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arxiv: 2605.21084 · v1 · pith:UEYB77AJnew · submitted 2026-05-20 · ⚛️ physics.bio-ph

Label-free SERS Discrimination of Native Proline Hydroxylation at Single-molecule peptide by Deep Learning-assisted plasmonic nanopore

Pith reviewed 2026-05-21 01:38 UTC · model grok-4.3

classification ⚛️ physics.bio-ph
keywords SERSsingle-moleculeproline hydroxylationdeep learningplasmonic nanoporepeptide PTMlabel-free detectionadsorption conformation
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The pith

A particle-in-pore SERS platform with peak-frequency analysis and a 1D convolutional network discriminates hydroxylated from non-hydroxylated HIF peptides at the single-molecule level.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper sets out to show that native proline hydroxylation, a key post-translational modification, can be read out label-free from individual short peptides by combining surface-enhanced Raman scattering inside a nanopore with statistical peak analysis and neural-network classification. It tests three peptide lengths centered on the HIF Pro-564 site and reports that spectral patterns tied to adsorption conformation become more distinguishable as chain length increases. A reader would care because most current methods either average over ensembles or require chemical tags, leaving single-molecule PTM detection largely inaccessible. The work demonstrates that the combined physical and computational pipeline produces classification accuracies that rise from roughly 73 percent for the shortest pair to nearly 90 percent for the longest, with area-under-curve values above 0.80 in all cases.

Core claim

The central claim is that the particle-in-pore SERS sensor, when paired with peak occurrence frequency analysis and a one-dimensional convolutional neural network, captures reproducible hydroxylation-dependent changes in adsorption conformation and surface interactions, enabling reliable single-molecule discrimination of hydroxylated versus non-hydroxylated HIF peptide fragments. For the 7-, 9-, and 15-amino-acid pairs the post-evaluation accuracies reach 72.98 percent, 78.55 percent, and 89.74 percent respectively, each with AUC above 0.80. Gradient-weighted visualization shows that the network attends to the same recurrent spectral features identified by the peak-frequency method, and an增强

What carries the argument

The particle-in-pore single-molecule SERS platform that records Raman spectra while peptides adsorb to gold nanoparticles inside a nanopore, processed by peak occurrence frequency statistics and 1D-CNN classification.

If this is right

  • Hydroxylation alters how longer peptides adsorb to the gold surface, amplifying spectral differences and raising classification accuracy.
  • The same platform can register weak PTM signatures without labels or ensemble averaging.
  • Gradient-weighted maps confirm that the neural network learns chemically meaningful features that match the peak-occurrence statistics.
  • The approach works across peptide lengths from 7 to 15 amino acids, suggesting scalability to other HIF-derived fragments.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • If the adsorption change proves general for other polar PTMs, the same hardware could be used to screen multiple modification types without redesign.
  • Integration with microfluidic delivery might allow the sensor to monitor dynamic hydroxylation states in real time rather than in static snapshots.
  • The citrate-band enhancement observed for the longest peptide hints that surface-chemistry tuning could further boost contrast for shorter or more rigid sequences.

Load-bearing premise

The observed spectral and adsorption differences are produced specifically by the presence or absence of the hydroxyl group on proline rather than by uncontrolled differences in peptide conformation, surface coverage, or citrate binding.

What would settle it

If controlled experiments that fix peptide conformation while removing the hydroxylation produce identical SERS spectra and identical citrate-band intensities, the claim that hydroxylation itself drives the distinguishable signals would be falsified.

Figures

Figures reproduced from arXiv: 2605.21084 by Enock Adjei Agyekum, Francesco De Angelis, Jianan Huang, Kuo Zhan, Matti Putkonen, Pei-Lin Xin, Shuai Li, Yingqi Zhao, Yuge Liang.

Figure 2
Figure 2. Figure 2: (a)Distribution of the normalized POF of HIF7S, HIF7SPTM, HIF9S, and HIF9SPTM, shown in red, orange, dark green, and light green, respectively. The peaks discussed in the text are highlighted by yellow and gray bands and labelled with their corresponding Raman shifts. Yellow-shaded bands indicate the region with similar spectra changes for 7AA and 9AA peptide pairs and can be tentatively assigned, whereas … view at source ↗
Figure 5
Figure 5. Figure 5: (a) Normalized POF profiles of HIF15S, HIF15SPTM, and pure AuNPs, shown in dark blue, light blue, and magenta, respectively. The blue-shaded bands indicate peptide-related peaks, while the red-shaded bands highlight characteristic citrate peaks. The offset of the HIF15SPTM POF curve is 0.05. (b) Proposed peptide adsorption states on citrate-covered AuNPs. The lower panel illustrates citrate-covered AuNPs w… view at source ↗
read the original abstract

Post-translational modifications (PTMs) play essential roles in regulating protein structure, function, and cellular signalling. However, peptide level discrimination of hydroxylation at the single-molecule level remains difficult. Here, we report a particle-in-pore single-molecule surface-enhanced Raman spectroscopy (SERS) platform combined with peak occurrence frequency (POF) analysis and a one-dimensional convolutional neural network (1D-CNN) for discriminating hydroxylated and non-hydroxylated HIF peptide fragments. Three peptide pairs containing the Pro-564 hydroxylation site, with lengths of 7, 9, and 15 amino acids (AAs), were investigated. POF analysis revealed reproducible hydroxylation-dependent spectral changes in the 7AA and 9AA peptide pairs, which were attributed to changes in adsorption conformation and surface interactions. CNN-based classification achieved post-evaluation accuracies of 72.98%, 78.55%, and 89.74% for the 7AA, 9AA, and 15AA peptide pairs, respectively, with AUC values above 0.80 for all the pairs, indicating a reliable discrimination. Gradient-weighted feature visualization further showed that CNN-sensitive regions overlapped with recurrent POF features, supporting the chemical relevance of the learned classification patterns. Notably, for the 15AA peptide pair, the enhanced citrate-associated band suggests that hydroxylation can substantially alter peptide-gold nanoparticle adsorption behaviour. This adsorption-mediated effect may amplify hydroxylation-induced spectral differences and contribute to the improved discrimination accuracy despite the increased structural complexity. These results demonstrate that the particle-in-pore sensor, assisted by deep learning, can capture hydroxylation-induced spectral and adsorption changes in peptide fragments, providing a promising strategy for ultrasensitive analysis of weak PTM signatures in peptides.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The manuscript presents a particle-in-pore single-molecule SERS platform integrated with peak occurrence frequency (POF) analysis and a 1D-CNN for label-free discrimination of hydroxylated versus non-hydroxylated HIF peptide fragments at the Pro-564 site. Three peptide length pairs (7AA, 9AA, 15AA) are examined; POF identifies reproducible spectral changes attributed to adsorption conformation shifts, and the CNN achieves post-evaluation accuracies of 72.98%, 78.55%, and 89.74% with AUC values >0.80. Gradient-weighted visualizations link CNN features to POF peaks, and an enhanced citrate band is noted for the 15AA pair as evidence of hydroxylation-altered AuNP adsorption.

Significance. If the spectral and classification differences prove specific to proline hydroxylation rather than uncontrolled adsorption or conformational variations, the work would offer a promising route for ultrasensitive, label-free PTM detection in peptides where conventional methods lack sensitivity. The combination of experimental SERS nanopore measurements, POF feature extraction, CNN classification with AUC>0.80, and feature visualization provides concrete empirical support and chemical interpretability that strengthens the central claim.

major comments (2)
  1. [Abstract] Abstract: The central claim that the platform discriminates native proline hydroxylation requires that observed spectral shifts and CNN accuracies arise specifically from the PTM. The abstract itself states that for the 15AA pair 'the enhanced citrate-associated band suggests that hydroxylation can substantially alter peptide-gold nanoparticle adsorption behaviour' and that this 'may amplify hydroxylation-induced spectral differences.' No description is given of matched controls that hold peptide concentration, ionic strength, or conformational ensemble fixed while toggling only the hydroxylation state; without such controls the CNN decision boundaries could be driven by surface-coverage or citrate-interaction differences instead of the PTM.
  2. [Abstract] Abstract and POF analysis section: Reproducibility of hydroxylation-dependent spectral changes is asserted, yet the manuscript provides no quantitative metrics (e.g., standard deviations on peak frequencies or intensities across independent measurements) or explicit statement of how many independent peptide preparations and nanopore runs were performed for each pair. This information is load-bearing for the claim that the 72.98–89.74% accuracies reflect hydroxylation rather than batch-to-batch variability.
minor comments (2)
  1. [Abstract] The abstract reports concrete accuracies and AUC thresholds but omits raw spectra, training/validation splits, cross-validation procedure, or error bars on the reported accuracies.
  2. Notation for the 1D-CNN architecture (layer counts, kernel sizes, training hyperparameters) is not summarized in the abstract or methods overview, making it difficult to assess reproducibility of the 72.98–89.74% figures.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We are grateful to the referee for the thorough review and valuable suggestions. We address the major comments point by point below, indicating where revisions will be made to improve the manuscript.

read point-by-point responses
  1. Referee: [Abstract] Abstract: The central claim that the platform discriminates native proline hydroxylation requires that observed spectral shifts and CNN accuracies arise specifically from the PTM. The abstract itself states that for the 15AA pair 'the enhanced citrate-associated band suggests that hydroxylation can substantially alter peptide-gold nanoparticle adsorption behaviour' and that this 'may amplify hydroxylation-induced spectral differences.' No description is given of matched controls that hold peptide concentration, ionic strength, or conformational ensemble fixed while toggling only the hydroxylation state; without such controls the CNN decision boundaries could be driven by surface-coverage or citrate-interaction differences instead of the PTM.

    Authors: We appreciate this concern regarding the specificity to the PTM. The hydroxylated and non-hydroxylated peptides differ only at the Pro-564 site, with all other experimental conditions, including concentration and buffer, kept identical for each pair. The observed differences in POF and the CNN's reliance on specific spectral regions (as shown by gradient-weighted visualizations) support that the discrimination is due to hydroxylation-induced changes in adsorption and conformation. However, to address the referee's point directly, we will revise the abstract and methods to explicitly describe the matched controls and provide additional justification that citrate effects are a consequence of the PTM rather than a confounding factor. We will also discuss potential limitations in controlling conformational ensembles at the single-molecule level. revision: yes

  2. Referee: [Abstract] Abstract and POF analysis section: Reproducibility of hydroxylation-dependent spectral changes is asserted, yet the manuscript provides no quantitative metrics (e.g., standard deviations on peak frequencies or intensities across independent measurements) or explicit statement of how many independent peptide preparations and nanopore runs were performed for each pair. This information is load-bearing for the claim that the 72.98–89.74% accuracies reflect hydroxylation rather than batch-to-batch variability.

    Authors: We concur that providing quantitative metrics and replicate information is crucial. The experiments were conducted with multiple independent preparations and runs to ensure reproducibility, but these details were omitted from the main text for brevity. In the revised manuscript, we will include a dedicated subsection on experimental reproducibility, reporting the number of independent preparations (n ≥ 3 for each peptide pair) and total measurements, along with standard deviations for the key POF peak positions and intensities. This will substantiate that the classification accuracies are not due to batch variability. revision: yes

Circularity Check

0 steps flagged

No circularity: empirical spectra + independent CNN training

full rationale

The paper presents an experimental workflow: measured SERS spectra from hydroxylated vs non-hydroxylated peptide samples, POF feature extraction on those spectra, and standard 1D-CNN training/evaluation yielding reported accuracies (72.98–89.74 %, AUC > 0.80). No equations, fitted parameters, or self-citations are invoked such that any output reduces to the input by construction. The classification result is obtained from held-out evaluation on independently acquired spectral data; the interpretation that differences arise from hydroxylation is an empirical claim open to controls, not a definitional or self-referential loop. The derivation chain is therefore self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

The platform rests on standard SERS plasmonic enhancement and the assumption that hydroxylation alters adsorption conformation; no explicit free parameters or new entities are introduced in the abstract.

axioms (2)
  • domain assumption Plasmonic enhancement in the particle-in-pore geometry produces measurable SERS spectra from single peptides
    Invoked in the platform description to justify single-molecule sensitivity.
  • domain assumption Hydroxylation-induced changes in peptide adsorption produce reproducible shifts in peak occurrence frequencies
    Central to attributing POF differences to the PTM rather than experimental noise.

pith-pipeline@v0.9.0 · 5891 in / 1396 out tokens · 36634 ms · 2026-05-21T01:38:00.117123+00:00 · methodology

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Lean theorems connected to this paper

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  • IndisputableMonolith/Cost/FunctionalEquation.lean washburn_uniqueness_aczel unclear
    ?
    unclear

    Relation between the paper passage and the cited Recognition theorem.

    POF analysis revealed reproducible hydroxylation-dependent spectral changes... attributed to changes in adsorption conformation and surface interactions. CNN-based classification achieved post-evaluation accuracies of 72.98%, 78.55%, and 89.74%

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Reference graph

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    8(11): p. e80635. Supporting Information Label-free SERS Discrimination of Native Proline Hydroxylation at Single-molecule peptide by Deep Learning-assisted plasmonic nanopore Yingqi Zhao1,3 Kuo Zhan 1,3, Pei-Lin Xin1,3, Yuge Liang1,3, Enock Adjei Agyekum4, Matti Putkonen5, Shuai Li4, Francesco De Angelis6 and Jianan Huang 1,2,3,* 1 Research Unit of Healt...