Photoassisted Synthesis of Luminescent Mannose-Au Nanodots for the Detection of Thyroglobulin in Serum

An Overview on Coinage Metal Nanocluster-Based Luminescent Biosensors via Etching Chemistry

The findings from the synthetic mechanism of metal nanoclusters yield the etching chemistry based on coinage metal nanoclusters. The utilization of such chemistry as a tool that can alter the optical properties of metal nanoclusters has inspired the development of a series of emerging luminescent biosensors. Compared with other sensors, the luminescent biosensors have the advantages of being more sensitive, saving time and saving cost. We reviewed topics on the luminescent sensors based on the etching of emissive coinage metal nanoclusters. The molecules possessing varied etching ability towards metal nanoclusters were categorized with discussions of corresponding etching mechanisms. The understanding of etching mechanisms favored the discussions of how to use etching methods to detecting biochemical molecules. The emerging luminescent biosensors via etching chemistry also provided challenges and new opportunities for analytical chemistry and sensors.

The Emission Mechanism of Gold Nanoclusters Capped with 11-Mercaptoundecanoic Acid, and the Detection of Methanol in Adulterated Wine Model

The absorption and emission mechanisms of gold nanoclusters (AuNCs) have yet to be understood. In this article, 11-Mercaptoundecanoic acid (MUA) capped AuNCs (AuNC@MUA) were synthesized using the chemical etching method. Compared with MUA, AuNC@MUA had three obvious absorption peaks at 280 nm, 360 nm, and 390 nm; its photoluminescence excitation (PLE) peak and photoluminescence (PL) peak were located at 285 nm and 600 nm, respectively. The AuNC@MUA was hardly emissive when 360 nm and 390 nm were chosen as excitation wavelengths. The extremely large stokes-shift (>300 nm), and the mismatch between the excitation peaks and absorption peaks of AuNC@MUA, make it a particularly suitable model for studying the emission mechanism. When the ligands were partially removed by a small amount of sodium hypochlorite (NaClO) solution, the absorption peak showed a remarkable rise at 288 nm and declines at 360 nm and 390 nm. These experimental results illustrated that the absorption peak at 288 nm was mainly from metal-to-metal charge transfer (MMCT), while the absorption peaks at 360 nm and 390 nm were mainly from ligand-to-metal charge transfer (LMCT). The PLE peak coincided with the former absorption peak, which implied that the emission of the AuNC@MUA was originally from MMCT. It was also interesting that the emission mechanism could be switched to LMCT from MMCT by decreasing the size of the nanoclusters using 16-mercaptohexadecanoic acid (MHA), which possesses a stronger etching ability. Moreover, due to the different PL intensities of AuNC@MUA in methanol, ethanol, and water, it has been successfully applied in detecting methanol in adulterated wine models (methanol-ethanol-water mixtures).

Design and validation of fiber optic localized surface plasmon resonance sensor for thyroglobulin immunoassay with high sensitivity and rapid detection

A simple optical fiber sensor based on localized surface plasmon resonance was constructed for direct and rapid measurement of thyroglobulin (Tg). Specific tests for Tg in patients that have undergone thyroidectomy are limited because of insufficient sensitivity, complicated procedures, and in some cases, a long time to yield a result. A sensitive, fast, and simple method is necessary to relieve the psychological and physical burden of the patient. Various concentrations of Tg were measured in a microfluidic channel using an optical fiber sensor with gold nanoparticles. The sensor chip has a detection limit of 93.11 fg/mL with no specificity for other antigens. The potential applicability of the Tg sensing system was evaluated using arbitrary samples containing specific concentrations of Tg. Finally, the sensor can be employed to detect Tg in the patient’s serum, with a good correlation when compared with the commercial kit.

Synergistic integration of metal nanoclusters and biomolecules as hybrid systems for therapeutic applications

Therapeutic nanoparticles are designed to enhance efficacy, real-time monitoring, targeting accuracy, biocompatibility, biodegradability, safety, and the synergy of diagnosis and treatment of diseases by leveraging the unique physicochemical and biological properties of well-developed bio-nanomaterials. Recently, bio-inspired metal nanoclusters (NCs) consisting of several to roughly dozens of atoms (<2 nm) have attracted increasing research interest, owing to their ultrafine size, tunable fluorescent capability, good biocompatibility, variable metallic composition, and extensive surface bio-functionalization. Hybrid core-shell nanostructures that effectively incorporate unique fluorescent inorganic moieties with various biomolecules, such as proteins (enzymes, antigens, and antibodies), DNA, and specific cells, create fluorescently visualized molecular nanoparticle. The resultant nanoparticles possess combinatorial properties and synergistic efficacy, such as simplicity, active bio-responsiveness, improved applicability, and low cost, for combination therapy, such as accurate targeting, bioimaging, and enhanced therapeutic and biocatalytic effects. In contrast to larger nanoparticles, bio-inspired metal NCs allow rapid renal clearance and better pharmacokinetics in biological systems. Notably, advances in nanoscience, interfacial chemistry, and biotechnologies have further spurred researchers to explore bio-inspired metal NCs for therapeutic purposes. The current review presents a comprehensive and timely overview of various metal NCs for various therapeutic applications, with a special emphasis on the design rationale behind the use of biomolecules/cells as the main scaffolds. In the different hybrid platform, we summarize the current challenges and emerging perspectives, which are expected to offer in-depth insight into the rational design of bio-inspired metal NCs for personalized treatment and clinical translation.

Selection and characterization of an ssDNA aptamer against thyroglobulin

Thyroglobulin (Tg) is a significant biomarker for the diagnose and postoperative monitoring of differentiated thyroid cancer, and its recognition is urgent due to the rising prevalence. In this study, an ssDNA aptamer against Tg was obtained by capillary electrophoresis-systematic evolution of ligands via exponential enrichment (CE-SELEX). Under the optimized conditions, the sub-library was enriched well through two selection rounds. After high-throughput sequencing, eight candidate sequences were picked out and their affinities towards Tg were observed not in accordance with the order of their frequencies, whereas sequence homology played a significant role in binding affinity. The high-affinity sequence Seq.T-2 with a dissociation constant (K_d) of 3.18 μM was finally selected as the aptamer, and its affinity was confirmed qualitatively by gold nanoparticles colorimetric and quantitatively by thin film interferometry (K_d, 4.51 nM). Besides, molecular docking and dynamics simulation were performed for their binding sites prediction and affinity confirmation. Furthermore, the aptamer was applied for Tg detection, which delivered a detection limit of 5.0 nM as well as with good selectivity, and showed a good linear relationship within a wide range of 10 nM-6.4 μM of Tg spiked into the serum matrix. This study first reported Tg's aptamer which also exhibited the potential in real applications.

Glyco-gold nanoparticles: synthesis and applications

Glyco-gold nanoparticles combine in a single entity the peculiar properties of gold nanoparticles with the biological activity of carbohydrates. The result is an exciting nanosystem, able to mimic the natural multivalent presentation of saccharide moieties and to exploit the peculiar optical properties of the metallic core. In this review, we present recent advances on glyco-gold nanoparticle applications in different biological fields, highlighting the key parameters which inspire the glyco nanoparticle design.

Synthesis, Optical Properties, and Sensing Applications of Gold Nanodots

In this Personal Account, we briefly address our journey in developing photoluminescent nanomaterials for sensing purposes, with a focus on gold nanodots (Au NDs). Their synthetic strategies, optical properties, and sensing applications are emphasized. The Au NDs can be simply prepared from the etching of small-sized Au nanoparticles (<3 nm in diameter) by thiol compounds such as 11-mercaptoundecanoic acid under alkaline conditions. This simple approach allows the preparation of various functional Au NDs by choosing different thiol compounds as etching agents. Since the optical properties of Au NDs are highly dependent on the core and shell of each Au ND, the selection of etching reagents is important. Over the years we have developed various sensing systems using Au NDs for the detection of metal ions, anions, and proteins, based on analyte-induced photoluminescence quenching/enhancement of Au NDs as a result of changes in their oxidation state, shell composition, and structure.

One-step synthesis of peptide conjugated gold nanoclusters for the high expression of FGFR2 tumor targeting and imaging

An effective method to synthesize gold nanoclusters that can specifically recognize fibroblast growth factor receptor2 (FGFR2) was reported.

Self-assembly of hybridized ligands on gold nanodots: tunable photoluminescence and sensing of nitrite

Highly photoluminescent gold nanodots (Au NDs) via etching and co-deposition of hybridized ligands [11-mercaptoundecanol (11-MU) and its complexes with amphiphilic ligands] on gold nanoparticles (∼3 nm) have been prepared and employed for the detection of nitrite based on the analyte-induced photoluminescence quenching.

Understanding thiol-induced etching of luminescent gold nanoclusters

Electron injection from thiol ligands to Au₈ clusters is a driving force for thiol-induced core etching of protein-stabilized Au₈ clusters.

Synthesis of fluorescent gold nanodot-liposome hybrids for detection of phospholipase C and its inhibitor

We report the synthesis of fluorescent 11-mercaptoundecanoic acid-gold nanodot-liposome (11-MUA-Au ND/Lip) hybrids by incorporation of gold nanoparticles (∼3 nm) and 11-MUA molecules in hydrophobic phospholipid membranes that self-assemble to form small unilamellar vesicles. A simple and homogeneous fluorescence assay for phospholipase C (PLC) was developed on the basis of the fluorescence quenching of 11-MUA-Au ND/Lip hybrids in aqueous solution. The fluorescence of the 11-MUA-Au ND/Lip hybrids is quenched by oxygen (O2) molecules in solution, and quenching is reduced in the presence of PLC. PLC catalyzes the hydrolysis of phosphatidylcholine units from Lip to yield diacylglycerol (DAG) and phosphocholine (PC) products, leading to the decomposition of Lip. The diacylglycerol further interacts with 11-MUA-Au NDs via hydrophobic interactions, leading to inhibition of O2 quenching. The 11-MUA-Au ND/Lip probe provides a limit of detection (at a signal-to-noise ratio of 3) of 0.21 nM for PLC, with high selectivity over other proteins, enzymes, and phospholipases. We have validated the practicality of using this probe for the determination of PLC concentrations in breast cancer cells (MCF-7 and MDA-MB-231 cell lines) and nontumor cells (MCF-10A cell line), revealing that the PLC activity in the first two is at least 1.5-fold higher than that in the third. An inhibitor assay using 11-MUA-Au ND/Lip hybrids demonstrated that tricyclodecan-9-yl potassium xanthate (D609) inhibits PLC (10 nM) with an IC50 value of 3.81 ± 0.22 μM. This simple, sensitive, and selective approach holds great potential for detection of PLC in cancer cells and for the screening of anti-PLC drugs.

Synthesis of aluminum oxide supported fluorescent gold nanodots for the detection of silver ions

Photoluminescent gold nanodots (Au NDs) on aluminum oxide nanoparticles (Al2O3 NPs) with the emission wavelengths ranging from 510 to 630 nm are unveiled. Orange Al2O3 NP@AuNDs show high selectivity and sensitivity towards Ag(+) ions by metallophilic Ag(+)-Au(+) interactions and induced fluorescence quenching of Au NDs.

Luminescent noble metal nanoclusters as an emerging optical probe for sensor development

In the past few years, highly luminescent noble metal nanoclusters (e.g., Au and Ag NCs or Au/Ag NCs in short) have emerged as a class of promising optical probes for the construction of high-performance optical sensors because of their ultrasmall size (<2 nm), strong luminescence, good photostability, excellent biocompatibility, and unique metal-core@ligand-shell structure. In this Focus Review, we briefly summarize the common syntheses for water-soluble highly-luminescent thiolate- and protein-protected Au/Ag NCs and their interesting luminescence properties, highlight recent progress in their use as optical sensors with an emphasis on the mechanisms underlying their selectivity, and finally discuss approaches to improving their sensitivity. The scope of the works surveyed is confined to highly luminescent thiolate- and protein-protected Au/Ag NCs.

Near-infrared fluorescent ribonuclease-A-encapsulated gold nanoclusters: preparation, characterization, cancer targeting and imaging

Ultra-small gold nanoclusters (AuNCs) have unique size-dependent optical, electrical and chemical properties. They have emerged as a new nanomaterial with broad applications in optoelectronics, catalysis, biosensing, and bioimaging. Several strategies have been exploited to prepare AuNCs of different "magic number" sizes, using different templates e.g. dendrimers, polyethyleneimines, peptides, and more recently, proteins. Notwithstanding, almost all bio-template-protected AuNCs reported so far exhibit fairly low fluorescence quantum yields (QYs), typically <5%, which is especially true for AuNCs prepared using the protein templates. In this paper, we report a facile, one-pot aqueous synthesis of highly fluorescent AuNCs using bovine pancreatic ribonuclease A (RNase-A) as the bio-template. The as-prepared AuNCs not only fluoresce strongly at the near-infrared (NIR) region (λ(em) = 682 nm), but also exhibit an elevated QY of ∼12%. Additionally, the RNase-A-encapsulated AuNC (RNase-A-AuNC) displays an exceptionally large Stokes shift of ∼210 nm as well as a single dominant fluorescence lifetime of ∼1.5 μs, about three orders of magnitude longer than biological autofluorescence. Furthermore, by coupling vitamin B(12) (VB(12)) to the RNase-A-AuNC, we develop a multifunctional nanoplatform that is suitable for simultaneous targeting and imaging of cancer at the cellular level using Caco-2 cell lines as an in vitro model. Since VB(12) has effective uptake pathways in the digestive system, this nanoplatform may have potential for targeted oral drug delivery in vivo.

Effect of protein adsorption on the fluorescence of ultrasmall gold nanoclusters

The interaction of proteins with ultrasmall gold nanoclusters (Au NCs) is investigated. Upon protein association, the fluorescence of Au NCs is significantly enhanced and, concomitantly, their luminescence lifetime is prolonged. The results stress the importance of investigating the behavior of fluorescent metal NCs in complex biological environment for advancing their bio-nanotechnology applications.

One-pot synthesis of near-infrared fluorescent gold clusters for cellular fluorescence lifetime imaging

A facile strategy to synthesize water-soluble fluorescent gold nanoclusters (Au NCs) stabilized with the bidentate ligand dihydrolipoic acid (DHLA) is reported. The DHLA-capped Au NCs are characterized by UV-vis absorption spectroscopy, fluorescence spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The Au NCs possess many attractive features including ultrasmall size, bright near-infrared luminescence, high colloidal stability, and good biocompatibility, making them promising imaging agents for biomedical and cellular imaging applications. Moreover, their long fluorescence lifetime (>100 ns) makes them attractive as labels in fluorescence lifetime imaging (FLIM) applications. As an example, the internalization of Au NCs by live HeLa cells is visualized using the FLIM technique.

Preparation of highly luminescent mannose-gold nanodots for detection and inhibition of growth of Escherichia coli

In this paper, we describe a novel, simple, and convenient method for preparing water-soluble biofunctional gold nanodots (Au NDs) for the sensitive and selective detection of Escherichia coli (E. coli) and the inhibition of its growth. We obtained luminescent mannose-capped Au NDs (Man-Au NDs) from as-prepared 2.9-nm Au nanoparticles (Au NPs) and 29,29'-dithio bis(3',6',9',12',15',18'-hexaoxa-nonacosyl α-D-mannopyranoside) (Man-RSSR-Man). To obtain improved quantum yield (>20%), luminescent Man-Au NDs (1.8 nm) were prepared from Au NPs (0.47 μM) and Man-RSSR-Man (2.5 mM) in the presence of sodium borohydride (NaBH(4); 1.0 mM). The highly luminescent properties of Man-Au NDs prepared by the NaBH(4)-assisted method were characterized by UV-vis absorption, photoluminescence, and X-ray photoelectron spectroscopies. The results supported the high-density coverage of the NDs surface by Man-RS ligands. Multivalent interactions between Man-Au NDs and FimH proteins located on the bacterial pili of E. coli resulted in the formation of aggregated cell clusters. After concentrating this agglutinative E. coli from a large-volume cell solution (5 mL), Man-Au NDs were displaced by mannose (100 mM) and stabilized by Man-RSSR-Man (5 mM). Monitoring the luminescence of Man-Au NDs allowed the detection of E. coli at levels as low as 150 CFU/mL. Man-Au NDs were also found to be efficient antibacterial agents, selectively inhibiting the growth of E. coli through Man-Au ND-induced agglutination. Our small-diameter Man-Au NDs, which provided an ultra high ligand density (local concentration) of mannose units for multivalent interactions with E. coli, have great potential for use as an antibacterial agent in other applications.