The data is in: our biophoton microscope is ready for business

The data is in. On 8 and 9 June 2026, the biophoton microscope at openUC2 in Jena completed its first full measurement campaign. The method is simple to state: an injured leaf is given a small dose of hydrogen peroxide, placed in front of a camera cold enough and quiet enough to register single photons, and recorded for twenty minutes in the dark.

The result is clear. An injured compass plant (Silphium laciniatum) leaf treated with H2O2 emitted 1.56 times more total light than an untreated injured leaf, under identical camera settings. The brightest regions were roughly twice as bright, which indicates the additional light comes from localised reaction hotspots rather than a uniform rise across the leaf. Living tissue under stress emits light, and here that light was measured.

A bushy compass plant (Silphium laciniatum) with deeply lobed green leaves growing in a raised bed outdoors. — The compass plant (*Silphium laciniatum*).

Three panels: a near-exponential per-pixel signal distribution, a bar chart showing injured+H2O2 at 1.56 times the total emission of injured alone, and a false-colour map of the injured leaf with bright hotspots. — Injured versus injured plus H2O2: 1.56x more total emission, and where on the leaf it comes from (right).

The character of the signal matters as much as its size. The per-pixel distribution is near-exponential, the signature of single photo-electrons amplified one at a time in the camera's electron-multiplying register. In other words, the detector was operating at its floor, counting light close to photon by photon. That is the regime required to measure emission this faint with confidence.

Three 3D surface plots of signal above baseline: a low flat dark-lid baseline on the left, the injured leaf with a few tall peaks in the centre, and injured plus H2O2 with many more and higher peaks on the right. — Signal above baseline as a landscape: the dark baseline (left), the injured leaf (centre), and injured plus H2O2 (right).

One limit should be stated plainly. Because the camera's true gain and sensitivity were not recorded in the acquisition metadata, the present numbers are relative rather than absolute. Closing that gap, with a calibration that converts counts into photons and carries a real error bar, is the next task, and it is being built directly into the open-source openUC2 control software so that a one-off correction becomes a tool the wider community can reuse.

The instrument

The measurements were run at openUC2 in Jena on the open-hardware microscopy platform developed by Benedict Diederich and his team, with the calibration work carried out together with Rainer Heintzmann and colleagues at the Leibniz IPHT in Jena. The rig itself is deliberately modest: a light-proofed enclosure, an Andor iXon EMCCD, a liquid cooler, and a laptop.

A CAD cutaway rendering of the openUC2 microscope, with a blue arrow marking the light path running vertically from the sample stage down through the objective to the detector. — The openUC2 microscope in cutaway: the light path from sample to detector, in blue.

A researcher leaning over a black light-proofed enclosure standing on a trolley in a lab, with a laptop, tubing, and a chiller on the shelf beneath it. — Benedict Diederich at the light-proofed biophoton rig, openUC2 Jena.

Close-up of a silver Andor iXon Ultra EMCCD camera mounted under a microscope, with clear cooling tubes running to it. — The Andor iXon EMCCD at the heart of the setup.

These are faint beginnings, in the most literal sense. The detector at the heart of the setup is a capable but costly scientific camera. Our aim is to develop a version of this instrument that performs the same measurement at a fraction of the price, and to bring it into as many hands as possible. An open instrument only advances open science if others can afford to build it.

Outlook

This campaign is the first step of a longer programme. The near-term work is to harden the Jena instrument into a fully reproducible rig, complete the calibration, and widen the study across plant species and stress conditions with proper biological replicates. From there, the aim is to use these plant screens to connect specific photon signatures to the underlying biology, and, further out, to translate the deep-cooled bench sensor into an affordable and eventually wearable detector, carrying the same measurement from a leaf on a bench toward the human body.

The faint light that living things emit was a recurring subject at our first community gathering at Etherlaken in June. Now it is something we can measure.