||(a) A Polyadenosine-Coralyne Complex as a Novel Fluorescent Probe for Sensitive and Selective Detection of Heparin in Plasma |
This study presents the development of a simple, label-free, sensitive, and selective-detection system for heparin based on the use of a complex of 20-repeat adenosine (A20) and coralyne. Coralyne emitted relatively weak fluorescence in an aqueous solution. Upon the addition of A20, coralyne molecules were placed into A20 through the A2-coralyne-A2 coordination. An increase in the fluorescence of coralyne was observed because coralyne stayed away from water in the hydrophobic environment of the folded A20. The presence of heparin forced coralyne to remove from the A20-corlayne complex as a result of the formation of the coralyne-heparin complex. Because heparin promoted coralyne dimerization, the fluorescence of coralyne decreased as a function of the concentration of added heparin. This detection method is effective because the electrostatic attraction between heparin and coralyne is much stronger than the coordination between A20 and coralyne. Under optimal conditions, the heparin selectivity of this probe is approximately 100-fold over hyaluronic acid and chondroitin sulfate. The probe’s detection limit for heparin was determined to be 4 nM. This study validates the practicality of the A20-corlayne complex to determine heparin in plasma.
(b) Fe3O4 Nanoparticles-induced Fluorescence Quenching of Adenosine Triphosphate-BODIPY Conjugates：Application to Alkaline Phosphatase.
This study report that Fe3O4 Nanoparticles act as an efficient quencher for BODIPY-ATP that is highly fluorescent in bulk solution. BODIPY-ATP molecules attached to the surface of Fe3O4 NPs through the coordination between the triphosphate group of BODIPY-ATP and Fe(3+)/Fe(2+) on the NP surface. The formed complexes induced an apparent reduction in the BODIPY-ATP fluorescence, because of an oxidative-photoinduced electron transfer (PET) from the BODIPY-ATP excited state to an unfilled d shell of Fe(3+)/Fe(2+) on the NP surface. Because alkaline phosphatase can hydrolyzes the triphosphate group of BODIPY-ATP, the hydrolyzed BODIPY-ATP was incaple of binding onto Fe3O4 NPs. As a result, the presence of alkaline phosphatase restore the fluorescence of BODIPY-ATP; the detection limits at a signal-to-noise ratio of 3 alkaline phosphatase were determined to be 0.2 pM. The selectivity of this assay for other enzyme and protein is particularly high.
(c) Tween 20-Stabilized Gold Nanoparticles Combined with Adenosine TriphosphateBODIPY Conjugates for the Fluorescence Detection of Adenosine with More Than 1000-Fold Selectivity
This study describes the development of a simple, enzyme-free, label-free, sensitive, and selective system for detecting adenosine based on the use of Tween 20-stabilized gold nanoparticles as an efficient fluorescence quencher for BODIPY-ATP and as a recognition element for adenosine. BODIPY-ATP can interact with Tween 20-AuNPs through the coordination between the adenine group of BODIPY-ATP and Au atoms on the NP surface, thereby causing the fluorescence quenching of BODIPY-ATP through the nanometal surface energy transfer (NSET) effect. When adenosine attaches to the NP surface, the attached adenosine exhibits additional electrostatic attraction to BODIPY-ATP. Accordingly, in this study, the AuNP-induced fluorescence quenching of BODIPY-ATP progressively increased as the concentration of adenosine increased. The proposed system reflected a detection limit of 60 nM adenosine. The selectivity of the proposed system was greater than 1000-fold more for adenosine than for any adenosine analogs and other nucleotides. Furthermore, the proposed system combined with a phenylboronic acid-containing column was successfully applied to the determination of adenosine in urine.