The cell count starts before the cell counter: Standardizing sample preparation with automated liquid handling.

However, the quality of the cell count depends in part on how the sample is prepared before it reaches the instrument. If cells settle before aspiration, experience shear stress during pipetting, or are inconsistently stained, the analyzer cannot recover the original biological state of the sample.1 Increasingly, researchers recognize that improving the consistency of cell counting requires attention to sample preparation, not just the instrument.

Why sample preparation is the hidden variable

Three pre-analytical variables can affect cell concentration and viability measurements:

1. Cell settling and clumping: Suspension cells begin settling almost immediately after mixing. A technician drawing from the top of a tube may measure a different concentration than one aspirating from the bottom. Manual mixing helps, but every researcher mixes differently, with some pipetting three times, others ten. These differences can introduce variability that is unrelated to the biological sample itself.²
2. Mechanical stress during pipetting: Not all cells tolerate pipetting equally. Primary cells, stem cells, suspension cultures, and engineered immune cells are particularly susceptible to mechanical stress. Rapid aspiration through narrow pipette tips can damage plasma membranes, lowering measured viability before the sample reaches the analyzer.³
3. Inconsistent staining: Whether using trypan blue or fluorescent dyes such as Acridine Orange/Propidium Iodide (AO/PI), reproducible viability measurements require consistent reagent ratios and consistent mixing. Uneven staining, incorrect ratios, or prolonged dye exposure can all influence results, independent of changes in the underlying sample.¹

A field application perspective

Tip: If cell count variability appears unexpectedly, verify the sample preparation workflow before troubleshooting the analyzer. Inconsistent mixing, prolonged delays before aspiration, or aggressive pipetting are common sources of variability that can affect the resulting measurement. Standardizing these steps often improves reproducibility without changing the analytical method.⁴

How automation solves these challenges

Automated liquid handling systems address some of the variability introduced during sample preparation.

By preparing every sample under identical, reproducible conditions, the aim is to reduce the variation introduced by the preparation process but still retain any biological variability between samples.

Standardizing the workflow before analysis

Revvity's AssayMate™ workstation can be used to automate defined sample preparation steps before cell counting.

The workflow includes four stages:

1. Load: Cell stock, culture media, and AO/PI solution are loaded into a 12-column reservoir. Integrated temperature control keeps samples and reagents stable during setup.
2. Dilute: Twelve biological replicates are prepared across four dilution fractions on a 96-well storage plate, with automated gentle mixing (10× per replicate).
3. Stain: AO/PI solution is added at a 1:1 ratio with controlled pipetting to minimize cell disruption during staining.
4. Transfer: Replicates are loaded into the 8×3 cell counting plate for scanning on the Cellaca™ MX or Cellaca PLX cell counters. Because handling is automated, every plate is processed under identical conditions.

In this workflow, automation replaces a series of repeated manual pipetting and mixing steps with a defined sequence that can be reproduced across runs. The reported workflow reduces 20 manual steps to four, and has demonstrated a 70% cut in hands-on preparation time while maintaining R² > 0.99 linearity. The primary benefit for most labs is the reduction in operator-to-operator variability.

The automation spectrum: choosing the right level

Cell counting automation is not one-size-fits-all. Laboratories can adopt technologies that match their throughput, budget, and operational requirements.

Many organizations follow a natural progression, starting manually to establish protocols, then adding benchtop automation for accuracy, integrating liquid handling to scale throughput, and ultimately deploying full work cells for commercial-scale manufacturing.

Looking beyond the cell counter

Advances in imaging algorithms and analysis software will continue to improve cell counting technology. However, improvements can be achieved now from better sample preparation, without waiting for the next instrument generation.

Automated liquid handling can standardize sample preparation, minimize mechanical stress, reduce operator variability, and integrate with imaging systems, incubators, robotic plate handlers, and LIMS.

For scientists working in drug discovery, bioprocess development, or cell-based research, this integrated approach provides a way to reduce the manual variation associated with sample preparation and frees researchers to focus on experimental design rather than repetitive manual preparation.

The most consistent cell count does not begin inside the cell counter. It begins with the quality of the sample delivered to it.