Selective Uropathogenic E. coli Detection Using Crossed Surface-Relief Gratings

Abstract

Urinary tract infections (UTIs) are one of the major burdens on public healthcare worldwide. One of the primary causes of UTIs is the invasion of the urinary tract by uropathogenic Escherichia coli (UPEC). Improper treatment of bacterial infections like UTIs with broad-spectrum antibiotics has contributed to the rise of antimicrobial resistance, necessitating the development of an inexpensive, rapid and accurate detection of UPEC. Here, we present real-time, selective and label-free detection of UPEC using crossed surface-relief gratings (CSRGs) as nanometallic sensors incorporated into an optical sensing platform. CSRGs enable real-time sensing due to their unique surface plasmon resonance (SPR)-based light energy exchange, resulting in detection of a very-narrow-bandwidth SPR signal after the elimination of residual incident light. The platform’s sensing ability is experimentally demonstrated by the detection of bulk refractive index (RI) changes, with a bulk sensitivity of 382.2 nm/RIU and a resolution in the order of 10−6 RIU. We also demonstrate, for the first time, CSRG-based real-time selective capture and detection of UPEC in phosphate-buffered saline (PBS) solution, in clinically relevant concentrations, as opposed to other UTI-causing Gram-negative bacteria. The platform’s detection limit is calculated to be 105 CFU/mL (concentration on par with the clinical threshold for UTI diagnosis), with a dynamic range spanning four orders of magnitude. This work paves the way for the development of inexpensive point-of-care diagnosis devices focusing on effective treatment of UTIs, which are a burden on public healthcare due to the rise in the number of cases and their recurrences in the recent past.

Cicada Wing Inspired Template-Stripped SERS Active 3D Metallic Nanostructures for the Detection of Toxic Substances

“…Fabrication of the CSRGs was performed using the rapid and high-throughput interferometric technique described elsewhere [ 19 , 21 , 26 ]. Azobenzene molecular glass (gDR1) solution (DR1-glass, 2.99 mM, 94%) was prepared according to the methods described elsewhere [ 45 ].…”

“…Nanostructures that support surface plasmon resonance (SPR) have been widely used for sensing and biosensing applications through the use of different techniques, including SPR spectroscopy [ 19 , 20 , 21 , 22 , 23 , 24 , 25 ], SPR imaging [ 26 , 27 , 28 , 29 ] and surface-enhanced Raman scattering (SERS) spectroscopy [ 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 ]. SERS, particularly, allows for highly sensitive detection and specific identification of analytes.…”

“…The polarization dependency of the nanostructures can be overcome by structuring them into a 2-dimensional (2D) arrangement. Crossed relief gratings (CSRGs) are 2D nanostructures that enable polarization-independent SERS detection, offering enormous potential for specific analyte sensing [ 19 , 21 , 26 ]. SPR excitation by one of the superimposed gratings is re-radiated by its orthogonal counterpart in a polarization state that is orthogonal to that of the incident light.…”

Nanophotonics for bacterial detection and antimicrobial susceptibility testing

“…Therefore, if the CSRG is placed between two cross polarizers and illuminated by broadband light, a peak in the transmission spectrum is observed and used for biosensing. This principle enabled to simplify the optical setup compared to traditional SPR, even though more modest LODs were achieved (<10 5 CFU/mL for Escherichia coli) [38].…”

FDTD Analysis of Hotspot-Enabling Hybrid Nanohole-Nanoparticle Structures for SERS Detection

“…Minute changes in RI cause a resonance shift in its reflection or transmission spectra, enabling not only the detection but also the quantification of analytes. In the context of (bio)sensing, this phenomenon has found applications in techniques such as SPR spectroscopy [ 1 , 2 , 7 , 8 ], SPR imaging [ 3 , 4 , 9 ], and surface-enhanced Raman scattering (SERS) spectroscopy [ 10 , 11 , 12 ]. SERS is a light scattering-based technique that enables the detection of chemical and biological analytes in a label-free fashion owing to the inherent and unique vibrational modes of the molecules.…”