Mass Photometry — Applications, Calibration & Limitations

What are the primary biological applications of mass photometry?

Studying protein oligomeric states, determining complex binding stoichiometry, performing therapeutic antibody quality control, and quantifying viral vector gene filling

How is mass photometry applied in therapeutic antibody quality control according to lab audio?

It evaluates whether bivalent antibodies bind one or two targets or form unwanted cross-linked immune complexes that trigger toxicity or adverse immune reactions

How does mass photometry characterize viral gene delivery vehicles like AAV capsids?

It distinguishes empty capsids, partially filled capsids, and full gene-loaded capsids that have identical hydrodynamic sizes but different masses

How does sample consumption and speed in mass photometry compare to SEC-MALS or ensemble static light scattering?

Mass photometry uses roughly 10000 times less sample material and completes measurements about 100 times faster without requiring prior chromatographic separation

How is a mass photometry calibration curve experimentally constructed?

Standard calibrant proteins of known mass are measured, gaussian peaks are fitted to contrast distributions, and linear regression is performed to plot mass versus contrast

What standard dilution volume is used when preparing calibrant protein stock on the instrument stage?

2 microliters of calibrant stock protein is mixed into 18 microliters of phosphate-buffered saline (PBS) buffer for a 10-fold dilution

What is the accuracy limit of mass photometry calibration across different biomolecules?

Calibration is accurate to within 5% for standard proteins and nucleic acids, but accuracy decreases when glycans, lipids, or detergent micelles are present

What target concentration range is strictly required for mass photometry measurements?

Low nanomolar concentrations typically between 10 and 50 nanomolar to ensure landing events remain spatially separated without overlapping on the camera

Why is mass photometry currently not optimal for studying protein complexes with micromolar Kd values?

Rapid sample dilution down to low nanomolar concentrations causes weakly bound complexes to dissociate before or during the measurement timescale

Why cannot mass photometry measure protein masses directly inside crude cell lysates or intact cellular environments?

Light scattering is generic to all biomolecules, causing heterogeneous background scattering in crude lysates to overwhelm single-molecule contrast unless selective fluorescent tags are used

How do buffer additives like glycerol or detergent micelles impact mass photometry data quality?

High glycerol increases solution viscosity and background noise, while detergent micelles scatter light and distort mass calibration accuracy

How does gaussian fitting of contrast peaks determine the mole fraction of each species in a mixture?

Fitting gaussian curves to distinct contrast peaks allows the integrated area under each peak to represent the relative mole fraction of that specific molecular weight specie