Part 1 Principles
1. Fluorescence microscope
2. Filterset in FL-Mic
3. How concocal differs?
. What is confocal?
5. Resolution in confocal
6. Optical sectioning
7. Confocal image formation
    and time resolution
8. SNR in confocal
9. Variations of confocal

10. Special features from
     Leica sp2 confocal

Part 2 Application
1. Introduction
2. Tomographic view
    (Microscopical CT)

3. Three-D reconstruction
4. Thick specimen
5. Physiological study
Fluorescence detecting
       General consideration
Multi-channel detecting
       Background  correction
       Cross-talk correction
            Cross excitation
            Cross emission
            Unwanted FRET

Part 3 Operation and

 1. Getting started
 2. Settings in detail
     Laser line selection
      Laser intensity and 
         AOTF control

      Beam splitter
      PMT gain and offset 
      Scan speed
      Scan format, Zoom
        and Resolution

     Frame average, and
         Frame accumulation
     Pinhole and Z-resolution
     Emission collecting rang
        and Sequential scan

When Do you need confocal?
Are you abusing confocal?

Confocal Microscopy tutorial


Q: when do I need confocal microscope for my fluorescence specimen?

AAs discussed in confocal application: Fluorescence detecting section, confocal microscopy is not the first choice for ordinary fluorescence detecting nor for a simple co-localization of multi fluorescence labeling. Considering following situation:

  1. If spatial distribution of the labeling or tomography of the cell structure has no impact on your study.

  2. If you do not need a z-series for 3-D reconstruction.

  3. If you do not have a thick specimen that is difficult to be resolved on conventional microscope.

  4. If you do not have Physiological studies or Living cell imaging of multi-labeled marker for highly dynamic events, which can not tolerate time delay between channels.

  5. If you don't have problematic fluorescence specimen which has enough intensity and SNR to meet the high demanding from confocal (see below for details)

You might not need confocal microscopy. Your tasks can be easily done by digital camera based conventional fluorescent microscopy without the bother of setting up more than 20 parameters, going through lengthy image optimization, and bleaching signal away before getting a satisfactory image: a frustrating process if the specimen does not have a high SNR required by confocal microscopy, as discussed in part 1: optical sectioning. The final results equal to or even worse than what you can easily get from a digital camera do not reward you for the efforts you have paid and the cost of consuming laser.

The folllowing four problematic situation in fluoresscence microscopy need confocal microscopy to deal with:

  • Multi-channel detection that must be performed simultaneously

In digital camera based fluorescece microscopy, multi-labeling is handled sequentially by change filterset in turn and take separate shot then display them in different channel with or without an overlay.  Time delay in several seconds between channels is inevitable. If the time delay is intolerable in your application, confocal is your only choice. In confocal system with maximum number of PMTs installed, up to six detecting channels can operate simultaneously without any time delay.

  • Severe Background suppression

Background fluorescence is sometimes the headache of fluorescence microscopy. It  makes picture looking bad,  buries weak signal in background and reduce general contrast thus reduce obtainable resolution. This problem is more severe in tissue section and thick specimen than in cultured cell specimen. In digital camera based system, the common way to overcome it is simply lessen the excitation intensity or reduce the exposure time.
In confocal system, most of the out-of-focal-plane signal is restricted by pinhole resulting a cleaner background and detected background can be further manipulated by play with parameter on PMTs, i.e. reducing gain and raising offset added on the PMTs, or averaging signal on the detected frames by digital image processing algorithm. It must be pointed out, the assumption here is you have a general strong signal that can survive the discard of most of the original signal due to the confocal effects.

  • Cross-talking correction

Cross-talking refers excitation spectra overlaps, emission spectra overlaps, excitation and emission spectra overlaps in multi-labeled specimen. It is a common problem for multi-labeled specimen. When a mixture of fluorophores exists and more than one excitation light apply to the mixture, there is a complex of interactions and it can be divided into three categories:

  1. Interaction between different excitation light and fluorophores: cross excitation

  2. Interaction between two fluorophores' emission: cross emission

  3. Interaction between emission from one fluorophore and another fluorophore: FRET

  • Far red emission which can not be detected by your eyes and CCD.

Recently, some new fluorophores appear in the market emitting at longer than 650 nm which is invisible to most of the eyes of human beings and many common CCD chips. These dyes, however, greatly expand the range of choice and possibility of three, or four fluorophores labeling. In this case, confocal can do a decent job for you to detect emission from 650 to 750 nm.

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This page was last updated 23.03.2004