Gold Nanoparticle-based Assay Research Articles

Photoluminescent Molecules and Materials as Diagnostic Reporters in Lateral Flow Assays.

The lateral flow assay (LFA) is a point-of-care diagnostic test commonly available in an over-the-counter format because of its simplicity, speed, low cost, and portability. The reporter particles in these assays are among their most significant components because they perform the diagnostic readout and dictate the test's sensitivity. Today, gold nanoparticles are frequently used as reporters, but recent work focusing on photoluminescent-based reporter technologies has pushed LFAs to better performance. These efforts have focused specifically on reporters made of organic fluorophores, quantum dots, lanthanide chelates, persistent luminescent phosphors, and upconversion phosphors. In most cases, photoluminescent reporters show enhanced sensitivity compared to conventional gold nanoparticle-based assays. Here, we examine the advantages and disadvantages of these different reporters and highlight their potential benefits in LFAs. Our assessment shows that photoluminescent-based LFAs can not only reach lower detection limits than LFAs with traditional reporters, but they also can be capable of quantitative and multiplex analyte detection. As a result, the photoluminescent reporters make LFAs well-suited for medical diagnostics, the food and agricultural industry, and environmental testing.

Femtomolar oligonucleotide detection by a one-step gold nanoparticle-based assay

A sequence-specific oligonucleotide detection method based on the tail-to-tail aggregation of functionalized gold nanoparticles in the presence of target analytes is presented together with its optimization and capabilities for detection of single nucleotide polymorphisms (SNPs). In this single-step method, capture probes are freely accessible for hybridization, resulting in an improved assay performance compared to substrate-based assays. The analytes bring the nanoparticles close to each other via hybridization, causing a red shift of the nanoparticle plasmon peak detected by a spectrophotometer or CCD camera coupled to a darkfield imaging system. Optimal conditions for the assay were found to be (i) use of capture probes complementary to the target without any gap, (ii) maximum possible probe density on the gold nanoparticles, and (iii) 1M ionic strength buffer. The optimized assay has a 1fM limit of detection andfM to 10pM dynamic range, with detection of perfect match sequences being three orders of magnitude more sensitive than targets with single nucleotide mismatches.

Plasmonic Semiconductor Nanocrystals as Chemical Sensors: Pb2+ Quantitation via Aggregation-Induced Plasmon Resonance Shift

We demonstrate, for the first time, the use of plasmonic semiconductor nanocrystals for the analysis of heavy metal ions in water. This highly sensitive localized surface plasmon resonance (LSPR)-based platform is built on glutathione (GSH) capped Cu2−xS nanocrystals, which exhibit LSPR at near infrared (NIR) wavelengths. Aggregation of GSH-capped Cu2−x S occurs specifically in the presence of lead ions, Pb2+, producing a shift in the LSPR absorbance peak. Under optimal assay conditions, the detection limit was as low as 0.25 μM (52.5 ppb) of Pb2+. This provides a new plasmonic semiconductor nanocrystal-based assay for the detection of environmentally hazardous materials. The assay employs non-toxic and earth-abundant elements and could potentially be produced at much lower cost than similar gold nanoparticle-based assays.

Biofunctionalized Gold Nanoparticles for Colorimetric Sensing of Botulinum Neurotoxin A Light Chain

Botulinum neurotoxin is considered as one of the most toxic food-borne substances and is a potential bioweapon accessible to terrorists. The development of an accurate, convenient, and rapid assay for botulinum neurotoxins is therefore highly desirable for addressing biosafety concerns. Herein, novel biotinylated peptide substrates designed to mimic synaptosomal-associated protein 25 (SNAP-25) are utilized in gold nanoparticle-based assays for colorimetric detection of botulinum neurotoxin serotype A light chain (BoLcA). In these proteolytic assays, biotinylated peptides serve as triggers for the aggregation of gold nanoparticles, while the cleavage of these peptides by BoLcA prevents nanoparticle aggregation. Two different assay strategies are described, demonstrating limits of detection ranging from 5 to 0.1 nM of BoLcA with an overall assay time of 4 h. These hybrid enzyme-responsive nanomaterials provide rapid and sensitive detection for one of the most toxic substances known to man.

A highly sensitive dual-readout assay based on poly(A) and gold nanoparticles for palmatine hydrochloride

This report presents a highly sensitive, poly(A)-stabilized gold nanoparticle-based assay with dual readouts (resonance light scattering and colorimetric) for detecting palmatine hydrochloride (PaH) in real samples. The detection mechanism is based on the fact that palmatine hydrochloride has strong affinity to poly(A), which can stabilize gold nanoparticles at high ionic strength, and cause the aggregation of poly(A)-stabilized AuNPs, resulting in the enhanced resonance light scattering (RLS). At the same time, the color change of poly(A)-stabilized AuNPs solution is from red to blue via purple. Thus a highly sensitive RLS assay for PaH has been developed with a linear range of 0.023–2.5μg/mL. The limit of detection (LOD, 3σ) is 2.3ng/mL. In this work, the reaction mechanism of this system was investigated by scanning electron microscope (SEM), dark-field light scattering images (DLSI), dynamiclight scattering (DLS) and circular dichroism (CD). This proposed method was also applied successfully for the determination of PaH in pharmaceutical preparations and urine samples with RSD⩽4.0%. The results are in good agreement with those from the official method.

Synthesis of oligo(lactose)-based thiols and their self-assembly onto gold surfaces

The ability to produce monomolecular coatings with well-defined structural and functional properties is of key importance in biosensing, drug delivery, and many recently developed applications of nanotechnology. Organic chemistry has proven to be a powerful tool to achieve this in many research areas. Herein, we present the synthesis of three oligo(lactosides) glycosylated in a (1→3) manner, and which are further functionalized with amide-linked short alkanethiol spacers. The oligosaccharides (di-, tetra-, and hexasaccharide) originate from the inexpensive and readily available lactose disaccharide. These thiolated derivatives were immobilized onto gold surfaces, and the thus formed self-assembled monolayers (SAMs) on planar gold were characterized by wettability, ellipsometry and infrared reflection–absorption spectroscopy. Further, the ability of these SAMs to stabilize gold nanoparticles in saline solutions was also demonstrated, indicating that the oligosaccharides may be used as stabilizing agents in gold nanoparticle-based assays.

Label-free colorimetric detection of picomolar amounts of hydrazine using a gold nanoparticle-based assay

We report the development of a simple and rapid colorimetric detection method for hydrazine in boiler feed water using label-free aggregation-based gold nanoparticles as probe. This assay relies upon the distance-dependent optical properties of gold nanoparticles. Hydrazine could rapidly induce the aggregation of gold nanoparticles, thereby resulting in visual color change from red to blue (or purple). The concentration of hydrazine can be determined by the naked eye or by a UV–vis spectrometer. Calibration curve was linear ranging from 1.0 × 10−11 to 1.0 × 10−7 M of hydrazine. The present limit of detection for hydrazine was 1.0 × 10−12 M. The method is rather simple, and the whole process including sample pretreatment takes only 15 min at room temperature. The merits (such as simplicity, rapidity, low cost and visual colorimetry) make the proposed method especially useful for on-site screening of hydrazine levels well in boiler feed water.

Label-free colorimetric detection of picomolar thrombin in blood plasma using a gold nanoparticle-based assay

We unveil a novel, label-free, colorimetric assay – using fibrinogen (Fib) and gold nanoparticles (Au NPs) – for the highly selective and sensitive detection of thrombin. Addition of fibrinogen to a solution of Au NPs (average diameter: 56 nm) led to ready conjugation, forming Fib–Au NPs through electrostatic and hydrophobic interactions. Introduction of thrombin (a serine protease) into the Fib–Au NPs solutions in the presence of excess fibrinogen induced the formation of insoluble fibrillar fibrin–Au NPs agglutinates through the polymerization of the unconjugated and conjugated fibrinogen. After centrifugation, the absorbance at 532 nm of the supernatants decreased upon increasing the concentration of thrombin. This Fib–Au NP probe provides high sensitivity [limit of detection (LOD): 0.04 pM] for thrombin, with remarkable selectivity over other proteins and proteases. The range of linearity for the absorbance against the thrombin concentration was 0.1–10 pM ( R 2 = 0.96). This approach provides an LOD for thrombin that is lower than those obtainable using other nanomaterial- and aptamer-based detection methods. We validated the utility of this Fib–Au NP probe through separate analyses of thrombin and Factor Xa at picomolar levels in plasma samples—without the need for sample pretreatment. This technique appears to have practical potential in the diagnosis of diseases associated with coagulation abnormalities and cancers (e.g., pulmonary metastasis).

Hydroxylamine-amplified gold nanoparticles for the naked eye and chemiluminescent detection of sequence-specific DNA with notable potential for single-nucleotide polymorphism discrimination

Herein, we report a hydroxylamine-amplified gold nanoparticle-based assay with naked eye and chemiluminescent (CL) detection of sequence-specific DNA. For the naked eye detection assay, the signal can be observed by naked eye directly, which provides a general way for other biological assays. In contrast, the CL detection method can improve the detection limit by two orders of magnitude as compared to the naked eye detection, and a limit as low as 10 amol of target DNA can be sensitively detected. Most importantly, stringent control of either temperature or salt concentration is not needed during washing steps, and this new methodology exhibits an excellent capability for differentiating a perfectly matched target oligonucleotide from eight kinds of one-nucleotide mismatched oligonucleotides, and this detection specificity indicates that the present protocol could be applied to single-nucleotide polymorphism (SNP) analysis in many fields.

Gold Nanoparticle-Based Assays for the Detection of Biologically Relevant Molecules

Metallic nanoparticles of different sizes, shapes and compositions are being avidly explored as materials for next-generation biological labels, therapeutic agents, 'artificial viruses' and diagnostic probes. Gold nanoparticles especially, are making a major impact in these areas, owing in large part to their ease of functionality, low toxicity and unique optical properties. In particular, gold nanoparticles are having a major role in the development of highly sensitive and selective assays for biologically relevant molecules. Some of the assays for nucleic acids and proteins developed in the last 10 years outperform established methods and may soon find routine use in hospital settings.

On the Structure and Desorption Dynamics of DNA Bases Adsorbed on Gold: A Temperature-Programmed Study

The structure and desorption dynamics of mono- and multilayer samples of adenine, cytosine, guanine, and thymine on polycrystalline gold thin films are studied using temperature-programmed desorption-infrared reflection absorption spectroscopy (TPD-IRAS) and temperature-programmed desorption-mass spectroscopy (TPD-MS). It is shown that the pyrimidines, adenine and guanine, adsorb to gold in a complex manner and that both adhesive (adenine) and cohesive (guanine) interactions contribute the apparent binding energies to the substrate surface. Adenine displays at least two adsorption sites, including a high-energy site (210 degrees C, approximately 136 kJ/mol), wherein the molecule coordinates to the gold substrate via the NH2 group in an sp3-like, strongly perturbed, nonplanar configuration. The purines, cytosine and thymine, display a less complicated adsorption/desorption behavior. The desorption energy for cytosine (160 degrees C, approximately 122 kJ/mol) is similar to those obtained for adenine and guanine, but desorption occurs from a single site of dispersed, nonaggregated cytosine. Thymine desorbs also from a single site but at a significantly lower energy (100 degrees C, approximately 104 kJ/mol). Infrared data reveal that the monolayer architectures discussed herein are structurally very different from those observed for the bases in the bulk crystalline state. It is also evident that both pyrimidines and purines adsorb on gold with the plane of the molecule in a nonparallel orientation with respect to the substrate surface. The results of this work are discussed in the context of improving the understanding of the design of capturing oligonucleotides or DNA strands for bioanalytical applications, in particular, for gold nanoparticle-based assays.