Physico-Chemical Aspects of Quantum Dot–Vasodialator Interaction: Implications in Nanodiagnostics

Abstract

The present work describes a comprehensive study on the interactions between the two components, namely, CdTe quantum dots (QDs) and tyrosine-bradykinin (tyr-BK), and explores the feasibility of probing bradykinin by a simple and fast quantum dot based optical method. The optical spectroscopic studies suggest that three amino acids of bradykinin are possibly involved in interactions between QDs and tyr-BK, leading to a conformational change in bradykinin. It was also observed through isothermal calorimetry that the interaction between CdTe QDs and bradykinin is an entropy driven process. The luminescence of QDs increases significantly even in the presence of micromolar concentrations of tyr-BK. The luminescence enhancement follows the Langmuir binding isotherm, and its dependence on size of QD, solvent polarity, and salt effect has also been investigated. The luminescence lifetime measurements indicate a possible association of QDs and tyr-BK. The present strategy is able to detect bradykinin in the range of 0.6–5 μM without involving any cumbersome processing. Studies investigating the roles of a physiologically important peptide hormone and the vasodialator bradykinin in disease states such as hypertension, sepsis, and asthma have been confounded by difficulties in measuring the concentration of this peptide. Therefore, such a method may be useful for quantification of bradykinin in the pathophysiology of many critical human diseases. Further, the present investigation shows that interactions between QDs and vasodialators should be taken into consideration for use of QDs in cellular imaging, drug delivery, etc., since blood is a key medium for transporting.