High Initial Sputter Rate Found for Vaccinia Virions Using Isotopic Labeling, NanoSIMS, and AFM

Area of Science:

• Biophysics
• Analytical Chemistry
• Materials Science

Background:

• Secondary ion mass spectrometry (SIMS) offers high-lateral-resolution, depth-resolved elemental and isotopic analysis.
• Characterizing sputter rates at shallow depths is crucial for analyzing small biological structures like virions and phage.
• Existing sputter models are insufficient for the unique matrix of biological virions.

Purpose of the Study:

• To develop and validate a nonlinear, nonequilibrium sputter rate model for biological virions.
• To determine sputter rates and sensitivity at shallow depths relevant to virions and phage.
• To assess the feasibility of using isotopic tracers for nanoscale biological imaging with SIMS.

Main Methods:

• Stable isotope labeling of vaccinia virion DNA.
• Correlated SIMS imaging depth profiling and atomic force microscopy (AFM).
• Development and validation of a nonlinear sputter rate model using Cs+, O-, and Ga+ beams.

Main Results:

• An unexpectedly high initial sputter rate was observed, rapidly declining to an asymptotic rate.
• The developed sputter rate model accurately predicted the depth of labeled DNA within virion cores (50-90 nm).
• Accurate isotopic ratios were obtained from the start of sputtering, indicating potential for nanoscale isotopic tracing.

Conclusions:

• The developed sputter rate model is effective for SIMS analysis of biological virions.
• SIMS, with appropriate modeling, can provide depth-resolved functional information from nanoscale biological structures.
• Isotopic tracing using SIMS is a viable technique for studying smaller virions and phage.