Single-strand DNA-scaffolded copper nanoclusters for the determination of inorganic pyrophosphatase activity and screening of its inhibitor

DNA-templated fluorescent metal nanoclusters and their illuminating applications

After the discovery of DNA during the mid-20th century, a multitude of novel methodologies have surfaced which exploit DNA for its various properties. One such recently developed application of DNA is as a template in metal nanocluster formation. In the early years of the new millennium, a group of researchers found that DNA can be adopted as a template for the binding of metal nanoparticles that ultimately form nanoclusters. Three metal nanoclusters have been studied so far, including silver, gold, and copper, which have a plethora of biological applications. This review focuses on the synthesis, mechanisms, and novel applications of DNA-templated metal nanoclusters, including the therapies that have employed them for their wide range of fluorescent properties, and the future perspectives related to their development by exploiting machine learning algorithms and molecular dynamics simulation studies.

Fluorescent metal nanoclusters: From luminescence mechanism to applications in enzyme activity assays

Metal nanoclusters (MNCs) have outstanding fluorescence property and biocompatibility, which show widespread applications in biological analysis. Particularly, evaluation of enzyme activity with the fluorescent MNCs has been developed rapidly within the past several years. In this review, we first introduced the fluorescent mechanism of mono- and bi-metallic nanoclusters, respectively, whose interesting luminescence properties are mainly resulted from electron transfer between the lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) energy levels. Meanwhile, the charge migration within the structure occurs through ligand-metal charge transfer (LMCT) or ligand-metal-metal charge transfer (LMMCT). On such foundation, diverse enzyme activities were rigorously evaluated, including three transferases and nine hydrolases, in turn harvesting rapid research progresses within past 5 years. Finally, we summarized the design strategies for evaluating enzyme activity with the MNCs, presented the major issues and challenges remained in the relevant research, coupled by showing some improvement measures. This review will attract researchers dedicated to the studies of the MNCs and provide some constructive insights for their further applications in enzyme analysis.

A universal approach for synthesis of copper nanoclusters templated by G-rich oligonucleotide sequences and their applications in sensing

Herein, five common G4 sequences have been selected, including three different length of telomere DNA, hemin aptamer, and thrombin aptamer, to synthesize Cu nanoclusters (Cu NCs) in-situ. All G4s are proper templates for Cu NCs with low temperature treatment. The particles (G4-Cu NCs) smaller than 3 nm in diameter were obtained and showed light green fluorescence. This is the first report of metal clusters templated by G4s in-situ. As proof of the concept, hemin and alkaline phosphatase (ALP) were used as the targets to test whether the system can monitor the interaction between G4s and its substrate. The results suggest that G4-Cu NCs can indicate the behavior of G4 and its interaction with hemin, and sensing ALP is achieved with the aid of ATP. The linear ranges of hemin and ALP are 300-4000 nM and 10-500 U/L, respectively, and the corresponding limits of detection as low as 97 nM for hemin and 2.8 U/L for ALP. Moreover, this present system has been successfully applied for the detection of ALP in human serum samples with satisfactory recoveries. This synthesis approach is universal, and it can be easily extended to evaluating the formation of G4, or monitoring the interaction between G4 and its substrate, or selective targeting individual G4, or sensitive detection of other important biomarkers by changing template G4 sequence.

Washing-Free and Label-Free Onsite Assay for Inorganic Pyrophosphatase Activity Using a Personal Glucose Meter

In this study, we demonstrated a personal glucose meter-based method for washing-free and label-free inorganic pyrophosphatase (PPase) detection, which relies on the cascade enzymatic reaction (CER) promoted by hexokinase and pyruvate kinase. In principle, the absence of target PPase enables adenosine triphosphate sulfurylase to catalyze the conversion of pyrophosphate (PPi) to ATP, a substrate of CER, which results in the significant reduction of glucose levels by the effective CER process. In contrast, the PPi cleavage activity works in the presence of target PPase by decomposing PPi to orthophosphate (Pi). Therefore, the CER process cannot be effectively executed, leading to the maintenance of the initial high glucose level that may be measured by a portable personal glucose meter. Based on this novel strategy, a quantitative evaluation of the PPase activity may be achieved in a dynamic linear range of 1.5-25 mU/mL with a detection limit of 1.18 mU/mL. Compared with the previous PPase detection methods, this method eliminates the demand for expensive and bulky analysis equipment as well as a complex washing step. More importantly, the diagnostic capability of this method was also successfully verified by reliably detecting PPase present in an undiluted human serum sample with an excellent recovery ratio of 100 ± 2%.

Fluorescent Biosensor Based on Hairpin DNA Stabilized Copper Nanoclusters for Chlamydia trachomatis Detection

Chlamydia trachomatis (C. trachomatis) is a kind of intracellular parasitic microorganism, which can causes many diseases such as trachoma. In this strategy, a specific hairpin DNA with the probe loop as specific regions to recognize C. trachomatis DNA with strong affinity was designed, and its stem consisted of 24 AT base pairs as an effective template for hairpin DNA-CuNCs formation. In the absence of C. trachomatis DNA, the detection system showed strong orange fluorescence emission peaks at 606 nm. In the presence of C. trachomatis DNA, the conformation of DNA probe changed after hybridizing with C. trachomatis DNA. Then, the amount of hairpin DNA-CuNCs was reduced and resulted in low fluorescence emission. C. trachomatis DNA displayed a significant inhibitory effect on the synthesis of fluorescent hairpin DNA-CuNCs due to the competition between C. trachomatis DNA and the specific hairpin DNA. Under the optimal experimental conditions, different concentrations of C. trachomatis were tested and the results showed a good linear relationship in the range of 50 nM to 950 nM. Moreover, the detection limit was 18.5 nM and this detection method possessed good selectivity. Finally, the fluorescent biosensor had been successfully applied to the detection of C. trachomatis target sequence in HeLa cell lysate, providing a new strategy for the detection of C. trachomatis.