Experimental Investigation of Surface Passivation Chemistries for Optical Nanotweezers

Abayomi Opadele; Justus C. Ndukaife; Kewei Li; Maxwell T. Ugwu; Theodore Anyika

arxiv: 2606.20914 · v1 · pith:FV5A7FROnew · submitted 2026-06-18 · ⚛️ physics.optics · physics.chem-ph

Experimental Investigation of Surface Passivation Chemistries for Optical Nanotweezers

Maxwell T. Ugwu , Kewei Li , Abayomi Opadele , Theodore Anyika , Justus C. Ndukaife This is my paper

Pith reviewed 2026-06-26 15:53 UTC · model grok-4.3

classification ⚛️ physics.optics physics.chem-ph

keywords surface passivationnanotweezersanti-foulingPSSATRPextracellular vesiclesoptical tweezersISCAT imaging

0 comments

The pith

Poly(sodium styrene sulphate) exhibits better anti-fouling than MUA against polystyrene nanoparticles in nanotweezers.

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

The paper tests surface passivation chemistries on gold-based interferometric electrohydrodynamic tweezers to reduce fouling and enable reversible trapping of nanoparticles and extracellular vesicles. It synthesizes poly(sodium styrene sulphate) via atom transfer radical polymerization and compares its performance to 11-mercaptoundecanoic acid and zwitterionic poly(methacryloyloxyethyl phosphorylcholine) using fluorescence and interferometric scattering imaging. The central goal is to identify a passivation layer that minimizes unwanted particle adhesion while supporting consistent trapping and release. If the chemistry is the decisive factor, these methods would make nanotweezers more practical for repeated use with biological samples.

Core claim

The results show that PSS exhibits superior anti-fouling performance against polystyrene nanoparticles when compared to 11-mercaptoundecanoic acid. By comparing the antifouling properties of PSS and zwitterionic poly(methacryloyloxyethyl phosphorylcholine) in preventing extracellular vesicle adhesion, we found that both exhibited similar performance. Overall, the ATRP technique is broadly applicable across nanotweezer substrates with appropriately chosen initiators.

What carries the argument

Surface passivation layer of poly(sodium styrene sulphate) grown by atom transfer radical polymerization on the interferometric electrohydrodynamic tweezers, monitored for adhesion via fluorescence and ISCAT imaging.

If this is right

PSS enables more reliable reversible trapping and release of polystyrene nanoparticles than MUA.
PSS and PMPC offer comparable protection against extracellular vesicle adhesion on the device surface.
ATRP-based passivation can be transferred to other nanotweezer substrates by selecting compatible initiators.

Where Pith is reading between the lines

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

These passivation layers could extend device usability in longer biological experiments by reducing surface contamination over time.
The imaging methods used here could be combined with automated feedback to adjust trapping parameters in real time.
Similar chemistries might be tested on non-gold substrates to broaden the range of compatible nanotweezer designs.

Load-bearing premise

Observed differences in trapping performance and particle adhesion arise from the passivation chemistry itself rather than from variations in device fabrication, imaging conditions, or nanoparticle preparation.

What would settle it

Recording equivalent fouling rates and trapping behavior when the same passivation chemistry is applied but fabrication batches or imaging parameters are deliberately varied.

Figures

Figures reproduced from arXiv: 2606.20914 by Abayomi Opadele, Justus C. Ndukaife, Kewei Li, Maxwell T. Ugwu, Theodore Anyika.

**Figure 2.** Figure 2: Fluorescence images of trapped and released polystyrene with a) unpassivated IET and b) IET passivated with 11-Mercaptoundecanoic acid (MUA). The green circles highlights some of the trapped particles at 3 kHz while the red circles highlight some adsorbed particles due to fouling c) Contact angle result of the bare and MUA functionalized IET and d) Infrared spectrum of 11-Mercaptoundecanoic acid (MUA) on g… view at source ↗

**Figure 3.** Figure 3: Classical Atom Transfer Radical Polymerization (ATRP) reaction steps for synthesizing a) poly(sodium styrene sulphate)(PSS) and poly(methacryloyloxyethyl phosphorylcholine) (PMPC) on gold surfaces. b) IR spectrum of PSS and c) PMPC. The passivation of our IET device with terminal groups tailored to reduce fouling of different classes of particles demonstrates the versatility of ATRP-based surface passivati… view at source ↗

**Figure 4.** Figure 4: a) Fluorescence images of trapped and released polystyrene with IET functionalized with PSS b) ISCAT images of trapped and released (left and right) extracellular vesicles in a PSS functionalized IET c) unpassivated IET and d) IET passivated with PMPC. The green circles highlights some of the trapped particles at 3 kHz while the red circles highlight the adsorbed particles due to fouling. Overrall, poly(so… view at source ↗

read the original abstract

Nanotweezers are actively investigated as a powerful means to reversibly trap and characterize nanoparticles with profound biological and environmental importance. To ensure that these particles can be reversibly trapped and released, surface passivation is essential. To mitigate the issue of fouling, we investigated the antifouling properties of poly(sodium styrene sulphate) (PSS) synthesized using the Atom Transfer Radical Polymerization (ATRP) technique on our previously reported gold-based Interferometric Electrohydrodynamic Tweezers (IET) device. Fluorescence and interferometric scattering (ISCAT) imaging were used to record trapping performance and study the antifouling properties of our passivated nanotweezer device. The results show that PSS exhibits superior anti-fouling performance against polystyrene nanoparticles when compared to 11-mercaptoundecanoic acid (MUA). By comparing the antifouling properties of PSS and zwitterionic poly(methacryloyloxyethyl phosphorylcholine) (PMPC) in preventing extracellular vesicle adhesion, we found that both exhibited similar performance. Overall, the ATRP technique is broadly applicable across nanotweezer substrates with appropriately chosen initiators.

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.

Desk Editor's Note private letter to a colleague

The paper gives a practical comparison of PSS, MUA, and PMPC passivation on IET nanotweezers but the abstract lacks the controls needed to confidently attribute results to chemistry alone.

read the letter

Your colleague should know that this work tests three surface chemistries on the authors' gold-based IET nanotweezers and reports that PSS via ATRP gives better anti-fouling against polystyrene nanoparticles than MUA, while PSS and PMPC perform similarly against extracellular vesicles. They used fluorescence and ISCAT imaging to observe trapping and adhesion.

What the paper does is apply ATRP grafting to their existing platform and run a head-to-head test with two imaging techniques. That is a useful incremental step for anyone trying to reduce fouling on similar devices. The claim that ATRP is broadly applicable is reasonable given the context.

The soft spots are in the evidence presented. The abstract mentions the results but supplies no quantitative values, no sample sizes, no error estimates, and no description of how many independent devices or runs were done for each chemistry. It also does not say whether the same device was cleaned and re-passivated or if separate devices were used. This leaves room for the differences to come from fabrication variations or imaging conditions rather than the passivation layer itself, which is the exact concern in the stress-test note. Until those details are in the full paper, the central attribution remains tentative.

The work is aimed at experimentalists working on optical nanotweezers for biological particles. A reader in that niche might find the comparison helpful as a starting point for their own surface prep, but it does not open new theoretical ground or address wider questions in surface science.

I would recommend sending it for peer review if the full manuscript includes the missing quantitative data and control experiments, because the question is concrete and the approach is standard. If those are absent, it would need more work before review.

Referee Report

3 major / 0 minor

Summary. The manuscript experimentally investigates surface passivation chemistries for gold-based Interferometric Electrohydrodynamic Tweezers (IET) nanotweezers. It synthesizes poly(sodium styrene sulphate) (PSS) via Atom Transfer Radical Polymerization (ATRP) and compares its anti-fouling performance against 11-mercaptoundecanoic acid (MUA) for polystyrene nanoparticles and against zwitterionic poly(methacryloyloxyethyl phosphorylcholine) (PMPC) for extracellular vesicles, using fluorescence and interferometric scattering (ISCAT) imaging to assess trapping and adhesion.

Significance. If the central experimental claims hold after addressing controls and quantification, the work would provide practical guidance on passivation strategies that reduce fouling in optical nanotweezers, enabling more reliable reversible trapping of biologically relevant nanoparticles. The use of ATRP on existing IET substrates is a straightforward extension that could be broadly applicable if the performance differences are robustly demonstrated.

major comments (3)

[Abstract] Abstract: The central comparative claims (PSS superior to MUA; PSS equivalent to PMPC) are stated without any quantitative metrics, error bars, sample sizes, number of independent devices, or statistical analysis, preventing assessment of whether observed differences exceed device-to-device or run-to-run variation.
[Abstract] Experimental design (implied in Abstract and Methods): The attribution of anti-fouling differences directly to passivation chemistry (PSS vs MUA) is load-bearing for the main claim, yet no information is given on controls for confounders such as gold substrate roughness, ATRP grafting uniformity, nanoparticle batch variation, or whether the same physical device was re-functionalized across chemistries; without this, the performance gap cannot be securely assigned to surface chemistry.
[Abstract] Results (implied): The equivalence claim between PSS and PMPC for extracellular vesicle adhesion similarly lacks reported metrics or controls for imaging condition variations between fluorescence and ISCAT modalities.

Simulated Author's Rebuttal

3 responses · 0 unresolved

We thank the referee for their constructive comments, which highlight opportunities to strengthen the clarity and robustness of our claims. We address each major point below and will revise the manuscript accordingly.

read point-by-point responses

Referee: [Abstract] Abstract: The central comparative claims (PSS superior to MUA; PSS equivalent to PMPC) are stated without any quantitative metrics, error bars, sample sizes, number of independent devices, or statistical analysis, preventing assessment of whether observed differences exceed device-to-device or run-to-run variation.

Authors: We agree that the abstract would benefit from quantitative support. In revision we will add specific metrics (e.g., mean adhesion fractions with standard deviations), sample sizes, number of independent devices, and any statistical tests performed for both the PSS–MUA and PSS–PMPC comparisons. revision: yes
Referee: [Abstract] Experimental design (implied in Abstract and Methods): The attribution of anti-fouling differences directly to passivation chemistry (PSS vs MUA) is load-bearing for the main claim, yet no information is given on controls for confounders such as gold substrate roughness, ATRP grafting uniformity, nanoparticle batch variation, or whether the same physical device was re-functionalized across chemistries; without this, the performance gap cannot be securely assigned to surface chemistry.

Authors: We acknowledge that explicit discussion of these controls is currently absent. Our protocol used matched substrate batches and the same nanoparticle stocks for paired comparisons; we will expand the Methods section to report AFM roughness data, grafting-density estimates (XPS/ellipsometry), batch details, and whether devices were reused or prepared in parallel. If any control was not performed, we will state this limitation transparently. revision: partial
Referee: [Abstract] Results (implied): The equivalence claim between PSS and PMPC for extracellular vesicle adhesion similarly lacks reported metrics or controls for imaging condition variations between fluorescence and ISCAT modalities.

Authors: We will revise both the abstract and main text to include quantitative metrics (adhesion rates, error bars, replicate counts) for the PSS–PMPC comparison. We will also add a brief description of imaging parameters and any cross-modality normalization or controls used to support the equivalence statement. revision: yes

Circularity Check

0 steps flagged

No circularity: experimental comparisons rest on direct imaging data

full rationale

The paper reports experimental measurements of particle adhesion via fluorescence and ISCAT imaging on devices passivated with PSS, MUA, and PMPC. No equations, models, or predictions are presented that reduce any result to fitted inputs or prior self-citations by construction. The reference to the authors' earlier IET device is purely contextual and does not carry the central claims about relative antifouling performance. The work is self-contained against external benchmarks (imaging of adhesion events) with no load-bearing self-citation chain or self-definitional steps.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

The central claim rests entirely on experimental imaging observations of particle adhesion on the IET device; no free parameters, mathematical axioms, or new postulated entities are introduced.

pith-pipeline@v0.9.1-grok · 5748 in / 1033 out tokens · 23190 ms · 2026-06-26T15:53:31.271055+00:00 · methodology

discussion (0)

Reference graph

Works this paper leans on

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