December 19, 2008

Two-Photon FLIM for Quantitative Ion Imaging in Living Tissue

Ion Sensing on MicroTime 200

Two-photon fluorescence lifetime imaging enables quantitative ion measurements in living tissue beyond intensity-based limitations. A new Technical Note outlines how 2P-FLIM was implemented and validated on the MicroTime 200 confocal microscope for intracellular pH and chloride mapping.
Two-photon fluorescence lifetime image of BCECF-loaded salivary duct showing intracellular pH distribution in living tissue.

The Quantification Challenge in Living Tissue

Quantifying intracellular ion concentrations in intact biological tissue is not trivial. Intensity-based fluorescence measurements are highly sensitive to dye concentration, excitation fluctuations, and scattering effects. In complex samples, this limits quantitative reliability.

Fluorescence lifetime imaging offers a fundamentally more robust readout. When combined with two-photon excitation, spatial confinement of excitation and reduced photodamage enable measurements under physiological conditions and at greater imaging depth.

Implementing 2P-FLIM on MicroTime 200

The Technical Note describes how two-photon fluorescence lifetime imaging was implemented on MicroTime 200 and experimentally validated.

It outlines:

  • verification of true two-photon excitation
  • characterization of the instrument response
  • integration of TCSPC-based lifetime detection
  • in situ calibration strategies for pH- and chloride-sensitive dyes
  • quantitative intracellular measurements in living tissue
Two-photon fluorescence lifetime image of BCECF-loaded salivary duct showing intracellular pH distribution in living tissue.
FLIM image (80 µm × 80 µm) of a BCECF-loaded salivary duct acquired using two-photon excitation. The optical section plane is indicated in the top right; dl = duct lumen, n = nucleus.

Rather than discussing 2P-FLIM conceptually, the document presents a complete experimental workflow from optical configuration to calibrated ion concentration maps.

Why This Matters

Quantitative ion imaging requires more than contrast. It requires validated calibration, controlled excitation conditions, and reliable lifetime analysis.

The Technical Note provides the methodological detail necessary to evaluate whether 2P-FLIM is suitable for your biological application.

Download the full Technical Note to explore the complete 2P-FLIM setup, calibration workflow, and quantitative validation data.

Visit MicroTime 200 >

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Evangelos Sisamakis

Product Manager, PicoQuant

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