Microplate readers are a type of spectrophotometer designed specifically for analyzing multiple samples in multi-well plates.

The readers detect light signals that result from biological, chemical, biochemical, or physical reactions. The signals are produced by, converted by, or transmitted through the samples and are measured by a detector. The detectors are usually photomultiplier tubes (PMT), which convert the released photons into electricity. The current is quantified by the reader’s software to produce the numerical result.

In some cases, samples are first excited by exposure to light of specific wavelengths. Filters or monochromators are used to select or restrict the wavelengths needed for emission or detection.

Single-mode microplate readers commonly measure absorbance, fluorescence, or luminescence. Multi-mode plate readers may measure absorbance, fluorescence, and luminescence with options for fluorescence polarization (FP). They may also include lasers for time-resolved fluorescence (TRF), TR-FRET, Amplified Luminescent Proximity Homogeneous Assays (ALPHA), and cell imaging.

Features may include:

• Monochromator- or filter-based wavelength selection
• Visible only or UV/Vis spectrum, fluorescence, and luminescence
• Multiple photomultiplier tubes (PMTs) for simultaneous assays
• Temperature and CO₂/O₂controls
• Modular design for adding functionality

Microplate readers are used for high-throughput screening (HTS), biomarker assays, nucleic acid and protein quantification, kinetics, ELISA assays, homogeneous time resolved fluorescence (HTRF) for measuring cytokines, bioluminescence resonance energy transfer (BRET), and other techniques.