Carbon dots (C dots) with biocompatibility, brightness, stability against photoirradiation and salt, and ease in preparation have become important materials for sensing and imaging. They can be ...prepared from natural materials and small organic molecules through hydrothermal, microwave‐assistant, and electrochemical methods, with advantages of simplicity and low cost. To enhance the quantum yields of C dots in the red and near‐infrared regions, doping of C dots with heteroatoms such as nitrogen and sulfur has been suggested. C dots both with and without being functionalized recognition elements such as antibodies and aptamers are selective and sensitive for sensing of analytes, including metal ions (e.g., Fe3+, Hg2+, Cu2+), small molecules (e.g., H2O2, cysteine, glutathione), and biopolymers like proteins, as well as for in vitro and in vivo imaging. Depending on the size, charge, and surface ligands of C dots used to label cells, fluorescence images of different organelles are shown. Multicolor images of bacteria, mammalian cells, and plant tissues incubated with C dots are realized when excited at different wavelengths. In this review, many excellent sensing and imaging examples of C dots are presented to highlight their features and to show their challenges for analytical applications.
Biocompatible, fluorescent, and stable carbon dots (C dots) are prepared from organic molecules, natural resources, and organic wastes through hydrothermal, microwave‐assistant, and electrochemical methods. The C dots both with and without functionalization can be used for selective and sensitive sensing of metal ions, small molecules, and biopolymers, as well as for in vivo and in vitro imaging.
A simple one-pot hydrothermal approach has been demonstrated for the preparation of highly water soluble and photoluminescent carbon nanodots (C-dots) from low-cost organic compounds. We found that ...the compounds incorporating amino and carboxylic acid groups are suitable for the preparation of highly photoluminescent and water-soluble C-dots.
Carbon nanodots (C-dots) possessing photoluminescence (PL) properties have become interesting materials for sensing and imaging, with the advantages of water-dispersibility, biocompatibility, ...chemical and photo stability. They can be prepared from organic matter such as tea, grass, coffee, and small organic molecules like glycine and glucose through hydrothermal routes. In this review, we focus on the recent advances in the synthesis and characterization of C-dots along with their optical (absorption, PL, upconverted PL) properties and analytical applications. Having bright PL, biocompatibility, chemical and photo stability, as well as low toxicity, C-dots have been used for the detection of metal ions and for cell imaging. C-dots prepared from organic matter such as used tea and ginger possess a great inhibitory effect on the growth of cancer cells, showing their excellent potential as new drugs.
Quenching upon aggregation: 11‐Mercaptoundecanoic acid (11‐MUA)‐protected Au nanoparticles (11‐MUA‐AuNPs) are much more stable and fluoresce much more strongly than the corresponding unmodified ...AuNPs. After addition of 2,6‐pyridinedicarboxylic acid, the 11‐MUA‐AuNPs bind to HgII with both high sensitivity and selectivity.
We have developed a one-pot approach to prepare fluorescent DNA-templated gold/silver nanoclusters (DNA-Au/Ag NCs) from Au3+, Ag+, and DNA (5′-CCCTTAATCCCC-3′) in the presence of NaBH4 in order to ...detect sulfide (S2‑) ions on the basis of fluorescence quenching. The as-prepared DNA-Au/Ag NCs have been characterized by UV–vis absorption, fluorescence, circular dichroism, X-ray photoelectron spectroscopy, and electrospray ionization-mass spectrometry measurements. Relative to DNA-Ag NCs, DNA-Au/Ag NCs are much more stable in high ionic strength media (e.g., 200 mM NaCl). The quantum yield of the as-prepared DNA-Au/Ag NCs is 4.5%. We have demonstrated that the fluorescence of DNA-Au/Ag NCs is quenched by S2‑ ions through the interaction between sulfide ions and gold/silver atoms/ions, a result which leads to changes in the conformation of the templated DNA from packed hairpin to random coil structures. These changes in fluorescence intensity allow sensitive detection of S2‑ ions at concentrations as low as 0.83 nM. To minimize interference from I– ions for the detection of S2‑ ions using the DNA-Au/Ag NCs, the addition of sodium peroxydisulfate to the solution is essential. We have validated the practicality of this probe for the detection of S2‑ ions in hot spring and seawater samples, demonstrating its advantages of simplicity, sensitivity, selectivity, and low cost.
An on-field colorimetric sensing strategy employing gold nanoparticles (AuNPs) and a paper-based analytical platform was investigated for mercury ion (Hg2+) detection at water sources. By utilizing ...thymine–Hg2+–thymine (T–Hg2+–T) coordination chemistry, label-free detection oligonucleotide sequences were attached to unmodified gold nanoparticles to provide rapid mercury ion sensing without complicated and time-consuming thiolated or other costly labeled probe preparation processes. Not only is this strategy’s sensing mechanism specific toward Hg2+, rather than other metal ions, but also the conformational change in the detection oligonucleotide sequences introduces different degrees of AuNP aggregation that causes the color of AuNPs to exhibit a mixture variance. To eliminate the use of sophisticated equipment and minimize the power requirement for data analysis and transmission, the color variance of multiple detection results were transferred and concentrated on cellulose-based paper analytical devices, and the data were subsequently transmitted for the readout and storage of results using cloud computing via a smartphone. As a result, a detection limit of 50 nM for Hg2+ spiked pond and river water could be achieved. Furthermore, multiple tests could be performed simultaneously with a 40 min turnaround time. These results suggest that the proposed platform possesses the capability for sensitive and high-throughput on-site mercury pollution monitoring in resource-constrained settings.
Nanoparticles (NPs) are useful as matrixes for the analyses of several types of biomolecules (including aminothiols, peptides, and proteins) and for mass spectrometric imaging through ...surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS), mainly because of their large surface area, strong absorption in the ultraviolet-near-infrared region, and ready functionalization. Metallic NPs, metal oxide NPs, and semiconductor quantum dots, unmodified or functionalized with recognition ligands, have a strong affinity toward analytes; therefore, they allow the enrichment of biomolecules, leading to improved sensitivity with minimal matrix interference in their mass spectra. SALDI-MS using NPs overcomes the two major problems commonly encountered in matrix-assisted laser desorption/ionization mass spectrometry: the presence of "sweet spots" and the high background signals in the low-mass region. In this
tutorial review
, we discuss the roles played by the nature, size, and concentration of the NPs, the buffer composition, and the laser energy in determining the sensitivity and mass ranges for the analytes. We describe internal standard SALDI-MS methods that allow the concentrations of analytes to be determined with low variation (relative standard deviations: <10%) and we highlight how the simplicity, sensitivity, and reproducibility of SALDI-MS approaches using various NPs allow the analyses of proteins and small analytes and the imaging of cells.
SALDI-MS using nanoparticles (without organic matrices) is simple, sensitive and reproducible for the detection of biomolecules.
Monitoring the levels of potentially toxic metal (PTM) ions (e.g., Hg(2+), Pb(2+), Cu(2+)) in aquatic ecosystems is important because these ions can have severe effects on human health and the ...environment. Gold (Au) nanomaterials are attractive sensing materials because of their unique size- and shape-dependent optical properties. This review focuses on optical assays for Hg(2+), Pb(2+), and Cu(2+) ions using functionalized Au nanomaterials. The syntheses of functionalized Au nanomaterials are discussed. We briefly review sensing approaches based on changes in absorbance resulting from metal ion-induced aggregation of Au nanoparticles (NPs) or direct deposition of metal ions onto Au NPs. The super-quenching properties of Au NPs allow them to be employed in 'turn on' and 'turn off' fluorescence approaches for the sensitive and selective detection of Hg(2+), Pb(2+), and Cu(2+) ions. We highlight approaches based on fluorescence quenching through analyte-induced aggregation or the formation of metallophilic complexes of Au nanodots (NDs). We discuss the roles of several factors affecting the selectivity and sensitivity of the nanosensors toward the analytes: the size of the Au nanomaterial, the length and sequence of the DNA or the nature of the thiol, the surface density of the recognition ligand, and the ionic strength and pH of the buffer solution. In addition, we emphasize the potential of using new nanomaterials (e.g., fluorescent silver nanoclusters) for the detection of PTM ions.
Photoluminescent gold nanodots (Au NDs) are prepared via etching and codeposition of hybridized ligands, an antimicrobial peptide (surfactin; SFT), and 1‐dodecanethiol (DT), on gold nanoparticles ...(≈3.2 nm). As‐prepared ultrasmall SFT/DT–Au NDs (size ≈2.5 nm) are a highly efficient antimicrobial agent. The photoluminescence properties and stability as well as the antimicrobial activity of SFT/DT–Au NDs are highly dependent on the density of SFT on Au NDs. Relative to SFT, SFT/DT–Au NDs exhibit greater antimicrobial activity, not only to nonmultidrug‐resistant bacteria but also to the multidrug‐resistant bacteria. The minimal inhibitory concentration values of SFT/DT–Au NDs are much lower (>80‐fold) than that of SFT. The antimicrobial activity of SFT/DT–Au NDs is mainly due to the synergistic effect of SFT and DT–Au NDs on the disruption of the bacterial membrane. In vitro cytotoxicity and hemolysis analyses have revealed superior biocompatibility of SFT/DT–Au NDs than that of SFT. Moreover, in vivo methicillin‐resistant S. aureus–infected wound healing studies in rats show faster healing, better epithelialization, and are more efficient in the production of collagen fibers when SFT/DT–Au NDs are used as a dressing material. This study suggests that the SFT/DT–Au NDs are a promising antimicrobial candidate for preclinical applications in treating wounds and skin infections.
Surfactin, an antimicrobial lipopeptide, when self‐assembled on photoluminescent gold nanodots (Au NDs) exhibits an >80‐fold improvement in its antimicrobial activity against multidrug‐resistant bacteria. Antibacterial wound‐healing assays further reveal that the surfactin–Au ND hybrid material is superior to that of surfactin alone on a bacteria‐infected flesh wound in rats.
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