Protamine-stabilized gold nanoclusters as a fluorescent nanoprobe for lead(II) via Pb(II)-Au(I) interaction

A Semi-Automatic Environmental Monitoring Device for Mercury and Cobalt Ion Detection

A syringe-based, semi-automatic environmental monitoring device is developed for on-site detection of harmful heavy metal ions in water. This portable device consists of a spring-embedded syringe and a polydimethylsiloxane (PDMS) membrane-based flow regulator for semi-automatic fix-and-release fluidic valve actuation, and a paper-based analytical device (PAD) with two kinds of gold nanoclusters (AuNCs) for sensitive Hg2+ and Co2+ ion detection, respectively. The thickness of the elastic PDMS membrane can be adjusted to stabilize and modulate the flow rates generated by the pushing force provided by the spring attached to the plunger. Also, different spring constants can drastically alter the response time. People of all ages can extract the fix-volume sample solutions and then release them to automatically complete the detection process, ensuring high reliability and repeatability. The PAD comprises two layers of modified paper, and each layer is immobilized with bovine serum albumin-capped gold nanoclusters (R-AuNCs) and glutathione-capped gold clusters (G-AuNCs), respectively. The ligands functionalized on the surface of the AuNCs not only can fine-tune the optical properties of the nanoclusters but also enable specific and simultaneous detection of Hg2+ and Co2+ ions via metallophilic Au+ -Hg2+ interaction and the Co2+ -thiol complexation effect, respectively. The feasibility of the device for detecting heavy metal ions at low concentrations in various environmental water samples is demonstrated. The Hg2+ and Co2+ ions can be seen simultaneously within 20 min with detection limits as low as 1.76 nm and 0.27 µm, respectively, lower than those of the regulatory restrictions on water by the US Environmental Protection Agency and the European Union. we expect this sensitive, selective, portable, and easy-to-use device to be valid for on-site multiple heavy metal ion pollution screenings in resource-constrained settings.

Protamine gold nanoclusters - based fluorescence turn-on sensor for rapid determination of Trinitrotoluene (TNT)

Determination of trace residues of 2,4,6-trinitrotoluene (TNT) is an analytical challenge as it is widely used in military, mining industry, civilian and counter-terrorism purposes. In this study, a gold nanocluster - based turn-on fluorescence sensor was developed for TNT determination. A one-pot approach was used to synthesize the fluorescent protamine - stabilized gold nanoclusters (PRT-AuNC). The proposed turn-on fluorometric sensor relies on the aggregation-induced emission enhancement mechanism. As a result of the donor-acceptor interaction between the non-fluorescent Meisenheimer anion formed from TNT and the amino groups of weakly fluorescent protamine, the PRT-AuNCs aggregate and an accompanying enhancement in fluorescence intensity is observed with a large Stokes shift (λ_ex = 300 nm, λ_em = 600 nm). The fluorescence enhancement increased linearly with TNT with an LOD of 12.44 µg/L. Similar energetic materials, common soil ions and explosive camouflage materials did not affect the proposed fluorometric sensing method. TNT in artificially contaminated soil was determined, and the results were comparable to those obtained by the HPLC-DAD system. The proposed turn-on sensor is an important tool for simple, fast, rapid and sensitive TNT determination, and has a potential to be converted to a kit format.

DNA dendrimer-templated copper nanoparticles: self-assembly, aggregation-induced emission enhancement and sensing of lead ions

Copper nanomaterials based on DNA scaffold (DNA-Cu NMs) are becoming a novel fluorescent material, but it is still challenging to obtain highly fluorescent DNA-Cu NMs with excellent stability. In this work, we report a kind of copper nano-assemblies (Cu NASs) with aggregation-induced emission enhancement (AIEE) property using DNA dendrimers with sticky end as template. The sticky end of the DNA dendrimers induced the formation of much bigger Cu NASs with average size ranging from 131 to 264 nm, depending on the length of the DNA dendrimer sticky end from 6 bases to 27 bases. Compared with complete complementary DNA dendrimer, nearly 6-fold fluorescence enhancement was achieved using DNA dendrimer with 27 bases sticky end. Moreover, the DNA dendrimer-Cu NASs demonstrated excellent stability in serum and could be rapidly quenched by Pb²⁺ ions. Based on the above property, highly sensitive and selective fluorescent detection of Pb²⁺ ions was possible with a linear range of 2.0-100 nM and a detection limit of 0.75 nM. Due to the sensitive and rapid response to Pb²⁺ as well as excellent stability in complex matrix, the proposed fluorescent Cu NASs demonstrated high potential as an excellent fluorescent probe for Pb²⁺ in complex matrix.

Coassembly of nucleus-targeting gold nanoclusters with CRISPR/Cas9 for simultaneous bioimaging and therapeutic genome editing

The clustered regularly interspaced short palindromic repeats (CRISPR)/associated protein 9 (CRISPR/Cas9) technology enables genome editing with high precision and versatility and has been widely utilized to combat viruses, bacteria, cancers, and genetic diseases. Nonviral nanocarriers can overcome several limitations of viral vehicles, including immunogenicity, inflammation, carcinogenicity, and low versatility, and thus represent promising platforms for CRISPR/Cas9 delivery. Herein, we for the first time develop the application of protamine-capped gold nanoclusters (protamine-AuNCs) as an effective nanocarrier for Cas9-sgRNA plasmid transport and release to achieve efficient genome editing. The protamine-AuNCs integrate the merits of AuNCs and protamine: AuNCs are able to promptly assemble with Cas9-sgRNA plasmids to allow efficient cellular delivery, while the cationic protamine facilitates the effective release of Cas9-sgRNA plasmids into the cellular nucleus. The AuNCs/Cas9-gRNA plasmid nanocomplexes can not only achieve successful gene editing in cells but also knock out the oncogenic gene for cancer therapy. Moreover, the AuNCs with excellent photoluminescence characteristics endow our nanoplatform with the functionality of bioimaging. Overall, our study provides strong evidence that demonstrates protamine-AuNCs as an effective CRISPR/Cas9 delivery tool for gene therapy.

Colorimetric determination of Pb2+ ions based on surface leaching of Au@Pt nanoparticles as peroxidase mimic

We report the first use of metallic nanozyme as colorimetric probe for Pb²⁺ determination. The method is based on the surface leaching of Au@PtNP nanozyme by Pb²⁺-S₂O₃^2- ions, accompanied by a decreased catalytic activity of the metallic nanozyme. To construct this colorimetric determination, the Pt deposition onto the AuNPs was carefully investigated and other experimental factors including kind of substrate and buffer were optimized. With increasing Pb²⁺ concentration, the catalytic activity of the Au@PtNPs decreased gradually. As a result, the blue color at 650 nm from the oxidation of 3,3',5,5'-tetramethylbenzidine by H₂O₂ faded gradually. A determination limit of 3.0 nM Pb²⁺ with a linear range from 20 to 800 nM was obtained. The assay demonstrated negligible response to common metal ions even at elevated concentrations. This colorimetric method was applied to the determination of Pb²⁺ ions spiked in lake water samples, and good recoveries (96.8-105.2%) were obtained. The above results indicate the potential application of metallic nanozymes in developing robust colorimetric assays. Graphical abstract Schematic representation of the surface leaching of Au@PtNP nanozyme by Pb²⁺-S₂O₃^2- ions, accompanying the decreased catalytic activity of the metallic nanozyme.

Microwave Synthesis of Gold Nanoclusters with Garlic Extract Modifications for the Simple and Sensitive Detection of Lead Ions

Novel bovine serum albumin (BSA)-gold nanoclusters with garlic extract modifications (mw_G-BSA-AuNCs) were prepared through microwave-assisted rapid synthesis. The modified nanoclusters were characterized and used for the simple and sensitive detection of Pb²⁺ ions. Both turn-on and turn-off methods were used and compared for Pb²⁺ ion detection. For Pb²⁺ ions, the preparation time for the modified nanoclusters was 10 min, and the detection time for the nanoclusters was 6 min. The modified nanoclusters were stable, and their fluorescence intensities changed by less than 10% in 60 days. The detection limit and linear range for the “off-on” method of mw_G-BSA-AuNCs for Pb²⁺ ion detection were 0.28 and 1–20 nM, respectively. The recoveries of the mw_G-BSA-AuNCs probe used for the detection of the Pb(II) ion in tap water ranged from 93.8% to 102.2%, with an average of 97.1%. The “off-on” method of mw_G-BSA-AuNCs can provide a lower detection limit, higher selectivity, and better recovery than the commonly used “turn-off” methods of mw_BSA-AuNCs for Pb²⁺ ion detection. The proposed method is superior to other methods proposed from 2018 to 2019 because it can provide a shorter preparation time and a lower detection limit with good selectivity. The microwave-assisted novel compound, mw_G-BSA-AuNCs, can be rapidly synthesized in a green manner and can provide a low detection limit, good selectivity, and a simple and fast reaction for Pb²⁺ ion detection.

Assay of 1-hydroxypyrene via aggregation-induced quenching of the fluorescence of protamine-modified gold nanoclusters and 9-hydroxyphenanthrene-based sensitization

This work describes a method for the determination of 1-hydroxypyrene (OH-Py) via aggregation-induced quenching of the emission of protamine-coated gold nanoclusters using 9-hydroxyphenanthrene (OH-Phe) as a sensitizer to boost the emission efficiency of nanoprobe. Under optimum conditions, the drop in fluorescence intensity at excitation/emission wavelengths of 300/596 nm is proportional to the concentrations of OH-Py in the range from 1.0 to 65 nM. The relative standard deviations are 4.2, 2.4 and 1.9% (for n = 11) at concentration levels of 8.0, 32 and 48 nM of OH-Py, respectively. The detection limit is 0.3 nM which is much lower than that of some previously reported methods. The recoveries from urine samples spiked with OH-Py ranged between 94.4 and 98.8%. Graphical abstract 1-Hydroxypyrene (OH-Py) can trigger the aggregation of protamine-gold nanoclusters (PRT-AuNCs), resulting in the emission quenching of PRT-AuNCs. 9-Hydroxyphenanthrene (OH-Phe) can boost the emission efficiency of nanoprobe. Thereby, a highly sensitive assay of OH-Py was established.

Colorimetric determination of lead(II) or mercury(II) based on target induced switching of the enzyme-like activity of metallothionein-stabilized copper nanoclusters

It is shown that metallothionein-stabilized copper nanoclusters (MT-CuNCs) display catalase-like activity. In the presence of either lead(II) or mercury(II), the catalase-like activity is converted to a peroxidase-like activity. On addition of Pb(II) or Hg(II), the inhibitory effect of MT-CuNCs on the chromogenic reaction of 3,3',5,5'-tetramethylbenzidine (TMB) with H₂O₂ is weakened. On the other hand, the catalytic effect of the nanoclusters on the chromogenic reaction is increased. The system MT-CuNCs-Pb(II)/Hg(II) exhibits high affinity for the substrates TMB and H₂O₂. Their catalytic behavior follows Michaelis-Menten kinetics. Based on these findings, a method was developed for visual detection (via the blue coloration formed) and spectrophotometric determination (at 450 nm) of Pb(II) and Hg(II). The linear range for Pb(II) extends from 0.7 to 96 μM, and the linear ranges for Hg(II) from 97 nM to 2.3 μM and from 3.1 μM to 15.6 μM. The detection limits are 142 nM for Pb(II) and 43.8 nM for Hg(II). Graphical abstract Metallothionein-stabilized copper nanoclusters (MT-CuNCs) display catalase-like activity. On addition of Pb(II) or Hg(II), the catalase-like activity is converted to a peroxidase-like activity. The latter catalyzes the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) by H₂O₂.

A label-free “turn-on” fluorescence platform for glucose based on AuNCs@MnO2 nanocomposites

The principle of sensitive detection of glucose in human serum using Bro-AuNCs @MnO₂ nanocomposites as a fluorescent sensor.