Highly Selective Fluorescence Determination of the Hematin Level in Human Erythrocytes with No Need for Separation from Bulk Hemoglobin

(Chemical Equation Presented) Hematin-induced fluorescence quenching of boron-doped graphene quantum dots (BGQDs) allows for determination of hematin concentration in human erythrocytes with no need for separating hematin from hemoglobin before performing the assay. The BGQDs are made by oxidizing a graphite anode by holding the voltage between a graphite rod and a Pt cathode at 3 V for 2 h in an aqueous borax solution at pH 7; then, the borate solution was filtered with BGQDs, and the borate was dialyzed from the filtrate, leaving a solution of BGQDs in water. The fluorescence intensity of BGQDs is measurable in real time, and its quenching is very sensitive to the concentration of hematin in the system but not to other coexisting biological substances. The analytical signal is defined as ΔF = 1 - F/F₀, where F₀ and F are the fluorescence intensities of the BGQDs before and after interaction with hematin, respectively. There is a good linear relationship between ΔF and hematin concentration, ranging from 0.01 to 0.92 μM, with the limit of detection (LOD) being ∼0.005 ± 0.001 μM at a signal-to-noise ratio of 3. This new method is sensitive, label-free, simple, and inexpensive, and many tedious procedures related to sample separation and preparation can be omitted, implying that this method has potential for applications in clinical examinations and disease diagnoses. For example, the determination of the hematin levels in two kind of red blood cell samples, healthy human and sickle cell erythrocytes, gives average concentrations of hematin of ∼(23.1 ± 4.9) μM (average of five samples) for healthy red cell cytosols and ∼(52.5 ± 9.5) μM (average of two samples) for sickle red cell cytosols.