Microplate Reader

A microplate reader shines light through or into microplate wells and measures the resulting signal to quantify analytes, cells, or reactions. Absorbance readers measure light transmission through samples (Beer-Lambert law) for protein quantification (Bradford, BCA), ELISAs, and spectrophotometric enzyme assays. Fluorescence readers excite fluorophores and detect emission at longer wavelengths—used for fluorescent ELISAs, calcium flux assays, and reporter gene assays. Luminescence readers detect light emitted from chemical or biological reactions without excitation light, critical for ATP-based viability assays and luciferase reporters. Multi-mode readers combine two or more detection modes in one instrument, with high-end models adding time-resolved fluorescence (TRF), fluorescence polarization (FP), and AlphaScreen/AlphaLISA capabilities. Monochromator-based systems offer wavelength flexibility, while filter-based systems provide higher sensitivity at specific wavelengths. Temperature control, shaking, and injector systems extend functionality for kinetic assays. Modern readers interface with laboratory software (Gen5, SoftMax Pro) for data analysis and can handle 96 to 1536-well formats depending on the model.

Why Agilent (formerly BioTek) is the benchmark

The Synergy H1 is the workhorse multi-mode reader in academic and biotech labs. It combines hybrid optics (filter-based + monochromator) for both sensitivity and flexibility, handles 6-384 well plates, includes temperature control to 65°C, and runs on the excellent Gen5 software. BioTek's market dominance means parts, service, and expertise are readily available. The H1 replaced the beloved Synergy HT/H4 and maintains backward compatibility with existing protocols.

What to look for

• Detection modes needed: absorbance-only is cheapest, multi-mode costs more but future-proofs
• Filter-based vs. monochromator: filters = better sensitivity, monochromator = flexibility
• Plate format compatibility: 96-well standard, 384/1536 for high-throughput screening
• Temperature control range and uniformity (critical for kinetic assays)
• Injector system availability if doing flash luminescence or kinetics
• Software licensing model: perpetual vs subscription, multi-seat options
• Bottom-read capability for cell-based assays through clear-bottom plates
• Dynamic range and sensitivity specifications for your assay requirements
• Read speed per plate (matters for large screening campaigns)
• Lamp type and expected lifespan (xenon flash, tungsten, LED)

Tips for buying used

• Request recent calibration verification using standard plates—sensitivity drift indicates lamp or detector degradation
• Check lamp hours or shot count: xenon flash lamps typically last 10 million flashes, replacement costs $1,500-3,000
• Verify all detection modes function by running test plates with known standards (rhodamine for fluorescence, p-nitrophenol for absorbance)
• Confirm software version and license transferability—BioTek Gen5 and Molecular Devices SoftMax Pro have different transfer policies
• Test temperature control accuracy with a calibrated thermometer in wells; drift >0.5°C indicates worn heating elements
• Inspect filter sliders and monochromator mechanisms for smooth operation; sticky filters cause read errors
• Check injector tubing for yellowing or cracks; dried reagent deposits indicate poor maintenance
• Verify plate carrier movement is smooth without grinding—stepper motor issues are expensive to repair
• Ask for service history documentation; regular preventive maintenance extends usable life significantly
• Test with your actual plate types; some readers have compatibility issues with certain plate geometries

Budget trade-offs

What you lose: Absorbance-only budget readers lack fluorescence, luminescence, and advanced modes like FP and AlphaScreen. Lower sensitivity limits detection of weak signals. No temperature control eliminates kinetic assay capability. Basic software lacks curve-fitting, protocol automation, and data management features. 96-well only format prevents miniaturized assays. Slower read times impact throughput. No bottom-read capability rules out many cell-based assays.

What you keep: Basic absorbance measurements for ELISAs, Bradford/BCA protein assays, and colorimetric enzyme assays work fine on budget readers. Endpoint measurements at common wavelengths (405, 450, 490, 595nm) are reliable. Data export to spreadsheets is standard. Sufficient accuracy for routine QC and teaching applications.

GMP & regulated use

For regulated environments, verify IQ/OQ/PQ documentation availability and 21 CFR Part 11 compliance in software. BioTek and Molecular Devices offer validation packages. Audit trail functionality, electronic signatures, and user access controls are essential for pharma/GLP work. Used instruments can be re-qualified, but budget $3,000-8,000 for third-party IQ/OQ services if documentation is unavailable.