Butanol accelerated entropy-driven DNA walking machine for rapid and ultrasensitive determination of alkaline phosphatase activity

Alkaline phosphatase (ALP) as an important biomarker as well as an index for the pasteurization degree of dairy food. However, there is a dilemma between the sensitivity and time-cost of ALP determination based on nucleic acid amplification approach. Herein, an ultrasensitive and rapid detection method for the ALP assay was developed based on entropy-driven DNA machine. In our design, the ALP catalyzed dephosphorylation of detection probe, which inhibited the digestion effect of lambda exonuclease. The remaining probe as a linker to tether the walking strand proximity to the surface of track strand modified gold nanoparticle, activating entropy-driven DNA machine. Accompany with walking strand moving, a large amount of assembled dye-labelled strand dissociated from gold nanoparticle with fluorescence recovery. More importantly, to further improve the walking efficiency, butanol was introduced to accelerated the signal amplification at interface, which short the incubation time from several hours to 5 min. Under the optimum condition, the change of fluorescence intensity was proportion to the concentration of ALP in the range from 0.05 U L^-1 to 5 U L^-1 with an ultralow limit of detection of 2.07 × 10^-3 U L^-1 was achieved, which is superior to other reported methods. Furthermore, the proposed method also successfully applied for the spiked milk sample assay with satisfactory recovery in the range of 98.83%-103.00%. This work proposed a new strategy for the application of entropy-driven DNA machine in the field of rapid and ultrasensitive detection.

Folic acid functionalized molybdenum oxide quantum dots for the detection of Cu2+ ion and alkaline phosphatase via fluorescence turn off-on mechanism

The assay of alkaline phosphatase (ALP) plays a key role in the diagnosis of various diseases. Herein, folic acid functionalized molybdenum oxide quantum dots (FA-MoO_x QDs) are explored as fluorescence "turn- off and on" probes for assaying of Cu²⁺ ion and ALP, respectively. This fluorescence sensing strategy was based on the quenching of emission peak of FA-MoO_x QDs at 445 nm by Cu²⁺ ion, followed by restoring of emission peak selectively with ALP. Based on the quenching and restoring of FA-MoO_x QDs emission intensity, quantitative assay was developed for the detection of Cu²⁺ ion (0.20 - 500 µM) and ALP (0.06 - 150 U/L) with detection limits of 29 nM and 0.026 U/L, respectively. The developed FA-MoO_x QDs-based fluorescence "turn- off and on" strategy exhibited satisfactory results for assaying of ALP in biofluids.

Silk Fibroin-Confined Star-Shaped Decahedral Silver Nanoparticles as Fluorescent Probe for Detection of Cu2+ and Pyrophosphate

A green, one-step method for the fabrication of silk fibroin (SF) protected silver decahedral nanoparticles (SF@AgNPs) has been developed. High-resolution transmission electron microscopy characterization demonstrated that the silver decahedral nanoparticles can provide more binding sites with (111) facets. Moreover, a facile strategy based on Cu²⁺ mediated SF@AgNPs was reported as an on-off-on fluorescent system for the detection of Cu²⁺, and the SF@AgNPs can be also used for the determination of pyrophosphate ion (P₂O₇^4-, PPi). The fluorescence of SF@AgNPs was quenched by Cu²⁺ as a complex formed between SF and Cu²⁺ and was restored when PPi was introduced into the system due to the higher binding affinity between PPi and Cu²⁺. Herein, a novel SF@AgNPs-Cu²⁺ fluorescent probe for Cu²⁺ and PPi detection is presented. The proposed assay shows a linear relationship at a Cu²⁺ concentration range from 1 to 6 μM with a detection limit of 33.3 nM. This simple, reliable, selective, and environmentally friendly fluorescent probe also has a wide concentration range from 100 to 700 μM with a detection limit of 6.7 μM for PPi. The 16 types of anions lead to negligible changes in the SF@AgNPs-Cu²⁺ complexes, while restoring the fluorescence intensity of the complexes when added with PPi. Additionally, it is demonstrated that the SF@AgNPs-based fluorescent assay works in real biological samples. It suggests that this proposed method has the potential for application in the clinical detection of Cu²⁺ and PPi.

Ratiometric fluorescent sensor for visual determination of copper ions and alkaline phosphatase based on carbon quantum dots and gold nanoclusters

In this work, a novel ratiometric fluorescent sensor, based on carbon dots (CDs) and gold nanoclusters (AuNCs), is developed for highly sensitive and selective visual colorimetric detection of Cu²⁺ and alkaline phosphatase (ALP). The ratiometric fluorescent sensor was synthesized by covalently linking 11-mercaptoundecanoic acid (11-MUA)-stabilized AuNCs to the surface of amino-functionalized CD/SiO₂ nanoparticles. The red fluorescence of the AuNCs can be quenched by Cu²⁺ owing to coordination between Cu²⁺ and 11-MUA; however, the blue emission of the CDs was insensitive to Cu²⁺ owing to the protective silica shell. The quenching of the AuNCs' fluorescence returned when PPi was added because of the higher affinity between Cu²⁺ and PPi than that between Cu²⁺ and 11-MUA. In the presence of ALP, PPi was catalytically hydrolyzed into phosphate (Pi), which showed a much weaker affinity for Cu²⁺. Thus, Cu²⁺ ions were released, and the fluorescence of the AuNCs was quenched once more. Based on this principle, Cu²⁺ and ALP could be simultaneously detected. The developed ratiometric fluorescent sensor could detect Cu²⁺ over a range from 0.025 to 4 μM with a detection limit of 0.013 μM and ALP over a range from 0.12 to 15 U/L with a detection limit of 0.05 U/L. The present method was successfully applied for the detection of Cu²⁺ and ALP in real water samples and in human serum samples, respectively. This ratiometric fluorescent approach may provide a highly sensitive and accurate platform for visual Cu²⁺ and ALP sensing in environmental monitoring and medical diagnosis.

Spectrophotometric, fluorimetric and electrochemical selective pyrophosphate/ATP sensing based on the dimethyltin(IV)-tiron system

Sensing of pyrophosphate anion (PPi) in the presence of nucleotide triphosphates allows the real time monitoring of the polymerase chain reaction. To get a deeper understanding of the factors involved in PPi/nucleotide triphosphate discrimination, a detailed study on the performance of a dimethyltin (IV)-catecholate complex capable of both separate fluorimetric or electrochemical detection of PPi in the presence of adenosine triphosphate (ATP) has been undertaken. Dimethyltin (IV) tightly binds PPi or ATP, and forms a stable 1:1 complex with tiron (4,5-dihydroxy-1,3-benzenedisulfonic acid) in water. The complexation equilibria with all components are characterized quantitatively by potentiometric and spectroscopic titrations. Pyrophosphate anion can be detected owing to its ability to release free tiron from the complex by measuring either a fluorimetric or an electrochemical signal. On the contrary, ATP does not displace tiron but causes an interference with PPi in the fluorimetric detection method due to the formation of a ternary Me₂Sn(IV)-tiron-ATP complex with optical properties intermediate between those of free and bound tiron. In the electrochemical (square wave voltammetry) method, the ternary ATP complex shows a separate peak which does not coincide with the peaks of neither free nor bound tiron, thus making possible the simultaneous detection of ATP in addition to PPi.

Enzyme-triggeredin situformation of Ag nanoparticles with oxidase-mimicking activity for amplified detection of alkaline phosphatase activity

ALP-triggeredin situformation of Ag NPs with high oxidase-mimicking activity for colorimetric detection of alkaline phosphatase activity.

An impedimetric determination of alkaline phosphatase activity based on the oxidation reaction mediated by Cu2+ bound to poly-thymine DNA

A novel impedimetric assay for the accurate determination of alkaline phosphatase (ALP) activity is developed based on the Cu²⁺-mediated oxidation of ascorbic acid on a poly-thymine DNA-modified electrode.

A novel glucosamine-linked fluorescent chemosensor for the detection of pyrophosphate in an aqueous medium and live cells

A glucosamine-linked Cu²⁺ ensemble has been successfully developed for detection of pyrophosphate (PPi) in aqueous medium and in live MD-AMB-231 cells.

Molybdenum oxide quantum dots prepared via a one-step stirring strategy and their application as fluorescent probes for pyrophosphate sensing and efficient antibacterial materials

MoO_x QDs were prepared using a one-step stirring treatment of MoO₃ powder in DMSO. They can be used as efficient fluorescent probes and antibacterial materials.

Cu0.89Zn0.11O, A New Peroxidase-Mimicking Nanozyme with High Sensitivity for Glucose and Antioxidant Detection

Nanomaterial-based enzyme mimetics (nanozymes) is an emerging field of research that promises to produce alternatives to natural enzymes for a variety of applications. The search for the most cost-effective and efficient inorganic nanomaterials, such as metal oxides, cannot be won by pristine CuO. However, unlike CuO, the Zn-doped CuO (Zn-CuO) nanoparticles reported in this paper reveal superior peroxidase-like enzyme activity. This places Zn-CuO in a good position to participate in a range of activities aimed at developing diverse enzyme applications. The peroxidase-like activity was tested and confirmed against various chromogenic substrates in the presence of H2O2 and obeyed the Michaelis-Menten enzymatic pathway. The mechanism of enhanced enzymatic activity was proved by employing terephthalic acid as a fluorescence probe and by electron spin resonance. The nanozyme, when tested for the detection of glucose, showed a substantial enhancement in the detection selectivity. The limit of detection (LOD) was also decreased reaching a limit as low as 0.27 ppm. Such a low LOD has not been reported so far for the metal oxides without any surface modifications. Moreover, the nanozyme (Zn-CuO) was utilized to detect the three antioxidants tannic acid, tartaric acid, and ascorbic acid and the relative strength of their antioxidant capacity was compared.

Aptamer-mediated universal enzyme assay based on target-triggered DNA polymerase activity

We herein describe an innovative method for a universal fluorescence turn-on enzyme assay, which relies on the target enzyme-triggered DNA polymerase activity. In the first target recognition step, the target enzyme is designed to destabilize detection probe derived from an aptamer specific to DNA polymerase containing the overhang sequence and the complementary blocker DNA, which consequently leads to the recovery of DNA polymerase activity inhibited by the detection probe. This target-triggered polymerase activity is monitored in the second signal transduction step based on primer extension reaction coupled with TaqMan probe. Utilizing this design principle, we have successfully detected the activities of two model enzymes, exonuclease I and uracil DNA glycosylase with high sensitivity and selectivity. Since this strategy is composed of separated target recognition and signal transduction modules, it could be universally employed for the sensitive determination of numerous different target enzymes by simply redesigning the overhang sequence of detection probe, while keeping TaqMan probe-based signal transduction module as a universal signaling tool.

Carbon quantum dots-based recyclable real-time fluorescence assay for alkaline phosphatase with adenosine triphosphate as substrate

A convenient, reliable, and highly sensitive real-time assay for alkaline phosphatase (ALP) activity in the continuous and recyclable way is established on the basis of aggregation and disaggregation of carbon quantum dots (CQDs) through the competitive assay approach. CQDs and adenosine triphosphate (ATP) were used as the fluorescent indicator and substrate for ALP activity assessment, respectively. Richness of carboxyl groups on the surface of CQDs enables their severe aggregation triggered by cerium ions, which results in effective fluorescence quenching. Under the catalytic hydrolysis of ALP, ATP can be rapidly transformed to phosphate ions. Stronger affinity of phosphate ions to cerium ions than carboxyl groups is taken advantage of to achieve fluorescence recovery induced by redispersion of CQDs in the presence of ALP and ATP. Quantitative evaluation of ALP activity in a broad range from 4.6 to 383.3 U/L with the detection limit of 1.4 U/L can be realized in this way, which endows the assay with high enough sensitivity for practical detection in human serum. The assay can be used in a recyclable way for more than three times since the generated product CePO4 as a precipitate can be easily removed from the standard assay system. This strategy broadens the sensing application of fluorescent CQDs with excellent biocompatibility and provides an example based on disaggregation in optical probe development.