Gold nanostars for the colorimetric detection of emerging bacterial contaminants that affect contact lens wearers

Abstract

 

Purpose

 

Biofilms formed on contact lens cases are a threat to wearers and lead to inflammatory complications. Several strategies have attempted to eliminate bacteria and biofilms but have been unsuccessful. This study provides a biosensor based on gold nanostars for detecting emerging pathogenic contaminants colorimetrically.

 

Methods

 

Two types of gold nanostars differing in size, morphology and color (blue and red) were synthesized using a seed-mediated surfactant-assisted growth method. In addition, the two nanostars were mixed in a 50:50 ratio to produce a third (purple) color and hence, three different colorimetric responses were possible in the presence of bacteria. Five strains of bacteria were tested: Staphylococcus aureus, Achromobacter xylosoxidans, Serratia marcescens, Delftia acidovorans and Stenotrophomonas maltophilia. A concentration dependent colorimetric response was obtained for each bacteria in the range of 10⁵ to 10⁹ CFU/mL. Transmission electron microscopy was used to image the interactions between the gold nanostars and the bacteria.

 

Results

 

The concentration dependent responses demonstrated a unique curve for each organism that was tested. These curves suggest that it is possible to distinguish between the five strains of bacteria if the three different nanoparticle solutions are used. Additionally, the gold nanostars were most sensitive towards Delftia acidovorans and least sensitive towards Achromobacter xylosoxidans with limits of detection of 5.6x10⁴ CFU/mL and 4.7x10⁶ CFU/mL respectively. Transmission electron microscopy showed that the mechanism of detection is the aggregation of gold nanostars around the bacteria due to electrostatic interactions. Such an aggregation causes a shift in the surface plasmon resonance of gold nanoparticles and hence leads to a color change.

 

Conclusions

 

Biosensors based on gold nanostars provide a simple colorimetric signal in the presence of bacteria. These biosensors are able to exploit the natural variation in charge and morphology on the surface of bacteria and do not require the use of expensive ligands such as antibodies or aptamers. Thus, gold nanostars used in this novel biosensor system are a promising platform for detecting and differentiating emerging contaminants in contact lens cases and lenses.

 

 

Three gold nanostar solutions produce a unique color change in the presence of different pathogenic bacteria.

 

Keywords: 607 nanotechnology • 477 contact lens • 496 detection