# Low volume liquid handling for drug discovery

By Andrew Stewart · CC BY 4.0

https://discoveryinpractice.com/compare/low-volume-liquid-handling/

Choosing among acoustic transfer digital dispensing and positive displacement

A dispensing system must deliver the intended concentrations throughout the working day. The smallest droplet is useful only if the stock remains soluble, the source volume is accessible and the addition reaches the sample in time. The best choice for compound dosing may leave reagent distribution to another instrument.

This comparison covers Beckman Coulter Echo 650 Plus acoustic systems, Tecan D300e digital dispensing, and SPT Labtech mosquito LV/HV and dragonfly discovery positive-displacement platforms. Compound transfer, plate reformatting and reagent or cell dispensing place different demands on them. The recommendations below separate published capabilities from proposed qualification tests, with particular attention to miniaturized 384- and 1536-well assays.

## Headlines

| The finding | Technology and product evidence | Trade-offs and controls | What it means |
| --- | --- | --- | --- |
| Choose the operation before choosing the dispenser.WORKFLOW FIT | Echo supports acoustic well-to-well transfer; D300e dispenses from loaded disposable heads. Mosquito transfers with positive-displacement tips; dragonfly dispenses reagents from disposable syringes. These are different routes through a screening workflow. | A compound library, a handful of titrations and a repeated bulk reagent addition do not have the same source-handling burden. Nominal dispensing speed omits preparation and plate movement. | Write down the actual source layout, number of compounds, destination volumes and addition order. Ask each supplier to execute that job. Evaluate paired instruments where compound dosing and cell or reagent distribution have incompatible requirements.Sources: L1, L2, L5, L6. Practical selection framework. |
| Concentration accuracy includes the stock and the well.ASSAY CONSEQUENCE | For an ideal, fully mixed addition, final concentration equals stock concentration multiplied by transferred volume divided by final volume. Dispensing precision describes only one term in that calculation. | Hydrated solvent, precipitation, adsorption and evaporation can move the true concentration while the volume record looks correct. A low dye CV leaves those systematic concentration errors unresolved. | Qualify volume delivery with an appropriate reference, then test recovery and biological response separately. Keep preparation records and actual transfer reports with the dose-response data. A systematic stock error can survive perfect replication across an entire plate.Sources: L8. Amount balance and proposed qualification. |

## Specifications

| The finding | Technology and product evidence | Trade-offs and controls | What it means |
| --- | --- | --- | --- |
| Echo requires a qualified source configuration.ACOUSTIC TRANSFER | The 650 Plus series advertises transfers down to 2.5 nL and qualified 384- or 1536-well sources. Sample tubes require a tube-enabled model. Destination specifications include 96-, 384- and 1536-well formats within stated geometry limits. | Source chemistry, calibration and labware compatibility belong in the configuration. The advertised maximum droplet rate does not establish end-to-end plate throughput or a universal fluid envelope. | Echo is a strong candidate for direct compound dosing from organized source libraries. Demonstrate the intended stocks at both high and low source fill levels. Include failed-transfer reporting, recovery and plate-handling time when judging unattended operation.Sources: L1. Manufacturer capability; suitability requires demonstration. |
| D300e minimum volume depends on the cassette and fluid.DIGITAL DISPENSING | The software guide lists a 13 pL DMSO minimum for standard-volume heads and 1 nL for high-volume heads. Standard-head minimum fill is 2 µL for DMSO and 4 µL for aqueous fluids; high-volume heads require 50 µL. | Minimum dispensed volume is distinct from minimum loaded volume. Dispense increments and normalization limits also vary. A picoliter dose therefore does not imply picoliter consumption of a precious stock. | Use the current software guide, Appendix E, when costing a titration. Calculate stock preparation, loaded volume, unused remainder and replacement heads for the whole experiment. Check the smallest requested doses in the generated dispensing report.Sources: L3. PDF pp 109–110; values are conditional specifications. |
| Mosquito LV and HV cover different volume windows.POSITIVE DISPLACEMENT TRANSFER | SPT's comparison brochure specifies 25 nL–1.2 µL for mosquito LV and 500 nL–5 µL for mosquito HV. Both list 96-, 384- and 1536-well plate formats. | The family name does not define a single volume range. Tip access, source geometry, residual liquid and the desired transfer pattern remain relevant at the lower end. | Consider these platforms when aspiration and dispensing, reformatting or serial transfer are central. Include the exact source plate and smallest transfer in the demonstration. A working protocol on HV does not establish the performance of LV, or the reverse.Sources: L5. Manufacturer specifications and configuration inference. |
| Dragonfly occupies the reagent assembly part of the workflow.POSITIVE DISPLACEMENT DISPENSING | SPT lists a 200 nL–4 mL dispensing range and 96-, 384- and 1536-well formats for dragonfly discovery. Its disposable syringe dispenses without contacting the destination liquid. | A broad dispense range does not describe source dead volume, reagent residence time or the number of different stocks that can be loaded conveniently. Those details affect expensive reagents and changing assay recipes. | Assess it for repeated reagent additions, assay optimization and compatible cell suspensions. Bring a realistic recipe with different volumes across the plate. Time loading, priming and changeover as well as the dispense itself.Sources: L5, L6. Manufacturer specifications; workflow recommendation. |

## Features

| The finding | Technology and product evidence | Trade-offs and controls | What it means |
| --- | --- | --- | --- |
| Aqueous compatibility can impose a formulation change.FLUID CHEMISTRY | Tecan's guidance specifies 70–100% DMSO stocks or supported aqueous formulations. Its buffer FAQ lists particular surfactants and concentrations. The software guide distinguishes aqueous classes and specified master mixes. | An added surfactant can affect proteins, membranes or compound behavior. The permissible stock formulation and the final assay formulation are separate questions. Compatibility should follow the actual current fluid class. | Test vehicle and surfactant controls at their final concentrations. If the assay cannot tolerate the required stock formulation, that is a selection constraint. Do not quietly reformulate a validated biological assay just to make its stocks dispensable.Sources: L4, L3. Manufacturer fluid requirements; proposed assay controls. |
| Direct dilution avoids a chain of intermediate transfers.DOSE RESPONSE DESIGN | Echo and D300e support direct dosing from stock solutions. Mosquito can perform serial transfers when that workflow is appropriate. Direct preparation removes the intermediate dilution chain. | It removes some intermediate dilution steps but retains stock errors, volume quantization and solvent differences. Serial dilution errors may be correlated because later points inherit earlier preparation errors. | Compare both strategies using a stable reference compound and independently prepared stocks. Inspect curve shape and potency across days, not only dispense CV. Neither a smooth curve nor agreement between duplicate wells proves the concentration axis is correct.Sources: L1, L2, L5. Error-propagation interpretation and proposed test. |
| Solvent normalization belongs in the method.VEHICLE CONTROL | D300e software provides fluid-class normalization. In a general direct-dosing workflow, lower compound doses can otherwise receive less stock solvent than higher doses, creating a second experimental variable. | Backfilling adds volume and another liquid-handling step. Normalizing one solvent does not normalize every excipient carried by different stocks, and an assumed final volume may omit those additions. | Calculate the vehicle fraction from every contributing stock and backfill. Inspect both requested and delivered layouts. Include matched vehicle wells at the actual final composition, especially when comparing compounds prepared in different solvent mixtures.Sources: L3. Software feature and proposed control. |

## Capabilities

| The finding | Technology and product evidence | Trade-offs and controls | What it means |
| --- | --- | --- | --- |
| Cell dispensing needs a cell-specific demonstration.BIOLOGICAL SAMPLES | SPT reports dragonfly dispensing of five cell lines into 1536-well plates at 2 µL per well, followed by cell-count and viability measurements after 24 hours. The D300e operating manual excludes dispensing cells from its intended uses. | Results for those cell lines do not establish tolerance for fragile primary cells, aggregates or every medium. A homogeneous dye cannot reveal preferential loss of large cells or declining viability. | Use the intended cell preparation and examine early and late plates. Measure recovered cell number, viability and the assay response. Include reservoir residence time and mixing, and avoid extending one manufacturer's application study to unrelated cell types.Sources: L7, L2. Study-specific evidence; proposed acceptance test. |
| Correct delivery can leave the well incompletely mixed.FIRST EXPOSURE | The NIH microplate guidance discusses slowly dispersing DMSO additions and the limitations of shaking small wells. Reagent arrival and concentration uniformity occur at different times. | An endpoint dye measurement may miss a transient high-concentration region near adherent cells. Plate motion alone does not establish liquid exchange within a well. | Compare the actual addition sequence with a separately premixed reference. Use a mixing-sensitive spatial or kinetic measurement, followed by biological confirmation. Qualify the time between compound arrival and the assay's first sensitive event, particularly for rapid reactions and solvent-sensitive cells.Sources: L8. Proposed mixing qualification; no experiment performed here. |
| Plate preparation should expose failed transfers.AUTOMATION AND TRACEABILITY | An unattended workflow needs a record of the plate identity, source well, destination well, requested dose and any transfer exception. Integrating instruments adds handoffs at which identity or timing can be lost. | A plate can leave the deck with wells that never received their addition. Blindly retrying an uncertain transfer can create a double dose; stopping after every warning can erase the expected throughput advantage. | During the demonstration, introduce a recoverable interruption and inspect the resulting record. Require a clear distinction among completed, failed and uncertain transfers. Agree how partial plates will be quarantined or resumed before purchasing the automation package.Proposed workflow acceptance criterion, not a claim about a specific product. |

## Downsides

| The finding | Technology and product evidence | Trade-offs and controls | What it means |
| --- | --- | --- | --- |
| Dead volume may dominate a small experiment.REAGENT ECONOMICS | In a constructed example, 100 transfers of 25 nL deliver only 2.5 µL. If the workflow requires a 20 µL load, only 12.5% reaches the destination, regardless of how accurate the individual transfers are. | The 20 µL value is hypothetical. Real residuals depend on the instrument, source vessel, liquid and loading protocol. Recoverable stock is not automatically reusable stock. | Compare total material committed per completed experiment, including priming, inaccessible residuals and failed runs. For scarce proteins, material committed to loading and priming can decide between two otherwise suitable instruments.Constructed amount-balance example, not a product specification. |
| Evaporation changes the experiment while it waits.ENVIRONMENT | The NIH guidance treats evaporation as a microplate concern. SPT lists humidity-control accessories for mosquito, while Tecan places limits on aqueous runs to manage evaporation. | An environmental accessory has a defined operating envelope. It does not automatically protect plates waiting elsewhere, and cooling can create condensation if the workflow crosses a dew point. | Qualify early and late plates under the actual room conditions, lid schedule and queue duration. Keep temperature consistent with the biology and downstream chemistry. For a room-temperature endpoint assay, plan equilibration after dispensing rather than assuming deck temperature equals liquid temperature.Sources: L8, L5, L3. Source guidance and proposed environmental qualification. |
| Noncontact transfer does not certify a contamination-free process.CARRYOVER AND CONTAMINATION | Eliminating a reused wetted transfer path can remove one route of carryover. Source handling, plate surfaces, shared reagents and the surrounding workflow still offer other routes. | Disposable tips or heads reduce particular risks while adding consumable handling. Claims of zero contamination should be interpreted within the conditions actually tested. | Run a challenging high–blank–low sequence with the relevant analyte. Choose a detection method sensitive enough for the receiving assay. Investigate isolated outliers as well as mean carryover, and retain the physical order of transfers in the analysis.Mechanistic reasoning and proposed contamination test. |

## Advantages

| The finding | Technology and product evidence | Trade-offs and controls | What it means |
| --- | --- | --- | --- |
| Small droplets can expand the usable dose range.QUANTIZATION EXAMPLE | For a constructed 5 µL final assay volume and a 10 mM stock, a 2.5 nL addition gives 5 µM. A 25 nL addition gives 50 µM. These calculations assume additive volumes and exact final volume. | The values illustrate concentration spacing; they do not compare accuracy at those volumes. Lower stock concentrations can reach lower doses but may require more preparation, solvent or storage positions. | Start with the concentration range the biology needs. Then work backward to compatible stocks and dispense increments. Fine volume resolution is valuable when it preserves useful points around the response transition, rather than merely extending an impressive theoretical range.Constructed concentration calculation. |
| Physical displacement can be useful for difficult liquids.VISCOSITY AND SURFACE TENSION | SPT describes positive-displacement operation and broad liquid compatibility. Dragonfly's manual states that liquid-class calibration is not required for its dispensing method. | That statement does not establish recovery of every protein or compatibility with every suspension. Material adsorption, bubbles and cell settling remain properties of the whole liquid-handling process. | Bring the actual viscous reagent or concentrated protein to a demonstration. Compare delivered volume, recovered analyte and functional activity. When difficult liquids drive the purchase, their recovery and activity should decide acceptance.Sources: L5, L6. Manufacturer mechanism; proposed functional verification. |
| A complementary pair can outperform an oversized compromise.SYSTEM DESIGN | Compound dosing and repeated reagent addition often place their largest burdens on different parts of an instrument. One emphasizes many source identities; the other may emphasize rapid distribution from a small number of reservoirs. | Two instruments add cost, scheduling and transfers between decks. The handoff can introduce evaporation or timing variation unless it is deliberately controlled. | Cost the complete assay recipe on one platform and on a practical two-platform route. Include staff time, consumables, discarded reagent and recovery from interruptions. Choose the arrangement that delivers qualified plates at the required frequency.Proposed selection framework; no quoted cost comparison. |

## Notable Details

| The finding | Technology and product evidence | Trade-offs and controls | What it means |
| --- | --- | --- | --- |
| Benchmark the assay at the edges of normal operation.DEMONSTRATION DESIGN | A useful challenge set contains the smallest dose, the highest solvent fraction, low source fill, a difficult liquid and the longest planned queue. Repeat across separate preparations rather than only repeating one plate. | Testing every extreme simultaneously makes a failure hard to diagnose. Start with representative conditions, then change one factor at a time before combining the realistic worst cases. | Record bias, precision, missing additions, material recovery and biological response. Set acceptance limits from the assay's decisions before seeing the vendor's results. Save the method and raw data so the demonstration becomes a reproducible installation test.Proposed qualification plan; acceptance limits are assay-specific. |
| The purchase decision should include the next year's work.TOTAL WORKFLOW | Ask for written configurations covering labware, tips or heads, software, integration, training, service and application support. Current public specifications do not establish the delivered price or the cost of a qualified assay. | A low initial quote can omit automation or consumables needed for the intended throughput. A highly capable system may demand more maintenance or operator attention than a small team can supply. | Make the final comparison per usable assay plate and per supported workflow, with explicit workload assumptions. Assess scientific flexibility separately from cost. A core lab and a fixed industrial screen can reasonably choose different winners from the same evidence.Procurement recommendation; prices remain quote-dependent. |

## About the sources

Manufacturer specifications describe the named product and configuration; they are not independent all-vendor benchmarks. Row-level source IDs link to the references below. Calculations and practical interpretations are identified separately. No physical comparison or procurement quotation is represented by these tables.

L1  [Echo 650 Plus series](https://www.beckman.com/liquid-handlers/echo-acoustic/echo-650-plus-series)

L2  [Tecan D300e operating manual](https://www.tecan.com/hubfs/Knowledgebase/Manuals/D300e/D300e%20Digital%20Dispenser%20Operating%20Manual.pdf?hsLang=en)

L3  [Tecan D300e software guide](https://www.tecan.com/hubfs/Knowledgebase/Manuals/D300e/Dispensing%20Software%20User%20Guide.pdf?hsLang=en)

L4  [Tecan D300e supported buffers](https://www.tecan.com/knowledge-portal/which-buffers-can-i-use-to-dispense-my-compounds-with-the-d300e-digital-dispenser)

L5  [SPT liquid handling brochure](https://discovery.sptlabtech.com/hubfs/Website/06%20-%20Products/01%20-%20mosquito/04%20-%20mosquito%20HV/SPT_Liquid_Handling_brochure_WEB_vTSVr6h.pdf)

L6  [dragonfly discovery specifications](https://www.sptlabtech.com/product-help-center/dragonfly-discovery-user-maual-specifications)

L7  [dragonfly cell dispensing application note](https://sptlabtech.com/hubfs/Website/09%20-%20Resources/Legacy%20PDFs/SPTL0084_DFD_Cell_Dispensing_App_Note_WEB_TGbjZSf.pdf)

L8  [Auld et al — Microplate Selection and Recommended Practices, NIH Assay Guidance Manual, chapter 2020; supplied 2026 compilation PDF pp 1573–1576](https://www.ncbi.nlm.nih.gov/books/NBK558077/)