TOI / MOI Optimizer

Plan Sf9 / Sf21 baculovirus infection: time of infection (TOI), multiplicity of infection (MOI), PFU required, predicted infected-cell fraction, and harvest window.

Strategy preset
High-MOI: synchronous infection, shorter run, larger virus volume. Low-MOI: 2-3 rounds of infection in-reactor, smaller virus stock, longer run.
Culture & infection setup
Cell density at infection (CCI) ?
× 106 cells/mL
Culture volume
L
MOI (PFU/cell) ?
Viral stock titer
PFU/mL
μ (pre-infection) ?
h−1
Product type

How TOI / MOI is calculated

PFU required: PFU = MOI × (CCI × volume). The total number of plaque-forming units you need to add.

Baculovirus volume to add: Vvirus = PFU / titer. If titer is in PFU/mL, this returns mL of viral stock.

Initial infected fraction (Poisson): P(infected) = 1 − e−MOI. At MOI 3, ~95% of cells are infected in the first round. At MOI 5, ~99.3%. At MOI 0.1, only ~9.5% — the rest rely on secondary virus progeny.

Infection progression: In low-MOI strategies, budded virus from the first round infects the remaining cells over ~2-3 generations, requiring longer post-infection culture times (typically 96 h vs 72 h for high MOI).

Harvest window: Secreted proteins, 48-72 hpi; intracellular proteins, 72-96 hpi; VLPs, 72-96 hpi; AAV, 96-120 hpi. Cell diameter peaks 24-48 h before maximum titer — use diameter kinetics as an at-line harvest signal.

High-MOI vs low-MOI strategy comparison

ParameterHigh MOILow MOI
Typical MOI3 – 100.01 – 0.1
Typical CCI1 – 2 × 1060.3 – 1 × 106
First-round infection> 95%1 – 10%
Virus stock usage per runHighLow
Infection rounds required12 – 3
Typical harvest (hpi)48 – 72 h96 – 120 h
Passage effect (MoP)More sensitiveLess sensitive
ScalabilitySimple, synchronousEconomical at large scale

Related tools

Harvest Window Predictor
Optimal harvest day from VCD, viability, glucose, and lactate data
Growth Curve Fitter
Extract μmax, doubling time from Sf9 pre-infection data
Cell Counting Calculator
Hemocytometer VCD and diameter for infection timing

Frequently asked questions

What is TOI and MOI in baculovirus infection?
TOI (time of infection) is when baculovirus is added to Sf9 culture, usually expressed as hours from inoculation or as CCI (cells/mL). MOI (multiplicity of infection) is the number of PFU added per cell. High-MOI: 3–10, CCI 1–2 × 106/mL. Low-MOI batch: 0.01–0.1, CCI 0.3–1 × 106/mL (cells need to grow between primary and secondary infection); with perfusion or fed-batch nutrient top-up, low-MOI can run at higher CCI.
What is the optimal CCI for Sf9?
Mid-log, 1–2 × 106 cells/mL for standard infection. Fed-batch or perfusion can go to 3–8 × 106 with nutrient top-up to avoid the "cell-density effect" (yield-per-cell decline above ~4 × 106/mL in batch).
How do I calculate baculovirus volume for a given MOI?
PFU required = MOI × CCI × volume. Virus volume = PFU / stock titer. Example: 1 L at CCI 2 × 106/mL, MOI 5, stock 1 × 108 PFU/mL → 1010 PFU → 100 mL viral stock. For MOI 0.1, only 2 mL.
When should I harvest an Sf9 culture?
Typically 48–96 hpi; peak yield usually 72 hpi. Key signals: cell diameter increases 20–40% post-infection, viability drops to 70–80%, peak diameter precedes peak titer by 1–2 days. Secreted proteins: earlier. VLPs / intracellular / AAV: 72–120 hpi.