Aptamer-modified gold nanoparticles for colorimetric determination of platelet-derived growth factors and their receptors

We have developed a highly specific sensing system for platelet-derived growth factors (PDGFs) and platelet-derived growth factor receptors (PDGFR) that uses gold nanoparticles (GNPs). We synthesized GNPs modified with an aptamer (Apt-GNPs) that is specific to PDGFs and used them to detect PDGFs by monitoring the changes in the color and extinction of the Apt-GNPs that occur as a result of aggregation. The color of the Apt-GNPs changes from red to purple at low concentrations (<400 nM), but changes only slightly at higher concentrations (>400 nM). We found that the sensitivity of the Apt-GNPs for the three PDGFs is highly salt-dependent, with an optimum condition of 200 mM NaCl. We obtained biphasic curves when plotting of the ratios of the extinction coefficients of the Apt-GNPs at 650 and 530 nm against the concentrations of PDGF-AA at various concentrations of Apt-GNPs. The linear ranges of the increases and decreases in this extinction ratio are 2.5-10 and 10-20 nM, respectively, for 0.42 nM Apt-GNPs and 25-75 and 75-200 nM, respectively, for 8.4 nM Apt-GNPs. When using 8.4 nM Apt-GNPs, the corresponding linear ranges of the increases and decreases in this extinction ratio are 15-100 and 100-400 nM, respectively, for PDGF-AB and 35-150 and 150-400 nM, respectively, for PDGF-BB. In addition, we have developed a homogeneous assay to detect the PDGF receptor-beta (PDGFR-beta) at concentrations as low as 3.2 nM, on the basis of the competition between the Apt-GNPs and PDGFR-beta for PDGF-BB. The results we present in this paper imply that there are practical applications of Apt-GNPs in protein analysis and cancer diagnosis.

Detection of mercury(II) based on Hg2+ -DNA complexes inducing the aggregation of gold nanoparticles

A DNA-Au NP probe for sensing Hg2+ using the formation of DNA-Hg2+ complexes through thymidine (T)-Hg2+ -T coordination to control the negative charge density of the DNA strands-thereby varying their structures-adsorbed onto Au NPs.

Detection of mercury(II) ions using colorimetric gold nanoparticles on paper-based analytical devices

An on-field colorimetric sensing strategy employing gold nanoparticles (AuNPs) and a paper-based analytical platform was investigated for mercury ion (Hg(2+)) detection at water sources. By utilizing thymine-Hg(2+)-thymine (T-Hg(2+)-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 Hg(2+), 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 Hg(2+) 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.

Selective Gold-Nanoparticle-Based “Turn-On” Fluorescent Sensors for Detection of Mercury(II) in Aqueous Solution

A new gold-nanoparticle (AuNP)-based sensor for detecting Hg(II) ions in aqueous solution has been developed. Rhodamine B (RB) molecules that are highly fluorescent in bulk solution fluoresce weakly when they are adsorbed onto AuNP surfaces as a result of fluorescence resonance energy transfer and collision with AuNPs. In the presence of metal ions such as Hg(II), RB molecules are released from the AuNP surface and thus restore the florescence of RB. The modulation of the photoluminescence quenching efficiency of RB-AuNPs in the presence of Hg(II) ions can achieve a large turn-on fluorescence enhancement (400-fold) in aqueous solution, and the entire detection takes less than 10 min. We have improved the selectivity of the probe further by modifying the AuNP surfaces with thiol ligands (mercaptopropionic acid, mercaptosuccinic acid, and homocystine) and adding a chelating ligand (2,6-pyridinedicarboxylic acid) to the sample solutions. Under the optimum conditions, the selectivity of this system for Hg(II) over other metal ions in aqueous solutions is remarkably high (50-fold or more), and its LOD for Hg(II) in the matrix pond water is 2.0 ppb. Our approach demonstrated the feasibility of using the developed nanosensor for rapid determination of Hg(II) in aqueous environmental samples and in batteries.

Oligonucleotide-based fluorescence probe for sensitive and selective detection of mercury(II) in aqueous solution

In this paper we unveil a new homogeneous assayusing TOTO-3 and the polythymine oligonucleotide T 33for the highly selective and sensitive detection of Hg (2+) in aqueous solution. The fluorescence of TOTO-3 is weak in the absence or presence of randomly coiled T 33. After T 33 interacts specifically with Hg (2+) ions through T-Hg (2+)-T bonding, however, its conformation changes to form a folded structure that preferably binds to TOTO-3. As a result, the fluorescence of a mixture of T 33 and TOTO-3 increases in the presence of Hg (2+). Our data from fluorescence polarization spectroscopy, capillary electrophoresis with laser-induced fluorescence detection, circular dichroism spectroscopy, and melting temperature measurements confirm the formation of folded T 33-Hg (2+) complexes. Under optimum conditions, the TOTO-3/T 33 probe exhibited a high selectivity (>or=265-fold) toward Hg (2+) over other metal ions, with a limit of detection of 0.6 ppb. We demonstrate the practicality of this TOTO-3/T 33 probe for the rapid determination of Hg (2+) levels in pond water and in batteries. This approach offers several advantages, including rapidity (<15 min), simplicity (label-free), and low cost.

Cancer cell targeting using multiple aptamers conjugated on nanorods

Molecular recognition toward specific cells is a key issue for effective disease, such as cancer, diagnosis and therapy. Although many molecular probes such as aptamers and antibodies can recognize the unique molecular signatures of cancer cells, some of these probes only have relatively weak binding affinities. This results in poor signaling and hinders cell targeting. Here, we use Au-Ag nanorods (NRs) as a nanoplatform for multivalent binding by multiple aptamers on the rod to increase both the signal and binding strengths of these aptamers in cancer cell recognition. Up to 80 fluorophore-labeled aptamers can be attached on a 12 nm x 56 nm NR, resulting in a much stronger fluorescence signal than that of an individual dye-labeled aptamer probe. The molecular assembly of aptamers on the NR surfaces also significantly improves the binding affinity with cancer cells through simultaneous multivalent interactions with the cell membrane receptors. This leads to an affinity at least 26-fold higher than the intrinsic affinity of the original aptamer probes. As determined by flow cytometric measurements, an enhancement in fluorescence signal in excess of 300-fold is obtained for the NR-aptamer-labeled cells compared with those labeled by individual aptamer probes. Therefore, the molecular assembly of aptamers clearly shows potential applications for the elucidation of cells with low density of binding sites, or with relatively weak binding probes, and can thus greatly improve our ability to perform cellular imaging and targeting. This is an excellent example of using nanomaterials to develop advanced molecular binders with greatly improved properties for cellular studies.

Highly selective DNA-based sensor for lead(II) and mercury(II) ions

We have developed a technique for the highly selective and sensitive detection of Pb(2+) and Hg(2+) using a thrombin-binding aptamer (TBA) probe labeled with the donor carboxyfluorescein (FAM) and the quencher 4-([4-(dimethylamino)phenyl]azo)benzoic acid (DABCYL) at its 5' and 3' termini, respectively. The TBA has a random coil structure that changes into a G-quartet structure and a hairpin-like structure upon binding Pb(2+) and Hg(2+) ions, respectively. As a result, the fluorescence decreases through fluorescence resonance energy transfer (FRET) between the fluorophore and quencher. These changes in fluorescence intensity allow the selective detection of Pb(2+) and Hg(2+) ions at concentrations as low as 300 pM and 5.0 nM using this TBA probe in the presence of phytic acid and a random DNA/NaCN mixture, respectively. The linear correlation existed between the fluorescence intensity and the concentration of Pb(2+) and Hg(2+) over the range of 0.5-30 nM (R(2) = 0.98) and 10-200 nM (R(2) = 0.98), respectively. To the best of our knowledge, this is the first example of a single DNA-based sensor that allows the detection of both Hg(2+) and Pb(2+) ions. This simple and cost-effective probe was also applied to separately determine Pb(2+) in soil samples and spiked Hg(2+) in pond samples.

Single neostriatal efferent axons in the globus pallidus: a light and electron microscopic study

Intracellularly labeled rat neostriatal projection neurons were analyzed with both light and electron microscopy. The axons of medium spiny neurons were traced into the globus pallidus and were found to make synaptic contacts with pallidal dendrites. Despite the common somato-dendritic morphology of the neostriatal projection neurons, two different distribution patterns of efferent axons were observed, indicating the presence of functionally different medium spiny neurons in the neostriatum.

Parameters for selective colorimetric sensing of mercury(II) in aqueous solutions using mercaptopropionic acid-modified gold nanoparticles

We unveil a new homogeneous assay-using mercaptopropionic acid-modified Au nanoparticles in the presence of 2,6-pyridinedicarboxylic acid for the highly selective and sensitive detection of Hg(2+) ions.

A Golgi study of rat neostriatal neurons: light microscopic analysis

At least two types of large neurons (somatic cross-sectional areas, SA greater than 300 microns2) and five-types of medium neurons (SA between 100 and 300 microns2) were distinguished in Golgi preparations of the adult rat neostriatum. Type I large cells had aspinous somata with long, radiating, sparsely spined dendrites which were sometimes varicose distally, whereas type II large cells had spines on both somatic and dendritic surfaces. Type I medium cells had aspinous somata and proximal dendrites, but their distal dendrites were densely covered with spines. Type II medium cells had somatic spines, and their radiating dendrites were sparsely spined. Other medium cells had no somatic spines: Type III cells had poorly branched and sparsely spined dendrites. Type IV cells had profusely branched, sparsely spined dendrites. Type V cells had radiating and varicose dendrites which could also be sparsely spined. Several small neurons (SA mostly less than 100 microns2) were also found in the rat neostriatum: Some had aspinous soma with sparsely spined dendrites; others had somatic spines. Except for the type II large cells, intrinsic axon collaterals were observed for every type of neuron, indicating that they all had local integrating functions.

Analysis of adenosine triphosphate and glutathione through gold nanoparticles assisted laser desorption/ionization mass spectrometry

This paper describes the use of aptamer-modified gold nanoparticles (Apt-AuNPs) as selective probes and AuNPs as the surface-assisted laser desorption/ionization (SALDI) matrixes for the determination of adenosine triphosphate (ATP) by mass spectrometry (MS). The aptamers were covalently attached to the surface of AuNPs to form Apt-AuNPs that provided selectivity toward ATP. However, Apt-AuNPs are less efficient laser desorption/ionization (LDI) matrixes when compared to AuNPs. By using Apt-AuNPs as selective probes and AuNPs as LDI matrixes, the MS approach provided the limit of detection (LOD) for ATP at a signal-to-noise ratio of 3 of 0.48 microM. When compared to conventional organic matrixes (e.g., 2,5-dihydroxybenzoic acid), AuNPs as LDI matrixes provide a number of advantages, including ease of preparation, selectivity, sensitivity, and repeatability. Sequential analysis of ATP and GSH in human cell lysates by SALDI with negative and positive MS modes, respectively, using Apt-AuNPs and AuNPs has been demonstrated. The present results demonstrate the practicality of the approach for monitoring the bioactivity of cells through determinations of the concentrations of ATP and GSH.

Nile Red-Adsorbed Gold Nanoparticle Matrixes for Determining Aminothiols through Surface-Assisted Laser Desorption/Ionization Mass Spectrometry

This paper describes the use of Nile Red-adsorbed gold nanoparticles (NRAuNPs) as selective probes and matrixes for the determination of aminothiols through surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS). The binding of three aminothiols-glutathione (GSH), cysteine (Cys), and homocysteine (HCys)-to the surfaces of these NRAuNPs induces their aggregation, which causes asubsequent changes in their color and fluorescence. Because arginine-a non-thiol amino acid-does not induce such aggregation, it is a straightforward process to use the NRAuNPs to selectively concentrate the aminothiols from a solution containing all four of these analytes; we were able to identify the three aminothiols in the precipitate, and arginine in the supernatant, directly through SALDI-MS measurements. Without using this preconcentration approach, the limits of detection (LODs) at a signal-to-noise ratio of 3 were 1.0, 2.0, and 1.3 microM for GSH, Cys, and HCys, respectively. In comparison, selective concentration using the NRAuNPs provided LODs of 25, 54, and 34 nM, for the determinations of GSH, Cys, and HCys, respectively. NRAuNP matrixes provide a number of advantages over the use of conventional organic matrixes (e.g., 2,5-dihydroxybenzoic acid), such as ease of preparation, selectivity, sensitivity, and repeatability. We validated the applicability of our method through the analyses of GSH in red blood cells and of Cys in plasma; we believe that this approach has great potential for diagnosis.

Use of fluorescent DNA-templated gold/silver nanoclusters for the detection of sulfide ions

We have developed a one-pot approach to prepare fluorescent DNA-templated gold/silver nanoclusters (DNA-Au/Ag NCs) from Au(3+), Ag(+), and DNA (5'-CCCTTAATCCCC-3') in the presence of NaBH(4) in order to detect sulfide (S(2-)) 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 S(2-) 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 S(2-) ions at concentrations as low as 0.83 nM. To minimize interference from I(-) ions for the detection of S(2-) 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 S(2-) ions in hot spring and seawater samples, demonstrating its advantages of simplicity, sensitivity, selectivity, and low cost.