Nitrite ion-induced fluorescence quenching of luminescent BSA-Au(25) nanoclusters: mechanism and application.

Fluorescence quenching is an interesting phenomenon which is highly useful in developing fluorescence based sensors. A thorough understanding of the fluorescence quenching mechanism is essential to develop efficient sensors. In this work, we investigate different aspects governing the nitrite ion-induced fluorescence quenching of luminescent bovine serum albumin stabilized gold nanoclusters (BSA-Au NCs) and their application for detection of nitrite in urine. The probable events leading to photoluminescence (PL) quenching by nitrite ions were discussed on the basis of the results obtained from ultraviolet-visible (UV-Vis) absorption spectroscopy, X-ray photoelectron spectroscopy (XPS), fluorescence measurements, circular dichroism (CD) spectroscopy, zeta potential and dynamic light scattering (DLS) studies. These studies suggested that PL quenching mainly occurred through the oxidation of Au(0) atoms to Au(i) atoms in the core of BSA-Au NCs mediated by nitrite ions. The interference caused by certain species such as Hg(2+), Cu(2+), CN(-), S(2-), glutathione, cysteine, etc. during the nitrite determination by fluorescence quenching was eliminated by using masking agents and optimising the conditions. Based on these findings we proposed a BSA-Au NC-modified membrane based sensor which would be more convenient for the real life applications such as nitrite detection in urine samples. The BSA-Au NC-modified nitrocellulose membrane (NCM) enabled the detection of nitrite at a level as low as 100 nM in aqueous solutions. This Au NC-based paper probe was validated to exhibit good performance for nitrite analysis in environmental water and urine samples, which makes it useful in practical applications.

Visual detection of copper(II) ions in blood samples by controlling the leaching of protein-capped gold nanoparticles.

We have developed a simple, low-cost, paper-based probe for the selective colorimetric detection of copper ions (Cu(2+)) in aqueous solutions. The bovine serum albumin (BSA)-modified 13.3-nm Au nanoparticle (BSA-Au NP) probe was designed to detect Cu(2+) ions using lead ions (Pb(2+)) and 2-mercaptoethanol (2-ME) as leaching agents in a glycine-NaOH (pH 12.0) solution. In addition, a nitrocellulose membrane (NCM) was used to trap the BSA-Au NPs, leading to the preparation of a nanocomposite film consisting of a BSA-Au NP-decorated membrane (BSA-Au NPs/NCM). The BSA-Au NPs probe operates on the principle that Cu deposition on the surface of the BSA-Au NPs inhibits their leaching ability, which is accelerated by Pb(2+) ions in the presence of 2-ME. Under optimal solution conditions (5 mM glycine-NaOH (pH 12.0), Pb(2+) (50 µM), and 2-ME (1.0 M)), the Pb(2+)/2-ME-BSA-Au NPs/NCM enabled the detection of Cu(2+) at nanomolar concentrations in aqueous solutions by the naked eye with high selectivity (at least 100-fold over other metal ions). In addition, this cost-effective probe allowed for the rapid and simple determination of Cu(2+) ions in not only natural water samples but also in a complex biological sample (in this case, blood sample).

Iron Hydroxide/Oxide-Reduced Graphene Oxide Nanocomposite for Dual-Modality Photodynamic and Photothermal Therapy In Vitro and In Vivo.

Minimal invasive phototherapy utilising near-infrared (NIR) laser to generate local reactive oxygen species (ROS) and heat has few associated side effects and is a precise treatment in cancer therapy. However, high-efficiency and safe phototherapeutic tumour agents still need developing. The application of iron hydroxide/oxide immobilised on reduced graphene oxide (FeOxH-rGO) nanocomposites as a therapeutic agent in integration photodynamic cancer therapy (PDT) and photothermal cancer therapy (PTT) was discussed. Under 808 nm NIR irradiation, FeOxH-rGO offers a high ROS generation and light-to-heat conversion efficiency because of its strong NIR absorption. These phototherapeutic effects lead to irreversible damage in FeOxH-rGO-treated T47D cells. Using a tumour-bearing mouse model, NIR ablated the breast tumour effectively in the presence of FeOxH-rGO. The tumour treatment response was evaluated to be 100%. We integrated PDT and PTT into a single nanodevice to facilitate effective cancer therapy. Our FeOxH-rGO, which integrates the merits of FeOxH and rGO, displays an outstanding tumoricidal capacity, suggesting the utilization of this nanocomposites in future medical applications.

Multivalent aptamer/gold nanoparticle-modified graphene oxide for mass spectrometry-based tumor tissue imaging.

The protein mucin1 (MUC1) is an attractive target for cancer biomarkers because it is overexpressed in most adenocarcinomas. In this study, we exploited a MUC1-binding aptamer (AptMUC1) as a targeting agent for nanoparticle-based imaging systems coupled with laser desorption/ionization mass spectrometry (LDI-MS). We found that AptMUC1-conjugated gold nanoparticles immobilized, through hydrophobic and π-π interactions, on graphene oxide (AptMUC1-Au NPs/GO) bound effectively to MUC1 units on tumor cell membranes. The ultrahigh density and high flexibility of AptMUC1 on the GO surface enhanced the platform's cooperative and multivalent binding affinity for MUC1 on cell membranes. After we had labeled MUC1-overexpressing MCF-7 cells (human breast adenocarcinoma cell line) with AptMUC1-Au NPs/GO, we used LDI-MS to monitor Au cluster ions ([Aun](+); n = 1-3), resulting in the detection of as few as 100 MCF-7 cells. We also employed this AptMUC1-Au NPs/GO-LDI-MS system to analyze four different MUC1 expression cell lines. In addition, the AptMUC1-Au NPs/GO platform could be used further as a labeling agent for tumor tissue imaging when coupled with LDI-MS. Thus, Apt-Au NPs/GO can function as a highly amplified signal transducer through the formation of large Au clusters ions during LDI-MS analysis.

Monitoring Cluster Ions Derived from Aptamer-Modified Gold Nanofilms under Laser Desorption/Ionization for the Detection of Circulating Tumor Cells.

In this paper, we describe the use of pulsed laser desorption/ionization mass spectrometry (LDI-MS) for the detection of tumor cells through the analysis of gold cluster ions [Aun](+) from aptamer-modified gold nanofilms (Au NFs). We observed not only the transformation of the Au NFs into gold nanoparticles (Au NPs) but also the formation of gaseous gold cluster ions ([Au(n)](+); n = 1-5) under irradiation with a nanosecond pulsed laser. The size and density of the formed Au NPs and the abundance of [Au(n)](+) ions were both highly dependent on the thickness of the Au NFs (10-100 nm). Thin Au NFs tended to form highly dense Au NPs on the substrate and favored the desorption and ionization of gold cluster ions. The signal intensities of the [Au(n)](+) species, monitoring using mass spectrometry, decreased upon increasing the thickness of the Au NF from 10 to 100 nm and after modification with thiolated DNA. Furthermore, we found that Au NFs modified with mucin1-binding aptamer (AptMUC1-Au NFs) could selectively enrich MCF-7 cells (human breast adenocarcinoma cell line) in blood samples; coupled with LDI-MS analysis of the [Au(n)](+) ions, we could detect MCF-7 cells selectively in blood samples at abundances as low as 10 cells. This approach offers the advantages of high sensitivity, selectivity, and throughput for the detection of circulating tumor cells, and has great potential for use as a powerful analytical platform for clinical diagnoses of tumor metastasis.

Photothermal therapeutic response of cancer cells to aptamer-gold nanoparticle-hybridized graphene oxide under NIR illumination.

The objective of this study was to synthesize a nanocomposite, aptamer-gold nanoparticle-hybridized graphene oxide (Apt-AuNP-GO), to facilitate targeted treatment of tumor cells by near-infrared (NIR) light-activatable photothermal therapy. We also investigated whether Apt-AuNP-GO with NIR illumination modulates heat shock proteins (HSPs) expression leading to therapeutic response in human breast cancer cells. These findings can provide strategies for improving the photothermal therapy efficacy of cancer. The self-assembled Apt-AuNP-GO nanocomposite could selectively target MUC1-positive human breast cancer cells (MCF-7) due to the specific interaction between the MUC1-binding-aptamer and the MUC1 (type I transmembrane mucin glycoprotein) on cell membrane. In addition, Apt-AuNP-GO has a high light-to-heat conversion capability for photoabsorption of NIR light, and it is able to exert therapeutic effects on MCF-7 cells at an ultralow concentration without inducing adverse effects in healthy cells. The Apt-AuNP-GO nanocomposites combine the advantages of GOs, AuNPs, and Apts, possess specific targeting capability, excellent biocompatibility, and tumor cell destruction ability, suggesting great potential for application in the photothermal therapy of breast cancer. Under NIR illumination, Apt-AuNP-GO induced transient increase in HSP70 expression, which decreased thereafter. This phenomenon may cause irreversible damage to Apt-AuNP-GO-treated MCF-7 cell under NIR illumination. We also demonstrated that the combination therapy of heat and HSP70 inhibitor could synergistically generate marked tumoricidal effects against breast cancer. These results suggest that the degree and duration of HSP70 protein expression are correlated with therapeutic effects against breast cancer for Apt-AuNP-GO-assisted photothermal therapy. We believe that such a nanocomposite can be readily extended to the construction of HSP70 inhibitors-loaded Apt-AuNP-GO, which could deliver both heat and HSP70 inhibitors to tumorigenic regions for the chemo-photothermal therapy.

Photoluminescent graphene quantum dots for in vivo imaging of apoptotic cells.

Apoptosis (programmed cell death) is linked to many incurable neurodegenerative, cardiovascular and cancer causing diseases. Numerous methods have been developed for imaging apoptotic cells in vitro; however, there are few methods available for imaging apoptotic cells in live animals (in vivo). Here we report a novel method utilizing the unique photoluminescence properties of plant leaf-derived graphene quantum dots (GQDs) modified with annexin V antibody (AbA5) to form (AbA5)-modified GQDs (AbA5-GQDs) enabling us to label apoptotic cells in live zebrafish (Danio rerio). The key is that zebrafish shows bright red photoluminescence in the presence of apoptotic cells. The toxicity of the GQDs has also been investigated with the GQDs exhibiting high biocompatibility as they were excreted from the zebrafish's body without affecting its growth significantly at a concentration lower than 2 mg mL(-1) over a period of 4 to 72 hour post fertilization. The GQDs have further been used to image human breast adenocarcinoma cell line (MCF-7 cells), human cervical cancer cell line (HeLa cells), and normal human mammary epithelial cell line (MCF-10A). These results are indispensable to further the advance of graphene-based nanomaterials for biomedical applications.

Monitoring thrombin generation and screening anticoagulants through pulse laser-induced fragmentation of biofunctional nanogold on cellulose membranes.

Thrombin generation (TG) has an important part in the blood coagulation system, and monitoring TG is useful for diagnosing various health issues related to hypo-coagulability and hyper-coagulability. In this study, we constructed probes by using mixed cellulose ester membranes (MCEMs) modified with gold nanoparticles (Au NPs) for monitoring thrombin activity using laser desorption/ionization mass spectrometry (LDI-MS). The LDI process produced Au cationic clusters ([Au(n)](+); n = 1-3) that we detected through MS. When thrombin reacted with fibrinogen on the Au NPs-MCEMs, insoluble fibrin was formed, hindering the formation of Au cationic clusters and, thereby, decreasing the intensity of their signals in the mass spectrum. Accordingly, we incorporated fibrinogen onto the Au NPs-MCEMs to form Fib-Au NPs-MCEM probes to monitor TG with good selectivity (>1000-fold toward thrombin with respect to other proteins or enzymes) and sensitivity (limit of detection for thrombin of ca. 2.5 pM in human plasma samples). Our probe exhibited remarkable performance in monitoring the inhibition of thrombin activity by direct thrombin inhibitors. Analyses of real samples using our new membrane-based probe suggested that it will be highly useful in practical applications for the effective management of hemostatic complications.

Detection of microRNA in tumor cells using exonuclease III and graphene oxide-regulated signal amplification.

In this study, we developed a label-free, ultrasensitive graphene oxide (GO)-based probe for the detection of oligonucleotides by laser desorption/ionization mass spectrometry (LDI-MS). On the basis of simple π-π stacking and electrostatic interactions between rhodamine 6G (R6G) and GO, we prepared the nanocomposite R6G-modified GO (R6G-GO). Signal intensities of R6G increased in mass spectra in the presence of single-stranded oligonucleotides under pulsed laser irradiation (355 nm) of R6G-GO. In addition, the signal intensity of R6G was stronger in the presence of short oligonucleotides. Because small oligonucleotides improve the LDI efficiency of R6G on GO, we designed an enzyme-amplified signal transduction probe system for the detection of microRNA (miRNA). After specific digestion of the probe DNA (pDNA) strand from pDNA/miRNA-hybridized complexes by exonuclease III (Exo III), the resulting small oligonucleotide fragments increased the R6G signal during LDI-MS of R6G-GO. In addition, the signal intensity of the R6G ions increased with increasing concentrations of the target miRNA. Coupling this enzyme reaction and R6G-GO with LDI-MS enabled the detection of miRNA at concentrations of the femtomolar (fM) level. We also demonstrated the analysis of miRNA in tumor cells and utilized this R6G-GO probe in the detection of a single-nucleotide polymorphism (SNP) in the Arg249Ser unit of the TP53 gene. This simple, rapid, and sensitive detection system based on the coupling of functional GO with LDI-MS appears to have great potential as a tool for the bioanalyses of oligonucleotides and proteins.

Graphene oxide modified with aptamer-conjugated gold nanoparticles and heparin: a potent targeted anticoagulant.

Graphene oxide (GO) modified with 29-mer thrombin-binding-aptamer-conjugated gold nanoparticles (TBA29-Au NPs/GO) can synergistically inhibit the thrombin-mediated cleavage of fibrinogen to fibrin. To further improve anticoagulation efficiency in human plasma, TBA29-Au NPs/heparin/GO has been prepared from TBA29-Au NPs/GO and heparin that can also bind thrombin. The dose-dependence of thrombin clotting time (TCT) delay caused by TBA29-Au NPs/heparin/GO is 21.4, 17.0 and >100 times higher than that caused by the TBA29-Au NPs, TBA29-Au NPs/GO and commercially available drugs (heparin, argatroban, hirudin or warfarin), respectively.