Determination of adenosine triphosphate based on the use of fluorescent terbium(III) organic frameworks and aptamer modified gold nanoparticles.

A thiol-labeled adenosine triphosphate (ATP) binding aptamer is covalently linked on the surface of gold nanoparticles (AuNPs). This warrants protection of the red AuNPs from aggregation in high salt condition. The dispersed AuNPs can quench the fluorescence of the Tb(III)-MOFs at 547 nm with the excitation wavelength of 290 nm. This is ascribed to the combined action of inner filter effect, dynamic quenching and fluorescence resonance energy transfer. If the aptamer binds ATP to form folded structures, the AuNPs aggregate in high salt medium and the green fluorescence of the Tb(III)-MOFs is recovered. This method shows good sensitivity and selectivity for ATP, and the linear range is from 0.5 to 10 µM of ATP with the detection limitat of 0.32 µM. It was applied to the determination of ATP in (spiked) human plasma with satisfactory recoveries (from 93.2% to 106.3%). Oppositely, when the unlabeled aptamer is used instead of thiol-labeled aptamer in this process, the ATP-aptamer complexes rather than unlabeled aptamer provide greater protection for AuNPs against salt-induced aggregation. It is found that when the aptamer covalently binds to AuNPs, the steric hindrance is dominant for the stabilization of AuNPs; for unlabeled aptamer, the electrostatic repulsion is responsible for their stability, irrespective of whether ATP is present or not. These two different forces lead to the aggregation or dispersion of AuNPs with addition of target in salt solution. Graphical abstractThe impact of two repulsive forces (electrostatic repulsion and steric repulsion) on the stabilization of gold nanoparticles, and its application in fluorescent terbium metal-organic frameworks as a nanoprobe for adenosine triphosphate.

Facile conversion of ATP-binding RNA aptamer to quencher-free molecular aptamer beacon.

We have developed RNA-based quencher-free molecular aptamer beacons (RNA-based QF-MABs) for the detection of ATP, taking advantage of the conformational changes associated with ATP binding to the ATP-binding RNA aptamer. The RNA aptamer, with its well-defined structure, was readily converted to the fluorescence sensors by incorporating a fluorophore into the loop region of the hairpin structure. These RNA-based QF-MABs exhibited fluorescence signals in the presence of ATP relative to their low background signals in the absence of ATP. The fluorescence emission intensity increased upon formation of a RNA-based QF-MAB·ATP complex.

A terbium-based metal-organic framework@gold nanoparticle system as a fluorometric probe for aptamer based determination of adenosine triphosphate.

This study reports on a method for fluorometric aptasensing of adenosine triphosphate (ATP). It is based on the interaction of dispersed (red) and agglomerated (blue) gold nanoparticles (AuNPs) with a water-dispered terbium(III) based metal-organic framework (Tb-MOF). The dispersed AuNPs quench the emissions of the Tb-MOF, while the aggregated AuNPs have little effect. Under the condition of high salt concentration, the free aptamer against ATP does not stabilize the AuNPs against aggregation. This causes a color change from red to blue and weak quenching of the fluorescence of the Tb-MOF (with peaks at 489 nm and 544 nm after excitation at 290 nm). On addition of ATP, it will be bound by its aptamer to form a complex that is adsorbed on the AuNPs. This protects the AuNPs from salt-induced aggregation and the color (with a peak at 525 nm) remains red. The two fluorescence bands of the Tb-MOF are therefore suppressed by fluorescence resonance energy transfer (FRET) between Tb-MOF and the dispersed AuNPs. Fluorescence drops linearly in the 50 nM to 10 µM ATP concentration range, and the detection limit is 23 nM. ATP analogs such as guanosine triphosphate, uridine triphosphate, cytidine triphosphate, adenosine monophosphate and cyclic adenosine monophosphate have no obvious interference. The method was successfully applied to the determination of ATP in (spiked) human plasma samples and gave satisfactory recoveries. Graphical abstract Schematic of a terbium-based metal-organic framework@gold nanoparticle system as a fluorometric probe for aptamer based determination of adenosine triphosphate. The dispersed gold nanoparticles (AuNPs) quench the fluorescence of the terbium-based metal-organic framework (Tb-MOF), while the aggregated AuNPs have little effect. In the presence of adenosine triphosphate (ATP), the aptamer-ATP complexes provide greater protection towards AuNPs than aptamer alone under high salt condition. Based on this, a novel Tb-MOF@AuNP platform is established for ATP detection.