Molecular-scale circuits that link together tiny transistors, wires, and switches to carry out basic computing operations were named this year’s top scientific achievement by the journal Science and its publisher, the American Association for the Advancement of Science (AAAS).

The nanocircuits, named the Breakthrough of the Year by Science‘s editors, leads their list of the top ten scientific developments in 2001. The top ten, chosen for their profound implications for society and the advancement of science, appear in the journal’s 21 December issue.

This year’s leap forward for molecular computing may pave the way to a future filled with tiny but extremely fast and powerful machines that can translate conversations on the fly or delve deep into your body to diagnose an illness. If these circuits can be combined into even more complex architecture, this would “undoubtedly provide computing power to launch scientific breakthroughs for decades to come,” say the Science editors.

The idea of using molecules and small chemical groups as the building blocks of a new generation of computers has been around for years. The quest has become more urgent over the last decade, however, as traditional silicon circuitry continues to shrink towards a point where it can no longer function. Researchers hope to skirt this problem by using molecules and small chemical groups to create billions of devices that could fit easily in the space of a current chip.

After expanding their repertoire of molecular-scale devices in 2000, several research teams took the next critical step and wired the devices together to form working circuits. Several papers published in Science this year detail the progress from communicating nanowires (26 January 2001) to nanotube and nanowire-based logic circuits (9 November 2001) to computational circuits using single-molecule transistors (8 November 2001, Science Express).

Molecular computers with the speed, reliability, and low cost of silicon computers are still years away, but this year’s Breakthrough has researchers charged up about the future.

Science also salutes nine other scientific achievements of 2001. Except for the first runner up, the others are in no particular order.

RNA Revolution: RNA revealed itself to be remarkably versatile in 2001, breaking out of its traditional role of genetic messenger and performing a number of unexpected tasks. Small snippets of RNA have already been shown to silence genes in plants, and this year researchers discovered that this “RNA interference” can happen in mice and humans as well. Cell biologists also uncovered key details of how messenger RNA–the biochemical link between DNA’s information and protein formation–is spliced together. As part of this process, other small RNAs team up with proteins to form a slicing “editor” of forming mRNA, and researchers were surprised to learn that it’s the RNAs that do the cutting, suggesting that RNA can act as an enzyme as well. The molecule’s expanding repertoire has rekindled interest in an “RNA world,” where RNA appeared before DNA in the earliest life forms.

Solar Mystery Solved: Scientific detectives cracked one of their toughest cases this year, solving the problem of the missing solar neutrinos. Neutrinos are particles with virtually no mass, and “electron” neutrinos are a byproduct of the nuclear furnace that drives the sun. In the late 1960s, researchers calculated the number of electron neutrinos that should be streaming away from the sun–but the actual number of detected neutrinos came up short. This year, researchers at the Sudbury Neutrino Observatory in Canada confirmed a hunch that earlier experiments had hinted at: the neutrinos weren’t disappearing, but going incognito. Their experiments established that solar neutrinos convert to two other neutrino flavors (muon and tau) after leaving the sun, thereby escaping detection.

Genomes Galore: An amazing race ended early this year with the simultaneous publication of two draft sequences of the entire human genome, years earlier than anyone had expected at the outset of the sequencing effort. In a surprising twist, the human gene count was low–only 35,000 genes, much less than that of “simple” creatures like the lowly worm C. elegans (although the estimate is being revised upward). Humans were only part of the genome gold rush of 2001: over 60 organisms now boast a sequenced genome, including several disease-causing microbes. Full genomes for research-important animals such as the rat, mouse, zebrafish, and a malaria mosquito are in the works.

Sizzling Superconductors: In 2001, superconductors were hot–well, hotter than expected, at least. The promise of resistance-free electricity transmission suggested by superconductor technology competes with the cold reality that materials become superconducting at far below room temperature. This year, two new superconductors pushed the temperature limits higher. Japanese scientists discovered that magnesium diboride, a simple lab compound, becomes a superconductor at 39 degrees Kelvin, beating the previous high temperature for a metallic compound by a factor of two. Carbon buckyballs expanded with organic molecules became superconductors at 117 degrees Kelvin, suggesting new possibilities for superconducting electronics.

Neuron Traffic Signals: Axons are the spindly arms of nerve cells that reach out to each other to form a neural communications network, and this year scientists gained insight into how axons know where to grow in the developing nervous system. This information could aid in the quest to repair damaged adult nerves. Research in the 1990s identified a number of beckoning and repelling molecular signals that guide wandering axons. In 2001, researchers learned more about how these signals interact and how axons integrate their often-conflicting messages. Other studies demonstrated how these signals are translated into action by the axon.

Cancer In The Crosshairs: 2001 marked the clinical appearance of a new breed of cancer-fighting drugs, specific “smart bombs” targeted to the precise biochemical defects that cause certain cancers. This year, the U.S. Food and Drug Administration approved the drug Gleevec, which inhibits a faulty enzyme associated with one type of leukemia. Enzymes that influence the growth of cancer cells are prominent targets in this new salvo against cancer, and dozens of clinical trials of other defect-correcting drugs are under way worldwide. Many common cancers such as breast, colon and lung cancer, however, involve several gene defects and may require multiple targeted drugs.

Cold Atoms Still Hot: The first Bose-Einstein condensate (BEC), a “superatom” of trapped and supercooled atoms in quantum lockstep, was published in a landmark Science article in 1995. Science authors Eric A. Cornell and Carl E. Wieman were awarded the 2001 Nobel Prize in Physics for their work, sharing the prize with Wolfgang Ketterle of MIT. The buzz about BECs continued this year, with an eye towards a future of atom lasers and ultraprecise measurements. Two French research teams created helium BECs for the first time, and lithium and potassium condensates also debuted. Scientists made strides in manipulating this new state of matter as well, imploding an atomic supernova (“bose nova”), stirring up whirlpool-like structures in the condensates, and trapping BEC clusters to create the first “squeezed” state of atomic matter.

Climate Consensus: It’s official: “most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations,” declared the International Panel on Climate Change (IPCC) this year, pinning the blame on human, rather than natural, causes. New data and new computer modeling led to a better understanding of climate change that confirms the human impact on an unnaturally warm 20th century, although uncertainty remains about the planet’s sensitivity to greenhouse gases. United States President George W. Bush, citing this uncertainty along with reservations about the high cost and unequal burden of implementing emission controls, pulled the U.S. out of the Kyoto Protocol, designed to reduce human-produced greenhouse gases worldwide.

Missing Sink Found: The United States is the world’s top greenhouse gas producer, but it’s also a “sink,” mopping up lots of carbon dioxide from the atmosphere. The size of the U.S. carbon sink has been a matter of dispute, but this year two opposing groups of scientists revised their estimates to come to an agreement on the sink’s extent. Atmospheric researchers shrunk their prediction of a giant sink with new analyses of data from a longer time period, while carbon counters on the land found new hiding places for carbon that upped their estimates of overall sink size. The result: a sink that absorbs around one-third of current U.S. emissions but may show signs of slowing within the next century.

Science After September 11: The international science and engineering community faces a “sobering new era” after the September 11 terrorist attacks on the United States, challenged by shrinking budgets, information-sharing and collaboration restrictions, and shifting research priorities. In a special section devoted to “The Year of Living Dangerously,” Science examines the consequences of the attacks for scientists, particularly regarding bioweapons and sweeping new security for top labs and universities.

The flip side of Science‘s top ten is its Breakdowns of the Year–less-than-inspiring moments in science and science policy in 2001. Featured this year are budget problems surrounding the International Space Station and the “scientific vacuum” in the Bush Administration.

Best Bets for Hot News in 2002: As in previous years, Science has chosen six hot topics to watch in 2002. This year, their choices include: U.S. stem cell research in private industry and abroad, the field of proteomics, the maiden voyage of several new telescopes, multifactorial diseases, optical clocks and fundamental constants, and visualizing complex molecules and biological interactions. The editors also check in on the 2000 scorecard to see how well they did with last year’s predictions.

As the world’s leading peer-reviewed general science journal, Science is uniquely suited to compile the most authoritative list of the year’s scientific accomplishments. The top ten list is the thirteenth since Science inaugurated the feature. Editor-In-Chief Donald Kennedy writes about the Breakthrough of the Year report in the 21 December issue’s editorial, which is available upon request.


Founded in 1880 by Thomas A. Edison, Science has been the official journal of the American Association for the Advancement of Science (AAAS) since 1900. The nonprofit AAAS is the world’s largest general scientific organization.