Development of uncoated near-spherical gold nanoparticles for the label-free quantification of Lactobacillus rhamnosus GG by surface-enhanced Raman spectroscopy

Surface‐enhanced Raman spectroscopy using uncoated gold nanoparticles for bacteria discrimination

“…As mentioned in our previous work, Raman signal enhancement of LGG bacterial strain using synthesized uncoated spherical AuNPs might be especially due to the combination of anion‐induced chemical enhancement and nanoparticle aggregation onto the bacteria cell wall. Aggregation was consecutive to non‐specific interactions likely with functions present in the components constitutive of the bacteria cell wall such as amine or carboxylic acid functions showing relatively great affinity for gold.…”

“…An increase in UV–Vis absorption intensity at longer wavelength region (between 600 and 800 nm) was also observed due to the LSPR feature of the aggregated nanoparticles (Figure b) . In case of AuNPs, no significant evolution in UV–Vis (Figure c) or size distribution properties was observable when R6G solution was added indicating that the suspension remained in its initial long‐term stability state …”

“…Data collection was operated using the Holoreact™ software. In case of AuNPs, the experimental protocol described in a previous study was followed . Briefly, 50 μl of the bacterial suspensions or R6G solution was added to 5 ml of the nanoparticle suspensions, and SERS signals were then recorded after an incubation time of 10 min.…”

“…Several studies have investigated the use of nanoparticles as SERS substrates for the label‐free detection, identification, or quantification of microorganisms: Most of them involved silver structures, and, to our knowledge, very few used non‐functionalized gold nanoparticles (AuNPs) . The invoked reason is that silver substrates usually exhibit the highest SERS activity.…”

“…In this context, we developed in a previous work a SERS method based on uncoated spherical AuNPs, which was successfully used for the quantification of Gram‐positive Lactobacillus rhamnosus GG ( LGG ) . Raman signal enhancement of the LGG bacteria appeared to be mainly due to the combination of anion‐induced chemical enhancement and an unexpected positive effect related to nanoparticle aggregation directly onto the bacteria cell wall.…”