Advanced Nanotechnology Engineering interview questions

125 questions with answers (NAN-301 to NAN-425). Try each one aloud before reading the answer.

Nanoscience Fundamentals

NAN-301 · A 5 nm gold catalyst loses activity after a few hours at 300 °C. What is happening and how would you fix it?

Small particles have high surface energy and sinter or undergo Ostwald ripening at elevated temperature, losing surface area and active sites. Anchor particles on a strongly interacting support (CeO₂, TiO₂), encapsulate them in porous shells, alloy them, or operate at lower temperature.

NAN-302 · How would you design an experiment to show a size-dependent property in a nanomaterial?

Synthesise a series of particles with narrow size distributions at several sizes (verified by TEM), keep composition, shape and surface chemistry constant, measure the property (melting point, optical absorption, catalytic rate) and plot it against size or inverse size. Controls rule out surface-ligand effects.

NAN-303 · How do you decide whether a property change is due to size or to surface chemistry?

Compare particles of the same size with different ligands, and of different size with the same ligand; use XPS and FTIR to characterise surfaces. If the property follows surface coverage rather than core size, surface chemistry dominates.

NAN-304 · How would you estimate the melting point depression of 4 nm tin particles?

Use the Gibbs–Thomson relation Tm(r) ≈ Tm,bulk(1 − 2σ/(ΔHf·ρ·r)) with surface energy, latent heat and density data. Very small particles can melt tens of degrees below bulk; DSC on size-selected particles verifies the prediction.

NAN-305 · How would you prevent agglomeration when adding nanoparticles to a polymer?

Functionalise particle surfaces to match the polymer (silane coupling, grafted chains), use high-shear mixing or ultrasonication in a solvent before compounding, and add dispersants. Check dispersion by TEM and rheology.

NAN-306 · How do you evaluate whether a nanocomposite truly benefits from the nanoscale filler?

Compare with micro-filler and unfilled controls at equal loading, measure mechanical, thermal or barrier properties, and correlate with dispersion quality. Benefits often depend on good dispersion and interfacial bonding, not just size.

NAN-307 · How do you scale up a nanoparticle synthesis from grams to kilograms?

Maintain mixing and heat transfer conditions (consider continuous flow reactors), control reagent addition rates and temperature uniformity, monitor size distribution online, and address purification, solvent recovery and safety. Batch-to-batch reproducibility is the key challenge.

NAN-308 · How would you choose between a top-down and bottom-up approach for producing nanowires?

Top-down lithography gives precise placement and integration with circuits but is limited in feature size and costly; bottom-up (VLS growth) gives high-quality crystalline wires cheaply but poor placement control. The application decides.

NAN-309 · How would you report nanoparticle size so that results from different labs can be compared?

State the technique and what it measures (TEM number-weighted core size, DLS intensity-weighted hydrodynamic size, BET surface-equivalent size), give the full distribution (mean, standard deviation or PDI, number of particles counted), sample preparation and dispersion conditions. A single number without method is not comparable.

NAN-310 · How would you design a nanostructured surface to be superhydrophobic?

Combine low surface energy coatings (fluorinated or silane) with hierarchical micro- and nano-roughness to achieve a Cassie-Baxter state where air is trapped under droplets, giving contact angles above 150° and low roll-off angles.

NAN-311 · How do you assess the stability of a nanoparticle dispersion over time?

Monitor particle size by DLS, zeta potential, sedimentation and UV-Vis absorbance over storage time and under different temperatures and ionic strengths.

Quantum & Size Effects

NAN-312 · How would you tune quantum dot emission from green to red?

Increase the dot size for a given material (larger dots have smaller band gaps), or change composition (CdSe to CdTe, alloyed dots), or use core-shell structures for type-II band alignment. Control growth time and temperature during synthesis.

NAN-313 · How do you explain why a 2 nm gold particle is not plasmonic?

Below about 2 nm, gold has discrete electronic levels (molecular-like clusters), so collective electron oscillations (plasmons) disappear and optical properties are dominated by discrete transitions.

NAN-314 · How would you measure the band gap of a quantum dot sample?

Use UV-Vis absorption to find the first excitonic peak, and photoluminescence for emission; Tauc plots can estimate optical band gap. Compare with theoretical predictions from size.

NAN-315 · How does quantum confinement affect solar cell design?

Quantum dots allow tunable band gaps to match the solar spectrum, multiple exciton generation and tandem designs, but surface defects and charge transport between dots must be managed.

NAN-316 · How do you calculate the tunnelling current dependence for an STM?

Tunnelling current I ∝ exp(−2κd), with κ = √(2mφ)/ħ. For typical work functions, the current changes about tenfold per 0.1 nm change in gap, giving STM its atomic resolution.

NAN-317 · How would you use superparamagnetic nanoparticles for magnetic separation?

Use particles above the superparamagnetic limit for strong response but small enough to avoid remanence, coat with functional groups to bind targets, and apply a magnetic field gradient to separate them.

NAN-318 · How does reduced dimensionality change thermal transport, and how can it be exploited?

Phonon scattering at boundaries reduces thermal conductivity in nanowires and superlattices. This is exploited in thermoelectrics to increase ZT while maintaining electrical conductivity.

NAN-319 · How would you observe Coulomb blockade experimentally?

Fabricate a small quantum dot or metal island coupled by tunnel junctions, cool to low temperature where charging energy exceeds thermal energy, and measure current-voltage characteristics showing steps or oscillations with gate voltage.

NAN-320 · How do you design plasmonic nanoparticles for near-infrared absorption?

Use gold nanorods with high aspect ratio, nanoshells or nanostars, tuning shape and size so the plasmon resonance shifts into the NIR window (650–900 nm), where tissue is more transparent.

NAN-321 · Quantum dots from a new batch emit 15 nm redder than the previous batch. What would you check?

A red shift usually means larger dots or a broader size distribution, so check TEM size and the first absorption peak, then review reaction temperature, precursor ratios, injection speed and growth time. Shell growth or ligand changes can also shift emission slightly.

NAN-322 · How does ballistic transport affect device design?

When channel length is shorter than mean free path, carriers travel without scattering, increasing speed. Design must consider contact resistance and quantum conductance limits.

Top-Down Fabrication & Lithography

NAN-323 · Patterned lines from e-beam lithography come out wider than designed and merge at tight pitch. How would you fix it?

This is the proximity effect from backscattered electrons. Apply proximity effect correction (dose modulation by pattern density), use thinner resist or a higher accelerating voltage to reduce forward scattering, and optimise development time and temperature.

NAN-324 · How would you fabricate a 20 nm gap between two gold electrodes?

Options: e-beam lithography with careful proximity correction and lift-off, electromigration break junctions, shadow evaporation at an angle, or FIB milling of a narrow line. Verify the gap by SEM and electrical measurements.

NAN-325 · How do you choose between wet and dry etching for a silicon nanostructure?

Wet etching is cheap and selective but mostly isotropic (except crystallographic KOH etching) and can undercut; dry (reactive ion) etching gives anisotropic, vertical profiles needed for high aspect ratio nanostructures, at higher equipment cost.

NAN-326 · How would you reduce line edge roughness in EUV-patterned features?

Optimise resist chemistry (chemically amplified or metal-oxide resists), dose (higher dose reduces shot noise), post-exposure bake and development, and use smoothing processes such as plasma treatment or hard-mask trimming.

NAN-327 · How would you design a process flow to make a MEMS cantilever with a nanoscale tip?

Pattern and etch the tip using anisotropic KOH etching or oxidation sharpening, deposit and pattern the cantilever layer, then release with a sacrificial layer etch and critical point drying to avoid stiction.

NAN-328 · How do you get good lift-off with a thick metal film?

Use a bilayer resist with an undercut profile so the metal film breaks cleanly at the edges, keep metal thickness below about one-third of resist thickness, evaporate with directional deposition, and soak in a suitable solvent with gentle agitation.

NAN-329 · How would you pattern features below the diffraction limit without EUV?

Use multiple patterning (SADP or SAQP), immersion lithography with resolution enhancement (OPC, phase-shift masks), e-beam lithography for small areas, or nanoimprint lithography for repeated patterns.

NAN-330 · How would you troubleshoot poor adhesion of a thin film on silicon?

Check surface cleaning (RCA clean, oxygen plasma), native oxide, use adhesion layers (Ti or Cr under gold), control film stress, and verify with tape tests or scratch tests.

NAN-331 · How do you control the sidewall profile in deep reactive ion etching?

Balance the passivation and etch steps in the Bosch process, adjusting cycle times, gas flows, pressure and bias power to control scalloping, tapering and undercut.

NAN-332 · How would you use nanoimprint lithography for large-area patterning?

Fabricate a master mould by e-beam lithography, replicate it in soft or hard stamps, imprint into a thermal or UV-curable resist, and transfer the pattern by etching. Defects and stamp wear must be managed.

NAN-333 · How do you minimise contamination in a nanofabrication cleanroom process?

Follow strict gowning, use dedicated tools for metal-free processes, clean wafers before critical steps, control particles and humidity, and monitor yields and defect rates.

Bottom-Up Synthesis

NAN-334 · Colloidal nanoparticles show a broad size distribution. How would you narrow it?

Separate nucleation from growth (hot injection or LaMer-type burst nucleation), control temperature and precursor addition, use suitable ligands, exploit size focusing during growth, and apply size-selective precipitation afterward.

NAN-335 · How would you grow vertically aligned silicon nanowires?

Use VLS growth with gold catalyst droplets on a (111) silicon substrate, control temperature and silane partial pressure, and pattern catalyst positions for alignment and placement.

NAN-336 · How do you control ALD film thickness precisely?

Thickness grows per cycle (growth per cycle) in a self-limiting manner; choose number of cycles and keep temperature within the ALD window to maintain consistent growth.

NAN-337 · How would you synthesise monodisperse silica nanoparticles of 100 nm?

Use the Stöber process, adjusting ammonia, water and TEOS concentrations and temperature to tune size, then purify by centrifugation and characterise by TEM and DLS.

NAN-338 · How would you make gold nanorods with a specific aspect ratio?

Use seed-mediated growth with CTAB surfactant and silver nitrate, adjusting silver ion concentration and seed amount to tune aspect ratio and plasmon resonance.

NAN-339 · How do you scale up graphene oxide synthesis safely?

Control exothermic oxidation (Hummers' method) by slow addition of oxidisers and temperature control, handle strong acids and oxidisers safely, and manage waste.

NAN-340 · How would you produce a metal-organic framework with high accessible surface area?

Use solvothermal synthesis with controlled metal-to-linker ratio, modulators and temperature to get crystalline material, then activate it carefully: exchange the high-boiling solvent for a volatile one and heat under vacuum (or use supercritical CO₂ drying) so the pores don't collapse. Confirm with PXRD and a BET isotherm.

NAN-341 · How is a DNA origami structure designed and verified?

Route a long single-stranded scaffold (often M13, about 7,249 bases) through the target shape with software such as caDNAno, generate the short staple strands that fold it, anneal the mixture with a slow temperature ramp in Mg²⁺ buffer, purify excess staples, and image the result by AFM or TEM.

NAN-342 · How would you use block copolymer self-assembly to pattern 15 nm features?

Pick a copolymer whose Flory–Huggins χ and molecular weight give the target pitch (high-χ polymers for sub-10 nm), guide orientation with chemical or topographic pre-patterns, anneal thermally or with solvent vapour to order the domains, remove one block selectively, and transfer the pattern by etching.

NAN-343 · Why use a microfluidic flow reactor for nanoparticle synthesis?

Small channels give fast, uniform mixing and heat transfer, so every particle sees the same conditions and nucleation is better controlled. Residence time is set by flow rate, reproducibility improves, and output is increased by running reactors in parallel rather than enlarging one vessel.

NAN-344 · How do you choose capping ligands for nanoparticles used in water?

Choose hydrophilic ligands that bind strongly to the surface (thiols on gold, phosphonates or catechols on oxides) and give charge (citrate) or steric (PEG) stability at the needed pH and salt level. Add functional end groups if targeting or bioconjugation is needed, and check that ligands don't desorb over time.

Carbon Nanomaterials (CNT, Graphene, Fullerenes)

NAN-345 · CVD graphene transferred to SiO₂ shows low mobility. What could be wrong and how would you improve it?

Grain boundaries, wrinkles, PMMA residues from transfer, charged impurities in SiO₂ and doping all scatter carriers. Grow larger single-crystal domains, use cleaner transfer (dry or polymer-free), anneal to remove residues, and use hBN encapsulation as substrate and top layer.

NAN-346 · How would you separate semiconducting from metallic carbon nanotubes for transistors?

Use density-gradient ultracentrifugation, selective polymer wrapping (e.g. polyfluorene derivatives), gel chromatography or aqueous two-phase extraction, then confirm purity by absorption spectroscopy and device on/off ratios.

NAN-347 · How do you make a conductive transparent film from CNTs or graphene?

Disperse CNTs or graphene with surfactants, deposit by spraying, rod coating or filtration-transfer, remove surfactant, and dope chemically (e.g. HNO₃) to lower sheet resistance; balance transmittance and sheet resistance for the application.

NAN-348 · How would you improve load transfer in a CNT-epoxy composite?

Functionalise CNTs (carboxyl or amine groups) to bond with the matrix, improve dispersion with sonication and surfactants, align tubes if directional strength is needed, and avoid excessive functionalisation that damages tube structure.

NAN-349 · How do you use Raman spectroscopy to judge defects in graphene?

The D/G intensity ratio indicates defect density, the 2D peak shape and position distinguish monolayer from multilayer, and peak shifts reveal strain and doping. Map across the sample for uniformity.

NAN-350 · How would you make a graphene-based gas sensor?

Fabricate graphene channels with electrodes, functionalise with receptors or decorate with nanoparticles for selectivity, measure resistance change on gas exposure, and handle humidity and baseline drift.

NAN-351 · How would you produce reduced graphene oxide with high conductivity?

Reduce GO chemically (hydrazine, ascorbic acid, HI) and/or thermally at high temperature to remove oxygen groups and restore sp² structure, then check C/O ratio by XPS and conductivity measurements.

NAN-352 · How do CNTs improve a lithium-ion battery electrode?

A small amount of CNTs forms a long-range conductive network that links active particles better than carbon black, improving rate capability, and it holds particles together as they swell and shrink, reducing cracking. Good dispersion and the right binder are essential, and CNT cost must be justified.

NAN-353 · How would you grow a vertically aligned CNT forest?

Deposit a thin iron catalyst film on an alumina buffer layer, anneal in hydrogen to form nanoparticles, then run CVD with ethylene or acetylene at about 700–800 °C. A trace of water vapour ("super-growth") removes amorphous carbon from the catalyst, allowing millimetre-tall, densely packed forests.

NAN-354 · How do you assess the purity of a CNT sample?

TGA in air measures residual metal catalyst as ash and shows the oxidation temperature of different carbons; Raman gives the D/G ratio for defects and RBM peaks for diameter; TEM shows amorphous carbon and tube walls; and absorption spectra estimate semiconducting versus metallic content.

NAN-355 · How are fullerenes used in organic solar cells, and what limits them?

Fullerene derivatives such as PCBM act as electron acceptors blended with a donor polymer in a bulk heterojunction, providing efficient charge separation and electron transport. They absorb little visible light and have limited energy-level tuning, so non-fullerene acceptors now give higher efficiencies.

Nanoparticles & Quantum Dots

NAN-356 · How would you design quantum dots for bioimaging with low toxicity?

Use cadmium-free cores (InP/ZnS or carbon dots), thick protective shells, and biocompatible coatings (PEG, zwitterionic ligands), keeping hydrodynamic size small for clearance. Test stability, photoluminescence quantum yield and cytotoxicity.

NAN-357 · How do you raise the photoluminescence quantum yield of quantum dots?

Passivate surface trap states with an epitaxial shell (e.g. ZnS on CdSe), use graded or alloyed shells to reduce lattice strain, optimise ligand coverage and avoid oxidation.

NAN-358 · How would you functionalise gold nanoparticles with antibodies?

Use thiol-PEG linkers with carboxyl or NHS ester groups to covalently attach antibodies via EDC/NHS chemistry, block remaining sites to reduce non-specific binding, and verify with UV-Vis shift and binding assays.

NAN-359 · How do you design magnetic nanoparticles for efficient MRI contrast?

Choose iron oxide size and crystallinity for high magnetisation, coat with biocompatible polymers, control hydrodynamic size and aggregation, and measure relaxivity (r₂).

NAN-360 · How would you manufacture silver nanoparticles for antimicrobial coatings?

Reduce silver salts with controlled reducing agents and stabilisers, control size and shape, incorporate into a coating matrix, and manage release rate and environmental impact.

NAN-361 · How do you stop copper nanoparticles from oxidising?

Copper oxidises quickly in air because of its high surface area. Protect it with strongly bound ligands or shells (carbon, silica, silver or polymer), synthesise and store under inert atmosphere, and use antioxidants such as ascorbic acid; printed copper inks are often sintered under reducing gas or by photonic curing.

NAN-362 · What must be solved to use perovskite nanocrystals in displays?

Their narrow, bright emission gives excellent colour purity, but they degrade with moisture, heat, light and polar solvents, and lead content raises regulatory concerns. Ligand engineering, shell or matrix encapsulation (glass, polymer) and lead-free compositions are used to improve stability.

NAN-363 · How do you control the size of iron oxide nanoparticles in thermal decomposition?

Decompose an iron precursor (such as iron oleate) in a high-boiling solvent with oleic acid; size grows with longer reaction times, higher temperatures and higher precursor-to-surfactant ratios, and seeded growth gives larger, monodisperse particles. Heating rate controls the nucleation burst.

NAN-364 · How do you measure the concentration of nanoparticles in a suspension?

Nanoparticle tracking analysis counts particles per mL directly, UV-Vis with a known extinction coefficient gives molar particle concentration for gold or silver, and ICP-MS gives total elemental mass, which can be converted to particle number using TEM size. Each method has different assumptions, so state which one is used.

NAN-365 · How would you develop a gold-nanoparticle lateral flow test?

Conjugate gold nanoparticles to a detection antibody, stripe a capture antibody (test line) and an anti-species antibody (control line) on nitrocellulose, and optimise conjugate pad, membrane pore size, buffer and particle size for sensitivity and flow time. Validate with known positives and negatives to set the detection limit.

Characterization Techniques

NAN-366 · DLS reports 180 nm for particles that TEM shows as 40 nm. How do you interpret this?

DLS measures intensity-weighted hydrodynamic diameter, including ligands and solvation shells, and is heavily biased toward large particles and agglomerates (scattering scales roughly with d⁶). The sample is probably partly agglomerated in solution; check PDI, filter or sonicate, and compare with NTA or number-weighted distributions.

NAN-367 · How would you build a characterisation plan for a new nanoparticle drug carrier?

Measure size and distribution (DLS, NTA, TEM), surface charge (zeta potential), morphology, drug loading and encapsulation efficiency, release kinetics, stability in serum, sterility and endotoxin. Combine orthogonal methods because each sees a different aspect.

NAN-368 · How do you confirm the composition of a core-shell nanoparticle?

Use STEM-EDS line scans or elemental mapping to show element distribution, HAADF contrast for heavier cores, XPS for surface composition, and XRD for crystal phases of core and shell.

NAN-369 · How do you avoid artefacts when imaging soft nanomaterials in TEM?

Use low-dose imaging, cryo-TEM to preserve hydrated structures, appropriate staining for contrast, and avoid drying artefacts that cause aggregation on the grid.

NAN-370 · How would you measure the thickness of a 2D material flake?

Use AFM step height (noting substrate and adsorbate effects), Raman signatures (e.g. 2D peak for graphene, peak separation for MoS₂), optical contrast calibrated on known samples, and TEM cross-sections for precise measurements.

NAN-371 · How do you use XPS to verify surface functionalisation?

Look for new elements (e.g. N or S from ligands), check chemical shifts in core-level peaks (C 1s components for C–O, C=O), and quantify atomic ratios. XPS probes only the top few nanometres.

NAN-372 · How do you measure the mechanical properties of a single nanowire?

Use in-situ SEM/TEM tensile testing with MEMS devices, AFM bending tests, or resonance methods, accounting for clamping and size effects.

NAN-373 · How do you choose between SEM and AFM for surface roughness?

AFM gives true 3D height data with sub-nanometre vertical resolution for roughness; SEM gives faster imaging of larger areas but not quantitative height without special methods.

NAN-374 · How do you validate a new nanoparticle sizing method?

Compare against reference materials with certified sizes (e.g. NIST gold or polystyrene), check repeatability and inter-method agreement, and document measurement uncertainty.

NAN-375 · How would you detect trace nanoparticles in an environmental water sample?

Use single-particle ICP-MS for size and number of metal particles, concentrate the sample if needed, and confirm with electron microscopy and EDS.

Nanoelectronics & Spintronics

NAN-376 · How do you decide between FinFET and gate-all-around nanosheet transistors for a node?

GAA nanosheets give better electrostatic control and allow width tuning for drive current, enabling further scaling below the FinFET limit, but are harder to fabricate (selective etching, inner spacers). The choice balances performance, leakage, density and process maturity.

NAN-377 · How would you reduce contact resistance in a 2D semiconductor transistor?

Use low-work-function or semimetal contacts (e.g. bismuth for MoS₂), edge contacts, phase engineering to metallic phases at contacts, and clean interfaces to avoid Fermi-level pinning.

NAN-378 · How would you design an MRAM cell for low write energy?

Use perpendicular MTJs with high TMR, reduce critical switching current through damping and anisotropy engineering, consider SOT switching, and balance thermal stability for data retention.

NAN-379 · The TMR of CoFeB/MgO junctions collapses after a 450 °C back-end anneal. What is likely happening?

Moderate annealing crystallises MgO and CoFeB into the coherent bcc(001) structure that gives high TMR, but excessive temperature drives boron and other elements (such as Ta from the cap) to diffuse into the barrier and interfaces, degrading spin-filtering. Use diffusion barriers, boron getters and a lower thermal budget, and check interfaces by TEM/EELS.

NAN-380 · How would you test a memristor for neuromorphic use?

Measure multilevel conductance states, linearity and symmetry of potentiation/depression, endurance, retention and variability across devices.

NAN-381 · How would you reduce leakage current in a scaled MOSFET?

Improve gate control with FinFET or gate-all-around geometry, use high-κ metal gates to cut gate tunnelling at the same EOT, raise threshold voltage where speed allows, use thinner channels and retrograde doping to reduce subthreshold and DIBL leakage, and power-gate idle blocks.

NAN-382 · Why is copper interconnect resistance rising sharply at advanced nodes, and what are the options?

Wire widths approach copper's electron mean free path (about 39 nm), so surface and grain-boundary scattering raise resistivity, while liners and barriers take up a growing share of the cross-section. Options include thinner barriers, alternative metals such as ruthenium or cobalt for narrow lines, and backside power delivery.

NAN-383 · How would you evaluate a new material for a spin-orbit torque device?

Measure its spin Hall angle and resistivity (power efficiency depends on both), switching current density, compatibility with the free layer (interface quality, thermal stability) and its process compatibility (deposition, etch, anneal tolerance).

NAN-384 · How do you characterise variability in nanoscale transistors?

Measure threshold voltage, drive current and leakage across many devices and wafers, separate random variation (dopant fluctuation, line edge roughness, metal grain effects) from systematic variation, and feed statistics into compact models for circuit design.

NAN-385 · How would you design a phase-change memory cell for lower reset current?

Shrink the active volume with confined cell geometries, use heater electrodes with small contact area, improve thermal insulation and choose materials with lower melting energy, while maintaining retention and endurance.

MEMS & NEMS

NAN-386 · A MEMS accelerometer shows offset drift with temperature. How would you address it?

Drift comes from thermal stress between package and die, mismatched thermal expansion of layers and electronics. Use stress-isolating die attach and package design, symmetric structures, temperature sensors with calibration and compensation algorithms.

NAN-387 · How would you design a MEMS resonator with a high quality factor?

Minimise damping: vacuum packaging to reduce air damping, anchor designs to reduce energy loss to the substrate, materials with low intrinsic loss (single-crystal silicon), and avoid thermoelastic damping by geometry choice.

NAN-388 · How do you prevent stiction during release of a MEMS device?

Use critical point drying or vapour HF release to avoid capillary forces, apply anti-stiction coatings (SAMs), add dimples to reduce contact area and design stiffer structures.

NAN-389 · How do you calculate the sensitivity of a capacitive MEMS accelerometer?

Displacement x = m·a/k, capacitance change ΔC ≈ ε·A·x/d². Sensitivity improves with larger proof mass, softer springs and smaller gaps, but softer springs reduce bandwidth and increase susceptibility to shock.

NAN-390 · How would you design a MEMS pressure sensor for an automotive application?

Use a silicon diaphragm with piezoresistors in a Wheatstone bridge or capacitive sensing, size diaphragm thickness for the pressure range, protect against media (gel coating), compensate temperature and qualify for automotive standards.

NAN-391 · How do you avoid electrostatic pull-in in a MEMS actuator?

For a parallel-plate actuator the moving plate snaps down once it travels about one-third of the gap, so either operate below the pull-in voltage, use charge control or closed-loop feedback, switch to comb drives whose force doesn't rise with displacement in the same way, or add mechanical stops and insulating bumps to prevent shorting.

NAN-392 · How would you design a NEMS resonator to weigh single molecules?

Make the resonator as light and stiff as possible (nanowires, nanotubes or graphene) for high frequency and mass responsivity, keep Q high with vacuum and low temperature, and read frequency shifts with low-noise electronics. Mass resolution scales roughly with effective mass divided by Q and signal-to-noise ratio.

NAN-393 · How is a MEMS gyroscope typically packaged?

The sense element is sealed at wafer level under vacuum (with a getter to hold the pressure) for high Q, mounted with stress-isolating die attach so package strain doesn't cause bias drift, and co-packaged with an ASIC for drive and sense electronics and shielding against EMI.

NAN-394 · How would you qualify the reliability of a MEMS sensor?

Run accelerated tests: thermal cycling and storage, high humidity, mechanical shock and vibration, fatigue cycling of moving parts and electrical stress. Monitor offset and sensitivity drift, stiction events and package leak rate, and analyse failures to fix their root causes.

NAN-395 · How is MEMS fabrication scaled to high volume?

Use CMOS-compatible processes and foundry-standard steps, wafer-level packaging and capping, automated wafer-level testing and calibration, and design-for-manufacturing rules that tolerate process variation. Yield and test cost dominate the price of high-volume MEMS.

Nanomedicine & Drug Delivery

NAN-396 · A liposomal drug shows good efficacy in mice but poor results in patients. What could explain this?

The EPR effect is strong and uniform in fast-growing mouse tumours but weak and variable in human tumours; protein corona and immune clearance also differ between species, and dosing schedules may not translate. Patient selection by imaging, and active targeting, are ways to respond.

NAN-397 · How would you design an mRNA lipid nanoparticle formulation?

Combine an ionizable lipid (for encapsulation and endosomal escape), a helper phospholipid, cholesterol and a PEG-lipid, mixed rapidly with mRNA in a microfluidic mixer at low pH. Optimise lipid ratios, N/P ratio and particle size (about 80–100 nm), and test encapsulation, potency, stability and immunogenicity.

NAN-398 · How do you control drug release rate from polymeric nanoparticles?

Choose polymer composition and molecular weight (e.g. PLGA lactide:glycolide ratio controls degradation), particle size, drug loading and coatings. Measure release in physiologically relevant media to tune the profile.

NAN-399 · How would you add active targeting to a nanoparticle?

Attach ligands (antibodies, peptides, aptamers, folate) for receptors overexpressed on target cells, using PEG spacers and controlled ligand density, and show improved uptake versus non-targeted controls in vitro and in vivo.

NAN-400 · How do you sterilise a nanomedicine without damaging it?

Many nanoparticles are damaged by autoclaving or gamma radiation, so use sterile filtration (0.22 µm) when size allows, aseptic manufacturing, or validate alternative sterilisation methods for stability.

NAN-401 · How do you scale up liposome manufacturing reproducibly?

Use controlled processes such as microfluidic or ethanol injection with defined mixing, extrusion or high-pressure homogenisation for size control, and in-process checks of size, encapsulation and sterility.

NAN-402 · How do you assess immune reactions to nanoparticles?

Test complement activation, cytokine release, hypersensitivity (CARPA) and anti-PEG antibodies, and monitor during preclinical and clinical studies.

NAN-403 · How would you design a theranostic nanoparticle for cancer?

Combine an imaging component (MRI contrast, fluorescence, PET label) with a therapeutic agent or photothermal function, ensuring biocompatibility, targeting and clearance.

NAN-404 · How do you evaluate biodistribution of nanoparticles in vivo?

Label particles (radiolabel, fluorescence, elemental tags), measure organ concentrations over time by imaging or ICP-MS of tissues, and assess clearance routes.

NAN-405 · How do regulators evaluate nanomedicines?

They assess quality (characterisation, reproducibility), safety (toxicology specific to nanoscale behaviour) and efficacy, often case-by-case with guidance specific to nanomaterials.

Nanotech for Energy & Environment

NAN-406 · A silicon nanoparticle anode loses capacity rapidly. How would you improve cycling?

Silicon expands about 300% on lithiation, cracking particles and the SEI. Use smaller particles or porous structures, carbon coatings or yolk-shell designs to accommodate expansion, elastic binders (CMC, PAA), and electrolyte additives (FEC) for a stable SEI.

NAN-407 · How would you extend a TiO₂ photocatalyst into visible light?

Dope with nitrogen or carbon to create mid-gap states, couple with narrow-band-gap semiconductors (heterojunctions), add plasmonic metal nanoparticles, or use dye sensitisation. Verify with action spectra and quantum efficiency measurements.

NAN-408 · How do you design a nanostructured membrane for desalination?

Use thin-film nanocomposite membranes or aligned nanochannels (graphene oxide, CNTs, aquaporin), optimise salt rejection and water flux, and address fouling and mechanical stability.

NAN-409 · How would you reduce platinum loading in a fuel cell catalyst?

Use Pt alloy nanoparticles (Pt-Co, Pt-Ni), core-shell structures with Pt shells, high-surface-area supports, and optimised catalyst layer structure to maintain activity with less Pt.

NAN-410 · How would you improve the stability of perovskite solar cells?

Use compositional engineering, encapsulation, stable charge-transport layers and interface passivation to resist moisture, heat and light.

NAN-411 · How would you design a nanostructured thermoelectric material with high ZT?

Reduce lattice thermal conductivity with nanoscale grains, inclusions and interfaces that scatter phonons across many wavelengths, while keeping carrier mobility and Seebeck coefficient high through band engineering and optimal doping. Bulk nanostructured materials made by ball milling and spark plasma sintering are practical routes.

NAN-412 · How would you test whether a nanoadsorbent is practical for removing arsenic from groundwater?

Measure adsorption isotherms and kinetics with real groundwater (competing ions such as phosphate and silica), test regeneration and capacity over cycles, check nanoparticle leaching into treated water, and compare cost per volume treated with conventional media.

NAN-413 · How do you design a supercapacitor electrode with high energy density?

Use high-surface-area carbons with pore sizes matched to electrolyte ions, add pseudocapacitive materials (MnO₂, MXenes, conducting polymers), use electrolytes with a wide voltage window (since E = ½CV²), and keep electrode thickness and conductivity balanced.

NAN-414 · How would you assess the environmental release of nanoparticles from a consumer product?

Simulate use and end-of-life (washing, weathering, abrasion, incineration), measure released particle number, size and form (free, matrix-bound, dissolved) by spICP-MS and microscopy, and model fate in wastewater and soil.

NAN-415 · How would you use nanomaterials for CO₂ capture?

Use high-surface-area sorbents such as amine-functionalised mesoporous silica or MOFs with selective binding sites, balancing capacity, selectivity, regeneration energy, stability under humid flue gas and cost.

Nanotoxicology, Safety & Ethics

NAN-416 · How would you design a safe handling procedure for a new nanopowder?

Apply control banding to estimate hazard and exposure, handle powders in ventilated enclosures or gloveboxes with HEPA filtration, prefer wet handling or dispersions, use appropriate PPE (P100/FFP3 respirators, gloves, lab coats), clean with HEPA vacuums or wet wiping, and monitor exposure.

NAN-417 · How would you test the cytotoxicity of nanoparticles reliably?

Use several orthogonal assays (metabolic, membrane integrity, ROS), check for nanoparticle interference with assay readouts, include positive and negative controls, characterise particles in the test medium (agglomeration, protein corona) and report dose in several metrics.

NAN-418 · How do you conduct a life cycle assessment for a nanoproduct?

Define the functional unit, inventory energy and materials for synthesis, processing, use and disposal, include nanoparticle release scenarios, and compare impacts with a conventional alternative. Data gaps on nano-specific toxicity are a common limitation.

NAN-419 · How would you apply safe-by-design to a nanomaterial in development?

Consider hazard early: choose less toxic compositions, coatings that reduce dissolution or reactivity, shapes that avoid fibre-like toxicity, and product designs that minimise release, while maintaining function.

NAN-420 · How do you measure worker exposure to airborne nanoparticles?

Use real-time particle counters (CPC, SMPS), compare with background levels, collect samples for electron microscopy to identify particles, and use personal samplers in the breathing zone.

NAN-421 · How would you communicate nanotechnology risks to the public?

Be transparent about known benefits, uncertainties and risks, avoid hype or alarmism, and engage stakeholders early with clear language and evidence.

NAN-422 · How do regulations treat nanomaterials in cosmetics?

In the EU, nanomaterials in cosmetics must be notified, labelled "(nano)" in ingredient lists, and assessed by the Scientific Committee on Consumer Safety. Other regions have varying requirements.

NAN-423 · How would you investigate a suspected health effect in a nanomaterials lab?

Review exposures and work practices, conduct exposure monitoring, involve occupational health professionals, and update controls. Document findings and communicate with staff.

NAN-424 · How do you dispose of nanomaterial waste safely?

Collect in sealed, labelled containers, avoid drains, treat as hazardous waste where required, and follow institutional and regulatory guidance.

NAN-425 · How would you handle ethical concerns about nanotech-enabled surveillance devices?

Assess privacy implications, apply privacy-by-design, ensure transparency and consent, and comply with data protection laws.

Other levels: Basic · Intermediate · Tricky · All Nanotechnology Engineering questions