In Applications of Chemiluminescence, Can CMOS replace CCD? The advantage of replacing CCD with CMOS for applications where every photon is important.

Chemiluminescence, whether generated by a fluorescent protein or a chemical reaction, is here to stay. It plays a fundamental role as a signaling mechanism in much of biological research and represents a vast improvement over absorption or radioactive methods, in terms of sensitivity, multi-signaling, amplification, sustainability, cost and the ability to bioengineer the signal.

Chemiluminescence is the main method for detecting protein quantity in Western blotting — and this is still today’s main method for protein detection. Because quantitation is so important, digital imaging system must have as perfect a linear response to chemiluminescent light emission as possible. The response linearity of complementary metal-oxide semiconductor (CMOS) sensors is excellent and reliable.

CMOS devices can be implemented with fewer components, use less power and give a faster readout than charge-coupled device (CCD) devices. This marries the cost advantage of CMOS devices with their speed, and makes them easily integrated into a handheld, low-power (or rechargeable) miniature device. Since virtually all smartphones now come with CMOS cameras, scientists are developing microscopy, spectroscopy and data-collecting applications to make these devices into truly mobile instruments.

Chemiluminescence reactions have less background emission than fluorescence reactions, so images of chemiluminescent materials contain less noise from light scattering. However, reaction times are shorter with chemiluminescence than fluorescence, so a bioimaging system for chemiluminescence must have fast, high-numerical-aperture lenses and a sensitive detector.

Unlike conventional fluorescence microscopy, the bioimaging system contains no internal source of illumination. The sample produces all the light available for creating an image, so every photon is important, making the choice of detector crucial.

Since the emission coming from the target cells is dim compared with a fully illuminated microscopy subject, the detector in the chemiluminescence imaging system will require long exposure times to produce usable images. For several decades, the CCD has been the gold standard in recording images under dim light. But can newer, less expensive cameras made with CMOS technology compete with CCD detectors? After all, both types of technology perform the same basic task.

When CMOS sensors were first introduced, they took poorer-quality long-exposure images than CCDs. However, engineers have worked steadily to improve CMOS-based cameras. Recently, Jenoptik´s CCD and CMOS detectors were tested in a series of chemiluminescence experiments. As a result there was no image quality difference between the CCD and CMOS cameras when taking long-exposure images. Many scientific research teams are already integrating CMOS sensors and cameras into high-throughput imaging systems.

So, when designing a system to conduct chemiluminescence imaging, long exposure times are no longer a hurdle. Choose a reliable, multi-component system backed by optical experts who have extensive know-how in bioimaging in a wide variety of environments. With today’s CMOS technology, you can pay less and still get state-of-the-art performance.

About Stefan Seidlein

Stefan Seidlein has been working for Jenoptik since 2000 in various positions in the field of Digital Imaging. As product manager, he currently focuses on the light microscope camera product portfolio and brings his entire digital imaging competence and experience to projects. As a graduated technician with a focus on energy technology and process automation, he is fascinated by digitalization and the many opportunities it offers both individuals and Jenoptik.