6th Commonwealth Chemistry Posters

Micro- and nanoplasticsare pervasive pollutants that evade routine monitoring [1,2]; graphene-supported, π-conjugated sensor interfaces offer a path to sensitive, selective, on-site detection [3–5]. Quantum-chemical modelling is used herein to evaluate two complementary probes for their capacity to transduce polymer adsorption into measurable signals.

The plastic fragments used:

Polyethylene (PE)
Polypropylene (PP)
Polyvinyl Chloride (PVC)
Polyurethane (PU)
Polyethylene Terephthalate (PET)
Polystyrene (PS)
Nylon6

Sensors investigated herein:

1-Pyrenebutanoic Acid Succinimidyl Ester (PBASE)
A pyrene-based, graphene-anchorable sensor interface evaluated in two configurations. Option 1 has the lowest energy (ΔE = −3.3 kcal mol–1) and therefore used for subsequent calculations.

Amphiphilic Perylene Diimide Probe (PDI-NH2):
An electrochemiluminescent (ECL) probe, sensitive to local environment; proximity of selected nanoplastic fragments can enhance signal via dispersion-driven complexation, microenvironment polarity, and charge-transfer effects.

Biosensor–polymer assemblies were built and inspected inChemcraft, then subjected to DFT geometry optimisations andharmonic frequency analyses in ORCA. Minima were verified by theabsence of imaginary modes. ZPE-corrected adsorption energieswere computed as the energy of the complex minus the sum of theisolated components at their optimised geometries. IR spectrawere generated from the harmonic intensities and post-processedin Python. Frontier and intrinsic bond orbitals were visualisedwith IboView. Vertical excited states were obtained with TDDFT,and the corresponding simulated absorption profiles were plotted.

PBASE–PET shows strong adsorption (ΔH = −14.16 kcal mol–1), consistent with a directional H-bond between the PET terminal –COOH and PBASE carbonyl/N–O sites, reinforced by π-contacts to the pyrene/graphene surface (right).
PU also binds favourably via urethane N–H···O/C=O interactions and dipolar coupling.
Hydrocarbon-only fragments (PE, PP) exhibit weak, dispersion-dominatedphysisorption and often prefer the graphene support over the probe.
PS engages in π–π stacking with graphene, yielding a comparatively favourable adsorption energy despite lacking strong specific H-bonding.

IR signature. An emergent band near 3500 cm–1 is assigned to the–OH stretch of PETupon hydrogen bonding to the PBASE, diagnostic of a –COOH···C=O(PBASE) interaction.

UV–Vis response. TDDFT predicts a redshift: the complex’s lowest-energy transitionoccurs at lower energy (longer wavelength) than the isolated components. Togetherwith the IR data, this supports PBASE as a sensor for functionalised nanoplastics.

PET forms a directional hydrogen bond via its terminal –COOH to PDI-NH2(imide carbonyl/amine sites), giving favourable adsorption.
PU shows the strongest binding, consistent with complementary amide↔imide H-bonding and π–π contacts between aromatic segments and the perylene core; the HOMO is delocalised across the interface (right).
By contrast, hydrocarbon nanoplastics(PE, PP) do not seem to exhibit strong binding to PDI-NH2, showing mainly weak, dispersion-dominated contacts.
A recent study [5] reported strong PP–PDI-NH₂ binding with enhanced ECL signal. Our model predicts weak adsorption for neutral, unoxidised PP fragments; the difference may reflect surface oxidation/functionalisation of PP, probe protonation/ionic strength, solvent effects, or particle size/curvature not captured in idealised fragment models.

Spectroscopic response. A hydrogen-bond signature appears near 3500 cm⁻¹ with greaterintensity than PBASE, consistent with stronger/more numerous H-bond contacts. The UV–Visprofile is largely conserved; only the highest-energy band shows a slight redshift, as with PBASE,indicating modest but distinct electronic coupling.

PBASE shows more favourable (ZPE-corrected) adsorption energies than PDI-NH2, indicating stronger interfacial capture on graphene.
PET/PU bind strongly via directional H-bonding and dipolar contacts; PE/PP are weak, often preferring the graphene support; PS engages π–π stacking with graphene, giving moderate binding.
A new ~3500 cm⁻¹ IR band marks H-bond formation (typically more intense for PDI-NH₂). TDDFT indicates small redshifts in the highest-energy UV–Vis band, consistent with modest electronic coupling.
Affinity increases with available donors/acceptors (–COOH, amide) and aromatic surface area; graphene anchoring with π-rich probes prolongs residence time and improves transduction.
PBASE is the more robust general interface; both probes are best suited to functionalised nanoplastics (e.g., PET, PU) rather than purely hydrocarbon fragments.
Next steps: Add explicit solvent, test larger and/or oxidised fragments and curvature, and validate via experiments.

6th Commonwealth Chemistry Posters

Computational Design of Graphene-Based Biosensors for Spectroscopic Detection of Microplastics

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