Active Surface Hydrophobicity Switching and Dynamic Interfacial Trapping of Microbial Cells by Metal Nanoparticles for Preconcentration and In-Plane Optical Detection

Abstract

The surface hydrophobicity of a microbial cell is known to be one of the important factors in its adhesion to an interface. To date, such property has been altered by either genetic modification or external pH, temperature, and nutrient control. Here we report a new strategy to engineer a microbial cell surface and discover the unique dynamic trapping of hydrophilic cells at an air/water interface via hydrophobicity switching. We demonstrate the surface transformation and hydrophobicity switching of Escherichia coli (E. coli) by metal nanoparticles. By employing real-time dark-field imaging, we directly observe that hydrophobic gold nanoparticle-coated E. coli, unlike its naked counterpart, is irreversibly trapped at the air/water interface because of elevated hydrophobicity. We show that our surface transformation method and resulting dynamic interfacial trapping can be generally extended to Gram-positive bateria, Gram-negative bacteria, and fungi. As the dynamic interfacial trapping allows the preconcentration of microbial cells, high intensity of scattering light, in-plane focusing, and near-field enhancement, we are able to directly quantify E. coli as low as 1.0 × 103 cells/ml by using a smartphone with an image analyzer. We also establish the identification of different microbial cells by the characteristic Raman transitions directly measured from the interfacially trapped cells.

Exposure to metal nanoparticles changes zeta potentials of Rhodococcus cells

“…Conversely, treatment with Fe 3 O 4 NPs resulted in a decrease in the adhesive activity of both R. jostii and R. ruber cells, especially at the highest concentration (1 g/L). There is only one report in the literature on the effect of metal nanoparticles on the surface hydrophobicity of microbial cells [ 27 ]. The authors proposed a new strategy to engineer a hydrophobic cell surface using the coating with gold NPs in order to increase the microbial adhesion at the air-water interface.…”

Microstructured Surfaces for Reducing Chances of Fomite Transmission via Virus-Containing Respiratory Droplets

“…Here, we proposed a robust particle capture surface that allows the directional particle aggregation of microdroplets by controlling the 3D geometry and surface chemistry of the substrate for low contact transfer from the fomites contaminated by respiratory droplets. Although we focused on the low efficacy of transfer from the contaminated microstructured surfaces to other clean surfaces in this study, we expect that the microcavity surfaces will help limit the contact transfer of various pathogens from contaminated objects (i.e., hands) to recipient surfaces due to their small contact area (∼0.21 for hexawall and ∼0.015–0.03 for ipyrawall). , The efficient particle capturing ability of the microcavity structures not only prevents fomite-based transmission but also may be utilized to preconcentrate target analytes, which may be useful for the environmental monitoring or Raman spectroscopy of pathogens, including SARS-CoV-2. − In addition to the mechanical and chemical stability of surfaces observed after spray cleaning (Figure S10) and the ability to capture particles even without cleaning (Figures S11–13), our engineered surfaces are highly compatible with large-scale manufacturing techniques. ,, For example, we have applied a R2R imprinting process to achieve scalable high-throughput fabrication of interconnected microcavity surfaces (Figure C). With cost-effective large-scale fabrication, our microstructured surfaces will find a wider range of applications in various fields.…”

Colloidal Multiscale Assembly via Photothermally Driven Convective Flow for Sensitive In‐Solution Plasmonic Detections

“…In Figure S11b in the Supporting Information, the concentration-dependent Raman spectra for E. coli show that E. coli was detectable at a low concentration of 2.3 × 10 2 CFU mL −1 , which is a 100-fold improvement in the detection limit for E. coli compared with previously reported values for bacterial detection. [37][38][39][40] To quantitatively investigate the Raman enhancement of E. coli in our method, we also measured the Raman enhancement of E. coli obtained using 2D GNR layers and pre-assembled 3D GNRs (Figure 5e). The Raman enhancement of E. coli at 1335 cm -1 for the pre-assembled GNRs was found to be slightly higher (approximately twofold) than that obtained from the 2D GNR monolayer.…”