Mass Photometry

Mass photometry is a cutting-edge technique used for analyzing the mass of individual molecules in solution by measuring the light scattering when they land on a sensor surface, such as a microscope slide. When it comes to Adeno-Associated Virus (AAV) particles, mass photometry can be particularly insightful. Full AAV particles, which contain the viral DNA payload, scatter more light compared to empty capsids, which lack the genetic material. This difference in light scattering leads to full particles appearing as darker spots on the sensor surface.

How does mass photometry work?

Mass photometry measures the interference between the light scattered by the molecule and the light reflected by the measurement surface. The signal measured is called the mass photometry contrast (or interferometric contrast) and is directly correlated with molecular mass (Young, et al. 2018).

Key Features of Mass photometry

1. 1. Label-Free Detection: Mass photometry does not require fluorescent or isotopic labeling of the sample, which can alter the native state of the biomolecule being studied.

1. 1. Real-Time Analysis: It allows for the observation of AAV samples in real time, providing insights into the processes of AAV preparations.

1. 1. High Sensitivity: The technique is highly sensitive and can detect single AAV particles, enabling the measurement of individual molecules’ masses.

1. 1. Wide Mass Range: Mass photometry can measure a broad range of molecular masses, typically from 30 kDa to 5MDa, which is perfect for AAV particles with empty and full particles.

1. 1. Quantitative: It provides quantitative data on the mass distribution of the samples, which is useful for determining the stoichiometry and heterogeneity of molecular complexes.

1. 1. Minimal Sample Preparation: It requires minimal sample preparation and can analyze molecules in their native state in solution, which is especially important when working with rare or expensive materials.

1. 1. Solvent Compatibility: Mass photometry can be performed in various buffer conditions, allowing the study of AAV particles under physiologically relevant conditions.

The ratio of full to empty AAV capsids is a crucial quality attribute, especially for gene therapy applications, where it’s important to know the dose of functional viral particles. By using the mass photometry, researchers can quantify the proportion of full versus empty capsids. This information can help in optimizing the production process, ensuring the purity of the viral preparation, and assessing the potential efficacy of the AAV-based therapeutic.