Transmission electron microscopes achieve the highest magnification and greatest resolution of any microscope technology. The current record holder is PICO, a transmission electron microscope at the Ernst Ruska-Centre in Jülich, Germany, which resolves details down to 50 picometers, or fifty billionths of a millimeter. That’s less than half the diameter of a hydrogen atom.
But the answer gets more interesting when you look at how different microscope types work, because “highest magnification” and “greatest resolution” are not the same thing, and the best tool depends entirely on what you’re trying to see.
Why Resolution Matters More Than Magnification
Magnification is simply how much larger an image appears compared to the real object. Resolution is how much fine detail you can actually distinguish. You can magnify a blurry photo as much as you want, but you won’t see anything new. The same principle applies to microscopes: a bigger image is useless if the resolution can’t keep up. Projecting a microscope image onto a larger monitor increases magnification, but the image stays exactly as sharp or blurry as the resolution allows.
This is why resolution is the number scientists actually care about. Higher-quality lenses and electron optics tend to deliver both better magnification and better resolution together, but resolution is the hard physical limit that determines what you can and can’t see.
Electron Microscopes: The Resolution Champions
Electron microscopes replaced light with a beam of electrons decades ago, and that single change is what makes their resolution so dramatically better. Light has a wavelength of roughly 400 to 700 nanometers, which puts a hard ceiling on optical microscopes at around 200 nanometers. Electrons can be accelerated to wavelengths thousands of times shorter, pushing resolution into the realm of individual atoms.
There are two main types. Transmission electron microscopes (TEM) fire electrons through an ultra-thin sample and capture the pattern on the other side. Scanning transmission electron microscopes (STEM) focus the beam to a fine point and scan it across the sample, building an image pixel by pixel. Both achieve sub-angstrom resolution (one angstrom is 0.1 nanometers), meaning they can resolve individual atoms and even the bonds between them.
PICO, the record-setting instrument in Germany, is a TEM equipped with advanced optics that correct for the imperfections inherent in electron lenses. These corrections, called aberration corrections, are what pushed its resolution to 50 picometers. To put that in perspective, the distance between two bonded carbon atoms is about 150 picometers. PICO can resolve features roughly a third of that bond length.
Electron Ptychography: Pushing Even Further
A newer computational technique called electron ptychography is closing the gap between expensive, aberration-corrected microscopes and more accessible instruments. Researchers at the University of Illinois demonstrated that by collecting overlapping diffraction patterns and reconstructing them with algorithms, they achieved resolution down to 0.44 angstroms (44 picometers) using a microscope that lacks the expensive corrective optics. Their ptychographic images resolved single atoms in samples where conventional imaging from the same instrument could only show the general crystal lattice. This approach rivals the best hardware-corrected instruments at a fraction of the cost.
Scanning Probe Microscopes: A Different Approach
Scanning tunneling microscopes (STM) and atomic force microscopes (AFM) don’t use light or electrons at all. Instead, they drag an impossibly sharp physical tip across a surface, sensing individual atoms through electrical current (STM) or physical force (AFM). Both resolve surface detail down to the atomic level, and STM can measure height differences between atoms with sub-picometer precision. Researchers have distinguished between two types of atomic positions on a surface separated by an average height difference of just 1.32 picometers.
The tradeoff is that scanning probe microscopes only image surfaces. They can’t see inside a sample or image a three-dimensional structure the way electron microscopes can. AFM has one practical advantage: it works on non-conducting samples, which makes it useful for imaging biological molecules like amino acid crystals and organic films. STM requires the sample to conduct electricity.
Cryo-Electron Microscopy: Best for Biology
For biological structures like proteins and viruses, cryo-electron microscopy (cryo-EM) holds the resolution record. This technique flash-freezes biological samples in a thin layer of ice, then images them with an electron beam. By capturing thousands of images from different angles and averaging them computationally, researchers reconstruct three-dimensional structures at near-atomic detail.
Two landmark studies achieved 1.2-angstrom resolution on a protein called apoferritin, marking the first true atomic-resolution structures obtained by cryo-EM. A later study reached 1.35 angstroms without any new instrument advances, suggesting the technique still has room to improve through better sample preparation and data processing alone. For membrane proteins, which are notoriously difficult to image, resolution jumped from about 2.5 angstroms to 1.7 angstroms in a single study of a brain receptor protein.
Cryo-EM can’t match the raw resolution of a dedicated materials-science TEM like PICO, but it doesn’t need to. Biological molecules are large enough that 1 to 2 angstroms reveals every atom that matters for understanding how a drug binds or how a virus infects a cell.
Optical Microscopes: Breaking the Old Limits
Standard light microscopes top out at about 200 nanometers of resolution, a limit set by the physics of light itself. That’s good enough to see cells and large structures inside them, but far too coarse for anything molecular. Several Nobel Prize-winning techniques have punched through this barrier.
STED microscopy uses a second laser beam shaped like a donut to shrink the effective spot of light, reaching 20 to 30 nanometers in biological samples. Commercial versions currently achieve about 70 nanometers. PALM and STORM take a different route, switching individual fluorescent molecules on and off one at a time, then pinpointing each one’s location to about 20 nanometers. In three dimensions, STORM achieves 20 to 30 nanometers laterally and 50 to 60 nanometers in depth, while a related technique called iPALM reaches 20 nanometers laterally and 10 nanometers axially.
These super-resolution optical methods still fall about 100 times short of electron microscopes in raw resolution, but they have a critical advantage: they work on living cells. You can watch a protein move in real time, something no electron microscope can do.
What It Takes to Hit Maximum Resolution
Achieving the highest resolution from any electron microscope requires an environment as controlled as the instrument itself. Temperature in the room must hold steady at around 20°C with fluctuations no greater than 0.1°C per hour. Floor vibrations need to stay below about 0.25 micrometers per second, which is why top-tier facilities mount their microscopes on massive concrete slabs, some weighing over 200 tons, suspended on pneumatic isolators. Electromagnetic interference from nearby equipment, power lines, or even passing elevators can blur images at the atomic scale.
Facilities like Brookhaven National Laboratory and Oak Ridge National Laboratory use isolation gaps between the microscope’s foundation and the rest of the building, filled with vibration-damping materials. The Max Planck Institute suspends its entire 215-ton concrete foundation on air springs with a resonance frequency below 1 hertz, essentially floating the microscope on a cushion of air. Without these measures, even the most advanced electron optics can’t reach their theoretical limits.
Choosing the Right Microscope for the Job
- Atomic structure of materials: Aberration-corrected TEM or STEM, with resolution down to 50 picometers. Best for metals, semiconductors, and crystalline samples.
- Surface atoms and bonds: STM or AFM, with atomic-level surface resolution and sub-picometer height sensitivity. Limited to surfaces only.
- Protein and virus structures: Cryo-EM, resolving biological molecules to 1.2 angstroms. The standard tool for structural biology and drug design.
- Living cells: Super-resolution optical microscopy (STED, PALM, STORM), reaching 20 to 30 nanometers. The only option that works on live specimens.
The transmission electron microscope wins on pure resolution numbers, but the “best” microscope is whichever one can image your specific sample at the detail you need. A cryo-EM map of a drug target or a super-resolution video of a living cell can be far more valuable than a 50-picometer image of a crystal, depending on the question you’re trying to answer.