Nanotechnology: The nanoscale and nanomaterials

The answer is the red blood cell. One nanometre is 10^-9 metre, a billionth of a metre, and ISO treats the nanoscale as roughly 1 to 100 nm. The DNA double helix is about 2 nm wide, the lipid bilayer of a cell membrane is about 5 nm thick, and the colloidal gold particles used in lateral-flow test strips are typically a few tens of nanometres across, so all three are nano-sized. A human red blood cell, however, is about 7 to 8 micrometres in diameter, that is about 7,000 to 8,000 nm, which is roughly seventy times larger than the upper limit of the nanoscale. It is a microscale object that can be seen under an ordinary light microscope. Converting every size into nanometres before comparing is the safest way to handle such questions.

The answer is Richard Feynman. On 29 December 1959, at the annual meeting of the American Physical Society held at the California Institute of Technology, physicist Richard Feynman gave the talk 'There's Plenty of Room at the Bottom'. He asked why the whole Encyclopaedia Britannica could not be written on the head of a pin and imagined manipulating and controlling things atom by atom, without using the word nanotechnology. The word itself came later: the Japanese engineer Norio Taniguchi coined 'nano-technology' in 1974 for processing materials to nanometre precision. K. Eric Drexler popularised molecular nanotechnology in his 1986 book Engines of Creation, and Sumio Iijima reported carbon nanotubes in 1991. Keeping the order straight (Feynman 1959, Taniguchi 1974, Drexler 1986, Iijima 1991) helps in chronology questions.

Statements 1 and 2 are correct. Kellar Autumn and colleagues showed (Nature 2000; PNAS 2002) that each gecko toe carries millions of setae that split into hundreds of nanoscale spatulae; their sticking power comes from van der Waals forces, since it works equally on water-loving and water-repelling surfaces, ruling out glue, suction or capillary action. The blue of Morpho butterflies is structural colour: ridges on the scales carry stacked chitin- and-air lamellae that reflect blue light by interference and diffraction, while melanin below only absorbs other colours to deepen the effect. Statement 3 is the reverse of the truth: Barthlott and Neinhuis (1997) showed that the lotus leaf is superhydrophobic because of a rough, hierarchical micro- and nanoscale wax texture; droplets bead up, roll off and carry dirt away (the lotus effect).

Statements 1 and 3 are correct. ISO 80004-1:2023, the core vocabulary prepared by ISO/TC 229 (the nanotechnologies committee set up in 2005), defines the nanoscale as the length range from approximately 1 nm to 100 nm. It defines a nano-object as a discrete piece of material with one, two or three external dimensions in the nanoscale. So a nanoplate or a graphene-like sheet (one dimension nano), a nanofibre or nanotube (two dimensions nano) and a nanoparticle (all three dimensions nano) are all nano-objects; statement 2 is therefore wrong. The standard notes that the lower limit of about 1 nm is approximate and is there mainly to avoid single atoms and small groups of atoms being labelled nano-objects or elements of nanostructures, which makes statement 3 correct.

The answer is the number-based 50% rule. The Commission Recommendation of 10 June 2022 (2022/C 229/01), which replaced the 2011 recommendation, defines a nanomaterial as a natural, incidental or manufactured material consisting of solid particles, alone or in aggregates or agglomerates, where 50% or more of the particles in the number- based size distribution have one or more external dimensions in the range 1 nm to 100 nm (with extra criteria for elongated and plate-like particles). Three features matter. First, the count is by number, not by mass: a few large particles can dominate the mass while most particles by number are tiny. Second, only one external dimension needs to be nanoscale. Third, the origin does not matter, so natural and incidental materials are covered too. The 2022 text also dropped the 2011 option of lowering the threshold.

Three pairs are correct. Norio Taniguchi of the Tokyo University of Science coined 'nano-technology' in 1974 to describe processing materials to nanometre precision (pair 1). Sumio Iijima of NEC reported multiwalled carbon nanotubes in Nature in 1991, followed by single-walled tubes in 1993 (pair 2). Paul Rothemund introduced scaffolded DNA origami in Nature in 2006, folding a long single strand of viral DNA into chosen shapes with about 200 short 'staple' strands (pair 4). Pair 3 is wrong: Harold Kroto shared the 1996 Nobel Prize in Chemistry with Robert Curl and Richard Smalley for the 1985 discovery of fullerenes (C60, buckminsterfullerene). Liposomes were first described by Alec Bangham in Cambridge in the mid-1960s.

Two statements are correct. The Lycurgus Cup, a fourth-century Roman glass cage cup in the British Museum, is dichroic: green in reflected light and wine-red in transmitted light. Analyses summarised by Freestone and colleagues (Gold Bulletin, 2007) traced this to roughly 50 to 100 nm particles of a silver-gold alloy (with some copper) dispersed in the glass, so statement 1 is correct. In 2006 Reibold and co-workers reported in Nature that a seventeenth-century Damascus sabre contained carbon nanotubes and cementite nanowires, offering one explanation for the legendary blades' properties (statement 2). Statement 3 is wrong: the effect in the cup is plasmonic, caused by collective oscillations of conduction electrons in metal nanoparticles that absorb and scatter particular colours; quantum confinement in semiconductor nanocrystals is a different mechanism used in quantum dots.

All three statements are correct. In metal nanoparticles much smaller than the wavelength of light, the free electrons oscillate together when light strikes them; at a particular frequency this surface plasmon resonance makes the particles absorb strongly. For small spherical gold particles (roughly 10 to 20 nm) the peak lies near 520 nm, in the green, so the transmitted light and the suspension look ruby red. As the particles become larger or clump together the resonance red-shifts and broadens, and the colour moves to purple and then blue, which is why aggregation can be read as a colour change in sensors. Commercial lateral-flow tests, including hCG pregnancy strips, carry antibodies attached to colloidal gold; when the target hormone is present the gold collects at the test line and makes it visible as a red or pink band. These are classic examples of nanotechnology in diagnostics.

Both are correct (c). Nanoparticles such as liposomes, dendrimers and gold particles can carry drugs straight to diseased cells like tumours, sparing healthy tissue (1). They also act as non-viral carriers of genes in gene therapy (2).

The lipid nanoparticles used in mRNA COVID-19 vaccines apply the same idea, wrapping fragile genetic material to carry it into cells. Nano-based diagnostics can also detect diseases earlier. Notice how a physics idea, the special behaviour of matter at the nanoscale, is reshaping medicine, though safety and toxicity questions remain.

Answer as per the official UPSC answer key.

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