Here's the breakdown:
1. Illumination:
* White light is the primary illumination source in most optical microscopes, including fluorescence microscopes. It illuminates the sample being viewed.
2. Fluorescence:
* In fluorescence microscopy, specific dyes (called fluorophores) are used to label the sample. These dyes emit light of a specific color when excited by light of a different color.
* Blue light is often used to excite green fluorescent proteins (GFP), which are commonly used as genetic markers.
* Red light is often used to excite red fluorescent proteins (RFP) or other dyes that emit red fluorescence.
3. Filters:
* The microscope uses filters to separate the excitation light from the emitted fluorescence.
* Excitation filter: This filter only allows the specific wavelength of light that excites the fluorophore to pass through.
* Emission filter: This filter only allows the specific wavelength of light emitted by the fluorophore to reach the observer.
Here's how it works:
1. Excitation: Blue light is directed onto the sample, exciting the GFP molecules within the sample.
2. Emission: The excited GFP molecules emit green light.
3. Filtering: The red excitation light is blocked by an emission filter, allowing only the green fluorescence to reach the observer's eye or the camera.
Why use blue and red?
* Distinct colors: Blue and red light are chosen for their distinct wavelengths, allowing them to excite and detect different fluorophores. This allows for the visualization of multiple targets within a single sample.
* Spectral separation: Blue and red light are relatively far apart on the electromagnetic spectrum, making it easier to filter out unwanted wavelengths and isolate the specific fluorescence.
In summary:
* Blue and red light are used in fluorescence microscopy to excite different fluorophores, but not as the primary illumination source.
* Filters are essential to separate the excitation light from the emitted fluorescence, enabling the visualization of specific targets within a sample.
