Complete Guide to Cryo-EM Grid Selection for Single Particle Analysis (SPA)
The cryo-EM grid you choose determines whether your particles enter the holes, stay intact, and yield high-resolution data. This guide compares all major support film types with published experimental data to help you make an informed decision.
What Is Single Particle Analysis (SPA)?
Single particle analysis is the most widely used cryo-EM technique for determining high-resolution structures of purified proteins and macromolecular complexes. The workflow involves:
Vitrification
Sample is applied to a grid and plunge-frozen in liquid ethane, trapping particles in a thin layer of vitreous ice.
Data Collection
Thousands of micrographs are collected at cryogenic temperature using a transmission electron microscope.
Particle Picking
Individual particle projections are extracted computationally from the micrographs.
3D Reconstruction
Particles are classified, aligned, and reconstructed into a 3D density map.
At the heart of this workflow, the support film — the thin perforated layer on the cryo-EM grid — plays an outsized role. Its material properties directly affect sample quality, data collection efficiency, and the final resolution you can achieve.
Why Grid Selection Matters for SPA
Three interconnected problems in cryo-EM sample preparation are fundamentally influenced by your choice of support film material:
Protein Adsorption & Air–Water Interface
Proteins at the air–water interface can denature within milliseconds. The support film surface determines how strongly proteins are adsorbed — carbon films strongly bind proteins (measured at 16.6 pN via AFM), causing aggregation, denaturation, and preferred orientation.
Beam-Induced Motion (BIM)
When the electron beam hits the grid, charge accumulates on poorly conductive films, causing physical movement that blurs high-resolution information. The electrical conductivity of the support film directly determines BIM magnitude.
Particle Distribution & Hole Entry
Ideally, particles should distribute evenly across grid holes. In practice, many particles are lost to non-specific adsorption on the support film itself, reducing the usable particle count per micrograph.
Grid Materials Compared
1. Holey Carbon Films (Quantifoil, C-flat)
Holey carbon is the traditional standard in cryo-EM. Carbon films are easy to manufacture, compatible with most plunge-freezing devices, and have decades of published protocols behind them.
Advantages
- Well-established, thousands of publications
- Wide range of hole sizes and patterns
- Compatible with all plunge-freezers
- Amorphous — suitable for TEM alignment
- Low cost, widely available
Limitations
- High protein adsorption (16.6 pN measured)
- Poor conductivity → significant BIM
- Hydrophobic surface → requires glow discharge
- Particle aggregation at hole edges common
- Preferred orientation frequent with membrane proteins
2. Gold Support Films (UltrAuFoil, HexAuFoil)
Gold films were introduced to address the BIM problem. With far better electrical conductivity than carbon, gold grids significantly reduce beam-induced motion, enabling higher-resolution reconstructions (Russo & Passmore, 2014).
Advantages
- Excellent conductivity → greatly reduced BIM
- Proven for sub-2 Å resolution SPA
- Uniform hole patterns available
Limitations
- Polycrystalline — cannot perform TEM alignment directly on film
- Higher cost than carbon
- Still requires glow discharge
- Complex data collection setup (alignment on separate area)
- Gold film can creep over time (mechanical instability)
3. Amorphous Alloy Films — ANTcryo™
ANTcryo is a novel support film made from amorphous nickel-titanium (NiTi) alloy, developed at the Institute of Biophysics, Chinese Academy of Sciences, and commercialized by NanoDim. It combines the conductivity advantages of metal films with the amorphous structure of carbon — addressing both BIM and TEM alignment simultaneously (Huang et al., Prog Biophys Mol Biol, 2020).
Advantages
- 4 orders of magnitude higher conductivity than carbon (3.4×10⁻⁶ Ω·m vs 0.5–5×10⁻² Ω·m)
- ~18× lower protein adsorption (0.94 pN vs 16.6 pN on carbon, AFM-measured)
- Amorphous structure — compatible with standard TEM coma-free alignment and automatic data collection
- Negligible magnetic moment — no practical effect on imaging (measured at 77 K, 3 T)
- Biocompatible — supports normal cell growth (rat hippocampal neuron test)
- Higher particle yield per micrograph (110k particles / 426 images vs 90k / 747 on carbon, same sample)
- Proven resolution improvement: 2.36 Å vs 2.59 Å on same apoferritin sample
Considerations
- Film thickness 22±3 nm — slightly thicker than carbon (~12–15 nm)
- Higher contrast film makes ice thickness estimation different from carbon
- Requires plasma cleaning before use (standard protocol: H₂/O₂ or O₂/Ar, 5 W, 30 s on Gatan Solarus)
- Higher cost than standard carbon grids (but comparable to gold grids)
- Newer technology — fewer published protocols than carbon
At-a-Glance Comparison
| Property | Holey Carbon | Pure Gold | ANTcryo (NiTi Alloy) |
|---|---|---|---|
| Structure | Amorphous | Polycrystalline | Amorphous ✓ |
| Conductivity (Ω·m) | 0.5–5 × 10⁻² | ~2.4 × 10⁻⁸ | 3.4 × 10⁻⁶ (4× better than carbon) |
| BIM | High | Very low | Low |
| Protein Adsorption | 16.6 pN (high) | Moderate | 0.94 pN (~18× lower) |
| TEM Alignment | ✓ Easy (amorphous) | ✗ Not possible on film | ✓ Easy (amorphous) |
| Plasma Cleaning | Required | Required | Required (standard protocol) |
| Magnetic | No | No | Negligible (same as carbon, measured) |
| Film Thickness | ~12–15 nm | ~50 nm (foil) | 22 ± 3 nm |
| Biocompatible | ✓ | ✓ (inert) | ✓ (TiO₂ passivation layer) |
| Resolution Benchmark | 2.59 Å (hFn @ 64k particles) | Sub-2 Å (best cases) | 2.36 Å (hFn @ 91k particles, same sample) |
Data sources: Huang et al. (2020), Progress in Biophysics and Molecular Biology 156, 3–13; Russo & Passmore (2014), Science; NanoDim product documentation.
Choosing the Right Grid for Your Sample
| Sample Type | Recommended Grid | Rationale |
|---|---|---|
| Membrane Proteins | ANTcryo or Gold | Low protein adsorption is critical — membrane proteins are highly vulnerable to air–water interface denaturation. ANTcryo's 18× lower adsorption gives more intact particles per hole. |
| Soluble Proteins (no adsorption issues) | Carbon or ANTcryo | If your protein distributes well on carbon with no orientation bias, carbon is sufficient. If you want the BIM reduction for higher resolution, ANTcryo adds value. |
| Large Complexes (>500 kDa) | ANTcryo (large holes) | Large complexes need larger holes for high entry rates. ANTcryo's low adsorption keeps these valuable particles in the imaging area rather than stuck to the film. |
| Small Particles (<150 kDa) | Gold or ANTcryo | Small particles are hardest to align and most affected by BIM. Either gold or ANTcryo can help — ANTcryo adds the benefit of standard TEM alignment workflow. |
| Virus / Virus-like Particles | Carbon, Gold, or ANTcryo | Selection depends on symmetry and orientation needs. ANTcryo's asymmetric surface may help with preferred orientation issues. |
Key Evidence: ANTA Film Performance Data
The following data is from Huang et al. (2020), the foundational paper characterizing amorphous nickel-titanium alloy (ANTA) film for cryo-EM, published in Progress in Biophysics and Molecular Biology. Human apoferritin (hFn) was used as the test sample, with data collected on the same microscope (Titan Krios 300 kV, K2 detector) under identical conditions.
2.36 Å
ANTA film resolution
vs 2.59 Å on carbon (same sample)
~18×
Lower protein adsorption
0.94 vs 16.6 pN (AFM, hPD-L1)
4×
Conductivity advantage
Orders of magnitude at cryo temp
Source: Huang X, Zhang L, Wen Z, et al. Amorphous nickel titanium alloy film: A new choice for cryo electron microscopy sample preparation. Prog Biophys Mol Biol 156: 3–13 (2020). | EMDB: EMD-30084 (ANTA), EMD-30083 (carbon). | PDB: 6M54 (ANTA), 6M52 (carbon).
Common SPA Grid Problems and Solutions
Preferred Orientation
Cause: Particles adsorb to the air–water interface or support film in a dominant orientation.
Solution: Switch to a low-adsorption support film (ANTcryo). The hydrophilic NiTi alloy surface and asymmetric film structure reduce orientation bias.
Particle Aggregation
Cause: Proteins denature at the hydrophobic carbon surface and form aggregates.
Solution: Use ANTcryo's hydrophilic metal surface, which shows ~18× lower non-specific protein interaction. If aggregates persist, add trace detergent (e.g., 0.01% DDM) to the sample buffer.
Few Particles in Holes
Cause: Most particles are lost to adsorption on the support film itself.
Solution: ANTcryo consistently shows higher particle density per hole (100+ vs 10–30 on carbon for RyR1; see Huang et al. Fig.6). Alternatively, try applying sample 2–3 times to saturate carbon film binding sites.
Poor Resolution Despite Good Particles
Cause: Beam-induced motion is blurring high-resolution features.
Solution: Switch to a higher-conductivity film (ANTcryo or gold). ANTA film's 4-order-of-magnitude conductivity advantage over carbon significantly reduces BIM. Use smaller beam-image shift during data collection.
Difficult TEM Alignment with Gold Films
Cause: Polycrystalline gold produces diffraction contrast that prevents coma-free alignment directly on the film.
Solution: Use ANTcryo instead — it is amorphous and fully compatible with standard TEM alignment and automatic data collection software (SerialEM, EPU), just like carbon.
Ice Too Thick or Too Thin
Cause: Blotting parameters or humidity not optimized.
Solution: Optimize blot time/force, chamber humidity (>95%), and temperature. ANTcryo films are slightly thicker (22 nm) than carbon — the higher contrast may require slight adjustment to ice thickness estimation.
Sample Preparation Tips for ANTcryo Grids
Plasma Clean Before Use
ANTcryo grids should be plasma-cleaned to increase surface hydrophilicity before sample application. Recommended protocol for Gatan Solarus: H₂/O₂ or O₂/Ar, 5 W, 30 seconds. This is the same procedure used for conventional carbon grids.
Sample Concentration
Because ANTcryo has lower protein adsorption, you may be able to use lower sample concentrations than on carbon while still achieving good particle density. Start with your usual concentration and adjust based on results.
Blotting Parameters
Standard Vitrobot / Leica EM GP parameters work well. Recommended starting point: blot force 0, blot time 3–5 s, 4°C, >95% humidity. Adjust based on your target ice thickness.
Data Collection Setup
ANTcryo is compatible with all major data collection software (SerialEM, EPU, Leginon). Because the film is amorphous, you can perform focus, coma-free alignment, and stigmation directly on the film — no need for a separate alignment area, unlike gold grids.
Storage
Store ANTcryo grids in a grid storage box in a dark, cool, and low-humidity environment. No expiration date, but recommended use within 2 years of purchase.
Recommended Reading
ANTcryo (ANTA) Film Characterization
Huang X, Zhang L, Wen Z, et al. Amorphous nickel titanium alloy film: A new choice for cryo electron microscopy sample preparation. Progress in Biophysics and Molecular Biology 156: 3–13 (2020).
The original paper describing ANTA film properties including conductivity, BIM reduction, protein adsorption measurements, and resolution benchmarks.
Gold Grid BIM Reduction
Russo CJ, Passmore LA. Ultrastable gold substrates for electron cryomicroscopy. Science 346(6215): 1377–1380 (2014).
The seminal paper demonstrating the BIM advantage of gold grids for cryo-EM.
Cryo-EM Grid Selection Review
Passmore LA, Russo CJ. Specimen preparation for high-resolution cryo-EM. Methods in Enzymology 579: 51–86 (2016).
Comprehensive review of grid preparation methods and material considerations for cryo-EM SPA.
Air–Water Interface Problem
Noble AJ, Wei H, Dandey VP, et al. Reducing effects of particle adsorption to the air–water interface in cryo-EM. Nature Methods 15(10): 793–795 (2018).
Demonstrates how the air–water interface causes preferred orientation and how support film choice can mitigate this.
View the complete list of 100+ papers using ANTcryo on our publications page.
Ready to Improve Your SPA Data?
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