Sampling effects, noise, and photobleaching in temporal image correlation spectroscopy.

Area of Science:

• Biophysics
• Microscopy techniques
• Quantitative imaging

Background:

• Temporal image correlation spectroscopy (TICS) is a powerful technique for analyzing molecular dynamics in biological systems.
• Accurate quantification of transport coefficients and number densities using TICS is crucial for understanding cellular processes.
• Factors such as spatiotemporal sampling, particle density, noise, and photobleaching can affect TICS accuracy.

Purpose of the Study:

• To extensively investigate the accuracy and precision of TICS.
• To determine the impact of various experimental parameters on TICS performance.
• To develop and validate a method for correcting photobleaching artifacts in TICS.

Main Methods:

• Simulations of laser scanning microscopy image time series were used to model TICS performance.
• Analysis of the effects of spatiotemporal sampling, particle density, noise, sampling frequency, and photobleaching.
• Derivation and application of a photobleaching correction equation.
• Experimental validation using two-photon microscopy of CHO cell basal membrane with EGFP/alpha-actinin.

Main Results:

• Transport coefficient recovery is primarily limited by spatial sampling.
• Accurate number density measurements are restricted by background noise.
• Photobleaching leads to overestimation of diffusion coefficients/flow rates and underestimation of number densities.
• The derived bleaching correction equation effectively removes these biases without adding fit parameters.

Conclusions:

• TICS accuracy is sensitive to experimental conditions, particularly spatial sampling and background noise.
• Photobleaching significantly compromises TICS results, but can be corrected using the derived equation.
• The developed correction method, validated in simulations and experiments, improves the reliability of TICS measurements.