Metal Ion Sensing with Phenylenediamine Quantum Dots in Blood Serum

Among numerous optical sensing techniques, lifetime analysis of fluorescent agents has several advantages, including high responsivity to local environmental changes and reduced susceptibility to random light-scattering events during through-tissue imaging. Monitoring ion concentrations in blood vessels is among the applications for which fluorescent approaches can be particularly beneficial. However, without additional biochemical conjugation approaches, fluorescent agents lack specificity; namely, they are either weakly sensitive to salt concentrations or provide a strong nonspecific response. Here we demonstrate the efficacy of phenylenediamine carbon dots exhibiting a strong fluorescence lifetime response to the common microelements in blood such as Fe²⁺, Fe³⁺, and Co²⁺ ions while remaining insusceptible to Na²⁺, Ca²⁺, Mn²⁺, Mg²⁺, Zn²⁺, and Ni²⁺ ions. The paper also discusses the physical mechanisms underlying the observed selective sensitivity of the obtained CDs. Sensing performances of the carbon dots were also demonstrated with model cells on pathways to in vivo applications.