Enhancing the optical properties of hydrophilic Ag₂Se NIR-II quantum dots by using chemometric approaches towards (bio)sensing applications

Silver chalcogenide quantum dots (QDs) are potential nanosensors for biological and environmental applications. These QDs present low toxicity and their narrow band gap makes them promising as near-infrared (NIR) photoluminescence (PL) probes, exhibiting images with higher penetrability. In addition, hydrophilicity is essential for applications in biological systems as well as detection in aqueous media. Using the same methodology, variations in synthesis conditions can alter the efficiency and performance of their intrinsic properties. Most studies seek the best conditions for each experimental variable in a univariate manner; however, multivariate strategies are a faster and more economical way to achieve this goal. Thus, in this work, we utilized chemometric approaches to enhance the NIR-II PL properties of Ag2Se QDs stabilized with 3-mercaptopropionic acid (MPA). Three experimental designs were used, totaling 58 syntheses, showing that the Ag2Se-MPA QDs, obtained under the conditions of [Ag+] of 2.5 mmol L-1, Ag : Se molar ratio of 8 : 1, MPA : Ag molar ratio of 6 : 1, heating at 70 degrees C, pH 10, and 180 min, presented the best emission profile with a maximum at 1070 nm and a FWHM of approximately 140 nm. The nanocrystals presented an average diameter of 6 nm and the orthorhombic crystalline phase. Preliminary surface-enhanced infrared absorption (SEIRA) spectroscopy assays were carried out for the detection of methyl violet 2B (MV) dye using these QDs. The enhancement factor obtained was higher than 3.5, which is comparable to those observed for other systems, namely Ag2Se-MSA QDs. These results showed the potential of the Ag2Se-MPA QDs for (bio)sensing applications.