# Modular Nanoparticle Platform for Solution-Phase Optical Sensing of Protein–Protein Interactions

## TL;DR

This paper introduces a nanoparticle-based method for detecting and measuring protein–protein interactions in solution using optical sensing.

## Contribution

A modular, economical nanoparticle platform for solution-phase optical sensing of protein interactions is developed.

## Key findings

- Gold-coated silver decahedral nanoparticles enable spectral shifts for detecting protein–protein interactions.
- The method allows quantification of equilibrium and kinetic binding parameters using UV–vis spectrophotometry.
- The platform requires minimal protein quantities and basic equipment for effective interaction analysis.

## Abstract

Protein–protein
interactions regulate essentially all cellular
processes. Understanding these interactions, including the quantification
of binding parameters, is crucial for unraveling the molecular mechanisms
underlying cellular pathways and, ultimately, their roles in cellular
physiology and pathology. Current methods for measuring protein–protein
interactions in vitro generally require amino acid
conjugation of fluorescent tags, complex instrumentation, large amounts
of purified protein, or measurement at extended surfaces. Here, we
present an elegant nanoparticle-based platform for the optical detection
of protein–protein interactions in the solution phase. We synthesized
gold-coated silver decahedral nanoparticles possessing high chemical
stability and exceptional optical sensing properties. The nanoparticle
surface is then tailored for specific binding to commonly used polyhistidine
tags of recombinant proteins. Sequential addition of proteins to the
nanoparticle suspension results in spectral shifts of the localized
surface plasmon resonance that can be monitored by conventional UV–vis
spectrophotometry. With this approach, we demonstrate both the qualitative
detection of specific protein–protein interactions and the
quantification of equilibrium and kinetic binding parameters between
small globular proteins. Requiring minimal protein quantities and
basic laboratory equipment, this technique offers a simple, economical,
and modular approach to characterizing protein–protein interactions,
holds promise for broad use in future studies, and may serve as a
template for future biosensing technologies.