Time-Gated Imaging

What is Time-Gated Imaging?

Time-Gated Imaging is a type of stroboscopic imaging process.  The Imagex™ camera generates Lamp Trigger Pulses at a user-defined frequency. For a period after the lamp pulse (know as the ‘Gate Delay’) the camera is insensitive. The camera then becomes sensitive for a user-defined time period (known as the ‘Gate Width’). This process repeats until enough ‘Gated’ signal has accumulated to readout as an image. Imagex™ cameras have cooled CCDs allowing them to integrate for 10s of seconds for each frame.

This process allows the user to suppress or ‘Gate Out’ unwanted short lifetime signals or alternatively to capture different components of a Long-Lifetime Fluorescence Decay to obtain Lifetime-related contrast

Imagex™ camera systems combine all the components of a time-gated imaging system within a single unit that can be programmed via the USB2.0 interface from a Windows PC using the supplied software.

 

Imagex™ camera systems combine all the components of a time-gated imaging system within a single unit that can be programmed via the USB2.0 interface from a Windows PC using the supplied software.

Detecting and Multiplexing Long-Lifetime labels

The ability to ignore or ‘Gate Out’ the signal during and shortly after the excitation pulse means that short-lifetime emission can be effectively suppressed. This means that the Imagex™ camera can carry on integrating for a longer time without becoming saturated with so-called ‘Background’ signal. This results in higher sensitivity and selectivity for your long lifetime probes. These include Lanthanide compounds such as Europium and Terbium chelates and cryptates, Oxygen- and Temperature-sensitive compounds including ruthenium complexes and metallo-porphyrins. For microsecond and millisecond probes we recommend the Imagex-TGi system.

The Imagex-nanoCCD system also allows shorter lifetime probes to be studied including the large family of semiconductor nanoparticles known as the Quantum Dots and is recommended for millisecond, microsecond and nanosecond probes.

 

 

The images above show an Eu Cryptate-labelled microarray deposited onto a nylon hybridisation membrane. The sample was detected with the Imagex-TGi system in ‘Ungated’ (20msec exposure) and ‘Gated’ (8000msec exposure) modes. The gating frequency for the ‘Gated’ Images was 300Hz with a Gate Delay of 300usec and a Gate Width of 2000usec. The excitation source was a pulsed Xenon flashlamp. The experiment shows the ability of the Imagex-TGi system to reject huge amounts of short-lifetime background fluorescence when used to detect a Long-Lifetime probe. Because the frequency response of Imagex camera systems is intrinsically wideband it is very well suited to multiplexing on the basis of fluorescence lifetime. This means that even where fluorescent probes have overlapping emission spectra they can easily be distinguished from each other if they have very different lifetimes.

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