The use of gold nanoparticles in diagnostics and detection

DNA functionalized gold nanoparticles for bioanalysis

Gold nanoparticles (Au NPs) have become one of the most interesting sensing materials because of their unique size- and shape-dependent optical properties, high extinction coefficients, and super-quenching capability. Au NPs that are bioconjugated with DNA (DNA-Au NPs) have been demonstrated for selective and sensitive detection of analytes such as mercury(ii) ions, platelet-derived growth factor (PDGF), and adenosine triphosphate (ATP). This review focuses on approaches using DNA-Au NPs for colorimetric, fluorescent, and scattering detection of biopolymers and small solutes. We highlight the important roles that the size and concentration of Au NPs, the length and sequence of DNA, the nature of the capping agents, and the ionic strength and pH of solution play in determining the specificity and sensitivity of the nanosensors for the analytes. The advantages and disadvantages of different detection methods for sensing of interesting analytes using DNA-Au NPs will be discussed.

Gold nanoparticles for molecular diagnostics

Gold nanoparticles (AuNPs) exhibit a unique phenomenon, known as surface plasmon resonance, which is responsible for their large absorption and scattering cross-sections, which are four to five orders of magnitude larger than those of conventional dyes. In addition, their optical properties can be controlled by varying their sizes, shapes and compositions. AuNPs can be easily synthesized and functionalized with different biomolecules including oligonucleotides. Numerous methods have been utilized for detecting AuNPs such as colorimetric, scanometric, fluorescence, surface-enhanced Raman scattering and electrochemical techniques. These unique aspects have permitted the development of novel AuNP-based assays for molecular diagnostics which promise increased sensitivity and specificity, multiplexing capability, and short turnaround times. AuNP-based colorimetric assays in particular show great potential in point-of-care testing assays. This review discusses properties of AuNPs and their utilization for the development of novel molecular assays.

Quantification and reactivity of functional groups in the ligand shell of PEGylated gold nanoparticles via a fluorescence-based assay

We present a fluorescence-based assay for the characterization of functionalized gold nanoparticles (AuNPs) capped with a self-assembled monolayer of mixed thiols derived from poly(ethylene glycol) (PEG). These water-soluble AuNPs carry primary amino groups at the solvent-exposed interface, which can be used for further conjugation of biologically active molecules. The reported assay allows quantification of the average number of functionalizable amino groups per particle (N(NH(2))) with a relative uncertainty below or equal to +/-14% (95% confidence interval), thus providing essential information for the successive derivatization of the AuNPs. Here, a fluorescently labeled derivative of peptide-neurotoxin conantokin-G was coupled to the amino groups of the particle ligand shell via a flexible linker. We quantitatively determined the average number of peptides per particle (N(pept)) and the yield of the two-step conjugation strategy. AuNPs carrying 50-70 copies of the peptide were obtained. In addition, we have gained insights into the deterioration of the self-assembled monolayer due to thiol desorption with time. Under ordinary storage conditions in solution and at room temperature, a decrease in N(NH(2)) between 48% and 75% could be observed at the end of the period of investigation (42-56 days). Slow desorption of the conjugated peptides upon storage was also observed and quantified ( approximately 25% in 14 days).

Gold nanoparticles in nanomedicine: preparations, imaging, diagnostics, therapies and toxicity

This critical review provides an overall survey of the basic concepts and up-to-date literature results concerning the very promising use of gold nanoparticles (AuNPs) for medicinal applications. It includes AuNP synthesis, assembly and conjugation with biological and biocompatible ligands, plasmon-based labeling and imaging, optical and electrochemical sensing, diagnostics, therapy (drug vectorization and DNA/gene delivery) for various diseases, in particular cancer (also Alzheimer, HIV, hepatitis, tuberculosis, arthritis, diabetes) and the essential in vitro and in vivo toxicity. It will interest the medicine, chemistry, spectroscopy, biochemistry, biophysics and nanoscience communities (211 references).

Enhanced detection of early-stage oral cancer in vivo by optical coherence tomography using multimodal delivery of gold nanoparticles

Contrast in optical coherence tomography (OCT) images can be enhanced by utilizing surface plasmon resonant gold nanoparticles. To improve the poor in vivo transport of gold nanoparticles through biological barriers, an efficient delivery strategy is needed. In this study, the improved penetration and distribution of gold nanoparticles were achieved by microneedle and ultrasound, respectively, and it was demonstrated that this multimodal delivery of antibody-conjugated PEGylated gold nanoparticles enhanced the contrast in in vivo OCT images of oral dysplasia in a hamster model.

Nanostructured materials for electrochemiluminescence (ECL)-based detection methods: recent advances and future perspectives

This review presents a general picture of the last advances and developments (2003-2008) related to novel nanostructured materials for electrochemiluminescence-based biosensors using. It briefly covers the basic mechanisms of ECL detection, and the recent developments in fabrication of solid-state ECL sensors using nanostructured materials such as carbon nanotubes, metal nanoparticles, quantum dots, thin films of metallopolymers and of inorganic metal complexes. Finally, challenges and perspectives of the use of such materials for biomedical diagnostics are discussed.

In vitro diagnostic prospects of nanoparticles

There is a constant need to improve the performance of current diagnostic assays as well as develop innovative testing strategies to meet new testing challenges. The use of nanoparticles promises to help promote in vitro diagnostics to the next level of performance. Quantum dots (QDs), gold nanoparticles (AuNPs), and superparamagnetic nanoparticles are the most promising nanostructures for in vitro diagnostic applications. These nanoparticles can be conjugated to recognition moieties such as antibodies or oligonucleotides for detection of target biomolecules. Nanoparticles have been utilized in immunoassays, immunohistochemistry, DNA diagnostics, bioseparation of specific cell populations, and cellular imaging. Nanoparticle-based diagnostics may open new frontiers for detection of tumours, infectious diseases, bio-terrorism agents, and neurological diseases, to name a few. More work is necessary to fully optimize use of nanoparticles for clinical diagnosis and to resolve some concerns regarding potential health and environmental risks related to their use. However, we envision further developments of nanoparticle-based diagnostics will yield unique assays with enhanced sensitivity and multiplexing capability for the modern clinical laboratory.

Gold--an introductory perspective

We introduce the collection of reviews in this thematic issue of Chemical Society Reviews that demonstrate and discuss the current cutting edge research in the field of gold chemistry and materials science as it stands today. We also highlight achievements in the fields of gold catalysis, gold nanoparticles and the preparative, structural and theoretical chemistry of gold, and discuss the remaining challenges and opportunities. Our aim is to inspire further discovery in these new and deeply fascinating fields.