance enhancement; Photons; point of care; Portability; optical design; electrochemiluminescence; point of care; chemiluminescence
• ISSN: 1864-063X; 1864-0648
• DOI: 10.1002/jbio.201900241

Critical biomarkers of disease are increasingly being detected by point‐of‐care assays. Chemiluminescence (CL) and electrochemiluminescence (ECL) are often used in such assays due to their convenience and that they do not require light sources or other components that could complicate or add cost to the system. Reports of these assays often include readers built on a cellphone platform or constructed from low‐cost components. However, the impact the optical design has on the limit of detection (LOD) in these systems remains unexamined. Here, we report a theoretical rubric to evaluate different optical designs in terms of maximizing the use of photons emitted from a CL or ECL assay to improve the LOD. We demonstrate that the majority of cellphone designs reported in the literature are not optimized, in part due to misunderstandings of the optical tradeoffs in collection systems, and in part due to limitations imposed on the designs arising from the use of a mobile phone with a very small lens aperture. Based on the theoretical rubric, we design a new portable reader built using off‐the‐shelf condenser optics, and demonstrate a nearly 10× performance enhancement compared to prior reports on an ECL assays running on a portable chip. Portable, low‐cost optical systems such as cell phones are attracting increasing interest as assay readers for point‐of‐care testing. However, little attention has been paid to the optical design of such systems. We demonstrate that a single number—the source‐normalized image intensity—determines how the optical system affects the limit of detection (LOD). By optimizing this number, we design a system that achieves a 10‐fold improved LOD compared to prior designs.