The above illustrations of the

The above illustrations of the possibility to trigger and monitor viscosity evolution of molecular reactions using a simple physical science method open up a wider array of biological or biomedical applications to directly monitor, for instance, the effect of a drug such as warfarin on blood viscosity [17] or potential leukemia drugs with minimal sample preparation restrictions. In addition, the Fmoc-L3-OMe self-assembly could be used to follow a plethora of other molecular reaction events interfacing with a well-calibrated viscosity evolution using the splash method.
Materials and methods
Results and discussion
Conclusion By being able to observe rheological changes in the sample state with a set of parameters accessible by the setup, we showed that medium viscosity can be used and be monitored using splash imaging to follow certain types of chemical reactions. By extension, we predict that the splash imaging setup will be well suited for providing clinicians with a simple and direct method to address sample viscosity and monitor its changes over time with a resolution <1min. Applications for diagnosing diseases using blood viscosity as a biomarker, e.g. leukemia, could provide a simple point-of-care device directly usable by clinicians or even patients.
Conflict of interest
Acknowledgments The authors acknowledge the technical assistance of Matthew Barrett, Brett Duane, and Stanley Smith at the Center for Applied Nanobioscience and Medicine. The authors thank Prof. Rein Ulijn\'s group at The University of Strathclyde (Glasgow, UK) for advice on dissolving the Fmoc-L3-OMe peptide into the aqueous buffer. They are grateful for funding from the Arizona Department of Health Services (Grant ADHS-13-031272) and a partnership with Scottsdale Healthcare Research Institute.
Introduction “Chemical nose” biosensors are gaining considerable attention as a replacement to their conventional counterparts that often require biomolecules such as aptamers and fluorescent probes [1-9]. A “chemical nose” has the ability to produce unique patterns in the presence of the analyte, which facilitate the identification of the analyte [10]. Gold nanoparticles have been implemented as a “chemical nose” biosensor for the detection of proteins [1,11], cancer cells [10,12], and bacteria [6,7]. A recent strategy for detecting bacteria using gold nanoparticles has been the use of electrostatic and hydrophobic interactions between bacterial cell walls and nanoparticle surfaces coated with cetyltrimethylammonium bromide (CTAB) [6,13]. This approach provides a versatile platform for applying gold nanoparticles for the detection, identification, and quantification of bacteria. In order to exploit the potential of a gold nanoparticle-based “chemical nose,” an understanding of the parameters that control specificity and sensitivity are necessary, but to-date are not well-understood. Here, we show that controlling the shape and concentration of gold nanoparticles determines the specificity and sensitivity of the “chemical nose” biosensor. We used four gold nanoparticle shapes: nanospheres, nanostars, nanocubes, and nanorods to detect two Gram-positive (Staphylococcus aureus and Enterococcus faecalis) and two Gram-negative (Escherichia coli and Pseudomonas aeruginosa) bacteria. These bacteria are notorious for contaminating food, water, and hospital surfaces and for leading to antibiotic resistant infections [14]. Detection and identification of these bacteria at the point-of-care using a “chemical nose” biosensor will help to prevent such infections.
Materials and methods Gold nanoparticles were synthesized using previously published methods [6,13,15,16], and kept in 1mM CTAB, except for gold nanorods, which were purchased from Nanopartz Inc. (Loveland, CO, United States) and used without purification. The shapes of nanoparticles were verified using transmission electron microscopy (TEM). The methods were chosen such that each nanoparticle shape would be approximately similar in size (∼40–60nm). Bacteria were cultured, washed, and normalized to an optical density at 660nm (OD660nm) of 0.1 to provide an approximate concentration of 1×108CFU/mL [13,17]. The bacteria were then serially diluted by a factor of two to obtain dilutions of 2x−64x. Then, 100μL of each bacterial solution (eight concentrations and four species) was mixed with 200μL of each gold nanoparticle solution in a 96-well microplate in triplicates. Saline was used as a control. The mixtures were incubated overnight and UV–Visible absorption spectra were obtained from 300 to 999nm in increments of 1nm. Further details of the experiments are provided in the Supplementary material.