Carbon-dots-referenced metal-organic frameworks for chemical sensing of tumor/mood biomarker 5-hydroxyindoleacetic acid in human urine: Covalent grafting blue-emitting carbon dots onto red-emitting MOF

5-HIAA (5-hydroxyindoleacetic acid) is a metabolite for 5-hydroxytryptamine which is excreted in urine and reflects human homeostatic sate. Thus, its monitoring is of great important for clinical diagnosis. In this work, blue-emitting carbon dots (BCD) were firstly synthesize and then covalently grafted onto red-emitting MOF (EuBTC), resulting in a composite sensing platform (BCD@EuBTC) with two emission bands (blue emission peaking at 441 nm and red emission peaking at 616 nm). This composite structure was characterized by means of XRD, IR, TGA, N₂ adsorption/desorption, and SEM/TEM. It was found that BCD was grafted on EuBTC surface, not loaded in its micropores, with doping level of 5.02 wt%. 5-HIAA replaced and released the BCD in BCD@EuBTC. The released BCD showed strong blue emission. In the meanwhile, EuBTC red emission was quenched by 5-HIAA thermal relaxation. As a consequence, a ratiometric sensing signal was observed for 5-HIAA. A linear working calibration curve was fitted as F/F₀ = 0.588 + 1.598*[5-HIAA], R² = 0.999, with detection of limit (LOD) determined as 0.3 μM, working region of 0.3-70 μM, and good selectivity. The practical sensing performance of BCD@EuBTC for 5-HIAA in human urine was confirmed, with recovery of 103%.

Simultaneous determination of biogenic monoamines in rat brain dialysates using capillary high-performance liquid chromatography with photoluminescence following electron transfer

Simultaneous determination of biogenic monoamines such as dopamine, serotonin, and 3-methoxytyramine in brain is important in understanding neurotransmitter activity. This study presents a sensitive determination of biogenic monoamines in rat brain striatum microdialysates using capillary high-performance liquid chromatography with the photoluminescence following electron-transfer detection technique. Separation conditions were optimized by changing the concentration of an ion-interaction agent and the percentage of an organic modifier. The high concentration of ion-interaction agent enabled the amines as a class to be separated from interfering acids, but also made the separation very long. To shorten the separation time, 10% (v/v) acetonitrile was used as the organic modifier. Eight chromatographic runs during a 3-h period were analyzed in terms of retention times, peak heights, and peak widths. Chromatograms are very reproducible, with less than 1% changes in peak height over 3 h. Typical concentration detection limits at the optimum separation conditions were less than 100 pM for metabolic acids and approximately 200 pM for monoamines. The injection volume of the sample was 500 nL. Thus, the mass detection limits were less than 50 amol for metabolic acids and approximately 100 amol for monoamines. Typical separation time was less than 10 min. To validate the technique, the separation method was applied to the observation of drug-induced changes of monoamine concentrations in rat brain microdialysis samples. Local perfusion of tetrodotoxin, a sodium channel blocker, into the striatum of an anesthetized rat decreased dopamine, 3-methoxytyramine, and serotonin concentrations in dialysates. Successive monitoring of striatal dialysates at a temporal resolution of 7.7 min showed that the injection of nomifensine transiently increased dopamine and 3-methoxytyramine concentrations in rat brain dialysate.