Nanosensing of ATP by fluorescence recovery after surface energy transfer between rhodamine B and curcubit[7]uril-capped gold nanoparticles

Simple and fast one-step FRET assay of therapeutic mAb bevacizumab using anti-idiotype DNA aptamer for process analytical technology

We developed an aptamer-based fluorescence resonance energy transfer (FRET) assay capable of recognizing therapeutic monoclonal antibody bevacizumab and rapidly quantifying its concentration with just one mixing step. In this assay, two fluorescent dyes (fluorescein and tetramethylrhodamine) labeled aptamers bind to two Fab regions on bevacizumab, and FRET fluorescence is observed when both dyes come into close proximity. We optimized this assay in three different formats, catering to a wide range of analytical needs. When applied to hybridoma culture samples in practical settings, this assay exhibited a signal response that was concentration-dependent, falling within the range of 50-2000 μg/mL. The coefficients of determination (r2) ranged from 0.998 to 0.999, and bias and precision results were within ±24.0 % and 20.3 %, respectively. Additionally, during thermal and UV stress testing, this assay demonstrated the ability to detect denatured samples in a manner comparable to conventional Size Exclusion Chromatography. Notably, it offers the added advantage of detecting decreases in binding activity without changes in molecular weight. In contrast to many existing process analytical technology tools, this assay not only identifies bevacizumab but also directly measures the quality attributes related to mAb efficacy, such as the binding activity. As a result, this assay holds great potential as a valuable platform for providing highly reliable quality attribute information in real-time. We consider this will make a significant contribution to the worldwide distribution of high-quality therapeutic mAbs in various aspects of antibody manufacturing, including production monitoring, quality control, commercial lot release, and stability testing.

Principles and Applications of Resonance Energy Transfer Involving Noble Metallic Nanoparticles

Over the past several years, resonance energy transfer involving noble metallic nanoparticles has received considerable attention. The aim of this review is to cover advances in resonance energy transfer, widely exploited in biological structures and dynamics. Due to the presence of surface plasmons, strong surface plasmon resonance absorption and local electric field enhancement are generated near noble metallic nanoparticles, and the resulting energy transfer shows potential applications in microlasers, quantum information storage devices and micro-/nanoprocessing. In this review, we present the basic principle of the characteristics of noble metallic nanoparticles, as well as the representative progress in resonance energy transfer involving noble metallic nanoparticles, such as fluorescence resonance energy transfer, nanometal surface energy transfer, plasmon-induced resonance energy transfer, metal-enhanced fluorescence, surface-enhanced Raman scattering and cascade energy transfer. We end this review with an outlook on the development and applications of the transfer process. This will offer theoretical guidance for further optical methods in distance distribution analysis and microscopic detection.

A dual-function oligonucleotide-based ratiometric fluorescence sensor for ATP detection

Adenosine triphosphate (ATP) is the main energy currency of life that plays a vital role in supporting physiological activities in living organisms, including humans. Therefore, accurate and sensitive detection of ATP concentration is necessary in biochemical research and clinical diagnosis. Herein, a ratiometric fluorescence aptasensor was developed for ATP detection. A dual-function DNA strand comprising an ATP-binding aptamer (ABA) and berberine-binding aptamer (BBA) was designed and optimized, in which ABA can capture ATP and thioflavin T (ThT), whereas BBA can capture berberine. Interestingly, the fluorescence intensity of both berberine and ThT were enhanced as they were captured by this dual-function DNA strand. In the presence of ATP, the ABA on the 3'-end of the DNA bound specifically to its target, causing ThT release and a significant drop in ThT fluorescence. However, ATP had no significant effect on the interaction between berberine and DNA, remaining the enhanced fluorescence intensity of berberine stable. Based on this interesting phenomenon, a ratiometric fluorescence sensor was constructed that used the enhanced fluorescence intensity of berberine as reference to measure the fluorescence intensity of ThT for ATP detection. This ratiometric fluorescence strategy had excellent selectivity and high sensitivity towards ATP with a detection limit (3σ) as low as 24.8 nM. The feasibility of application of this method in biological samples was evaluated in human serum and urine samples, where it exhibited a good detection performance.

Determination of aminophylline based on fluorescence quenching of amino-functionalized graphene quantum dots induced by photoilluminated riboflavin-aminophylline system

A new method based on fluorescence spectroscopy for the sensitive determination of aminophylline (AP), an antiasthmatic drug, was developed in this work. Amino-functionalized graphene quantum dots (afGQDs) were synthesized based on a two-step method and they were characterized by transmission electron microscope, UV-vis absorption spectrum and infrared spectrum. The fluorescence of afGQDs was quenched by riboflavin (Rf) via both dynamic quenching and inner filter effect. Photoilluminated Rf-AP system in the presence of oxygen produced hydroxyl radicals (OH). The latter accepted electrons from afGQDs owing to a photo-induced electron transfer process and led to the further fluorescence decline. The changing extent of the fluorescence intensity was found to be proportional to the concentration of AP in the range of 0.10-10 μg mL^-1 and the limit of detection arrived at 40 ng mL^-1. The proposed method was successfully employed for the determination of AP in a pharmaceutical sample and the recovery rate varied in the range of 99%-106%.

One-step and ultrasensitive ATP detection by using positively charged nano-gold@graphene oxide as a versatile nanocomposite

A versatile nanocomposite was simply prepared based upon the electrostatic adsorption of positively charged gold nanoparticles with negatively charged graphene oxide (nano-gold@GO), and utilized as a novel fluorescence quenching platform for ultrasensitive detection of adenosine triphosphate (ATP). In the designed system, DNA-stabilized Ag nanoclusters (DNA/AgNCs) were used as fluorescent probes, DNA duplex was formed in the presence of ATP, and they can electrostatically adsorb onto the surface of nano-gold@GO to quench the fluorescence signal. Upon the addition of exonuclease III (Exo III), the DNA duplex would be hydrolyzed into DNA fragments and resulted in the recovery of the fluorescence signals due to the diffusion of AgNCs away from nano-gold@GO. Based on these, sensitive detection of ATP was realized with a detection range of 5.0 pM-20 nM. Notably, a good recovery in the range of 94-104% was obtained when detecting ATP in human serum samples, indicating a promising application value in early disease diagnosis. Graphical abstract A functional positively charged nano-gold@graphene oxide was fabricated and utilized as an enhanced fluorescence quenching platform for the detection of ATP, coupled with exonuclease III-assisted signal amplification.

Ultrasensitive and label-free detection of ATP by using gold nanorods coupled with enzyme assisted target recycling amplification

Abnormal concentration of adenosine triphosphate (ATP) is directly asscociate with several diseases. Thus, sensitive detection of ATP is essential to early diagnosis of disease. Herein, we described an ultrasensitive strategy for ATP detection by using positively charged gold nanorods ((+)AuNRs) as an efficient fluorescence quenching platform, coupled with exonuclease Ⅲ (Exo Ⅲ) assisted target recycling amplification. To construct the sensor, DNA template that contained ATP aptamer was used for the formation of Ag nanoclusters signal probe (DNA/AgNCs), the structure of it could change to duplex after the interaction of it with ATP. Such DNA template or duplex DNA product could electrostatically adsorb onto (+)AuNRs surface, resulting in the quenching of the fluorescence signal due to the vicinity of AgNCs to (+)AuNRs. With the addition of Exo Ⅲ, DNA duplex could be hydrolyzed and released from (+)AuNRs surface, leading to the recovery of a strong fluorescent signal, while ATP could be regenerated for next target recycling. Combing the good fluorescence quenching ability of (+)AuNRs and the Exo Ⅲ assisted signal amplification, a low detection limit of 26 pM was achieved for ATP detection. Notably, the proposed method can be successfully applied for detecting ATP in serum samples, indicating a potential application value in early cancer diagnosis.

A fluorometric displacement assay for adenosine triphosphate using layered cobalt(II) double hydroxide nanosheets

A turn-on fluorometric method is described for the determination of adenosine-5'-triphosphate (ATP). It is based on the displacement of a dye-labeled oligonucleotide from a cobalt(II) based layered double hydroxide (LDH). Due to the electrostatic and ligand exchange interaction, the FAM-labeled DNA is readily adsorbed on the LDH. This leads to complete and fast quenching of the green fluorescence of the label. However, on addition of ATP, the DNA is detached from the LDH because of the stronger affinity of ATP for LDH. This results in the restoration of the green fluorescence. The effect was used to design a sensitive assay that has a linear response in the 0.5-100 μM ATP concentration range and a 0.23 μM lower detection limit. It was applied to the determination of ATP in spiked serum samples. Graphical abstract Schematic presentation of a fluorometric ATP assay based on the displacement of a dye-labeled oligonucleotide from a layered double hydroxide (LDH).

A bioinspired antifouling zwitterionic interface based on reduced graphene oxide carbon nanofibers: electrochemical aptasensing of adenosine triphosphate

An antifouling electrochemical aptasensor for ATP is described that has a zwitterionic self-assembled sensing interface on a glassy carbon electrode modified with a reduced graphene oxide carbon nanofiber (GO-CNF). The GO-CNF was first modified by self-polymerization of dopamine which provided a platform for simultaneously self-assembly of the ATP aptamer and cysteine. By using hexacyanoferrate as the electrochemical probe, in the presence of ATP, the aptamer strands fold around ATP molecules, thus leading to the variation of the electrochemical signal. The aptasensor has a linear response in the 0.1 pM to 5 nM ATP concentration range, and a 13 fM lower detection limit. The electrode is strongly resistant to nonspecific adsorption and biofouling. This enabled the detection of ATP even in spiked human plasma. Graphical abstract An antifouling electrochemical aptasensor employing reduced graphene oxide carbon nanofiber as conductive substrate and zwitterionic cysteine as antifouling material for adenosine triphosphate detection.

A colorimetric ATP assay based on the use of a magnesium(II)-dependent DNAzyme

A colorimetric assay for ATP is described that uses a strategy that combines the concept of split Mg(II)-dependent DNAzyme, split aptamer, and hybridization-induced aggregation of gold nanoparticles (AuNPs). Both ATP aptamer and Mg(II)-dependent DNAzyme are split into two fragments which are allocated to two well-designed DNA probes. The probes also possess mutually complementary stem sequences and spacer sequences. In the presence of ATP, the separated DNAzyme sequences in the two probes assemble via the synchronous recognition of ATP with two fragments of the aptamer. Then, the activated DNAzyme catalyzes multiple cycles of the cleavage of its substrate DNA sequence. The latter acts as a linker and induces the aggregation of two types of ssDNA-modified AuNP through the hybridization between the complementary sequences. Thus, the color of the AuNP solution remains red. However, in the absence of ATP, the detached aptamer cannot induce the assembly of DNAzyme to cleave the linker DNA. This results in the aggregation of AuNP and a concomitant color transition from red to purple. This ATP assay, performed at a wavelength of 530 nm, has a linear detection range that extends from 10 pM to 100 nM, with a detection limit of 5.3 pM. It was applied to the detection of ATP in human serum. Conceivably, the strategy has a wide scope in that it may be applied to the colorimetric detection of various other analytes through the split aptamer configuration. Graphical abstract Schematic presentation of colorimetric assay for adenosine triphosphate (ATP) based on the use of a split Mg(II)-dependent DNAzyme, a split aptamer, and by exploiting the hybridization-induced aggregation of gold nanoparticles that leads to a color change from red to purple.