Microplate Absorbance Photometer

What is the Microplate Absorbance Photometer?

A microplate absorbance photometer reads 96- or 384-well plates at filter-selected wavelengths from 340 to 750 nm, measuring each well in seconds. It is the standard detector for ELISA, protein and cell viability assays, and other plate-based colorimetric methods.

Overview

A microplate absorbance photometer passes light from a xenon or halogen lamp vertically through each well, using interference filters to select the wavelength. A photodiode or a bank of eight detectors in a row reads the plate, so a 96-well plate is measured in 5 to 15 seconds. Because the light path passes through the liquid column, the effective path length depends on volume, typically 0.3–0.6 cm in a 200 µL well, so many instruments offer path length correction. Shaking and incubation functions support kinetic ELISA and enzyme assays. Filter-based designs are simpler and less costly than monochromator readers, and they cover the common wavelengths of 405, 450, 492, 540, 570, 595, 620 and 650 nm. Plate-reader software handles curve fitting with four-parameter logistic models, cutoffs for qualitative tests and export to LIMS.

How does it work?

A photometer consists of a light source, a wavelength-selecting element, a sample compartment and a detector. Unlike a spectrophotometer, wavelength selection is fixed, using interference filters or narrow-band LEDs, which makes the optical path simple, robust and inexpensive. In absorbance photometry, the detector measures the light transmitted through a colored solution, and concentration is found from a calibration curve using the Beer–Lambert relationship. In flame photometry, a nebulized sample is burned in a fuel and air flame, where sodium, potassium, lithium and calcium atoms emit characteristic light at 589, 766, 671 and 622 nm; a filter isolates the line and a photodetector measures intensity. Microplate photometers read 96- or 384-well plates in seconds by measuring absorbance at filter-selected wavelengths through each well from above.

What are the key features?

• Reads 96-well plates in approximately 5 to 15 seconds using an eight-channel detector.
• Filter wheel covers 405, 450, 492, 540, 570, 595, 620 and 650 nm.
• Shaking function mixes wells before reading to improve reproducibility.
• Path length correction normalizes absorbance to a 1 cm equivalent.
• Four-parameter curve fitting and cutoff calculation are included in the software.
• Optional incubation to 37 °C supports kinetic enzyme assays.

What are the technical specifications?

A typical microplate absorbance photometer configuration offers plate formats of 96-well and 384-well (SBS standard), wavelength range of 340–750 nm (filter-based), filters supplied of 405, 450, 492, 620 nm (extendable to 8 filters), absorbance range of 0–4.0 A, accuracy of ±1 % ±0.010 A at 0–3 A and repeatability of ≤0.5 % ±0.005 A. Values are indicative of the product class; the exact figures for each configuration are confirmed on the quotation and the calibration documents supplied with the instrument.

Which applications is it used for?

The Microplate Absorbance Photometer is used in ELISA and immunoassays, BCA, Bradford protein assays, cell viability (MTT, CCK-8) assays and endotoxin and microbial assays. Across the wider Photometers class, laboratories also deploy it for serum sodium and potassium analysis, water quality colorimetric testing and soil and plant nutrient analysis.

Which standards and certifications apply?

Relevant standards and methods include ISO 8655-related photometric checks, ISO 6060 (chemical oxygen demand), ISO 7150-1 (ammonium), GB/T 6682, JJG 1032 (flame photometer verification) and IEC 61010-1. Certification candidates for this model are CE and ISO 9001 manufacturing; each is to be confirmed for the specific configuration before shipment, and certificates are supplied only where they have been issued.

Install flame photometers in ventilated areas with regulated LPG, propane or natural gas supply and compressed air, and fit leak detection. Use deionized water and clean glassware to avoid sodium contamination. Calibrate with at least three standards bracketing the expected range and run a check standard regularly. For absorbance photometers, keep filters and optics free of dust and condensation, and verify with neutral-density or solution standards on schedule. Follow local rules for gas cylinder storage and documented calibration intervals. Clinical users should check local regulations regarding analyzer quality control.

How do I select the right Microplate Absorbance Photometer?

Choose a filter-based absorbance reader when workflows are standardized to a few wavelengths. Select a monochromator reader when spectra or flexible wavelengths are needed. In an RFQ, state plate formats, required filters, incubation and shaking needs, and whether software compliance with audit trails or integration with liquid handlers is necessary.

How does it compare with other Photometers variants?

The first decision is the measurement principle: flame emission for alkali and alkaline-earth metals, absorbance for colorimetric assays, or plate-based absorbance for high throughput. Check that the filter set or LED wavelengths match your methods, since these cannot be changed freely afterward. Consider the analyte range and detection limit; for example, flame photometers for serum sodium and potassium need resolution of about 0.1 mmol/L. Sample format matters: cuvette, test vial or microplate. Consider reagent ecosystems and whether preprogrammed methods exist for your parameters. For regulated or clinical use, look at data handling, calibration storage and quality control features. Finally, evaluate fuel and gas supply for flame systems, and portability and ingress protection for field units.