Electroplating based engineering of plasmonic nanorod metamaterials for biosensing applications

TL;DR

This paper develops an optimized electroplating method for fabricating vertical gold nanorod metamaterials, enhancing biosensing capabilities by improving structure control and reducing costs compared to traditional vacuum deposition techniques.

Contribution

It introduces a detailed electroplating process for gold nanorod arrays, including pH and parameter optimization, offering a cost-effective alternative to physical vapor deposition for biosensor applications.

Findings

Optimal pH range for immersion deposition identified (6.0-7.0).

Electroplating time and DC voltage control nanorod geometry.

Electroplating provides a faster, cheaper fabrication method.

Abstract

Sensing lower molecular weight in a diluted solution using a label-free biosensor is challenging and requires a miniaturized plasmonic structure, e.g., a vertical Au nanorod (AuNR) array based metamaterials. The sensitivity of a sensor mainly depends on transducer properties and hence for instance, the AuNR array geometry requires optimization. Physical vapour deposition methods (e.g., sputtering and e-beam evaporation) require a vacuum environment to deposit Au, which is costly, time-consuming, and thickness-limited. On the other hand, chemical deposition, i.e., electroplating deposit higher thickness in less time and at lower cost, becomes an alternative method for Au deposition. In this work, we present a detailed optimization for electroplating based fabrication of these metamaterials. We find that slightly acidic (6.0 < pH < 7.0) gold sulfite solution supports immersion deposition, which should be minimized to avoid uncontrolled Au deposition. Immersion deposition leads to plate-like (for smaller radius AuNR) or capped-like, i.e., mushroom (for higher radius AuNR) structure formation. The electroplating time and DC supply are the tuning parameters that decide the geometry of the vertically aligned AuNR array in area-dependent electroplating deposition. This work will have implications for developing plasmonic metamaterial based sensors.