Quasi-spherical silver nanoparticles for human prolactin detection by surface-enhanced Raman spectroscopy

Prolactin is a polypeptide hormone made of 199 amino acids; 50% of the amino acid chain forms helices, and the rest forms loops. This hormone is typically related to initiating and maintaining lactation, although it is also elevated in various pathological conditions. Serum prolactin levels of 2 to 18 ng ml-1 in men, up to 30 ng ml-1 in women, and 10 to 210 ng ml-1 in pregnant women are considered normal. Immunoassay techniques used for detection are susceptible to error in different clinical conditions. Surface-enhanced Raman spectroscopy (SERS) is a technique that allows for obtaining the protein spectrum in a simple, fast, and reproducible manner. Nonetheless, proper characterization of human prolactin's Raman/SERS spectrum at different concentrations has so far not been deeply discussed. This study aims to characterize the Raman spectrum of human prolactin at physiological concentrations using silver nanoparticles (AgNPs) as the SERS substrate. The Raman spectrum of prolactin at 20 ng ul-1 was acquired. Quasi-spherical AgNPs were obtained using chemical synthesis. For SERS characterization, decreasing dilutions of the protein were made by adding deionized water and then a 1 : 1 volume of the AgNPs colloid. For each mixture, the Raman spectrum was determined. The spectrum of prolactin by SERS was obtained with a concentration of up to 0.1 ng ml-1. It showed characteristic bands corresponding to the side chains of aromatic amino acids in the protein's primary structure and the alpha helices of the secondary structure of prolactin. In conclusion, using quasi-spherical silver nanoparticles as the SERS substrate, the Raman spectrum of human prolactin at physiological concentration was determined.

TNF-α detection using gold nanoparticles as a surface-enhanced Raman spectroscopy substrate

Background: TNF-α is a cytokine involved in inflammation. Surface-enhanced Raman spectroscopy (SERS) could be useful in its detection. Aim: Identify the TNF-α in an aqueous solution, using gold nanoparticles (AuNPs) as a SERS substrate. Materials & methods: Raman and SERS spectra were obtained from TNF-α samples, combined with AuNPs, with decreasing concentrations of TNF-α. The samples were analyzed using optical transmission spectroscopy, dynamic light scattering, and transmission electron microscopy. Results: Transmission electron microscopy/dynamic light scattering determined a change in the average diameter of the TNF-α/AuNPs (∼9.6 nm). Raman bands obtained were associated with aromatic amino acid side chains. We observe Raman signals for TNF-α concentrations as low as 0.125 pg/ml. Conclusion: TNF-α signal at physiological concentrations was determined with SERS.