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categories: ["nanomedicine"]categories: ["nanomedicine"]tags: ["nanotechnology", "mechanosynthesis", "manufacturing", "molecular machines", "drexler", "chemistry"]tags: ["nanotechnology", "mechanosynthesis", "manufacturing", "molecular machines", "drexler", "chemistry"]summary: "A proposed machine that would build objects by positioning individual atoms, central to Drexler's nanotechnology programme and disputed by chemists since the 1990s."summary: "A proposed machine that would build objects by positioning individual atoms, central to Drexler's nanotechnology programme and disputed by chemists since the 1990s."updated: "2026-07-27"updated: "2026-08-23"issues: ["Claims about current hydrogen depassivation lithography work carry no citation."]------ ```infobox```infoboxlines 70–82 → 69–8155 unchanged lines not shown
Solution chemistry went a different way. Supramolecular chemists built rotaxanes, catenanes, and light-driven rotary motors, work recognised by the 2016 Nobel Prize in Chemistry. David Leigh's group built an artificial machine that reads a molecular strand and assembles a peptide in the specified sequence — an explicit ribosome mimic, and the strongest existing demonstration that programmed molecular construction is possible.[^leigh2013] It operates in solution by self-assembly, not by mechanical positioning.Solution chemistry went a different way. Supramolecular chemists built rotaxanes, catenanes, and light-driven rotary motors, work recognised by the 2016 Nobel Prize in Chemistry. David Leigh's group built an artificial machine that reads a molecular strand and assembles a peptide in the specified sequence — an explicit ribosome mimic, and the strongest existing demonstration that programmed molecular construction is possible.[^leigh2013] It operates in solution by self-assembly, not by mechanical positioning. [[dna-nanotechnology]] delivered the most useful form of programmable construction: structures folded to specification from sequence, at nanometre resolution, in a test tube. The addressability is real, the material is soft, and the products are shapes rather than machines. Writing whole [[synthetic-genomes]] extended the same logic to the largest molecules anyone has assembled to specification, again by biological rather than mechanical means. [[ai-protein-design|Learned models of protein structure]] have taken it furthest: specifying a fold that does not occur in nature and obtaining a molecule that adopts it is now a practical exercise, and it is atomic precision reached through sequence rather than through positioning.[[dna-nanotechnology]] delivered the most useful form of programmable construction: structures folded to specification from sequence, at nanometre resolution, in a test tube. The addressability is real, the material is soft, and the products are shapes rather than machines. Writing whole [[synthetic-genomes]] extended the same logic to the largest molecules anyone has assembled to specification, again by biological rather than mechanical means. [[ai-protein-design|Learned models of protein structure]] have taken it furthest: specifying a fold that does not occur in nature and obtaining a molecule that adopts it is now a practical exercise,[^watson2023] and it is atomic precision reached through sequence rather than through positioning. The technologies that turned nanoscale control into medicine — [[lipid-nanoparticles]], antibody-drug conjugates, the particles discussed in [[targeted-drug-delivery]] — use none of this. They are formulations whose behaviour comes from surface chemistry and biodistribution. The devices that move under external control, surveyed in [[microrobots-in-medicine]], are machined by conventional lithography and assembled at scales a thousand times coarser than the assembler debate concerns.The technologies that turned nanoscale control into medicine — [[lipid-nanoparticles]], antibody-drug conjugates, the particles discussed in [[targeted-drug-delivery]] — use none of this. They are formulations whose behaviour comes from surface chemistry and biodistribution. The devices that move under external control, surveyed in [[microrobots-in-medicine]], are machined by conventional lithography and assembled at scales a thousand times coarser than the assembler debate concerns. ## Where the question stands## Where the question stands As of 2026 there is no assembler, no mechanosynthetic tooltip in the laboratory, and no funded programme attempting one at scale. A small literature continues to publish computational studies of proposed diamond-mechanosynthesis reactions, and a handful of groups pursue atomically precise fabrication on silicon surfaces using hydrogen depassivation lithography, which is atomically precise patterning rather than three-dimensional construction.As of writing no assembler exists, no mechanosynthetic tooltip has been demonstrated in a peer-reviewed report, and no large programme is funded to attempt one. A small literature continues to publish computational studies of proposed diamond-mechanosynthesis reactions. The nearest experimental work is hydrogen depassivation lithography, in which a scanning tunnelling microscope strips hydrogen atoms one at a time from a passivated silicon surface: one group used it to write rewriteable atomic memories that survive room temperature,[^achal2018] another to place individual dopant atoms and build single-atom transistors around them.[^wyrick2019] Both are atomically precise patterning of a surface rather than three-dimensional construction, and neither forms a bond with a positioned reactive tip. The strongest argument for the concept remains the ribosome: an existence proof that programmable, error-corrected, atom-by-atom construction of complex covalent structures is physically possible, because it happens continuously in every living cell. The strongest argument against is that biology achieves this with soft, water-based, self-assembling machinery of a kind quite unlike a diamondoid factory, and that no one has shown how to get from one to the other.The strongest argument for the concept remains the ribosome: an existence proof that programmable, error-corrected, atom-by-atom construction of complex covalent structures is physically possible, because it happens continuously in every living cell. The strongest argument against is that biology achieves this with soft, water-based, self-assembling machinery of a kind quite unlike a diamondoid factory, and that no one has shown how to get from one to the other. lines 84–90 → 83–891 unchanged line not shown
## Outlook## Outlook The question that would move the field is narrow and experimental: can a designed tooltip transfer a carbon dimer to a specified site on a diamond surface and withdraw cleanly, repeatedly, under positional control? It has been proposed in computational form for two decades and never attempted seriously in a laboratory. Until someone tries, the debate over assemblers remains a disagreement about extrapolation rather than about data, and the [[technology-readiness-level]] of everything downstream — including every proposal in this wiki that assumes atomically precise machinery — stays pinned at the bottom of the scale.The question that would move the field is narrow and experimental: can a designed tooltip transfer a carbon dimer to a specified site on a diamond surface and withdraw cleanly, repeatedly, under positional control? It has been proposed in computational form for two decades, and no laboratory attempt at it has been reported. Until someone tries, the debate over assemblers remains a disagreement about extrapolation rather than about data, and the [[technology-readiness-level]] of everything downstream — including every proposal in this wiki that assumes atomically precise machinery — stays pinned at the bottom of the scale. ## See also## See also lines 106–109 → 105–11115 unchanged lines not shown
[^eigler1990]: `paper` Eigler, D.M. and Schweizer, E.K. "Positioning single atoms with a scanning tunnelling microscope." *Nature*, 1990. {The xenon atoms were slid across a nickel surface at liquid-helium temperature in ultra-high vacuum; no covalent bond was made or broken.}[^eigler1990]: `paper` Eigler, D.M. and Schweizer, E.K. "Positioning single atoms with a scanning tunnelling microscope." *Nature*, 1990. {The xenon atoms were slid across a nickel surface at liquid-helium temperature in ultra-high vacuum; no covalent bond was made or broken.}[^leigh2013]: `paper` Lewandowski, B. et al. "Sequence-specific peptide synthesis by an artificial small-molecule machine." *Science*, 2013. {The machine works in solution and is driven along its track by thermal motion, so it demonstrates programmed sequence rather than positional control.}[^leigh2013]: `paper` Lewandowski, B. et al. "Sequence-specific peptide synthesis by an artificial small-molecule machine." *Science*, 2013. {The machine works in solution and is driven along its track by thermal motion, so it demonstrates programmed sequence rather than positional control.}[^drexler2013]: `book` Drexler, K.E. *Radical Abundance: How a Revolution in Nanotechnology Will Change Civilization.* PublicAffairs, 2013.[^drexler2013]: `book` Drexler, K.E. *Radical Abundance: How a Revolution in Nanotechnology Will Change Civilization.* PublicAffairs, 2013.[^achal2018]: `paper` Achal, R. et al. "Lithography for robust and editable atomic-scale silicon devices and memories." *Nature Communications*, 2018. {Patterning and repassivation of a hydrogen-terminated surface; the structures are arrangements of missing hydrogen atoms, and no new covalent bond is formed by a positioned tool.}[^wyrick2019]: `paper` Wyrick, J. et al. "Atom-by-Atom Fabrication of Single and Few Dopant Quantum Devices." *Advanced Functional Materials*, 2019. {The dopants are placed by lithographic patterning followed by a gas-phase reaction and overgrowth, not by mechanically positioning an atom onto a workpiece.}[^watson2023]: `paper` Watson, J.L. et al. "De novo design of protein structure and function with RFdiffusion." *Nature*, 2023. {Precision is achieved through the designed amino-acid sequence and the protein's own folding; nothing is positioned.} removed, struck through added, underlinedLine numbers count the serialised markdown of each revision, frontmatter included.
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