{"id":"7e8c38bc-7bfd-4eed-b1c7-879f743ccb1e","arxiv_id":"2507.20970","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":5.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":0,"one_line_summary":"Cryo-atom-probe analysis of a plunge-frozen ferritin solution is feasible, but slow freezing destroys ferritin shells, and high-pressure frozen water shows the needed future route.","lead":"This paper tried to prepare frozen droplets of a ferritin solution for atom probe tomography, a method that maps atoms in 3D. The workflow works for bulk frozen liquids, but slow freezing destroyed the protein shells, and high-pressure frozen water is offered as the path forward.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"HPF proof-of-principle rests on unconfirmed amorphous ice; devitrification would void the forward-looking claim.","rationale":"The reader's weakest_assumption matches this concern: the unverified vitreous state. The paper is transparent about the caveat and explicitly calls the HPF results preliminary, so the primary claim of feasibility for APT of bulk frozen liquid is supported by the ferritin data regardless of the HPF issue. The forward-looking HPF claim is conditional on an assumption that could be checked with a single experiment. Since the reader already assigned CONDITIONAL and this concern does not invalidate the primary demonstration, no verdict adjustment is needed.","tokens_in":21139,"tokens_out":3590,"duration_ms":41917,"concrete_test":"Re-run the HPF workflow on an identical DI-water specimen and, before APT insertion, transfer the prepared needle into a cryo-TEM under the same cryo-UHV suitcase conditions and acquire electron diffraction (or cryo-EM) patterns from the ice. If the pattern shows sharp Debye-Scherrer rings (crystalline ice), the HPF proof-of-principle claim fails; if it shows diffuse halos (amorphous ice), the assumption is confirmed. If cryo-TEM is unavailable, record the specimen temperature continuously with a sensor on the cryo-puck through transfer, FIB, and APT to verify it never exceeds -135 °C; however, diffraction is the decisive check because the paper itself identifies it as 'a final proof.'","verdict_should_be":"UNCHANGED","load_bearing_attack":"The paper's forward-looking claim that intact biomacromolecules could be analyzed via high-pressure freezing depends on the assumption that the high-pressure-frozen water remained vitreous through cryo-transfer, FIB preparation, and APT. Section 3.4 states that 'the vitreous state of our samples could not be confirmed,' and Section 4.3 bases the expectation on 'we assume that the specimen is maintained... below the temperature that would cause significant sublimation and/or crystallization.' The only HPF dataset is from pure deionized water, so it cannot by itself establish biomolecule preservation; it serves as a workflow proof-of-principle only if the ice is amorphous. If devitrification occurred, the HPF data are equivalent to the crystalline plunge-frozen data, and the claim that the workflow 'can be used for samples prepared by high-pressure freezing' in a way that preserves native biomolecular structure is unsupported. This is the single load-bearing assumption for the paper's most significant forward-looking conclusion.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"This manuscript reports cryo-atom probe tomography (cryo-APT) experiments on plunge-frozen ferritin solution and on high-pressure-frozen deionized water. Using cryo-lift-out from nanoporous brass substrates and cryo-transfer under UHV, the authors acquired APT datasets of up to 69 million ions, detected protonated water clusters and various elemental and molecular ions, and identified Fe-rich particles near the ice/metal interface along with C-, Na-, and Cl-containing signals. They conclude that the workflow is feasible for bulk hydrated biological samples, but that LN2 plunge freezing is too slow to vitrify the solution and causes irrecoverable damage to ferritin. A single HPF water dataset is presented as a proof-of-principle that the same workflow could eventually analyze intact biomacromolecules, while explicitly noting that the vitreous state could not be confirmed.","tokens_in":21313,"tokens_out":5787,"duration_ms":64133,"significance":"The paper's main value is a candid, experimentally grounded demonstration of an end-to-end cryo-APT pipeline for frozen biological solutions, including a 69-million-ion dataset and repeatable lift-out from dealloyed brass. It consolidates earlier frozen-water APT work and documents many substrate and preparation failures, which is practically useful for the community. If the ferritin-specific peak assignments and the amorphous state of the HPF specimen were independently confirmed, the forward-looking claim about near-native-state biomacromolecule analysis would be considerably strengthened; as it stands, the significance is incremental but real. The manuscript is honest about background, peak-overlap, and reconstruction limitations, and its central observations are independent experimental evidence rather than circular derivations. The strengths are the actual datasets, the explicit reporting of negative results, and the use of a comparison metric (CIR) consistent with prior published water-APT data.","major_comments":[{"comment":"The attribution of organic peaks to ferritin shell fragments is not supported by a ferritin-free control. The authors state that 'normally the solution only contains NaCl' and that most non-water peaks 'could be related to fragments from the polypeptide chains,' but no buffer-only mass spectrum is shown, and Section 4.4 concedes that unambiguous identification is impossible at the achieved mass resolution (e.g., C2H4+, CNH2+, and CO+ overlap near 28 Da). Because the claim that elements from the ferritin shell are detected is central to the biological interpretation, a control spectrum of 0.15 M NaCl (and ideally of the brass substrate leachate) is needed before these peaks are assigned to ferritin. As written, the shell detection is plausible but not demonstrated.","section":"Section 3.2, Figure 4 and Suppl. Table 1"},{"comment":"The HPF proof-of-principle is conditional on an unverified assumption: the text admits 'the vitreous state of our samples could not be confirmed' (Section 3.4) and later 'we assume that the specimen is maintained... below the temperature that would cause significant sublimation and/or crystallization' (Section 4.3). If devitrification occurred during transfer or FIB preparation, the HPF dataset would be equivalent to the crystalline plunge-frozen data and would not support the conclusion that the workflow preserves biomacromolecules in their native state. Moreover, the HPF specimen is pure deionized water, so it provides no direct evidence of biomolecule preservation. I recommend either confirming the amorphous state by an independent method (cryo-TEM/electron diffraction or cryo-Raman) or explicitly limiting the conclusion to frozen, not vitreous, specimens.","section":"Section 3.4 and Section 4.3"},{"comment":"The evidence for ferritin cores rests on one Fe-rich cluster and one region of overlapping 54/56 Da distributions, while the main 56 Da peak in the dataset is admitted to be misidentified (C2O2+ or C2NOH+ at the same mass). The proximity histogram in Figure 6d reports nearly 80 at% Fe, but the manuscript does not give the background/range correction parameters or the spatial cluster statistic used to define the particle. Given the strong local magnification and trajectory aberrations expected at the ice/brass interface (Section 4.1), an alternative explanation as a reconstruction artifact is not excluded. Please report the analysis parameters and a significance test for Fe clustering.","section":"Section 3.3, Figure 6"}],"minor_comments":[{"comment":"The word 'vitrified' is used for HPF water before the caveat in Section 3.4; please rephrase as 'frozen by high-pressure freezing' to avoid making a claim the paper later retracts.","section":"Abstract and Section 2.3"},{"comment":"The sentence 'even if the these cannot be monitored' contains a typo and should read 'even if these cannot be monitored'.","section":"Section 3.1"},{"comment":"The text says the composition profile is plotted in Figure 6c, but the caption labels the proximity histogram as (d); please check and correct the cross-reference.","section":"Figure 6 and text"},{"comment":"The sentence 'our experimental infrastructure does now allow for transferring the specimen into a TEM' appears to mean 'does not allow'; please correct.","section":"Section 4.3"},{"comment":"The caption contains a typo: 'the underlying meta substratel' should be 'the underlying metal substrate'.","section":"Suppl. Figure 9 caption"},{"comment":"Thanking 'the two reviewers' in the acknowledgements is unusual in a submitted manuscript and may need to be removed before review.","section":"Acknowledgements"}],"recommendation":"major_revision","confidential_remarks":"This paper fits the journal as a preliminary methods report. My main concern is not novelty or circularity but the gap between what is demonstrated (cryo-APT of frozen liquids, with Fe-rich particles) and what is claimed in the abstract and conclusion (a path to intact biomacromolecules). A ferritin-free control, clearer reporting of the Fe-cluster analysis parameters, and either confirmation of the amorphous state or a softened claim would close that gap. The heavy self-citation is concentrated in the methods sections and is appropriate to the specific protocols being reused."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Short version: this is a genuine, transparent methods report, and the HPF-water dataset is new and worth publishing, but it does not show intact biomolecules, and the forward-looking claim hinges on the vitreous-ice assumption that the authors themselves admit they cannot verify.\n\nWhat's actually new: the systematic comparison of substrates (brass, nanoporous gold, magnesium, aluminum), the detailed ice/metal interface characterization, and—most importantly—the first cryo-lift-out APT dataset on high-pressure-frozen water. The HPF water shows larger protonated water clusters (up to n=12) than plunge-frozen samples, consistent with amorphous ice. The authors also document failures and dead ends honestly, which is refreshing and useful for the community.\n\nThe ferritin part is incremental: Fe cores and C-containing shell fragments are detected, but the particles are destroyed by ice crystals. That negative result is worth reporting, but it is not a breakthrough, and the paper says so itself.\n\nSoft spots, in order of importance. First, the HPF proof-of-principle rests on the assumption that the high-pressure-frozen water remained vitreous through transfer and FIB preparation. Section 3.4 admits 'the vitreous state of our samples could not be confirmed.' If the ice devitrified, the HPF data is just another crystalline-water spectrum, and the claim that this workflow could eventually analyze intact biomacromolecules is unsupported. The authors hedge carefully—'could be analyzed through a similar workflow in the future'—so this is a weakness in the forward claim, not a fatal flaw in what they report. Second, there is no ferritin-free control, so the assignment of C peaks to the protein shell is not definitive. Third, peak identification is acknowledged to be ambiguous; the 56 Da misassignment is a good example of the general problem. Fourth, no raw data is deposited, and a few quantitative comparisons (CIR, peak ratios) lack error propagation.\n\nWho is this for? Anyone working on cryo-APT of frozen liquids, and to a lesser extent structural biology method developers. It deserves serious peer review: the methods are reproducible enough to referee, and the negative results and substrate comparisons are genuinely useful. My recommendation: accept after revision, with the main requests being a ferritin-free control, a direct test of the ice phase (electron diffraction, or at least a clear statement that it remains absent), and deposition of raw data. I would cite this in the context of cryo-APT methods.","headline":"Honest cryo-APT methods report on hydrated ferritin: real data, clear limitations, but the HPF path to intact biomolecules rests on an unconfirmed vitreous state.","tokens_in":21832,"tokens_out":2430,"would_cite":true,"duration_ms":28186,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"The paper demonstrates a cryo-atom-probe pipeline for bulk frozen aqueous samples and shows that plunge freezing destroys ferritin, while high-pressure-frozen water passes through the same workflow as a route to intact biomacromolecules.","keywords":["atom probe tomography","cryo-APT","ferritin","vitrification","high-pressure freezing","frozen-hydrated biological samples","cryo-lift-out","ice crystallization"],"falsifier":"Run a high-pressure-frozen ferritin solution through the same cryo-lift-out and transfer workflow, then before atom probe analysis record electron diffraction in a cryo-TEM: sharp Debye-Scherrer rings from crystalline ice, or an APT mass spectrum with only small protonated water clusters ($n\\le3$) and iron segregated at the ice/metal interface, would show that the vitreous path to intact biomacromolecules is not yet established.","tokens_in":1952,"feed_emoji":"🧊","tokens_out":2299,"duration_ms":75115,"temperature":0.7,"pith_summary":"The paper sets out to test whether atom probe tomography can map the three-dimensional chemistry of biomacromolecules in their native, hydrated state. Using ferritin in saline buffer as a model system, the authors show that bulk frozen liquid can be lifted out, shaped into a needle, transferred under cryogenic vacuum, and field-evaporated ion by ion. The resulting 3D reconstructions contain iron, sodium, carbon fragments, and protonated water clusters, so the pipeline itself works. The key negative result is that the ferritin particles are destroyed: plunge freezing in liquid nitrogen is too slow to vitrify the solution, ice crystals form, and the protein shells end up shredded and dispersed. The paper then reports a proof-of-principle analysis of high-pressure-frozen deionized water through the same workflow, arguing that this is the route to intact, near-native biomacromolecules, provided the ice stays vitreous.","feed_headline":"Plunge freezing shreds ferritin before atom probe sees it","feed_subtitle":"Cryo-atom-probe pipeline works on bulk water, but only high-pressure freezing may keep proteins intact.","key_machinery":"The load-bearing piece is the cryogenic specimen pipeline: re-deposition cryo-lift-out, in which a chromium lamella is sputtered from a manipulator to weld the frozen lamella to a silicon post, followed by annular FIB milling and transfer in a cryo-UHV suitcase held below roughly $-180\\,^\\circ\\mathrm{C}$ (90 K). Into this pipeline the paper inserts two freezing routes: manual plunge freezing into liquid nitrogen, which the results show is too slow to vitrify, and high-pressure freezing (HPF) on an aluminum planchette, which is intended to produce amorphous ice. The cluster ion ratio (CIR), the abundance ratio of larger to smaller protonated water clusters, is used as a field-sensitive fingerprint to compare datasets and to argue that longer clusters from the HPF specimen signal vitreous rather than crystalline ice.","core_discovery":"The central claim is that a complete cryogenic specimen-preparation-to-atom-probe pipeline—plunge freezing on a metal substrate, cryogenic lift-out with chromium redeposition welding, transfer in a cryo-vacuum suitcase, and laser-pulsed field evaporation—can be applied to bulk hydrated samples, but that the freezing step, not the analysis, is currently the bottleneck. In the ferritin datasets, Fe-rich particles appear near the ice/metal interface with the iron isotope ratio of ferritin cores, surrounded by carbon-enriched shells but with sodium concentrated at roughly 30 at% in the surrounding brine; the authors interpret this as crystallization-driven damage, with solutes rejected into the last liquid and the protein shell unfolded and dispersed. In high-pressure-frozen pure water, the same workflow produced protonated water clusters up to $(\\mathrm{H_2O})_{12}\\mathrm{H}^+$, in contrast to the small clusters ($n=1$–$3$) from crystalline ice, which the authors take as evidence that vitreous ice can survive cryo-transfer and FIB preparation and that intact biomacromolecules could be analyzed this way in the future.","pith_inferences":["If the HPF ice had devitrified during transfer or FIB milling, the long water clusters would not prove vitreous compatibility; a cryo-TEM electron diffraction check on a specimen from the same planchette would settle that.","The paper attributes damage to freezing, but Ga implantation (up to nearly 100 at% in some clusters) and FIB heating are documented in the HPF specimen; separating these damage channels will require a vitrified protein sample that is FIB-milled and compared with one that is not.","Because ferritin cores contain roughly 80 at% Fe and a defined isotope ratio, counting intact cores per analyzed volume could become a quantitative preservation metric once vitrification is confirmed.","The observed laser-side/shadow-side asymmetry in cluster fragmentation suggests that local field variations across a frozen biological specimen can be read off the mass spectrum, which could be used as an internal field calibration during reconstruction."],"forward_implications":["Bulk aqueous solutions, not just thin ice layers on pre-sharpened tips, can be prepared into atom probe needles by cryo-lift-out and analyzed at near-atomic scale.","Plunge freezing in liquid nitrogen is not an acceptable preservation route for hydrated biomacromolecules: the crystallization it produces destroys protein shells and redistributes their elements, so future work must use vitrification.","High-pressure-frozen water is compatible with the existing cryo-lift-out and cryo-transfer workflow, so vitrified biological solutions can be targeted in the same setup.","Even when ferritin is destroyed, its iron core leaves a detectable isotopic signature, giving a built-in marker for assessing particle preservation in future experiments."],"supporting_citations":[{"why":"Supplies the cryo-lift-out protocol with chromium redeposition welding that the workflow is built on.","marker":"(Eric V Woods et al., 2023)"},{"why":"Establishes the prior demonstration of frozen water analysis and the observation of solutes concentrated at the ice/metal interface.","marker":"(El-Zoka et al., 2020)"},{"why":"Provides the baseline field-evaporation behavior of pure water tips, including protonated water cluster formation.","marker":"(Schwarz et al., 2020)"},{"why":"Reports prior cryo-atom-probe analysis of hydrated ferritin, which this work extends to bulk frozen solutions.","marker":"(Qiu et al., 2020)"},{"why":"Supplies the resin-embedded ferritin atom-probe baseline, including phosphorus detection, that the authors compare against.","marker":"(Perea et al., 2016)"},{"why":"Provides DFT calculations on water field evaporation that the authors use to interpret OH+ formation and field strengths.","marker":"(Segreto et al., 2022)"},{"why":"Documents cluster ion formation during field desorption of amorphous ice, supporting the interpretation of long water clusters from the HPF specimen.","marker":"(Stintz & Panitz, 1993)"},{"why":"Defines the cluster ion ratio (CIR) and reports biomolecule-related fragmentation trends used to compare datasets.","marker":"(Woods et al., 2025)"},{"why":"Describes in-situ sputtering from the micromanipulator, the key step enabling cryogenic lift-out without gas-injection welding.","marker":"(Douglas et al., 2023)"}],"fun_headline_variants":["Ice crystals, not the atom probe, destroy ferritin","Atom probe sees ferritin core, but ice crystals destroy the shell","Cryo-APT pipeline works, but plunge freezing wrecks proteins","High-pressure freezing may keep proteins intact for atom probe"],"cache_read_input_tokens":24064,"weakest_assumption_plain":"The load-bearing premise is that the high-pressure-frozen water stayed amorphous from freezing through transfer and FIB milling, since the paper could not confirm the vitreous state of its HPF samples.","fun_headline_variants_meta":{"raw":{"variants":["Ice crystals, not the atom probe, destroy ferritin","Atom probe sees ferritin core, but ice crystals destroy the shell","Cryo-APT pipeline works, but plunge freezing wrecks proteins","High-pressure freezing may keep proteins intact for atom probe"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000922,"raw_usage":{"total_tokens":3990,"prompt_tokens":1017,"completion_tokens":2973,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":633,"completion_tokens_details":{"reasoning_tokens":2900}},"tokens_in":633,"tokens_out":2973,"duration_ms":26167,"temperature":1.0,"reasoning_tokens":2900,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-06T13:04:29.159524+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Run a high-pressure-frozen ferritin solution through the same cryo-lift-out and transfer workflow, then before atom probe analysis record electron diffraction in a cryo-TEM: sharp Debye-Scherrer rings from crystalline ice, or an APT mass spectrum with only small protonated water clusters ($n\\le3$) and iron segregated at the ice/metal interface, would show that the vitreous path to intact biomacromolecules is not yet established.","supporting_citations":[{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Establishes the prior demonstration of frozen water analysis and the observation of solutes concentrated at the ice/metal interface."},{"cited_title":"E., Liu, J., Bartrand, J., Dicken, Q., Thevuthasan, S","cited_arxiv_id":null,"evidence_quote":"Supplies the resin-embedded ferritin atom-probe baseline, including phosphorus detection, that the authors compare against."},{"cited_title":"In addition, the data contains peaks of Al1–3+, Mg1–2+, and Si2+","cited_arxiv_id":null,"evidence_quote":"Documents cluster ion formation during field desorption of amorphous ice, supporting the interpretation of long water clusters from the HPF specimen."}],"review_version":1}