Short communication “Chemical nose” for the visual identification of emerging ocular pathogens using gold nanostars Mohit S. Verma a,b,1 , Paul Z. Chen a,1 , Lyndon Jones a,c , Frank X. Gu a,b,n a Department of Chemical Engineering, University of Waterloo, 200 University Avenue W, Waterloo, Ontario, Canada N2L 3G1 b Waterloo Institute for Nanotechnology, University of Waterloo, 200 University Avenue W, Waterloo, Ontario, Canada N2L 3G1 c Center for Contact Lens Research, University of Waterloo, 200 University Avenue W, Waterloo, Ontario, Canada N2L 3G1 article info Article history: Received 26 March 2014 Received in revised form 16 May 2014 Accepted 19 May 2014 Available online 27 May 2014 Keywords: Color change Visual detection Microbial keratitis Contact lens cases Gold nanoparticles Point-of-care abstract Ocular pathogens can cause serious damages in the eye leading to severe vision loss and even blindness if left untreated. Identification of pathogens is crucial for administering the appropriate antibiotics in order to gain effective control over ocular infection. Herein, we report a gold nanostar based “chemical nose” for visually identifying ocular pathogens. Using a spectrophotometer and nanostars of different sizes and degrees of branching, we show that the “chemical nose” is capable of identifying the following clinically relevant ocular pathogens with an accuracy of 99%: S. aureus, A. xylosoxidans, D. acidovorans and S. maltophilia. The differential colorimetric response is due to electrostatic aggregation of cationic gold nanostars around bacteria without the use of biomolecule ligands such as aptamers or antibodies. Transmission electron microscopy confirms that the number of gold nanostars aggregated around each bacterium correlates closely with the colorimetric response. Thus, gold nanostars serve as a promising platform for rapid visual identification of ocular pathogens with application in point-of-care diagnostics. & 2014 Elsevier B.V. All rights reserved. 1. Introduction Microbial keratitis poses a great risk for vision loss (Bertino, 2009). Contact lenses are the most common risk factor that predispose wearers to keratitis (Tilia et al., 2014; Stapleton and Carnt, 2012; Bui et al., 2010; Hall and Jones, 2010; Green et al., 2008; Keay et al., 2006; de Oliveira et al., 2003). The fundamental challenge in mitigating keratitis is detecting these pathogens early and more importantly, identifying the species for designing a more effective treatment regimen (Mascarenhas et al., 2014; Inoue and Ohashi, 2013; Hau et al., 2010). The current gold standard for identifying the pathogens relies on microbial cultures or genomic analysis, which must be done in a central laboratory (Taravati et al., 2013). Recent advances in biosensors offer the potential to perform these tests at the point-of- care (Chan and Gu, 2013; Verdoy et al., 2012). Common approaches employ a colorimetric method (Safavieh et al., 2014; Li et al., 2011) or microelectronics for sensing (Oh et al., 2013; Safavieh et al., 2012; Siddiqui et al., 2012; Pohlmann et al., 2009). A recent study has shown improvement of detection capabilities to allow sub-cellular measurements of individual cells (Kanwal et al., 2013). However, a major challenge remains to be solved: identifying species of bacteria at the point-of-care, which is crucial because of growing antibiotic resistance (Bertino, 2009) and unique drug susceptibility profiles of pathogens (Jacquier et al., 2012). Lately, the prevalence of Gram- negative Achromobacter (Park et al., 2012; Ahmed and Pineda, 2011; Kiernan et al., 2009), Stenotrophomonas (Dantam et al., 2011) and Delftia (Ray and Lim, 2013) has been emphasized because of their innate ability to form biofilms in contact lenses and their accompany- ing cases. Moreover, these pathogens present an increasing problem due to their capability to survive in contact lens care solutions (Wiley et al., 2012) and cause microbial keratitis (Hall and Jones, 2010). Hence, there exists a need for a platform that rapidly identifies multiple pathogens affecting contact lens wearers. Gold nanoparticles have been used extensively as colorimetric biosensors due to their high absorption coefficients, enhanced scattering, unique localized surface plasmon resonance and high surface area to volume ratio (Azzazy et al., 2012; Li et al., 2012; Chen et al., 2010). The optical properties of gold nanoparticles can be further exploited by varying their shape, size and surface characteristics. Gold nanostars are an interesting class of nano- particles; their optical properties can be fine-tuned by altering the size and degree of branching (Verma et al., 2014; Shao et al., 2012; Kumar et al., 2008). Nanostars coated with specific antibodies have demonstrated the colorimetric detection of a single species of Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/bios Biosensors and Bioelectronics http://dx.doi.org/10.1016/j.bios.2014.05.045 0956-5663/& 2014 Elsevier B.V. All rights reserved. n Corresponding author at: Department of Chemical Engineering, University of Waterloo, 200 University Avenue W, Waterloo, Ontario, Canada N2L 3G1. Tel.: þ1 519 888 4567x38605; fax: þ1 519 888 4347. E-mail address: frank.gu@uwaterloo.ca (F.X. Gu). 1 Authors contributed equally. Biosensors and Bioelectronics 61 (2014) 386–390