A red emissive covalently bonded graphene quantum dot-Tetraaminophenylporphyrin hybrid as a probe for the sensing of L-proline

Abstract

L-Proline, the exclusive secondary amino acid with proteinogenic properties, is a vital contributor to body metabolism and the maintenance of muscle repairs, playing a pivotal role in numerous physiological processes in the human body. However, the current understanding of proline sensing is limited. In this study, we have used Tetraaminophenylporphyrin (TAPP) covalently functionalized graphene quantum dot (GQD) as a probe for the selective and sensitive detection of L-Proline. Analytical studies carried out under the optimized conditions reveal a good linear range of 9.8×10−5 M to 3.5×10−3 M with 1.6×10−7 M limit of detection. Photophysical studies reveal a ground state complex formation between the probe and proline which is responsible for the turn-off behaviour. This is not present in the case of the individual components GQD and TAPP separately which highlights the importance of covalent functionalization. The stabilization energy of the complex between the probe and different aminoacids and the corresponding hydrogen bond distances between these two moieties were calculated theoretically using density functional theory. This corroborates the enhanced stability of complex formation and the selectivity of probe towards proline compared to other aminoacids. The practical utility of the developed probe for the detection of proline in real samples like commercial milk and artificial urine is also demonstrated by spike recovery analysis which results in a recovery percent and RSD values within the acceptable limit.