Luminescent carbogenic dots for the detection and determination of hemoglobin in real samples

Abstract

4,7,10-Trioxa-1,13-tridecanediamine (TTDDA) is widely used for surface passivation during the synthesis of 0D quantum dots (QDs), whereas alcohol is commonly used as the reaction medium. However, following the completion of the reaction, the fate of excess TTDDA is hardly known. Herein, it is reported that luminescent carbogenic dots (Cdots) are simultaneously produced through the polymerization of TTDDA while preparing tin dioxide nanocrystals (SnO₂ NCs) even at low temperatures (80 °C). The structural characteristics of the SnO₂ NCs and Cdots were analyzed using spectroscopic and microscopic techniques. It is surmised that the oxidative coupling of TTDDA takes place initially, resulting in polymeric fragments. Such polymeric fragments undergo carbonization in the subsequent stages to generate highly luminescent carbogenic dots (termed as Cdots). The emission characteristics of Cdots (4.1 ± 0.8 nm) are found to be highly sensitive and selective towards the detection of trace amounts of hemoglobin (H_b), resulting in the turn-off of photoluminescence. Using spectrometric techniques, the limit of detection (LOD) for the H_b measurement is found to be 16 nM. The ground state complexation between Cdots and H_b accomplishes exceptional quenching behaviour. A fluorescent test strip fabricated with Cdots was prepared for the rapid on-spot determination of H_b. Finally, the as-prepared Cdots and their emission properties were successfully used for the selective detection and exact quantification of H_b in blood samples collected from volunteers. Also, the presence of trace amounts of blood in human urine was detected with a fluorescent test strip using the turn-off photoluminescence of Cdots. The present results suggest that the formation of luminescent carbogenic polymeric dots occurs as a side reaction during the synthesis of SnO₂ NCs that results in highly fluorescent as-synthesized products.