Chip-based scanometric detection of mercuric ion using DNA-functionalized gold nanoparticles

We have developed a chip-based scanometric method for the detection of mercuric ion (Hg (2+)). This method takes advantage of the cooperative binding and catalytic properties of DNA-functionalized gold nanoparticles and the selective binding of a thymine-thymine mismatch for Hg (2+). The limit of detection of this assay in buffer and environmentally relevant samples (lake water) is 10 nM (2 ppb) Hg (2+), which is the U.S. Environmental Protection Agency (EPA) limit of [Hg (2+)] for drinkable water and 1 order of magnitude lower than previous colorimetric assays. This assay is capable of discriminating Hg (2+) from 15 other environmentally relevant metal ions. The method is attractive for potential point-of-use applications due to its high throughput, convenient readout, and portability.     

Unmodified gold nanoparticles as a colorimetric probe for visual methamphetamine detection

In recent years, in addition to the classic drugs, addiction to a series of new drug classes known as club drugs has increased significantly. Fast and low-cost bioassay for the detection of amphetamine-based drugs can be an effective strategy towards reducing their abuse. In this study, we designed a sensitive bioassay strategy using gold nanoparticles (GNPs) and the aptamers that possess high affinity toward methamphetamine (MA). It is suggested that the aptamer adopts different tertiary structures in the presence and/or absence of its specific target and GNPs can effectively differentiate between these two states by their characteristic surface plasmon resonance-based colour change. Visual detection of MA and 3,4-methylenedioxy-N-methylamphetamine (MDMA) in the low micromolar range is possible within minutes with the use of this method.     

Fast colorimetric detection of copper ions using L-cysteine functionalized gold nanoparticles

This communication reports an efficient visual detection method of Cu2+ by L-cysteine functionalized gold nanoparticles in aqueous solution. Upon exposure to Cu2+, the gold nanoparticle solution changed from red to blue, in response to surface plasmon absorption of dispersed and aggregated nanoparticles. This colorimetric sensor allows a rapid quantitative assay of Cu2+ down to the concentration range of 10(-5) M. Recognition of Cu2+ and formation of the aggregates are proposed to occur via a 2 : 1 sandwich complex between L-cysteine and Cu2+.     

Gram-scale synthesis and biofunctionalization of silica-coated silver nanoparticles for fast colorimetric DNA detection

A direct silica-coating method has been developed for the gram-scale synthesis of well-dispersed Ag@SiO(2) nanoparticles. Subsequent surface functionalization via the well-established silica surface chemistry provided arching points for straightforward bioconjugation with amino-terminated oligonucleotides. Fast hybridization kinetics of the resulting robust oligo-modified Ag@SiO(2) nanoprobes with complementary target oligonucleotides render themselves very useful for the fast colorimetric DNA detection based on the sequence-specific hybridization properties of DNA. Additionally, the reliable protocols developed in this study for preparing and functionalizing Ag@SiO(2) nanoparticles can be readily extended to other silica-coated nanoparticles, which can also provide a specific platform for the covalent attachment of biomolecules such as amino-rich proteins, enzymes, or amino-terminated oligonucleotides for diverse bioapplications.     

Gold and silica-coated gold nanoparticles as thermographic labels for DNA detection

The infrared emissivity of Au and silica-coated Au nanoparticles (Au NPs) deposited on indium tin oxide substrates was investigated. NPs were irradiated with laser light at a frequency close to the Au plasmon resonance band, and the blackbody radiation emitted as a result was monitored with an IR camera equipped with an InAs array detector. The differences in temperature before and after laser irradiation were recorded (T-jumps) and were found to be directly proportional to the number of particles present on the slide and to the laser power used in the experiment. Coating Au NPs with silica increased the measured T-jumps 2-5 times, depending on the thickness of the silica shell. This was in agreement with the observation that silica has a much higher IR emissivity than Au. Both Au and silica-coated Au NPs were then tested as labels for thermographic DNA detection. Target DNA concentrations as low as 100 pM were recorded when Au NPs were used as labels and as low as 10 pM when silica-coated Au NPs were used.     

Gold nanoparticles with asymmetric polymerase chain reaction for colorimetric detection of DNA sequence

We developed a novel strategy for rapid colorimetric analysis of a specific DNA sequence by combining gold nanoparticles (AuNPs) with an asymmetric polymerase chain reaction (As-PCR). In the presence of the correct DNA template, the bound oligonucleotides on the surface of AuNPs selectively hybridized to form complementary sequences of single-stranded DNA (ssDNA) target generated from As-PCR. DNA hybridization resulted in self-assembly and aggregation of AuNPs, and a concomitant color change from ruby red to blue-purple occurred. This approach is simpler than previous methods, as it requires a simple mixture of the asymmetric PCR product with gold colloid conjugates. Thus, it is a convenient colorimetric method for specific nucleic acid sequence analysis with high specificity and sensitivity. Most importantly, the marked color change occurs at a picogram detection level after standing for several minutes at room temperature. Linear amplification minimizes the potential risk of PCR product cross-contamination. The efficiency to detect Bacillus anthracis in clinical samples clearly indicates the practical applicability of this approach.     

DNA-functionalized nanochannels for SNP detection

We have developed ultrahigh density array of functionalized nanochannels by using a block copolymer having end di-COOH group. This approach provides a facile route for direct functionalization of wall surface of the nanochannels and immobilization site for molecular recognition agents (MRAs). By using overhanging single-stranded DNA as MRAs, the DNA-functionalized nanochannels showed high resolution to detect a single-base mismatch as well as to discriminate single-mismatched sequence at various locations by hybridization preference with MRAs.     

Highly selective colorimetric detection of hydrochloric acid using unlabeled gold nanoparticles and an oxidizing agent

We report a colorimetric system for the detection of HCl in aqueous environments using unlabeled gold nanoparticle (AuNP) probes. This nonaggregation-based detection system relies on the ability of chloro species to cause rapid leaching of AuNPs in an aqueous dispersion containing a strong oxidizing agent, such as HNO(3) or H(2)O(2). The leaching process leads to remarkable damping of the surface plasmon resonance peak of the AuNP dispersion. This method works only with AuNPs of a particular size (～30 nm diameter). It is highly selective for HCl over several common mineral acids, salts, and anions. This simple and cost-effective sensing system provides rapid and simple detection of HCl at concentrations as low as 500 ppm (far below the hazard limit) in natural water systems.     

Paper-based tuberculosis diagnostic devices with colorimetric gold nanoparticles

Abstract

A colorimetric sensing strategy employing gold nanoparticles and a paper assay platform has been developed for tuberculosis diagnosis. Unmodified gold nanoparticles and single-stranded detection oligonucleotides are used to achieve rapid diagnosis without complicated and time-consuming thiolated or other surface-modified probe preparation processes. To eliminate the use of sophisticated equipment for data analysis, the color variance for multiple detection results was simultaneously collected and concentrated on cellulose paper with the data readout transmitted for cloud computing via a smartphone. The results show that the 2.6 nM tuberculosis mycobacterium target sequences extracted from patients can easily be detected, and the turnaround time after the human DNA is extracted from clinical samples was approximately 1 h.     

One-pot polymerase chain reaction with gold nanoparticles for rapid and ultrasensitive DNA detection

We report a novel method for rapid, colorimetric detection of a specific deoxyribonucleic acid (DNA) sequence by carrying out a polymerase chain reaction in the presence of gold nanoparticles functionalized with two primers. Extension of the primers when the target DNA is present as a template during the polymerase chain reaction process affords the complementary sequences on the gold nanoparticle surfaces and results in the formation of gold nanoparticle aggregates with a concomitant color change from red to pinkish/purple. This method provides a convenient and straightforward solution for ultrasensitive DNA detection without any further post-treatment of the polymerase chain reaction products being necessary, and is a promising tool for rapid disease diagnostics and gene sequencing.     

Accelerated colorimetric immunosensing using surface-modified porous monoliths and gold nanoparticles

Abstract

A rapid and sensitive immunoassay platform integrating polymerized monoliths and gold nanoparticles (AuNPs) has been developed. The porous monoliths are photopolymerized in situ within a silica capillary and serve as solid support for high-mass transport and high-density capture antibody immobilization to create a shorter diffusion length for antibody–antigen interactions, resulting in a rapid assay and low reagent consumption. AuNPs are modified with detection antibodies and are utilized as signals for colorimetric immunoassays without the need for enzyme, substrate and sophisticated equipment for quantitative measurements. This platform has been verified by performing a human IgG sandwich immunoassay with a detection limit of 0.1 ng ml^?1. In addition, a single assay can be completed in 1 h, which is more efficient than traditional immunoassays that require several hours to complete.     

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.     

Fluorescence near gold nanoparticles for DNA sensing

We investigated fluorescence quenching and enhancement near gold nanoparticles (GNP) of various sizes using fluorescently labeled hairpin DNA probes of different lengths. A closed hairpin caused intimate contact between the fluorophore and the gold, resulting in an efficient energy transfer (quenching). Upon hybridization with complementary DNA, the DNA probes were stretched yielding a strong increase in fluorescence signal. By carefully quantifying the amount of bound fluorescent probes and the GNP concentrations, we were able to determine the quenching and enhancement efficiencies. We also studied the size and distance dependence theoretically, using both FDTD simulations and the Gersten-Nitzan model and obtained a good agreement between experiments and theory. On the basis of experimental and theoretical studies, we report over 96.8% quenching efficiency for all particle sizes tested and a maximal signal increase of 1.23 after DNA hybridization. The described results also demonstrate the potential of gold nanoparticles for label free DNA sensing.     

Stimuli-responsive releasing of gold nanoparticles and liposomes from aptamer-functionalized hydrogels

Controlled release of therapeutic agents is important for improving drug efficacy and reducing toxicity. Recently, hydrogels have been used for controlled release applications. While the majority of the previous work focused on releasing the cargo in response to physical stimuli such as temperature, light, electric field, and pH, we aim to trigger cargo release in the presence of small metabolites. In our system a DNA aptamer that can bind to adenosine, AMP, and ATP was used as a linker to attach either DNA-functionalized gold nanoparticles or liposomes to DNA-functionalized hydrogels. In the presence of the metabolite, both the nanoparticle and liposome cargos were released. The effect of salt, temperature, target concentration, and drying has been systematically studied. Interestingly, we found that the gel can be completely dried while retaining the DNA linkages and adenosine induced release was still achieved after rehydration. Our work demonstrates that aptamers can be used to control the release of drugs and other materials attached to hydrogels.