{"id":"36aadfbe-5c67-443a-bdef-032906f6dc7c","arxiv_id":"2508.21144","paper_version":1,"verdict":"CONDITIONAL","confidence":"HIGH","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":3,"one_line_summary":"In a dual nanopore tug-of-war, long T4 DNA is held asymmetrically between the pores, and the DNA free end escapes with an electrophoretic mobility roughly 1000 times larger than during tug-of-war.","lead":"Using a dual-nanopore device, researchers measured how long DNA molecules stay trapped in a tug-of-war between two pores, and how fast the DNA free end travels when it escapes. The results show long DNA sits asymmetrically between the pores and that free-end speed is much higher than expected, which matters for building better nanopore-based DNA mapping tools.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Free-end mobility is internally inconsistent with reported Tf: k≈30 µm/ms·mV implies sub-0.1 µs inter-pore transit, whereas Tf≈10 µs and d≈0.6 µm give k≈0.1–0.3 µm/ms·mV; the 1000x claim may be a units or Tf-interpretation artifact.","rationale":"The paper presents an impressive dual-nanopore dataset and a plausible first-passage framework for TOW dwell times. The reader's conditional verdict correctly identifies that the model parameters are fitted to the same dwell-time data and depend on the assumption of a highly stretched, fixed inter-pore segment. However, the most load-bearing issue I find is more direct and more damaging to the central quantitative claim: the free-end mobility values reported in the text are not compatible with the reported time-of-flight and inter-pore distance. This is an internal inconsistency, not just a disagreement with prior literature. The Tf measurement is the sole basis for the free-end velocity, and if Tf includes not only the inter-pore gap crossing but also the time for the remaining DNA to clear P2, then the inferred velocity is not the free-end velocity at all. Even if the reported k is a typo (e.g., µm/s·mV instead of µm/ms·mV), the paper's claim of a 1000-fold mobility enhancement would collapse to a factor of about 2–20, which would fundamentally change the interpretation. The relative slowdown in the presence of a fold is a separate, likely more robust observation, but the absolute mobility and the friction coefficients derived from it inherit the Tf ambiguity. Because the data are not yet available to check raw Tf values, I retain CONDITIONAL rather than outright rejection, but the condition should explicitly include resolving this internal inconsistency before the central claim is accepted.","tokens_in":14964,"tokens_out":15294,"duration_ms":165870,"concrete_test":"Using the raw event-level data (or Fig. 5c if raw data are unavailable), compute the mean Tf for each exiting-pore voltage bin and compare v_Tf = 0.6 µm / mean Tf with the velocity axis reported in Fig. 5c. If v_Tf / V2 is ~0.1–0.3 µm/ms·mV rather than ~30, the reported k is internally inconsistent. Then, to determine whether Tf includes trans-side contour clearing, measure Tf for events with systematically different initial α (e.g., compare the same DNA length under different capture protocols) or for a shorter DNA where the channel-2 contour is much smaller; if Tf changes with the amount of trans-side contour, then Tf is not simply an inter-pore time-of-flight and the free-end velocity must be redefined. Finally, re-derive the mobility ratio after converting all mobilities to identical units (µm/ms·mV or µm/s·mV); if the ratio is ~2–20 instead of ~10^3, the central quantitative claim s","verdict_should_be":"CONDITIONAL","load_bearing_attack":"The central claim—that the DNA free-end mobility is ~30 µm/ms·mV, roughly 1000× the TOW sliding mobility—rests on converting the measured interval between P1 and P2 current recoveries, Tf, into a velocity via v = d/Tf with d ≈ 0.6 µm. The paper reports Tf on the order of 10 µs and a timing precision of 4 µs. If Tf ≈ 10 µs, then v ≈ 0.6 µm / 10 µs = 60 µm/ms. For exiting-pore voltages in the 200–500 mV range, this gives k = v/V ≈ 0.1–0.3 µm/ms·mV, not 29–32. Conversely, k = 32 µm/ms·mV at V2 = 400 mV gives v ≈ 12,800 µm/ms, so Tf = 0.6 µm / 12,800 µm/ms ≈ 0.047 µs—three orders of magnitude below the stated Tf and below the 4 µs timing resolution. These numbers cannot all be correct. A second, independent problem is the meaning of Tf: it is the interval between the P1 current returning to baseline and the P2 current returning to baseline. After the chain leaves P1, P2 remains occupied by the chain, and P2 clears only after the remaining contour (including the trans-side segment in channel 2) has fully translocated. Thus Tf may include time for the entire remaining chain to exit P2, not just the time for the free end to traverse the 0.6 µm inter-pore gap. If so, dividing 0.6 µm by Tf underestimates the speed and the mobility comparison is not a clean free-end velocity. Either the reported k has a units error (e.g., µm/s·mV instead of µm/ms·mV, which would reduce the ratio to ~2×) or Tf is not the inter-pore time-of-flight. In both cases, the headline '3-orders-of-magnitude higher mobility' and the derived friction coefficients (ξs, ξd) are not supported as stated.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript reports dual-nanopore tug-of-war (TOW) experiments on T4 and lambda DNA. The authors measure TOW dwell-time distributions as a function of voltage difference, fit them to a 1D convection-diffusion first-passage model with free parameters D, v, and alpha, and extract a TOW sliding mobility A ≈ 14–15 µm/s·mV. They also measure the interval Tf between the P1 and P2 current recoveries at TOW disengagement, equate it to the time of flight of the DNA free end across the inter-pore gap (≈0.6 µm), and report a free-end mobility k ≈ 30 µm/ms·mV, which they claim is ~10^3 times larger than the TOW mobility. Experiments with a folded conformation show a slowed free end. The paper argues that a highly extended, short inter-pore segment with reduced cis-side friction explains the enhanced mobility.","tokens_in":15511,"tokens_out":8252,"duration_ms":81207,"significance":"The experimental platform is sophisticated, and the raw TOW dwell-time asymmetry for long T4 DNA is a reproducible and physically interesting observation. If the free-end mobility claim were correct, it would provide new insight into cis-side friction near the end of translocation. The first-passage model is a reasonable framework, but its parameters are fitted to the same data used for validation, limiting the strength of the agreement. More importantly, the central quantitative claim about the ~10^3-fold enhanced free-end mobility is internally inconsistent with the reported Tf and pore spacing, and the interpretation of Tf as a pure time of flight is questionable. As presented, the main result is not supported by the data.","major_comments":[{"comment":"The reported free-end mobility k≈30 µm/ms·mV is inconsistent with the stated Tf≈10 µs and pore spacing d≈0.6 µm. Dividing d by Tf gives v≈60 µm/ms, i.e. k≈0.12–0.30 µm/ms·mV for V2=200–500 mV. Conversely, k=30 µm/ms·mV at V2=400 mV implies v≈12,000 µm/ms and Tf≈0.05 µs, three orders of magnitude below the 4 µs timing resolution and the observed 10 µs. The velocities in Fig. 5c cannot be derived from the reported Tf; one of these quantities, or the unit used for k, must be mis-stated.","section":"DNA free end time-of-flight between pores"},{"comment":"Tf is defined in Fig. 2e as the interval between the P1 and P2 current recoveries. After the chain leaves P1, P2 remains blocked until the entire remaining contour—including the inter-pore segment and any trans-side/channel-2 contour—has exited P2. Thus Tf includes the full terminal translocation through P2, not simply the free end's transit across the 0.6 µm gap. The estimate v=d/Tf conflates these processes; a correction for P2 threading time and for recoil/slack of the inter-pore strand is needed before claiming a free-end mobility.","section":"DNA free end time-of-flight between pores"},{"comment":"The model is not validated against independent data. The paper states 'we leave the diffusion coefficient D, the drift velocity v and the initial fractional contour in channel 1 (α) as fitting parameters' and optimizes them on the same dwell-time distributions that are then shown as 'fits' in Fig. 3. The P1 exit probabilities in Fig. 4 are also computed from this fitted model. The agreement is therefore a consistency check of the fitting form, not a prediction. The abstract's claim that the findings 'validate theoretical predictions' is too strong; an out-of-sample test (e.g., using parameters from one voltage to predict another) would be needed.","section":"Quantifying DNA Dwell Time in Tug-of-War"},{"comment":"The comparison to single-pore mobilities contains a unit inconsistency. The text states that the single-pore λ-DNA mobility is approximately 5×10^4 µm/ms·mV and is 'only greater than our TOW measurement by a factor of around 2.' With the TOW sliding mobility A≈14 µm/s·mV = 0.014 µm/ms·mV, this ratio is ~3.6×10^6; with the free-end k≈30 µm/ms·mV, the ratio is ~1.6×10^3. Neither is 'around 2'. The mobility values or their units must be corrected before the comparison can be evaluated.","section":"DNA free end time-of-flight between pores"}],"minor_comments":[{"comment":"Typo: 'T4-DNA-DNA' appears in the paragraph describing the TOW event.","section":"DNA Tug-of-War"},{"comment":"Units: velocities are given in µm/ms in Fig. 5 but in µm/s elsewhere (e.g., A values). Add explicit unit conversions in the text and figure captions, and ensure the reported k values are expressed with consistent units.","section":"DNA free end time-of-flight between pores"},{"comment":"Fig. 3d: the model error bars are stated to be smaller than the marker size; this should be stated in the caption or the markers enlarged for visibility.","section":"Quantifying DNA Dwell Time in Tug-of-War"},{"comment":"The 'theoretical curve' in Fig. S1 uses the fitted D and A values; this should be stated explicitly in the caption so readers do not mistake it for an independent prediction.","section":"Supplementary Figure S1"},{"comment":"Reference 26 is cited as 'D. Ling et al.' in the text, but the work has two authors (Ling and Ling); correct the citation style.","section":"References"},{"comment":"The abstract and discussion repeatedly claim a '3-orders-of-magnitude' enhancement of the free-end mobility. Given the inconsistencies in the supporting numbers, this claim should be re-evaluated and softened until the velocity analysis is corrected.","section":"Abstract and Discussion"}],"recommendation":"reject","confidential_remarks":"The TOW dwell-time asymmetry for T4 DNA is an interesting experimental observation that could form the basis of a revised manuscript after the free-end velocity analysis is corrected. As written, the central quantitative claim is not internally consistent, and the Tf interpretation conflates transit and full P2 translocation. A resubmission with corrected units, a clear definition of what Tf measures, and an out-of-sample model test would be worth reconsidering."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Punchline: the paper has a nice experimental dataset and one robust new observation—long DNA sits very asymmetrically in a tug-of-war—but its headline free-end mobility number does not survive arithmetic. I checked the reported Tf, inter-pore spacing, and mobility: they cannot all be correct. Even ignoring the later slope, Tf ~10 µs and d ~0.6 µm give v ~60 µm/ms, so k ~0.2 µm/ms·mV at 300 mV, which is about two orders below the reported 32 µm/ms·mV. The quoted k implies an inter-pore transit of ~0.07 µs, far below their own 4 µs timing resolution. The stress-test note is right: the 1000x claim and the derived friction coefficients are not supported.\n\nWhat is good: the dwell-time histograms for T4 DNA show a clear asymmetry between positive and negative δV, and the P1 exit probability data are clean. The two-peak structure at -50 mV is a nice fingerprint of unbalanced initial partitioning, and the first-passage model does capture the shape of the distributions. The folded-strand comparison—free-end transit slower when a second filament is present—is qualitative and robust, since it compares within the same event. That part is a useful addition.\n\nSoft spots: the fit parameters (D, v, alpha) are extracted from the same dwell-time data used to validate the model, so the \"validation\" claim is weaker than stated. Alpha=0.92 is interesting but model-dependent. The free-end velocity interpretation is the big one: Tf is the interval between P1 and P2 current recoveries, which includes the time for the entire remaining chain to exit P2, not just the time to cross the 0.6 µm gap. Dividing the gap by that interval is not a time-of-flight. No raw data or code is provided, which makes the inconsistency harder to chase.\n\nOverall: worth a referee because the dual-pore system and the asymmetric partitioning observation are relevant, and the errors are correctable in revision. But the central quantitative claim about free-end mobility has to be either fixed or removed before publication. I would like to see the authors justify what Tf actually measures, provide the raw histograms, and redo the mobility comparison. If they can, this could be a solid methods paper; as it stands, the headline is wrong.","headline":"Asymmetric TOW partitioning is real and worth a look, but the free-end mobility claim is off by orders of magnitude and needs to be fixed or removed.","tokens_in":16002,"tokens_out":6042,"would_cite":false,"duration_ms":59356,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"A DNA strand escaping a dual-pore tug-of-war crosses the inter-pore gap with a mobility near 30 µm/ms per mV—about 1,000 times its tug-of-war sliding mobility—and a second folded strand slows it.","keywords":["dual nanopore","tug-of-war","DNA translocation dynamics","first-passage model","electrophoretic mobility","folded DNA translocation","translocation control","solid-state nanopores"],"falsifier":"Measure the inter-pore strand's extension directly while the tug-of-war is held, for example by attaching fluorescent labels at two points on the linking segment and imaging them, or vary the pore spacing: if the strand is not near full extension, or if the free-end mobility does not fall when the pore spacing (and hence inter-pore contour) increases, the fixed-stretch, one-variable model is not the right description.","tokens_in":14929,"feed_emoji":"🧬","tokens_out":12355,"duration_ms":127799,"temperature":0.7,"pith_summary":"The paper studies what happens when a long double-stranded DNA molecule is caught simultaneously by two solid-state nanopores and pulled in opposite directions—a 'tug-of-war' that slows translocation enough for sensing. Working with 166 kbp T4 DNA and 48.5 kbp λ-DNA, the authors try to establish two things: how dwell time in the tug-of-war depends on voltage when the chain starts off-center, and how fast the chain's free end travels to the remaining pore once one side lets go. They find that T4 DNA enters the tug-of-war with about 92% of its contour on one side, which makes the dwell-time distribution asymmetric and bimodal, and that a one-dimensional diffusion-with-drift first-passage model reproduces the measured dwell times. The central quantitative result is that the escaped free end moves with a mobility of roughly 30 µm/ms per mV, about three orders of magnitude above the mobility measured while the chain is sliding in the tug-of-war, and that a second strand from a fold lowers that mobility. If these numbers hold, the free-end transit exposes the frictional cost of the final ~1% of cis-side contour, and it gives dual-pore devices a voltage-tunable way to measure chain mobility and detect folded segments.","feed_headline":"Escaped DNA end crosses dual-pore gap 1,000x faster","feed_subtitle":"A dual-nanopore timing measurement reveals the friction the chain feels in its final microseconds—and a fold slows it down.","key_machinery":"The load-bearing object is the first-passage model of tug-of-war as 1D biased diffusion. The DNA strand stretched between the pores is assumed to be held at roughly 90% extension, which fixes the contour length between the pores; the only dynamical variable is x, the amount of DNA contour in the reservoir adjoining pore 1. The probability density P(x,t) obeys a Smoluchowski equation ∂P/∂t = D ∂²P/∂x² − v ∂P/∂x with absorbing boundaries at x=0 and x=L, so the dwell time is the first-passage time to empty either reservoir. Fitting the cumulative dwell-time distribution fixes the diffusion coefficient D, drift velocity v, and initial contour fraction α; P1-exit probability is then obtained from","core_discovery":"Using a dual-nanopore chip with pores about 600 nm apart and feedback-based control to form and hold tug-of-war states, the authors measured dwell-time histograms and free-end time-of-flight for λ-DNA and T4 DNA. They report three connected findings. First, longer T4 DNA enters the tug-of-war with an asymmetric starting partition (fitted α = 0.92), so dwell times depend strongly on the sign of the voltage difference and show separate diffusion-dominated and drift-dominated escape peaks; the same 1D convection-diffusion first-passage model used previously for λ-DNA fits these distributions and yields a tug-of-war sliding mobility around 15 µm/s·mV for both molecules. Second, once the free end","pith_inferences":["If free-end friction is indeed dominated by the short inter-pore segment, then translocation models with cis-side friction proportional to total remaining contour will systematically mispredict the final ~1% of a translocation; the terminal regime may need to be modeled as a separate short-chain problem with a recoiling strand.","The fitted α ≈ 0.92 for T4 suggests that tug-of-war starting asymmetry is set by the capture protocol, so varying the pre-capture tail length could deliberately tune dwell times and make mapping of longer molecules more reproducible.","The voltage-independent difference between folded and unfolded free-end friction suggests the extra drag comes from geometry or confinement of two adjacent strands rather than from voltage-dependent pore forces; changing pore spacing or ionic strength would test whether the extra friction scales with confinement.","The λ-versus-T4 velocity offset was attributed to trans-side crowding; adding crowders or changing salt in the common chamber could turn that hypothesis into a quantitative trans-side packing probe."],"forward_implications":["For genomic-length DNA, tug-of-war dwell-time data are not symmetric in voltage because the chain starts with an unbalanced partition; analysis pipelines and control algorithms must fit α as well as D and v.","Tug-of-war sliding mobility is linear in the voltage difference and nearly identical for λ- and T4-DNA, so the dual-pore setup can in principle measure a molecule's charge-to-friction ratio and distinguish biopolymers by mobility rather than only by current blockade.","The free-end time-of-flight gives a direct readout of the velocity and mobility of the last remaining cis-side contour, providing a clean experimental limit for single-pore translocation theories.","Folded-chain free-end transit is reproducibly slower than unfolded transit, with a voltage-independent friction difference, giving a quantitative handle for detecting and characterizing folds during dual-pore translocation.","Free-end velocity fluctuations peak near 300 mV, indicating that a constant-diffusivity model is not sufficient for the escape stage and motivating more detailed simulations coupling pore threading with strand recoil."],"supporting_citations":[{"why":"Introduces the dual-pore tug-of-war feedback protocol and the first-passage model this work extends to longer DNA.","marker":"[17]"},{"why":"Provides the all-glass two-pore chip fabrication and resensing measurement used in every experiment.","marker":"[20]"},{"why":"Supplies the driven-polymer first-passage formulation adapted here with two absorbing boundaries in the contour coordinate.","marker":"[22]"},{"why":"Gives the 0.13 pN/mV pore-force calibration used to convert measured free-end velocities into friction coefficients.","marker":"[15]"},{"why":"Demonstrates that nanopore drag increases with the number of dsDNA strands, the basis for interpreting fold-induced slowdown.","marker":"[36]"},{"why":"Supplies the tension-propagation framework used to justify the large effective diffusivities and short-segment friction.","marker":"[28]"},{"why":"Provides a single-nanopore translocation mobility comparison point for the free-end mobility.","marker":"[29]"}],"fun_headline_variants":["Tug-of-war nanopore traps long DNA with asymmetric ends","Dual-nanopore tug-of-war reveals escape speed governed by folds","DNA free-end escape slows when strands fold between pores","Asymmetric DNA partition sets tug-of-war dwell time peaks","First-passage model validated for DNA escape from dual pores"],"cache_read_input_tokens":2688,"weakest_assumption_plain":"The central assumption is that the DNA segment between the two pores stays stretched to about 90% of its contour length during the tug-of-war, so the contour between pores is effectively fixed and the chain's motion reduces to one-dimensional biased diffusion of one contour variable; if the inter-pore segment goes slack or changes extension, the fitted asymmetry, diffusion, and mobility parameters lose their simple meaning.","fun_headline_variants_meta":{"raw":{"variants":["Tug-of-war nanopore traps long DNA with asymmetric ends","Dual-nanopore tug-of-war reveals escape speed governed by folds","DNA free-end escape slows when strands fold between pores","Asymmetric DNA partition sets tug-of-war dwell time peaks","First-passage model validated for DNA escape from dual pores"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.001003,"raw_usage":{"total_tokens":4092,"prompt_tokens":769,"completion_tokens":3323,"prompt_tokens_details":{"cached_tokens":256},"prompt_cache_hit_tokens":256,"prompt_cache_miss_tokens":513,"completion_tokens_details":{"reasoning_tokens":3238}},"tokens_in":513,"tokens_out":3323,"duration_ms":25650,"temperature":1.0,"reasoning_tokens":3238,"cache_read_input_tokens":256,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-05T14:32:36.576325+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure the inter-pore strand's extension directly while the tug-of-war is held, for example by attaching fluorescent labels at two points on the linking segment and imaging them, or vary the pore spacing: if the strand is not near full extension, or if the free-end mobility does not fall when the pore spacing (and hence inter-pore contour) increases, the fixed-stretch, one-variable model is not the right description.","supporting_citations":[{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Introduces the dual-pore tug-of-war feedback protocol and the first-passage model this work extends to longer DNA."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Provides the all-glass two-pore chip fabrication and resensing measurement used in every experiment."},{"cited_title":"K.; Nelson, D","cited_arxiv_id":null,"evidence_quote":"Supplies the driven-polymer first-passage formulation adapted here with two absorbing boundaries in the contour coordinate."},{"cited_title":"F.; Koeleman, B","cited_arxiv_id":null,"evidence_quote":"Gives the 0.13 pN/mV pore-force calibration used to convert measured free-end velocities into friction coefficients."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Demonstrates that nanopore drag increases with the number of dsDNA strands, the basis for interpreting fold-induced slowdown."},{"cited_title":"Theory of pore-driven and end-pulled polymer translocation dynamics through a nanopore: an overview","cited_arxiv_id":null,"evidence_quote":"Supplies the tension-propagation framework used to justify the large effective diffusivities and short-segment friction."},{"cited_title":"W.; Wells, D","cited_arxiv_id":null,"evidence_quote":"Provides a single-nanopore translocation mobility comparison point for the free-end mobility."}],"review_version":1}