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What is a sensor?

A sensor responds to a physical or chemical property and makes the change readable. That could be temperature, pressure, light, movement or the presence of a particular substance. To obtain a useful measurement, we also need to know what its output means. [1]

Think of a digital thermometer. Heat affects a temperature-sensitive element. Electronics read the change, a conversion produces degrees and a display presents the result. The sensor, conversion and presentation are different parts of the same measurement chain.

Sensor, biosensor and algorithm

A biosensor uses a biological recognition element, such as an enzyme, together with a way to read the reaction. A sensor measuring a bodily signal does not necessarily contain such an element. Optical pulse sensing records changing light; an algorithm then estimates pulse rate from that signal. [1]

A molecule with a readable sequence

DNA consists of two chains of building blocks containing the bases A, T, C and G. In the double helix, A pairs with T and C with G. Their order is biological information, but that information gains function through the cell’s machinery and the environment in which it is used. [2]

A protein-coding gene can be copied into messenger RNA. Ribosomes then use that RNA message to assemble amino acids into a protein. Other RNA molecules perform functions of their own. DNA, RNA and protein are therefore different levels of information, not interchangeable measurements. [2] [3]

How does the molecule become digital?

Sequencing determines the order of bases. Instrument observations are converted into digital sequences that can be compared, organised and analysed. A sequence file records what was read; interpretation also needs the sample’s origin, the analytical method and quality checks. [4]

To ask which genes are being used in a sample, researchers can instead examine RNA, for example through RNA sequencing. A skin sample and a nerve cell can have very similar DNA but different active gene programmes. One measurement layer therefore does not describe the cell’s entire state. [3] [5]

Why does shape matter?

Proteins are chains of amino acids that can form three-dimensional structures. Shape and chemical properties influence which molecules a protein can interact with. A structural model therefore provides a way to ask more precise questions about biological function. [7]

AlphaFold2 was a major milestone because it demonstrated highly accurate structure prediction in the CASP14 assessment. Its output consists of calculated atomic positions derived from a sequence and other model information. This makes many structural hypotheses easier to formulate. [7]

How to read a model

Start with the question you want to answer. Are you exploring the shape of one region, the relative position of two regions or whether a proposed contact is worth examining? Different questions require different evidence.

pLDDT describes local model confidence on a scale from 0 to 100. PAE describes uncertainty in the relative positions of regions. Two locally well-modelled regions can therefore still have uncertain placement relative to one another. Read both when your question concerns the whole structure. [8] [9]

What does quantum biology mean?

Quantum biology examines how quantum processes can influence biological functions. One concrete question is whether electron spins in light-activated molecules can contribute to animals’ magnetic sensitivity. Molecular chemistry, physics and measurable biological questions meet here. [10]

Spin is a quantum property of particles such as electrons. A radical pair contains two molecular parts with unpaired electrons. A magnetic field can influence how their joint spin state changes and, under suitable conditions, which reaction pathways become available. [10]

What has actually been demonstrated?

In 2021, Xu and colleagues demonstrated magnetic sensitivity in the photochemistry of robin cryptochrome 4 in the laboratory. The study supports a possible molecular mechanism. On its own, it does not establish the entire pathway from the protein to a bird’s orientation. [10]

Later studies examined cryptochrome evolution and how cryptochrome 4a can interact with lipid membranes. Such results help researchers ask where the molecule acts and how a molecular change might be passed on as a biological signal. [11] [12]

An atomic defect as a measuring tool

An NV centre in diamond consists of a nitrogen atom replacing carbon and a neighbouring vacancy in the crystal. The electron spin’s energy levels respond to the magnetic field. That turns a very small part of a material into a tool for examining its surroundings. [13]

In a common readout scheme, green light illuminates the diamond, which emits red light. Microwaves influence the spin state. By tracking when the red-light intensity changes, the instrument can infer the magnetic field. Optics, electronics and analysis work together here. [13] [14]

How does this become a digital measurement?

A detector collects the light. The reading is associated with the instrument settings, and a computational model converts the response into a field value. At the data level, the same care is needed as for simpler sensors: units, timing, measurement conditions and uncertainty.