Silver Nanosphere SERS Probes for Sensitive Identification of Pathogens

Abstract

The identification and timely detection of pathogenic bacteria is critical to ensuring safe food, health, and water. Although surface enhanced Raman scattering (SERS) methods have been used for pathogen characterization and single molecule sensing, the challenge of detecting pathogens in very low numbers using an optimal substrate that is sensitive and reproducible is still a challenge. In this report, we have developed and explored a novel SERS active substrate of 60-80 nm diameter through the assembly of Ag nanocrystals (AgNCs) into Ag nanospheres (AgNSs). A finite difference time domain (FDTD) analysis of the electromagnetic field produced by these structures and the enhancement factor calculations indicated that an enhancement of 10 8 was possible using the 633 or 785 nm excitation. The exact enhancement factors (EF) through the experimental results were calculated to be 2.47 × 10 7 , which is close to that obtained through the FDTD analysis. Preliminary characterization of the SERS substrate was demonstrated using various labels from the fluorescent dye and nonfluorescent small molecules. More importantly, these novel SERS active substrates when used for pathogenic bacteria detection could detect cells as few as 10 colony forming units/mL (CFU/ mL). Using canonical variate analysis (CVA) in conjunction with Raman spectra, differentiation of three key pathogens (E. coli O157, S. typhimurium, and S. aureus) including live and dead cells was also accomplished. With further optimization of the SERS substrate, single cell detection is possible.

Surface-enhanced Raman spectroscopy at single-molecule scale and its implications in biology

“…Organisms such as pathogens were detected successfully by a label-free approach with high sensitivity using the highly resonant plasmonic nanostructures that can give rise to the formation of multiple hot spots. For instance, pathogens were detected with silver nanospheres as SERS particles, which exhibit multiple hot spots within the structure [95]. Figure 5 demonstrates the possibility of using SM-SERS to examine the intracellular conformation and structure of biological components, a field that has not been significantly explored up to now.…”

SERS Nanotags and Their Applications in Biosensing and Bioimaging

“…3A) for protein biomarkers, providing a sound basis for the development SERS-based immunoassay. Three key components were proposed in their SERS-based immunoassay platform: [1] use of a capture substrate to specifically extract and concentrate antigens from solution; [2] selective tagging of captured antigens with functionalized external SERS nanoparticles; and [3] readout by Raman spectroscopy [126]. Microfluidic based platforms are often employed to conduct SERS-based immunoassay.…”

“…Conventional Raman spectroscopy is not sensitive and in most cases requires a large integration time, potentially resulting in damage to the sample [1]. However, the situation changed since 1970s as enhanced Raman scattering of molecules was observed by using a roughened metal surface such as silver (Ag), which could enhance by several orders of magnitude for the Raman signal of an analyte located in its proximity [2][3][4].…”

Plataformas nanoestructuradas de plata para identificación cualitativa de Escherichia coli mediante espectroscopia Raman intensificada por efecto de superficie “prueba de concepto del sistema”

“…Posteriormente, producto de la presencia de las bacterias y su interacción con el láser incidente, los pilares se alinean entre sí creando de este modo hot spots (zonas de aumento de campo electromagnético) que incrementan la intensidad de la señal Raman. Este mismo efecto ha sido utilizado para explicar el efecto SERS en otros estudios, utilizando sustratos diferentes [3,7,[16][17][18][19].…”