A new label-free and turn-on strategy for endonuclease detection using a DNA-silver nanocluster probe

A Sensitive Fluorescence Sensor for Tetracycline Determination Based on Adenine Thymine-Rich Single-Stranded DNA-Templated Copper Nanoclusters

A sensitive fluorescent sensor has been developed for the determination of tetracycline (TC) using adenine thymine (AT)-rich single-stranded DNA (ssDNA) templated copper nanoclusters (CuNCs) as a fluorescent probe. Fluorescent ssDNA-CuNCs were synthesized by employing AT-rich ssDNA as templates and ascorbic acid as reducing agents through a facile one-step method. The as-prepared ssDNA-CuNCs exhibited strong fluorescence with a large Stokes shift (240 nm) and stable fluorescence emission. In the presence of TC, the fluorescent intensity of ssDNA-CuNCs was obviously decreased through the inner filter effect, due to the spectral overlapping between ssDNA-CuNCs and TC. Under the optimal conditions, the strategy exhibited sensitive detection of TC with a linear range from 2 nM to 30 μM and with a limit of detection of 0.5 nM. Furthermore, the sensor was successfully applied for the detection of TC in milk samples. Therefore, it provided a simple, rapid, and label-free fluorescent method for TC detection.

Paper-based device for the selective determination of doxycycline antibiotic based on the turn-on fluorescence of bovine serum albumin-coated copper nanoclusters

An enhanced ratiometric fluorescence sensor was built for on-site visual detection of doxycycline (DOX) through the interaction with bovine serum albumin on the surface of red emissive copper nanoclusters. Upon the addition of weakly fluorescent DOX, the red fluorescence from copper nanoclusters gradually decreased through the inner-filter effect (IFE), while a green fluorescence appears and significantly increases, forming an interesting fluorescent isosbestic point, which was assigned to DOX due to sensitization effect of bovine serum albumin. On the basis of this ratiometric fluorescence, the system possessed good limit of detection (LOD) of 45 nM and excellent selectivity for DOX over other tetracyclines. Based on these findings, a paper-based sensor has been fabricated for distinct visual detection of trace DOX and combined with smartphone color recognizer for quantitative detection of DOX (LOD = 83 nM). This method shows broad application prospects in environmental monitoring and food safety.

DNA Templated Silver Nanoclusters for Bioanalytical Applications: A Review

Due to their unique programmability, biocompatibility, photostability and high fluorescent quantum yield, DNA templated silver nanoclusters (DNA Ag NCs) have attracted increasing attention for bioanalytical application. This review summarizes the recent developments in fluorescence properties of DNA templated Ag NCs, as well as their applications in bioanalysis. Finally, we herein discuss some current challenges in bioanalytical applications, to promote developments of DNA Ag NCs in biochemical analysis.

L-Histidine-DNA interaction: a strategy for the improvement of the fluorescence signal of poly(adenine) DNA-templated gold nanoclusters

An interesting phenomenon is described that the fluorescence signal of poly(adenine) (A) DNA-templated gold nanoclusters (AuNCs) is greatly improved in the presence of L-histidine by means of L-histidine-DNA interaction. The modified nanoclusters display strong fluorescence emission with excitation/emission maxima at 290/475 nm. The fluorescence quantum yield (QY) is improved from 1.9 to 6.5%. Fluorescence enhancement is mainly ascribed to the L-histidine-DNA interaction leading to conformational changes of the poly(A) DNA template, which offer a better microenvironment to protect AuNCs. The assay enables L-histidine to be determined with good sensitivity and a linear response that covers the 1 to 50 nM L-histidine concentration range with a 0.3 nM limit of detection. The proposed method has been applied to the determination of imidazole-containing drugs in pharmaceutical samples. A turn-on fluorescent method has been designed for the sensitive detection of L-histidine as well as imidazole-containing drugs on the basis of the L-histidine-DNA interaction.

DNA-templated silver nanoclusters as an efficient catalyst for reduction of nitrobenzene derivatives: a systematic study

Nitrobenzene compounds are highly toxic pollutants with good stability, and they have a major negative impact on both human health and the ecological environment. Herein, it was found for the first time that fluorescent DNA-silver nanoclusters (DNA-AgNCs) can catalyze the reduction of toxic and harmful nitro compounds into less toxic amino compounds with excellent tolerance to high temperature and organic solvents. In this study, the reduction of p-nitrophenol (4-NP) as a model was systematically investigated, followed by expending the substrate to disclose the versatility of this reaction. This report not only expanded the conditions for utilizing catalytic reduction conditions of DNA-AgNCs as an efficient catalyst in the control of hazardous chemicals but also widened the substrate range of DNA-AgNCs reduction, providing a new angle for the application of noble metal nanoclusters.

Fabrication of multiple molecular logic gates made of fluorescent DNA-templated Au nanoclusters

A universal platform of label-free multiple molecular logic gates have been constructed by taking the advantage of DNA-AuNCs.

A turn-on fluorescence strategy for biothiols determination by blocking Hg(II)-mediated fluorescence quenching of adenine-rich DNA-templated gold nanoclusters

Fluorescent adenine (A)-rich DNA-templated gold nanoclusters were demonstrated to be a novel probe for determination of biothiols (including cysteine, glutathione, and homocysteine). Fluorescence intensity of adenine-rich DNA-templated gold nanoclusters could be greatly quenched by Hg(II) ions through the formation of a gold nanoclusters-Hg(II) system. When biothiols (cysteine as the model) were introduced into the system, the fluorescence intensity recovered due to the formation of a more stable Hg(II)-thiol coordination complex using Hg-S metal-ligand bonds, which inhibited the Hg(II)-mediated fluorescence quenching of adenine-rich DNA-templated gold nanoclusters. Based on this fluorescence phenomenon, an on-off-on fluorescence strategy was designed for the sensitive determination of biothiols. The method allowed sensitive detection of cysteine with a linear detection range from 100 nM to 5 μM and a limit of detection of 30 nM. Additionally, the assay can be applied for detection of biothiol levels in human plasma samples. Therefore, it can provide a simple and rapid fluorescent platform for biothiol detection.

Poly(adenine)-templated fluorescent Au nanoclusters for the rapid and sensitive detection of melamine

A rapid and label-free fluorescence sensing strategy has been established for the sensitive determination of melamine (MA) on the basis of poly(adenine) (poly (A))-templated Au nanoclusters (AuNCs). The poly(A)-templated AuNCs possessed excellent luminescence and photo-stability. In the presence of Hg²⁺, the luminescence of AuNCs was quenched by Hg²⁺ through the metallophilic interactions between Au⁺ and Hg²⁺. When melamine was introduced, the fluorescence intensity of sensing system could be recovered. There was a greater coordination interaction between Hg²⁺ and melamine, which blocked the Hg²⁺-mediated fluorescence quenching of AuNCs. The assay allowed sensitive determination of melamine with a linear detection range from 50 nM to 100 μM. The limit of detection was as low as 16.6 nM. Furthermore, the label-free strategy was successfully employed for the detection of melamine concentration in real samples.

DNA-templated Au nanoclusters coupled with proximity-dependent hybridization and guanine-rich DNA induced quenching: a sensitive fluorescent biosensing platform for DNA detection

In this paper, the fluorescence signal of poly(A) DNA-templated Au nanoclusters (AuNCs) is found to be greatly quenched by photoinduced electron transfer (PET) when they are close to guanine (G)-rich DNA. Based on the findings, we have designed a low-cost fluorescence biosensing strategy for the sensitive detection of DNA. Highly luminescent and photo-stable poly(A) DNA-AuNCs were utilized as the fluorescent indicator and G-rich DNA was utilized as the fluorescent quencher. In the absence of target DNA, DNA-AuNCs failed to hybridize with the G-rich DNA and did not form the duplex DNA structure. Strong fluorescence intensity at 475 nm was observed due to the DNA-AuNCs being far away from the G-rich DNA. However, in the presence of target DNA, the DNA-AuNCs together with G-rich DNA could hybridize with the target DNA, leading to the 5' terminus of the DNA-AuNCs and the 3' terminus of G-rich DNA being in close proximity and promoting the cooperative hybridization. Therefore, a "Y" junction structure was formed and the G-rich sequences were brought close to the AuNCs. Therefore, the fluorescence intensity of the sensing system decreased significantly. Taking advantage of the poly(A) DNA-templated Au nanoclusters and G-rich DNA proximity-induced quenching, the strategy could be extended to determine other biomolecules by designing appropriate sequences of DNA probes.

Fluorescent S1 nuclease assay utilizing exponential strand displacement amplification

We devise a simple, label-free S1 nuclease activity assay by exploiting target-induced inhibition of exponential strand displacement amplification (eSDA).

The presence of a single-nucleotide mismatch in linker increases the fluorescence of guanine-enhanced DNA-templated Ag nanoclusters and their application for highly sensitive detection of cyanide

Fluorescence of DNA-templated silver nanoclusters can be enhanced by more than 100-fold by placing the nanoclusters in proximity to guanine-rich DNA sequences after hybridization. We found that the fluorescence of the guanine-enhanced silver nanoclusters is not increased with the guanine-rich DNA sequence closer to the silver nanoclusters. By studying the different numbers of mismatches in the linker sequences, we found that the presence of a single-nucleotide mismatch in the linker increases fluorescence more than the complementary nucleotide. Further study indicated the mismatch position of the linker sequence also affects the fluorescence of the hybridized DNA-Ag NCs. The evidence reported here indicated that the mismatch of the linker sequence affects the fluorescence enhancement of guanine-enhanced silver nanoclusters. We also found that DNA-Ag NCs is an excellent fluorescence sensor for cyanide, as cyanide effectively quenches the fluorescence of NCs at a very low concentration with high selectivity. Cyanide in the range from 0.10 μM to 0.35 μM could be linearly detected, with a detection limit of 25.6 nM.

MnO2 Nanosheet-based Fluorescence Sensing Platform for Sensitive Detection of Endonuclease

A novel fluorescence sensing platform for ultrasensitive detection of S1 nuclease activity has been constructed based on MnO₂ nanosheets and FAM labeled single-stranded DNA (FAM-ssDNA). In this system, MnO₂ nanosheets were found to have different adsorbent ability toward ssDNA and mono- or oligonucleotide fragments. FAM-ssDNA could adsorb on MnO₂ nanosheets and resulted in significant fluorescence quenching through fluorescence resonance energy transfer (FRET), while mono- or oligonucleotide fragments could not adsorb on MnO₂ nanosheets and still retained strong fluorescence emission. With the addition of S1 nuclease, FAM-ssDNA was cleaved into mono- or oligonucleotide fragments, which were not able to adsorb on MnO₂ nanosheets and the fluorescence signal was never quenched. The different fluorescence intensity allowed for examination of S1 nuclease activity. The developed method can detect S1 nuclease activity in the range of 0 - 20 U mL^-1 with a detection limit of 0.05 U mL^-1. Benefits of the system include less time-consuming processes and more simple design compared to other endonuclease assays. Satisfactory performance for S1 nuclease in complex samples has been successfully demonstrated with the system. The developed assay could potentially provide a new platform in bioimaging and clinical diagnosis.

DNA metallization: principles, methods, structures, and applications

This review summarizes the research activities on DNA metallization since the concept was first proposed in 1998, covering the principles, methods, structures, and applications.

A turn-on fluorescence assay of alkaline phosphatase activity using a DNA–silver nanocluster probe

A label-free fluorescence assay has been developed for the detection of alkaline phosphatase based on DNA–silver nanocluster probes.

A surface acoustic wave biosensor synergizing DNA-mediated in situ silver nanoparticle growth for a highly specific and signal-amplified nucleic acid assay

An SAW biosensor harmonizes the surface mass effect for signal-amplified and sequence-specific DNA detection in blood serum.

Colorimetric detection of hepatitis B virus (HBV) DNA based on DNA-templated copper nanoclusters

DNA detection plays an important role in early diagnosis of genetic disease. The conventional detection methods of DNA are based on expensive equipment, which do not meet the demands of developing countries. Thus, we developed a colorimetric method, which could be observed with naked eye and used copper nanoclusters for cost-effective. Moreover, the target of this method is the DNA in Hepatitis B virus that is one of the most popular chronic viral infections in developing countries over the past years. Our method was sensitive and the limit of detection was 12 × 10(9) molecules. Three-base-pair mismatches target DNA was detected easily. These results revealed the favorable sensitivity and selectivity of this approach. Most importantly, our method may have potential applications in correct diagnosis of genetic disease and monitoring of gene therapy in the poverty-stricken areas.

A sensitive fluorescence sensor for glutathione detection based on MnO2 nanosheets–copper nanoclusters composites

A sensitive fluorescence sensor has been developed for glutathione detection based on MnO₂ nanosheets–Cu NCs composites.

A nanocluster beacon based on the template transformation of DNA-templated silver nanoclusters

We developed a novel light-up nanocluster beacon for sensitive and selective DNA detection based on the template transformation by shuttling dark Ag nanoclusters to a bright scaffold through hybridization.

DNA assembled metal nanoclusters: synthesis to novel applications

In this review, we have discussed the emergence of promising environmental-benign DNA assembled fluorescent metal nanoclusters and their unique electronic structures, unusual physical and chemical properties.

A rapid, sensitive and label-free sensor for Hg(ii) ion detection based on blocking of cysteine-quenching of fluorescent poly(thymine)-templated copper nanoparticles

A rapid fluorescence sensor was developed for Hg²⁺ detection based on blocking of cysteine-quenching of poly T templated Cu NPs.

A dual-amplification fluorescent sensing platform for ultrasensitive assay of nuclease and ATP based on rolling circle replication and exonuclease III-aided recycling

A ultrasensitive, easy operated and robust assay of S1 nuclease in real samples and ATP has been successfully achieved with the dual-amplification strategy based on rolling circle replication and Exo III-aided recycling.

H2O2-mediated fluorescence quenching of double-stranded DNA templated copper nanoparticles for label-free and sensitive detection of glucose

A label-free fluorescent sensor has been developed for glucose detection based on H₂O₂-mediated fluorescence quenching of ds-DNA templated Cu NPs.

Inhibition of double-stranded DNA templated copper nanoparticles as label-free fluorescent sensors for l-histidine detection

A label-free fluorescent sensing strategy was reported for l-histidine detection by the inhibition of double-stranded DNA templated copper nanoparticles.