Nanozyme Inhibited Sensor Array for Biothiol Detection and Disease Discrimination Based on Metal Ion-Doped Carbon Dots.

Developing highly active and sensitive nanozymes for biothiol analysis is of vital significance due to their essential roles in disease diagnosis. Herein, two metal ion-doped carbon dots (M-CDs) with high peroxidase-like activity were designed and prepared for biothiol detection and identification through the colorimetric sensor array technique. The two M-CDs can strongly catalyze the decomposition of H2O2, accompanied by color changes of 3,3',5,5'-tetramethylbenzidine (TMB) from colorless to blue, indicating peroxidase-mimicking activities of M-CDs. Compared with pure carbon dots (CDs), M-CDs exhibited enhanced peroxidase-like activity owing to the synergistic effect between metal ions and CDs. However, due to the strong binding affinity between biothiols and metal ions, the catalytic activities of M-CDs could be inhibited by different biothiols to diverse degrees. Therefore, using TMB as a chromogenic substrate in the presence of H2O2, the developed colorimetric sensor array can form differential fingerprints for the three most important biothiols (i.e., cysteine (Cys), homocysteine (Hcy), and glutathione (GSH)), which can be accurately discriminated through pattern recognition methods (i.e., hierarchical clustering analysis (HCA) and principal component analysis (PCA)) with a detection limit of 5 nM. Moreover, the recognition of a single biothiol with various concentrations and biothiol mixtures was also realized. Furthermore, actual samples such as cells and sera can also be well distinguished by the as-fabricated sensor array, demonstrating its potential in disease diagnosis.

An Emerging Fluorescent Carbon Nanobead Label Probe for Lateral Flow Assays and Highly Sensitive Screening of Foodborne Toxins and Pathogenic Bacteria.

By virtue of the fascinating merits of low cost, rapid screening, and on-site detection, fluorescence lateral flow assays (FLFAs) have attracted considerable attention. Their detection limits are closely associated with the label probes used. The development of high-performance and robust phosphors remains a great challenge. Herein, we presented a new label probe, i.e., fluorescent carbon nanobeads (FCNBs), for FLFAs. Monodispersive, water-soluble, and highly emissive FCNBs were facilely prepared via a hydrothermal carbonization manner. Their abundant amino groups were beneficial for versatile surface functionalization. After being modified by biomolecules, the fabricated FCNB reporter probes were adopted for the construction of lateral flow test strips toward representative foodborne toxins, i.e., aflatoxin B1 (AFB1), and pathogenic bacteria, i.e., Staphylococcus aureus (S. aureus), respectively. The detection limits (0.01 ng/mL for AFB1 and 102 cfu/mL for S. aureus) were about 1 or 2 orders of magnitude lower than most reported methods. Furthermore, the proposed test strips were successfully applied for the quantitative, accurate, and rapid screening of AFB1 and S. aureus in food samples. This work provided a promising label probe for FLFAs and would open the opportunity to exploit a sensing platform by modifying different ligands onto the FCNBs.

DNA Nanoribbon for Efficient Anti-miRNA Peptide Nucleic Acid Delivery and Synergistic Enhancement of Cancer Cell Apoptosis.

Antisense peptide nucleic acid (asPNA), an effective antisense drug, has been employed as a gene therapy agent and a useful tool in molecular biology. Gaining control over the delivery of asPNA to target tissues has been a major hindrance to its wide application in clinical practice. A simple and efficient DNA nanoribbon (DNR)-based drug delivery process has been designed in this study that releases the asPNA agent to inhibit oncogenic microRNAs (miRNAs). Furthermore, we demonstrated how the AS1411 aptamer that binds nucleolin on the cell membranes works as a control mechanism capable of identifying target cancer cells and enhancing the enrichment capacity of DNR. With the biodegradability of DNR, we can efficiently initiate the release of asPNA into the cytoplasm, particularly targeting the intended miR-21 and synergistically increasing programmed cell death 4 (PDCD4) expression to enhance cell apoptosis. We assume that this well-defined delivery mechanism will aid in designing antisense site-specific treatments for various diseases, including cancer.

A colorimetric sensor array for the discrimination of Chinese liquors.

Although some colorimetric sensor arrays have been developed for the identification of Chinese liquors, they usually require the confirmation of volatile markers in the liquors by chromatography and mass spectrometry firstly. Herein, we present a simple colorimetric sensor array to identify various Chinese liquors in the liquid phase without the aid of other analytical techniques. The colorimetric sensor array consists of six commercially available and inexpensive solvatochromic dyes, and the sensing mechanism of this array is based on the response of solvatochromic dyes to their local polarity. On the basis of the colour changes of the sensor array, different Chinese liquors are discerned readily using pattern recognition methods, and the statistical analysis results (i.e., hierarchical clustering analysis and principal component analysis) reveal that the as-fabricated sensor array can distinguish the subtle differences between different liquors from the same winery and the same flavor type. Moreover, the developed sensor array can even distinguish diverse diluted liquors from the pristine ones.

A conjugated carbon-dot-tyrosinase bioprobe for highly selective and sensitive detection of dopamine.

In this work, a bioprobe for the detection of dopamine was designed and fabricated through covalently linking fluorescent carbon dots (CDs) and tyrosinase (TYR). The bioprobe (named CDs-TYR) can catalyze oxidation of dopamine and produce dopaquinone, and consequently the fluorescence of the CDs was quenched due to an efficient electron transfer mechanism from excited CDs to dopaquinone. The fluorescence intensity of CDs decreased in a dopamine-concentration-dependent manner, which built the foundation of dopamine quantification. The bioprobe provided a wide linear range from 0.1 to 6.0 µM for dopamine sensing. Additionally, excellent selectivity of the bioprobe to dopamine was achieved because of the specific catalytic character of the conjugated TYR. Furthermore, the bioprobe was successfully employed for the detection of dopamine in spiked human serum. To the best of our knowledge, this is the first example of the construction of a bioprobe through conjugating CDs and an enzyme. This work would open new opportunities to develop CD-based photoinduced electron transfer bioprobes for other analytes via linking typical enzymes onto CDs.

Carbon-Dots-Based Lab-On-a-Nanoparticle Approach for the Detection and Differentiation of Antibiotics.

Fluorescent carbon dots (CDs) have received considerable attention in recent years due to their superior optical properties. To take further advantages of these unique features, herein, a CDs-based "lab-on-a-nanoparticle" approach for the detection and discrimination of antibiotics is developed. The sensing platform was designed based on the different channel's fluorescence recoveries or further quenching of the full-color emissive CDs (F-CDs) and metal ion ensembles upon the addition of antibiotics. The F-CDs exhibited unusually comparable emission intensity nearly across the entire visible spectrum even as the excitation wavelength is shifted, making it very suitable for the construction of multi-channel sensing systems. The sensing platform was fabricated on the basis of the competing interaction of metal ions with the F-CDs and antibiotics. Three metal ions (i.e., Cu2+ , Ce3+ and Eu3+ ) can efficiently quench the fluorescence of the F-CDs. Upon the addition of antibiotics, the fluorescent intensities either recovered at different emission wavelengths or were further quenched to various degrees. The fluorescence response patterns at different emission wavelength were characteristic for each antibiotic and can be quantitatively differentiated by standard statistical methods (e.g., hierarchical clustering analysis and principal component analysis). Moreover, as an example, the proposed method was applied for quantitative detection of oxytetracycline with a limit of detection to be 0.06 µm. Finally, the sensing system was successfully employed for residual antibiotics detection and identification in real food samples.

Applying Carbon Dots-Metal Ions Ensembles as a Multichannel Fluorescent Sensor Array: Detection and Discrimination of Phosphate Anions.

Fluorescent carbon dots (CDs) are attracting much attention in sensing recently thanks to their superior optical properties and abundant surface functional groups. To take further advantages of these unique features, CDs are considered to be possible for facilely fabricating multichannel sensor arrays. As a proof-of-concept research, CDs-metal ions ensembles are screened and designed as a triple-channel fluorescent sensor array in this study for the identification of various phosphate anions (e.g., ATP, ADP, AMP, PPi, and Pi) for the first time. Further studies reveal that the selected three metal ions (i.e., Ce3+, Fe3+, and Cu2+) could induce aggregation of the CDs, resulting in quenching of their fluorescence. However, disaggregation or further aggregation of the CDs-metal ions ensembles occurs with the addition of phosphate anions. Consequently, fluorescence of the CDs is recovering or further quenching. On account of various numbers of phosphate group and steric hindrance effects of phosphate anions, their affinities to the sensor array can be distinguished through fluorescence changes of the CDs-metal ions ensembles. By means of statistical analysis methods, the as-developed array is shown excellent capabilities in the detection and discrimination of phosphate anions. Furthermore, practicability of the sensor array is validated by the successful identification of phosphates in serum and blind samples. Compared to previous reports, the as-developed multichannel sensor array manifests numerous advantages, such as simple fabrication process, flexible adjusting detection ranges, and possible extension to other analytes having similar chemical structures or properties.

Colorimetric sensor array for detection and identification of organophosphorus and carbamate pesticides.

Due to relatively low persistence and high effectiveness for insect and pest eradication, organophosphates (OPs) and carbamates are the two major classes of pesticides that broadly used in agriculture. Hence, the sensitive and selective detection of OPs and carbamates is highly significant. In this current study, a colorimetric sensor array comprising five inexpensive and commercially available thiocholine and H2O2 sensitive indicators for the simultaneous detection and identification of OPs and carbamates is developed. The sensing mechanism of this array is based on the irreversible inhibition capability of OPs and carbamates to the activity of acetylcholinesterase (AChE), preventing production of thiocholine and H2O2 from S-acetylthiocholine and acetylcholine and thus resulting in decreased or no color reactions to thiocholine and H2O2 sensitive indicators. Through recognition patterns and standard statistical methods (i.e., hierarchical clustering analysis and principal component analysis), the as-developed array demonstrates not only discrimination of OPs and carbamates from other kinds of pesticides but, more interestingly, identification of them exactly from each other. Moreover, this array is experimentally confirmed to have high selectivity and sensitivity, good anti-interference capability, and potential applications in real samples for OPs and carbamates.

A colorimetric indicator-displacement assay array for selective detection and identification of biological thiols.

A simple, inexpensive yet highly selective colorimetric indicator-displacement assay array for the simultaneous detection and identification of three important biothiols at micromolar concentrations under physiological conditions and in real samples has been developed in this work. With use of an array composed of metal indicators and metal ions, clear differentiation among cysteine, homocysteine and glutathione was achieved. On the basis of the colour change of the array, quantification of each analyte was accomplished easily, and different biothiols were identified readily using standard chemometric approaches (hierarchical clustering analysis). Moreover, the colorimetric sensor array was not responsive to changes with 19 other natural amino acids, and it showed excellent reproducibility. Importantly, the sensor array developed was successfully applied to the determination and identification of the three biothiols in a real biological sample.

Polydopamine modified colloidal gold nanotag-based lateral flow immunoassay platform for highly sensitive detection of pathogenic bacteria and fast evaluation of antibacterial agents.

Bacterial infection is a great threat to human health. Lateral flow immunoassays (LFIAs) with the merits of low cost, quick screening, and on-site detection are competitive technologies for bacteria detection, but their detection limits depend on the optical performance of the adopted nanotags. Herein, we presented a LFIA platform for bacteria detection using polydopamine (PDA) functionalized Au nanoparticles (denoted as Au@PDA) as the nanotag. The introduction of PDA could provide enhanced light absorption of Au, as well as numerous functional groups for conjugation. Small recognition molecules i.e. vancomycin (Van) and p-mercaptophenylboronic acid (PMBA) were covalently anchored to Au@PDA, and selected as the specific probes towards Gram-positive (G+) and Gram-negative (G-) bacteria, respectively. Taken Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) as the representative targets of G+ and G- bacteria, two LFA strips were successfully constructed based on the immuno-sandwich principle. They could quantitatively detect S. aureus and E. coli both down to 102 cfu/mL, a very competitive detection limit in comparison with other colorimetric or luminescent probes-based LFIAs. Furthermore, the proposed two strips were applied for the quantitative, accurate, and rapid detection of S. aureus and E. coli in food and human urine samples with good analytical results obtained. In addition, they were integrated as a screening platform for quick evaluation of diverse antibacterial agents within 3 h, which is remarkably shortened compared with that of the two traditional methods i.e. bacterial culture and plate-counting.

Emerging and Versatile Platforms of Metal-Ion-Doped Carbon Dots for Biosensing, Bioimaging, and Disease Therapy.

Metal ions possess abundant electrons and unoccupied orbitals, as well as large atomic radii, whose doping into carbon dots (CDs) is a facile strategy to endow CDs with additional physicochemical characteristics. After being doped with metal ions, CDs reveal obvious changes in their optical, electronic, and magnetic properties by adjustments to their electron density distribution and the energy gaps, leading them to be promising and competitive candidates as labeling probes, imaging agents, catalysts, nanodrugs, and so on. In this review, we summarize the fabrication methods of metal-ion-doped CDs (M-CDs), and highlight their biological applications including biosensing, bioimaging, tumor therapy, and anti-microbial treatment. Finally, the challenging future perspectives of M-CDs are analyzed. We hope this review will provide inspiration for further development of M-CDs in various biological aspects, and help readers who are interested in M-CDs and their biological applications.

An ultrasensitive lateral flow immunoassay platform for foodborne biotoxins and pathogenic bacteria based on carbon-dots embedded mesoporous silicon nanoparticles fluorescent reporter probes.

Lateral flow immunoassays (LFIAs) are routine methods for rapid foodborne pollutants screening, with detection limits that are closely associated with the label probes used. The exploitation of high performance and robust probe is highly desirable, and remains a great challenge. Herein, we reported an emerging fluorescent nanobeads i.e. carbon-dots (CD) covalently incorporated mesoporous silicon nanoparticles (CD-MSNs) for LFIAs. CD-MSNs revealed brighter fluorescence, larger particle size and more modification sites in comparison with those of single CD. After bio-functionalisation, CD-MSNs probes were introduced to construct LFIA test strips, and designed for ultrasensitive detection of aflatoxin B1 (AFB1) and Staphylococcus aureus (S. aureus), two representative foodborne pollutants, based on the competitive and sandwich models, respectively. Very competitive quantitative detection limits i.e. 0.05 ng/mL and 102 cfu/mL were correspondingly obtained. Additionally, the test strips were successfully applied to rapidly and accurately screen AFB1 and S. aureus in food samples, highlighting their practicality.

DNA Nanomaterial-Empowered Surface Engineering of Extracellular Vesicles.

Extracellular vesicles (EVs) are cell-secreted biological nanoparticles that are critical mediators of intercellular communication. They contain diverse bioactive components, which are promising diagnostic biomarkers and therapeutic agents. Their nanosized membrane-bound structures and innate ability to transport functional cargo across major biological barriers make them promising candidates as drug delivery vehicles. However, the complex biology and heterogeneity of EVs pose significant challenges for their controlled and actionable applications in diagnostics and therapeutics. Recently, DNA molecules with high biocompatibility emerge as excellent functional blocks for surface engineering of EVs. The robust Watson-Crick base pairing of DNA molecules and the resulting programmable DNA nanomaterials provide the EV surface with precise structural customization and adjustable physical and chemical properties, creating unprecedented opportunities for EV biomedical applications. This review focuses on the recent advances in the utilization of programmable DNA to engineer EV surfaces. The biology, function, and biomedical applications of EVs are summarized and the state-of-the-art achievements in EV isolation, analysis, and delivery based on DNA nanomaterials are introduced. Finally, the challenges and new frontiers in EV engineering are discussed.

Protein-templated gold nanoclusters as fluorescence probes for the detection of methotrexate.

In this contribution, bovine serum albumin stabilized gold nanoclusters as novel fluorescent probes were successfully utilized for the detection of methotrexate for the first time. Our prepared gold nanoclusters exhibited strong emission with peak maximum at 633.5 nm. However, the addition of methotrexate induced the strong fluorescence intensity of the gold nanoclusters to decrease. The decrease in fluorescence intensity of the gold nanoclusters caused by methotrexate allowed the sensitive detection of methotrexate in the range of 0.0016 µg mL(-1) to 24 µg mL(-1). The detection limit for methotrexate is 0.9 ng mL(-1) at a signal-to-noise ratio of 3. The present sensor for methotrexate detection possessed a low detection limit and wide linear range. In addition, the real samples were analyzed with satisfactory results.

A resonance light scattering quenching system for studying DNA sequence recognition of actinomycin D.

The DNA sequence recognition study of DNA-targeted anticancer drugs is a theoretical basis for improving the selectivity of anticancer drugs. With the high synergy effect of cocoamidopropyl hydroxy sulfobetaine (HSB), a resonance light scattering (RLS) quenching system for DNA sequence recognition studies of actinomycin D (ACTD) was developed in this contribution. By the strategy, DNA sequence selectivity as well as the recognition mechanisms of ACTD was systematically investigated. The results suggested that ACTD had the selectivity to single-stranded DNA (ssDNA) with an equilibrium constant (K(RLS)) of 12.4 mmol mg(-1). Also it had a preference for Guanine and Cytosine bases with a K(RLS) of 6.69 L mmol(-1). The selectivity mechanism between ACTD and DNA was also well discussed with the help of UV-Vis absorption spectroscopy. Compared with other methods, the RLS quenching system has the advantages of reliability and speediness, and it avoids complex modification processes and is a better bionic system for the above research. Results obtained from this work would supply a theoretical basis for improving anticancer activity and designing similar anticancer drugs.

A resonance light scattering sensor based on methylene blue-sodium dodecyl benzene sulfonate for ultrasensitive detection of guanine base associated mutations.

A resonance light scattering (RLS) sensor for guanine base associated mutations has been developed on the basis of the high selectivity of methylene blue (MB) for guanine bases in the presence of sodium dodecyl benzene sulfonate (SDBS). MB, when bound to SDBS, underwent a dramatic enhancement of its RLS intensity. However, the addition of double-stranded DNA (dsDNA) and single-stranded DNA (ssDNA) caused the strong RLS intensity of MB-SDBS to decrease, and the RLS intensity of MB-SDBS-ssDNA was much lower than that of MB-SDBS-dsDNA. Consequently, it can be concluded that the binding abilities of MB-SDBS with ssDNA and dsDNA were different. Besides, the experimental results showed that MB-SDBS could bind specifically to oligonucleotides rich in guanine bases. Short DNA targets with sequences related to ß-thalassaemia, thrombophilia and psoriasis, all of which are guanine base relevant mutations, were synthesized. It was found that MB-SDBS could recognize the single-base mismatches in the mutational DNA, followed by different RLS signal changes between MB-SDBS-normal DNA systems and MB-SDBS-mutational DNA systems. The ultrasensitive sensor allows simple, rapid, sensitive and selective detection of guanine base associated mutations, indicating its potential application in the medical field.

A new way to detect the interaction of DNA and anticancer drugs based on the decreased resonance light scattering signal and its potential application.

A novel assay has been developed to detect the interaction of DNA and anticancer drugs based on the decreased resonance light scattering (RLS) technique. The proposed method can be used to study those drugs which do not produce a RLS-signal after binding to DNA. RLS was used to monitor the interaction of five anticancer drugs with DNA. The reaction between anticancer drugs and DNA took place in BR buffer solution. From the RLS assay, the sequence of five anticancer drugs activities was as follows: CTX < MTX < Pt < MMC < 5-Fu. Mammary cancer cell DNA (mcDNA) was involved to validate the RLS assay. The results showed that the sensitivities of the five anticancer drugs targeting both mcDNA and ctDNA increased in the same order. However the sensitivity of each drug to mcDNA was higher than that to ctDNA It is a significant innovation of the RLS method to detect the interaction of DNA and anticancer drugs and to obtain drug sensitivity, which provides new strategies to screen DNA targeted anticancer drugs.

A persistent luminescence-based label-free probe for the ultrasensitive detection of hemoglobin in human serum.

Hemoglobin (Hb) plays an important role in oxygen carriage for mammals, which is also a typical biomarker for certain diseases. Although numerous methods had been developed for the detection of Hb in red blood cells, analytical technology for the monitoring of low-abundance Hb in serum or plasma is still a challenge. Herein, persistent luminescence nanoparticles (PLNPs) with strong near-infrared (NIR) emission character behaving as a label-free probe for the highly sensitive and selective detection of Hb were developed. Further studies revealed that the sensing mechanism should be attributed to the Hb-induced dynamic quenching process. Moreover, the nanoprobe showed high selectivity to Hb against the common existing substances in human serum and a linear response to Hb ranging from 1 to 50 nM with an extremely high limit of detection (LOD) of 0.13 nM. Finally, applicability of the proposed probe for the detection of Hb in human serum samples was validated.

An inner filter effect-based near-infrared probe for the ultrasensitive detection of tetracyclines and quinolones.

Antibiotics play important roles in the treatment and prevention of bacterial infections. However, the over-use of antibiotics can lead to a lot of adverse side-effects like nerve damage, anaphylaxis and drug tolerance. Herein, we report an inner filter effect (IFE)-based near-infrared (NIR) fluorescent probe for highly sensitive and selective detection of tetracyclines (TCs) and quinolones (QNs), of which being the most frequently applied antibiotics. NIR emissive carbon-dots (NIR-CDs) that displayed broad excitation range, stable and strong emission were selected as label-free fluorophores. In the presence of TCs or QNs, efficient IFE from CDs to the two types of antibiotics occurred because of the good spectrum overlap between the ultraviolet absorption of TCs/QNs and the excitation of NIR-CDs. As a result, fluorescence emission of the NIR-CDs was obviously quenched, and this builds the foundation of TCs and QNs quantification. The probe provides linear detection ranges, i.e. 1-80 nM and 0.01-0.2 µM for oxytetracycline (OTC, an example for TCs) and norfloxacin (NOR, an example for QNs) with detection limits of 0.5 nM and 6.3 nM, respectively. To the best of our knowledge, this is the first report on NIR fluorescent probe for antibiotics assay. Moreover, the probe has been demonstrated to be very robust, and was successfully adopted for the determination of OTC and NOR in milk samples.

A colorimetric sensor array based on sulfuric acid assisted KMnO4 fading for the detection and identification of pesticides.

Pesticides play a critical role in improving crop yield in modern agriculture, but their residues significantly harm the environment and human health. Herein, a novel and simple colorimetric sensor array built on sulfuric acid assisted KMnO4 fading strategy has been developed for pesticides detection and discrimination. This sensor array is facilely fabricated by KMnO4 and sulfuric acid through simply adjusting their concentrations and ratios. Hierarchical clustering analysis (HCA) demonstrates that the as-fabricated colorimetric sensor array has a high dimensionality, and shows excellent capability to recognize common kinds of pesticides from potential interferants. Semi-quantitative detection was achieved through combining HCA and corresponding fitting curves. Moreover, the proposed sensor array was successfully applied to detect pesticide residues (e.g. carbaryl) in real samples. The strategy described herein will not only "maximally" simplify the design and fabrication approach, but expand the application fields of colorimetric sensor array methodology towards weak-reactive analytes.