Optical Trapping of a Single Virus in a Host Cell Based on Active-Passive Calibration for Trap Stiffness

Optical tweezers are considered a tool for trapping and measuring forces on single molecules and small particles. Current research mainly focuses on measuring force spectral information on particles suspended in solution. However, the viscoelastic environment within the cell presents additional challenges for the in situ calibration of force spectroscopy data. To address this issue, we used an active-passive calibration method to calibrate the optical trap stiffness in live cells through sinusoidal oscillation and spontaneous fluctuation responses. This technique was applied to in situ measurements of the optical trap stiffness and viscoelastic modulus of viruses inside the host cell. The results indicate that this method can measure the optical trap stiffness and related parameters of intracellular viruses at different frequencies. Moreover, we proceeded to confirm that using quantum dots labeled viruses inside cells increased the stiffness of the viral optical trap similar to that in fluid. This provides more robust support for future force measurements and analysis of the transport mechanisms of viruses trapped within live cells using optical tweezers.