Image created by Dr. Michael J. Miller
In a study published in the Gold Bulletin journal by a group of researchers from the Center for Applied Physics and Advanced Technology (CFATA) and National School of Higher Education (ENES), Leon, both from the National Autonomous University of Mexico (UNAM), Mexico, proposes the use of glycan-targeting nanoparticles, namely gold nanoparticles encapsulated with Concanavalin A (lectin), for the detection of bacteria using label-free, surface-enhanced Raman spectroscopy (SERS).
Bacterial infections represent one of the major threats to public health, especially due to the increase in drug-resistant strains. Rapid, precise and inexpensive methods are needed to detect or treat diseases caused by infections. In this work, researchers explore the use of Raman spectroscopy for detection purposes.
Raman spectroscopy has become an inevitable tool in biomedicine as it allows nondestructive, fast and reliable analysis of specific structures. Under an interesting variation, gold nanoparticles can be added to significantly enhance Raman signals, a phenomenon due to nanogold electromagnetic features.
However, cells, tissues and microorganisms display lots of chemical compounds on their surfaces, making the development of Raman-based sensors extremely difficult.
In this work, we have functionalized gold nanoparticles with Concanavalin A, a protein specifically binding to glucose and mannose. While these two sugars are commonly found in bacterial cell surfaces, the complex structures to which they are attached frequently correspond to highly species-specific glycans. Therefore, the sugar-binding gold nanoparticles may allow the enhancement of Raman signals mainly from those highly specific glycans.
Our approach made a proof of concept by adding the functional particles to three distinct bacterial samples, Escherichia coli, Bacillus subtilis, and Mycobacterium fortuitum, before Raman analysis.
As expected, nanoparticles were readily attached to bacterial cell surface components, and distinct Raman spectra could be obtained from each strain. Notwithstanding, a great diversity of lectins is now available, opening novel possibilities for the search for sensing methods in other biomedical applications. The reported approach is now being assessed for microbial detection in real-world samples.
Reference
Ravichandran Manisekaran et al, Concanavalin A-functionalized nanogold—a glycan tag for surface enhanced Raman spectroscopy, Gold Bulletin (2025). DOI: 10.1007/s13404-025-00367-9
Abstract
Bacterial infections constitute one of the major health issues for the next decades, and their detection through affordable methods is currently an urgency. Cell surface glycans constitute interesting biomarkers, since they are specific, abundant, and diverse. However, their identification has been commonly based on sophisticated, high-cost techniques, such as mass spectrometry or immunolabeling. We herein propose a surface-enhanced Raman spectroscopy (SERS) approach based on optically active gold nanoparticles targeted to D-mannoside and D-glucoside, two common terminal sugars of bacterial glycans. To do so, nanoparticles were decorated with Concanavalin A through a simple physisorption step before using them to generate Raman signals. The use of the construct with beta-methyl-D-mannoside, a well-known Concanavalin A ligand, was found to generate SERS signals of dose-dependent intensities. Moreover, the application of the functional system with three different bacterial species induced differential SERS profiles that included Raman bands specific to cell surface glycolipids. Transmission electron microscopy analyses of bacterial-nanogold preparations revealed that both cell surface and secreted glycans can be tagged by using the gold-lectin construct. Further research is therefore encouraged to better assess this functional nanotag in microbial detection.