Upconversional Nanoprobes with Highly Efficient Energy Transfer for Ultrasensitive Detection of Alkaline Phosphatase.

Sensitive detection of alkaline phosphatase (ALP) activity in human serum is important for diagnosis of various diseases. In this work, a novel sandwich-structured upconversion nanoparticle, NaYF4:Yb/Er@NaErF4@NaYF4, is fabricated to construct an upconversional nanoprobe for ultrasensitive detection of phosphate and ALP activity. The inner shell of NaErF4 bridges the emitters in the core with the external luminescence quenchers to greatly improve the energy transfer efficiency. The quencher, herein, is a coordination complex formed between sulfosalicylic acid and ferric ions. Owing to the higher affinity for phosphate, ferric ions dissociate from the complex and potently combine with phosphate ions, thus interrupting the energy transfer process and recovering the luminescence. This upconversional nanoprobe shows rapid and sensitive detection of phosphate with a limit of detection of 2.5 nM. Because ALP catalyzes the hydrolysis of p-nitrophenyl phosphate to form p-nitrophenol and inorganic phosphate ions, the nanoprobe is further utilized to achieve sensitive detection of ALP with a limit of detection of 0.5 µU/mL. This novel strategy offers a new opportunity for developing sensitive upconversional nanoprobes and many other energy transfer-based applications.

Real-Time Visualization of Cysteine Metabolism in Living Cells with Ratiometric Fluorescence Probes.

Sulfite from cysteine metabolism in living cells plays a crucial role in improving the water solubility of metabolic xenobiotics for their easier excretion in urine or bile. However, an imbalance of sulfite in vivo would lead to oxidative stress or age-related diseases, and an effective strategy for real-time imaging of cysteine metabolism in living cells is still lacking due to its low metabolite concentration and rapid reaction kinetics. Herein, a cyanine moiety based ratiometric fluorescence probe was developed for highly selective and sensitive detection of sulfite in aqueous solution and living cells. The free probe exhibited an orange emission color, and the fluorescence color would gradually change to blue once sulfite anions selectively reacted with the unsaturated carbon double bonds in the probe molecule. This ratiometric fluorescence manner endowed the probe excellent sensitivity with a detection limit of 0.78 nM, which was then explored to image the kinetic process of sulfite release in hepatic BRL cells after incubating with an excess amount of cysteine. This strategy opens new opportunities for revealing thiol-containing species metabolism and even quantitatively tracking their distributions in live cells or organelles.

A facile hydrothermal approach towards photoluminescent carbon dots from amino acids.

A facile one-pot method to fabricate photoluminescent carbon dots (CDs) was developed by the hydrothermal treatment of amino acids at mild temperatures. Derived from three different kinds of amino acids including serine, histidine, and cystine, the resultant CDs show uniform spherical morphology with the diameters in the range of ∼2.5-4.7nm. These amino acid derived CDs also manifest excellent photoluminescence behavior with the quantum yields (QYs) of ∼7.5% and high stability. More importantly, this method provides the opportunity to modify the sizes, structures, and photoluminescent behavior of CDs by the utilization of diversified amino acids with different structural characteristics.