How Do You View?

Invaluable for their ability to deliver direct quantitation at the single-molecule level, radiolabeled chemicals were once the only method for following dynamic biochemical processes. However, radioisotope usage has gradually declined from a peak towards the end of the last century, as safer alternatives have been developed.

Still, for some applications, the advantages of radiolabeled compounds outweigh the risks, which can be ameliorated through the use of safety procedures.

Highly specific, extremely sensitive, safer than radioisotope imaging, and more amenable to signal amplification than fluorophores, chemiluminescent assays such as ELISAs and Western blots are almost ubiquitous in life science laboratories. However, because chemiluminescence harnesses biological reactions, its reproducibility is affected by experimental and environmental factors such as reaction duration, reactant amount, light exposure, and environmental conditions (e.g., temperature, buffers).

The Enzyme-Luminol Reaction

Simple, selective, and effective, luminol is arguably the most well-known chemiluminescent dye. Luminol generates chemiluminescence when the dianion form is oxidized, creating excited intermediates which produce light during stabilization to the ground state.

Commonly used oxidizing agents include ozone, ferricyanide, singlet oxygen, hydrogen peroxide, and hypochlorites. Often, hydrogen peroxide is made more usable by horseradish peroxidase (HRP) or other catalysts.

Detection depends on the emission range of luminol, which is near the blue region at roughly 425–450 nm and is thus often visualized most effectively with low background conditions.

Often associated with microscopy, fluorescence-based techniques have been rapidly expanding from the microscope slide and into the heart of the lab. Another alternative to radioactivity, non-microscopy uses for fluorescence became more widespread in part as a result of the human genome sequencing project and the development of dye-based sequencing. From there, rapid advances in detector technology and powerful computer processors have facilitated fluorescence use for protein detection, such as in Western blots, where the ability to use several fluorophores at once (multiplexing) can greatly enhance experimental efficiency.

The original infographic includes a large fluorescence spectrum graphic. Per your instructions, that graphic has not been recreated here; instead, the page preserves the source text in a clean, text-based layout.

Visible fluorescence enables flexible multiplex assay design by matching fluorophores with distinct excitation and emission profiles. Near-infrared fluorescence imaging, which generally spans roughly 650 nm to 900 nm, offers minimal autofluorescence and strong tissue penetration, making it useful for applications such as ex vivo whole tissue imaging.

Mutations in GFP can change its fluorescence spectra; taking advantage of this, scientists have engineered GFP derivatives for each color in the visible spectrum.