Fluorescent Dyes and Probes

Antibodies are essential tools for biomedical research as they allow researchers to identify specific proteins or molecules. Our catalog of over 425,000 antibodies from our R&D Systems™ and Novus Biologicals™ brands have been validated for specificity and reproducibility in over 25 species for more than 15 applications, ensuring that you will find one for your research needs.

Fluorescent light-up aptamers (FLAPs) or Light-up RNA aptamers are genetically engineered RNA sequences designed to bind to specific fluorogenic dyes with high affinity. The fluorogenic dyes light-up only when bound to a light-up aptamer, so fluorescence can be ‘switched-on’ upon RNA expression. We offer a large selection of fluorogens for popular light-up aptamers such as Spinach, Mango, Corn, Broccoli and more.

Bioluminescent Substrates are used in bioluminescence imaging (BLI) to monitor biological processes in vitro and in vivo. Red-shifted analogues of luciferin, together with modified luciferase enzymes, allow improved BLI performance for deep tissue imaging and in vivo applications. Discover our Bioluminescent Substrates range.

Fluorescent probes for imaging bacteria are useful for advancing bacterial research and antibiotic design. The strategy for fluorescent probes detecting bacteria is to target bacterial surfaces, cell walls, proteins, nucleic acids, and enzymes. One such category of probes is Fluorescent D-amino acids (FDAAs) which incorporates into the peptidoglycan (PG) component of cell walls in live bacteria enabling visualization of bacterial growth.

Fluorescence is the emission of light after a substance (fluorophore) absorbs radiation at a given wavelength (the absorption: Abs) and emits light radiation at a higher wavelength (the emission: Em). The maximum absorption and emission wavelengths of a fluorophore are denoted (λ_Abs and λ_Em) and are expressed in nanometres (nm).

Important characteristics for fluorophores:

• Stokes shift is the difference between the maximum absorption and maximum emission wavelengths.
• Fluorescence lifetime is the duration a fluorescent compound spends in the excited state before returning to the ground state by emitting a photon.
• Quantum yield (φ) is the ratio of the number of photons emitted to the number of photons absorbed, indicating the efficiency of the fluorescence process.
• Extinction coefficient (ε) determines how strongly a fluorophore absorbs or reflects radiation or light at a particular wavelength.

The overall brightness of a fluorophore is equal to the multiplication of (ε) by (φ).

Factors that influence fluorescence emission or detection:

• Quenching of fluorescence decreases the fluorescence intensity of fluorescent molecules and can be caused by molecular rearrangements, energy transfer, collisional quenching, and excited state reactions.
• Photo bleaching is when a fluorophore permanently loses its ability to fluoresce due to damage induced by illumination.
• Background fluorescence decreases the signal-to-noise ratio and reduces assay sensitivity. Causes of background fluorescence include sample autofluorescence and excess fluorophore that is not localized to a specific target (or is bound non-specifically).

The most appropriate choice of fluorophore is dependent on the specific experiment being performed. Here are some guiding principles that can be generally applied:

• Excitation and emission properties should be compatible with the laser and filter setting of your instrument
• Extinction coefficient at the excitation wavelength should be as high as possible
• Quantum yield should be as high as possible
• Live/dead cell permeability
• Background caused by unspecific binding
• Photostability of the fluorophore