# Enhanced Refractive Index Sensitivity of Linearly Assembled Gold Nanoantennae for Biosensing Applications

## TL;DR

Researchers developed a scalable method to create gold nanoparticle arrays that can detect changes in refractive index, improving biosensing for applications like detecting cancer-related proteins.

## Contribution

A scalable and sensitive plasmonic biosensing platform using linearly assembled gold nanoantennae is introduced.

## Key findings

- Linear assemblies of gold nanoparticles show up to a 5-fold signal enhancement in plasmonic resonance peak shifts.
- Both laser interference lithography and wrinkle-assisted patterning yield comparable sensing performance.
- The platform successfully detects Tumor Necrosis Factor-Alpha (TNF-α) as a proof-of-concept.

## Abstract

Compared to individual nanoparticles, supracolloidal structures offer unique plasmonic properties with enhanced susceptibility to variations in the local refractive index. In this study, we report the template‐assisted fabrication of large‐scale (ca. 1 cm2) linear periodic assemblies of AuNPs and demonstrate their polarization‐dependent biosensing performance at the proof‐of‐concept level. We explore two complementary approaches for template fabrication: i) laser interference lithography (LIL), offering high‐fidelity patterns over moderate areas, and ii) wrinkle‐assisted patterning, a more scalable and cost‐effective strategy. Despite structural differences, both approaches yield comparable sensing performances. This demonstrates the broad potential utility of the developed biosensing platform. First, sensors are characterized through varying concentrations of glycerol/water mixtures with known refractive indices. Next, as a proof‐of‐concept application, we perform biofunctionalization and detection of the antibody for Tumor Necrosis Factor‐Alpha (TNF‐α). TNF‐α is a pro‐inflammatory cytokine that plays a multifaceted role in cancer prognosis. The shifts in plasmonic resonance peaks of the AuNP assemblies are quantified using polarized‐light vis‐NIR spectrometry during various stages of the functionalization and detection process. The experimental results reveal a pronounced polarization‐dependent plasmonic resonance peak shift (Δλ). Overall, a signal enhancement of up to 5‐fold is observed in the longitudinal mode over the transversal case, a feature consistently achieved across both LIL and wrinkled templates. These findings present an innovative supracolloidal structuring approach for the development and scalable production of highly sensitive, plasmonic biochips.

This study presents scalable methods for fabricating linear arrays of gold nanoparticles using template‐assisted self‐assembly. These supracolloidal structures show strong polarization‐dependent plasmonic responses for biosensing. Using antibody detection for Tumor Necrosis Factor‐Alpha (TNF‐α) as a proof‐of‐concept, the assemblies exhibit up to five‐fold plasmonic peak shifts in the longitudinally coupled case, highlighting their sensitivity and potential for developing advanced plasmonic biosensors.