- [Resource Hub](/) - [Field Guide](/?resource-type=field-guide#library) - The Mixed Population Dilemma: When One Cassette Can't Capture Everything # The Mixed Population Dilemma: When One Cassette Can't Capture Everything The Bottom Line Up Front: When your sample contains both small and large cells, no single cassette optimizes measurement for both populations. The solution: run the same sample twice - once with S+ or S to get accurate small cell counts, once with M+ or M to get accurate large cell counts. This dual-cassette workflow delivers accurate data for both populations rather than compromised data for everyone. WHICH CASSETTES FOR YOUR INSTRUMENT Moxi V and Moxi GO II use S+ and M+ cassettes. Moxi Z uses S and M cassettes. Same sizing principles, same selection logic — just match the cassette type to your instrument. All recommendations in this guide apply across the Moxi family. ## The Physics of Compromise The Coulter principle creates an inherent trade-off: aperture size optimizes for a specific cell size range. Too small, and large cells clog. Too large, and small cells generate weak signals below detection threshold. When you've got a mixed population, you're forced into compromise with a single cassette. Neither option captures the full population accurately. The compromise isn't a neutral middle ground - it's systematic error affecting both populations differently. Dual-cassette workflows eliminate this compromise entirely. ### TL;DR - Mixed Population Solutions - Mixed populations spanning the 15μm boundary require dual-cassette workflows - Run once with S+ or S for small cells, once with M+ or M for large cells - TIL counting and immune cell killing assays are classic dual-cassette applications - Report each population from its optimized measurement - Extra run takes minutes but prevents systematic errors in downstream analysis ## Mastering Dual-Cassette Workflows Learn when and how to run samples twice for accurate counting of both small and large cell populations. Why No Single Cassette Works Why No Single Cassette Works for Mixed Populations + The Coulter principle creates an inherent trade-off: aperture size optimizes for a specific cell size range. Too small, and large cells clog. Too large, and small cells generate weak signals. ### The Compromise Problem When you've got a mixed population with a small cell type and a large cell type, you're forced into compromise with a single cassette. Either your small cells are poorly resolved (weak signals in M+ cassettes), or your large cells risk clogging (oversized for S+ cassettes). SYSTEMATIC ERROR The compromise isn't a neutral middle ground - it's systematic error affecting both populations in different ways. Dual-cassette workflows eliminate this entirely by optimizing each measurement for its target population. The Dual-Cassette Protocol The Dual-Cassette Protocol + Running samples twice sounds like extra work, but the protocol is straightforward: ### Step-by-Step Workflow - Prepare sample: Standard single-cell analysis preparation - First measurement: Run with S+ or S cassette - record small cell count and size data - Change cassette: Switch to M+ or M cassette - Second measurement: Run same sample - record large cell count and size data - Report: Each population from its optimized measurement SAME SAMPLE, OPTIMAL RESULTS The same sample, same experimental conditions, but each population measured through its optimal aperture. The extra run takes minutes but prevents systematic errors that propagate through all downstream analysis. TIL Counting Application TIL Counting: Classic Dual-Cassette Application + Tumor-infiltrating lymphocyte counting is one of the immediate applications for dual-cassette workflows. The challenge is fundamental: T cells are small (6-10 μm), tumor cells are large (15-30+ μm). ### The Challenge A single cassette measurement forces impossible choices. Count T cells accurately with S+ cassettes, but risk missing tumor cells? Or ensure tumor cell passage with M+ cassettes while accepting undercounts of T cells? THE SOLUTION Dual-cassette workflows solve this directly: S+ for T cell quantification, M+ for tumor cell quantification. Your ratio calculations use optimized counts for both populations. Immune Cell Killing Assays Immune Cell Killing Assays + Immune cell killing assays present the identical scenario: cancer cells big, your T cells small. Whether you're evaluating CAR-T efficacy, NK cell cytotoxicity, or antibody-dependent killing, the size mismatch is inherent. ### Why Dual-Cassette Matters The experimental readout depends on accurate counts of both populations. Effector:target ratios, killing percentages, surviving target quantification - all require reliable numbers for both small effector cells and large target cells. PUBLICATION-QUALITY DATA Dual-cassette workflows aren't optional for these assays; they're the only way to get publication-quality data. The extra measurement time is negligible compared to the experimental setup, and the data quality improvement is substantial. Combining Results Combining and Reporting Dual-Cassette Results + How do you report results when different populations come from different measurements? ### Reporting Guidelines - Report from optimized sources: Small cell counts from S+ measurements, large cell counts from M+ measurements - Calculate ratios from optimized values: E:T ratios use the optimized count for each population - Document methodology: Note dual-cassette measurements for publications - this is methodological rigor OVERLAP CONSIDERATION For total cell reporting, recognize that cells in the 12-18 μm overlap range may appear in both counts. For most applications, optimized individual population counts are more valuable than approximate totals. ## Troubleshooting Mixed Population Counting Problem: Large cell counts much lower than expected in S+ measurement Solution: This is expected behavior - S+ cassettes may miss large cells due to clogging or signal saturation. Use the M+ measurement for large cell quantification. Problem: Small cell counts seem lower in M+ measurement Solution: Weak signals from small cells in large apertures fall below detection. This confirms why you need S+ for small cell quantification - use that measurement. Problem: Worried about sample volume for two runs Solution: Each measurement uses minimal sample (as little as 60μL depending on instrument model). Plan sample preparation to accommodate both measurements. The total volume requirement is still modest. Problem: Unsure if dual-cassette is necessary for my samples Solution: If your populations span the 15μm boundary significantly, dual-cassette is beneficial. Run a comparison to see whether the difference matters for your application. ## Common Questions About Mixed Population Counting How do I count mixed populations with both small and large cells? Run the same sample twice - once with S+ or S cassette to accurately count small cells, and once with M+ or M cassette to accurately count large cells. This dual-cassette workflow captures both populations optimally rather than compromising accuracy for either. When should I use a dual-cassette workflow? Use dual-cassette workflows when your sample contains cell populations that span both sides of the 15-micrometer boundary. Classic applications include TIL counting, immune cell killing assays, and co-culture experiments with disparate cell types. Why can't I just use one cassette for all cell sizes? No single aperture optimizes measurement for both small and large cells. With S+ cassettes, small cells are measured accurately but large cells risk clogging. With M+ cassettes, large cells pass safely but small cells generate weak signals that may fall below detection. Each cassette type optimizes for its target size range. How do I combine results from dual-cassette measurements? Report each population from its optimized cassette measurement: small cell counts from S+ runs, large cell counts from M+ runs. For ratio calculations, use these optimized values directly. The dual-cassette approach gives you more accurate individual counts than any single compromise measurement. ### Key Takeaway Mixed populations demand dual-cassette solutions. When your sample contains both small and large cells, a single cassette means accepting systematic error in one population or the other. Running twice with S+ or S and M+ or M takes extra minutes but delivers accurate data for both. For TIL counting, immune cell killing, and any heterogeneous sample, dual-cassette workflows are the only way to get it right. [Back to all resources](/#library) ## Similar resources [Field Guide](/resources/06-fifteen-micron-boundary/) Moxi GO II Moxi V Moxi Z 2026 ### The 15-Micrometer Decision: A Practical Cassette Selection Framework The 15 μm boundary provides clear selection criterion: cells under 15 micrometers use S+ cassettes, cells over 15 micrometers use M+ cassettes. This boundary isn't arbitrary - it's where each aperture size achieves the optimal 15-40% cell-to-aperture ratio for signal quality and sizing resolution. Know your cell size, follow the boundary, and cassette selection becomes automatic. [Read Field Guide](/resources/06-fifteen-micron-boundary/) [Field Guide](/resources/01-optimization-burden/) Moxi GO II Moxi V 2026 ### The Optimization Burden: Hours Wasted on Viability Protocol Development Every hour spent optimizing viability dye concentrations is an hour not spent on your actual experiments. It's optimized for use - that's the important thing. You don't have to optimize it as a customer. Pre-optimized viability reagents eliminate the titration experiments, the incubation testing, the cell-type-specific protocol development. Why spend time optimizing when validated performance is available from the first use? [Read Field Guide](/resources/01-optimization-burden/) [Field Guide](/resources/02-unknown-product/) Moxi GO II Moxi V 2026 ### The Unknown Product: Most Moxi Users Don't Know This Exists Most of the issue with viability reagents is that most people don't even know they exist. If you're running viability assays on Moxi V or Moxi GO II with generic dyes you optimized yourself, there's a better option you may not have heard about: pre-optimized, ready-to-use viability reagents designed specifically for your instrument. Now you know. [Read Field Guide](/resources/02-unknown-product/) [Field Guide](/resources/04-protocol-hunt/) Moxi GO II Moxi V 2026 ### The Protocol Hunt: Searching for Methods That Already Exist Searching for viability protocols, adapting literature methods, trial-and-error until something works - this is time you don't need to spend. The user manual is designed to be super easy. Concentration-based instructions tell you exactly what to do: put X amount of viability reagent and put X amount of sample, incubate and go. No protocol hunting required. [Read Field Guide](/resources/04-protocol-hunt/) [Field Guide](/resources/05-diy-mentality/) Moxi GO II Moxi V 2026 ### The DIY Mentality: When Making Your Own Viability Reagent No Longer Makes Sense That's why people - including me - just buy premixed gel loading dye and don't make my own from powder like my PI wanted me to. The same logic applies to viability reagents. Buy the damn gels rather than making them - consistency and data. When convenience and consistency matter more than tradition, pre-made beats DIY. [Read Field Guide](/resources/05-diy-mentality/) [Field Guide](/resources/05-suboptimal-resolution/) Moxi GO II Moxi V Moxi Z 2026 ### The Suboptimal Resolution Problem: Why Your Cell Populations Look Merged Using an aperture much larger than necessary reduces sizing resolution by creating smaller signal differences between cell sizes. Cell populations that should be distinguishable appear merged when the aperture is too large for the cells being measured. Target 15-40% of aperture diameter for optimal resolution. If you're counting lymphocytes on M+ cassettes because it works, you're sacrificing the sizing resolution that S+ cassettes would provide. [Read Field Guide](/resources/05-suboptimal-resolution/) [Field Guide](/resources/06-batch-consistency/) Moxi GO II Moxi V 2026 ### Viability Reagent Batch-to-Batch Consistency: Why Your Results Vary Over Time When you make your own viability reagents, every batch is different. When you buy pre-optimized reagents with QC'd lot consistency, every lot performs the same. Long-term experiments need long-term consistency - and that consistency comes from manufacturing quality control, not from hoping your technique stays identical over months of work. [Read Field Guide](/resources/06-batch-consistency/) [Field Guide](/resources/07-training-new-users/) Moxi GO II Moxi V 2026 ### Training New Users: Why Pre-Optimized Reagents Simplify Onboarding New lab members need to generate valid data quickly. Teaching protocol optimization takes weeks. Teaching protocol execution takes minutes. The user manual is designed to be super easy - put X amount of viability reagent, put X amount of sample, incubate and go. When reagents are pre-optimized, training focuses on execution, not development. [Read Field Guide](/resources/07-training-new-users/) [Field Guide](/resources/04-coincidence-artifact/) Moxi GO II Moxi V Moxi Z 2026 ### The Coincidence Artifact: When Two Cells Count as One Coincidence - multiple cells in the aperture simultaneously - causes two cells to be counted as one, corrupting both count and size data. Optimal aperture utilization means targeting 15-40% of aperture diameter so cells generate strong signals while avoiding coincidence artifacts. Match your cassette to your cell size, stay within concentration guidelines, and coincidence becomes a non-issue. [Read Field Guide](/resources/04-coincidence-artifact/) [Ebook](/resources/your-cell-count-is-a-safeguard/) Moxi GO II Moxi V Moxi Z 2026 ### Your Cell Count is a Safeguard The debris problem: Membrane fragments, aggregates, media residue, and lysed cell debris are present in virtually every biological preparation. How does your counting method distinguish a cell from a piece of debris? [Read Ebook](/resources/your-cell-count-is-a-safeguard/) [App Note](https://precisioncellsystems.com/wp-content/uploads/2026/02/Moxi-Applications-Compendium.pdf) Moxi GO II Moxi V Moxi Z 2026 ### Applications Compendium Scientists are concerned with speed, accuracy, and convenience, and those running the lab and industries are concerned with the cost typically associated with high-performing instruments. Our proprietary Coulter Principle-based system delivers on all three accounts, and is therefore a perfect fit for any cell biology benchtop. [Download App Note](https://precisioncellsystems.com/wp-content/uploads/2026/02/Moxi-Applications-Compendium.pdf) [Field Guide](/resources/07-til-immune-killing-optimization/) Moxi GO II Moxi V Moxi Z 2026 ### TIL Counting and Immune Cell Killing: Dual-Cassette Optimization Guide TIL counting and immune cell killing assays are immediate applications for dual-cassette workflows. Cancer cells are large, T cells are small - no single cassette optimizes both. Run S+ for accurate T cell counts, M+ for accurate tumor/target counts. The extra run takes minutes but delivers publication-quality E:T ratios and killing percentages. [Read Field Guide](/resources/07-til-immune-killing-optimization/)