Thermal Transport through CTAB- and MTAB-Functionalized Gold Interfaces Using Molecular Dynamics Simulations

Thermal transport coefficients, notably the interfacial thermal conductance, were determined in planar and spherical gold interfaces functionalized with CTAB (cetyltrimethylammonium bromide) or MTAB (16-mercapto-hexadecyl-trimethylammonium bromide) using reverse nonequilibrium molecular dynamics (RNEMD) methods. The systems of interest included (111), (110), and (100) planar facets as well as nanospheres (r = 10 Å). The effect of metal polarizability was investigated through the implementation of the density-readjusted embedded atom model (DR-EAM), a polarizable metal potential. We find that conductance is higher in MTAB-capped interfaces, due in large part to the metal-to-ligand coupling provided by the Au-S bond. Alternatively, CTAB does not couple strongly with either the metal or the solvent, and it is largely a barrier to heat transfer, resulting in a much lower interfacial thermal conductance. Through analysis of physical contact between the ligand and the solvent, we find that there is significantly more overlap in the MTAB systems than the CTAB systems, mirroring the trends we observed in the conductance.

Antibody-modified Gold Nanobiostructures: Advancing Targeted Photodynamic Therapy for Improved Cancer Treatment

Photodynamic therapy (PDT) is an innovative, non-invasive method of treating cancer that uses light-activated photosensitizers to create reactive oxygen species (ROS). However, challenges associated with the limited penetration depth of light and the need for precise control over photosensitizer activation have hindered its clinical translation. Nanomedicine, particularly gold nanobiostructures, offers promising solutions to overcome these limitations. This paper reviews the advancements in PDT and nanomedicine, focusing on applying antibody-modified gold nanobiostructures as multifunctional platforms for enhanced PDT efficacy and improved cancer treatment outcomes. The size, shape, and composition of gold nanobiostructures can significantly influence their PDT efficacy, making synthetic procedures crucial. Functionalizing the surface of gold nanobiostructures with various molecules, such as antibodies or targeting agents, bonding agents, PDT agents, photothermal therapy (PTT) agents, chemo-agents, immunotherapy agents, and imaging agents, allows composition modification. Integrating gold nanobiostructures with PDT holds immense potential for targeted cancer therapy. Antibody-modified gold nanobiostructures, in particular, have gained significant attention due to their tunable plasmonic characteristics, biocompatibility, and surface functionalization capabilities. These multifunctional nanosystems possess unique properties that enhance the efficacy of PDT, including improved light absorption, targeted delivery, and enhanced ROS generation. Passive and active targeting of gold nanobiostructures can enhance their localization near cancer cells, leading to efficient eradication of tumor tissues upon light irradiation. Future research and clinical studies will continue to explore the potential of gold nanobiostructures in PDT for personalized and effective cancer therapy. The synthesis, functionalization, and characterization of gold nanobiostructures, their interaction with light, and their impact on photosensitizers' photophysical and photochemical properties, are important areas of investigation. Strategies to enhance targeting efficiency and the evaluation of gold nanobiostructures in vitro and in vivo studies will further advance their application in PDT. The integrating antibody-modified gold nanobiostructures in PDT represents a promising strategy for targeted cancer therapy. These multifunctional nanosystems possess unique properties that enhance PDT efficacy, including improved light absorption, targeted delivery, and enhanced ROS generation. Continued research and development in this field will contribute to the advancement of personalized and effective cancer treatment approaches.

Gold nanocrystals: optical properties, fine-tuning of the shape, and biomedical applications

Noble metal nanomaterials with special physical and chemical properties have attracted considerable attention in the past decades. In particular, Au nanocrystals (NCs), which possess high chemical inertness and unique surface plasmon resonance (SPR), have attracted extensive research interest. In this study, we review the properties and preparation of Au NCs with different morphologies as well as their important applications in biological detection. The preparation of Au NCs with different shapes by many methods such as seed-mediated growth method, seedless synthesis, polyol process, ultrasonic method, and hydrothermal treatment has already been introduced. In the seed-mediated growth method, the influence factors in determining the final shape of Au NCs are discussed. Au NCs, which show significant size-dependent color differences are proposed for preparing biological probes to detect biomacromolecules such as DNA and protein, while probe conjugate molecules serves as unique coupling agents with a target. Particularly, Au nanorods (NRs) have some unique advantages in the application of biological probes and photothermal cancer therapy compared to Au nanoparticles (NPs).

State of the art: Lateral flow assays toward the point-of-care foodborne pathogenic bacteria detection in food samples

Diverse chemicals and some physical phenomena recently introduced in nanotechnology have enabled scientists to develop useful devices in the field of food sciences. Concerning such developments, detecting foodborne pathogenic bacteria is now an important issue. These kinds of bacteria species have demonstrated severe health effects after consuming foods and high mortality related to acute cases. The most leading path of intoxication and infection has been through food matrices. Hence, quick recognition of foodborne bacteria agents at low concentrations has been required in current diagnostics. Lateral flow assays (LFAs) are one of the urgent and prevalently applied quick recognition methods that have been settled for recognizing diverse types of analytes. Thus, the present review has stressed on latest developments in LFAs-based platforms to detect various foodborne pathogenic bacteria such as Salmonella, Listeria, Escherichia coli, Brucella, Shigella, Staphylococcus aureus, Clostridium botulinum, and Vibrio cholera. Proper prominence has been given on exactly how the labels, detection elements, or procedures have affected recent developments in the evaluation of diverse bacteria using LFAs. Additionally, the modifications in assays specificity and sensitivity consistent with applied food processing techniques have been discussed. Finally, a conclusion has been drawn for highlighting the main challenges confronted through this method and offered a view and insight of thoughts for its further development in the future.

Photothermal and Photodynamic Therapy of Tumors with Plasmonic Nanoparticles: Challenges and Prospects

Cancer remains one of the leading causes of death in the world. For a number of neoplasms, the efficiency of conventional chemo- and radiation therapies is insufficient because of drug resistance and marked toxicity. Plasmonic photothermal therapy (PPT) using local hyperthermia induced by gold nanoparticles (AuNPs) has recently been extensively explored in tumor treatment. However, despite attractive promises, the current PPT status is limited by laboratory experiments, academic papers, and only a few preclinical studies. Unfortunately, most nanoformulations still share a similar fate: great laboratory promises and fair preclinical trials. This review discusses the current challenges and prospects of plasmonic nanomedicine based on PPT and photodynamic therapy (PDT). We start with consideration of the fundamental principles underlying plasmonic properties of AuNPs to tune their plasmon resonance for the desired NIR-I, NIR-2, and SWIR optical windows. The basic principles for simulation of optical cross-sections and plasmonic heating under CW and pulsed irradiation are discussed. Then, we consider the state-of-the-art methods for wet chemical synthesis of the most popular PPPT AuNPs such as silica/gold nanoshells, Au nanostars, nanorods, and nanocages. The photothermal efficiencies of these nanoparticles are compared, and their applications to current nanomedicine are shortly discussed. In a separate section, we discuss the fabrication of gold and other nanoparticles by the pulsed laser ablation in liquid method. The second part of the review is devoted to our recent experimental results on laser-activated interaction of AuNPs with tumor and healthy tissues and current achievements of other research groups in this application area. The unresolved issues of PPT are the significant accumulation of AuNPs in the organs of the mononuclear phagocyte system, causing potential toxic effects of nanoparticles, and the possibility of tumor recurrence due to the presence of survived tumor cells. The prospective ways of solving these problems are discussed, including developing combined antitumor therapy based on combined PPT and PDT. In the conclusion section, we summarize the most urgent needs of current PPT-based nanomedicine.

The effect of photodynamic therapy by gold nanoparticles on Streptococcus mutans and biofilm formation: an in vitro study

In this experimental study, we aimed to evaluate the antibacterial and anti-biofilm effects of photodynamic therapy with a photosensitizer in conjunction with Gold nanoparticles against Streptococcus mutans as an important cariogenic bacterial agent. This experimental in vitro study evaluated the antibacterial and anti-biofilm effect of five groups as followed against S. mutans: methylene blue (MB), Gold nanoparticles (AuNPs), methylene blue conjugated with Gold nanoparticles (MB-AuNPs), MB mediated photodynamic therapy (MB mediated PDT) and methylene blue conjugated with Gold nanoparticles mediated photodynamic therapy (MB-AuNPs mediated PDT). InGaAlP laser (Azor-2 K) with 25 mW total output, 660 nm wavelength and laser probe cross-section of 0.78 cm² was used for methylene blue activation. Total dose of 19.23 J/cm² for 10 min was irradiated to each group. Minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and colony forming unit (CFU) were determined. Bacterial biofilm formation inhibition was assessed by crystal violet staining (The microtiter plate biofilm assay). The viability of S. mutans cells was assessed by MTT assay. MB mediated PDT and MB-AuNP mediated PDT were the most effective method for S. mutans biofilm inhibition (P < 0.05). MB alone, MB-AuNP alone and MB mediated PDT and MB-AuNP mediated PDT had the same effect against the planktonic phase of S. mutans (P > 0.05). Also they had similar pattern for bacterial growth inhibition and bactericidal effect (P > 0.05). Gold nano particle mediated photodynamic therapy represented antibacterial and antibiofilm activity against S. mutans; but this modality was not more effective than routine PDT.

Transcription-Based Amplified Colorimetric Thrombin Sensor Using Non-Crosslinking Aggregation of DNA-Modified Gold Nanoparticles

Gold nanoparticles (AuNPs) have been employed as colorimetric biosensors due to the color difference between their dispersed (red) and aggregated (blue) states. Although signal amplification reactions triggered by structural changes of the ligands on AuNPs have been widely used to improve measurement sensitivity, the use of ligands is limited. In this study, we designed a AuNP-based signal-amplifying sandwich biosensor, which does not require a conformational change in the ligands. Thrombin was used as a model target, which is recognized by two different probes. In the presence of the target, an extension reaction occurs as a result of hybridization of the two probes. Then RNA synthesis is started by RNA polymerase activation due to RNA promoter duplex formation. The amplified RNA drives aggregation or dispersion of the AuNPs, and a difference of the color if the AuNP solution is observed. As this detection system does not require a conformational change in the ligand, it can be generically applied to a wide range ligands.

Combination of Loop-Mediated Isothermal Amplification and AuNP-Oligoprobe Colourimetric Assay for Pork Authentication in Processed Meat Products

Pork adulteration is a major concern for Muslims and Jews whose diets are restricted by religious beliefs, as well as those who are allergic to pork meat and its derivatives. Accurate pork authentication is of great importance to assist this demographic group of people in making decision on their product purchase. The aim of this study was to develop a new analytical method for pork authentication in processed meat products based on a combination of loop-mediated isothermal amplification (LAMP) and AuNP-nanoprobe colourimetric assay. The LAMP conditions were first optimised to obtain the highest yield of amplified DNA products within the shortest time. Oligoprobe-functionalised AuNPs were then hybridised with LAMP-DNA amplicons and subsequently challenged with MgSO4 at a high concentration to induce AuNP aggregation. In the presence of pork DNA, the colloidal AuNP-probe remained unchanged in its red colour, which indicates the dispersion of AuNPs. In contrast, in the absence of pork DNA, the colour was changed to colourless as a result from the aggregation of AuNPs. The LAMP-AuNP-nanoprobe assay offers a high sensitivity with a limit of detection as low as 100 pg of pork DNA. The assay is highly specific to pork content without cross-reactivity with the other meat species tested. The assay developed herein can become a simple, inexpensive, precise, and rapid analytical tool for small laboratories or the general public interested in halal food authentication.

Multifunctional nanotheranostic gold nanocages for photoacoustic imaging guided radio/photodynamic/photothermal synergistic therapy

In this work, we developed a novel multifunctional nanoplatform based on hyaluronic acid modified Au nanocages (AuNCs-HA). The rational design of AuNCs-HA renders the nanoplatform three functionalities: (1) AuNCs-HA with excellent LSPR peak in the NIR region act as contrast agent for enhanced photoacoustic (PA) imaging and photothermal therapy (PTT); (2) the nanoplatform with high-energy rays (X-ray) absorption and auger electrons generation acts as a radiosensitizer for radiotherapy; (3) good photocatalytic property and large surface area make AuNCs-HA a photosensitive agent for photodynamic therapy (PDT). In vivo results demonstrated that AuNCs-HA presented excellent PA imaging performance after intravenous injection, which provided contour, size, and location information of the tumor. Moreover, because AuNCs-HA could combine radiotherapy and phototherapy together, the tumors treated with AuNCs-HA showed complete growth inhibition, comparing to that with each therapy alone. Taken together, our present study demonstrates that AuNCs-HA is of great potential as a multifunctional nanoplatform for PA imaging-guided radio- and photo-therapy of tumor. STATEMENT OF SIGNIFICANCE: In this study, a commendable theranostic nanoplatform based on hyaluronic acid modified AuNCs (AuNCs-HA) was developed. In our approach, the dilute solution of Gold(III) chloride is slowly dripped into Ag nanocubes solution, then the Au nanocages were obtained by redox reaction, and followed by HA modification. We explored them, simultaneously, as radiosensitizers for RT, photosensitizers for PDT, and therapeutic agents for PTT. Compared to that of each therapies alone, the combination of radio-therapy and photo-therapy results in a considerably improved tumor eliminating effect and efficiently inhibited tumor growth. In addition, AuNCs-HA exhibited remarkably strong PA signals for precise identification of the location, size, and boundary of the tumor, thereby facilitating imaging-guided therapy. In brief, our design of AuNCs-HA represents a general and versatile strategy for building up cancer-targeted nanotheranostics with desired synergistic imaging and therapy functionalities.

Self-Assembly of Uniform Branched Gold Nanoparticles Induced by Using Thiol-Terminated Poly(ethylene glycol)

Branched gold nanoparticles with a sufficiently monodisperse distribution of size and shape were successfully synthesised using a tree-type multi-amine-head surfactant (C18N3) with a 100% yield using a seed-mediated method. C18N3 coated branched gold nanoparticles possess a positive zeta potential of ~40eV, which can keep branched gold nanoparticles stable in aqueous solution for several months without precipitation and transfiguration. However, C18N3 molecules were partially replaced by thiol-terminated poly(ethylene glycol) (mPEG-SH), due to the branched morphology of the as prepared gold nanoparticles, to make branched gold nanoparticles passivated by the adsorbing polymer with a positive zeta potential (17eV). The mPEG-SH passivated branched gold nanoparticles behaved as quasi-hard particles to overcome the restrictions of the rotational and positional degrees of freedom in neighbouring nanoparticles at high volume fractions, which favours the hydrophilic thiol-terminated poly(ethylene glycol) polymer passivated branched gold nanoparticles to self-arrange into close-packed 2D ensembles. Thus, the as prepared branched gold nanoparticles and their ensembles possess significant potential in bio-labelling, imaging, biosensing, therapeutic applications, and surface-enhanced Raman scattering.

Gold nanoparticle-based colorimetric biosensors

Gold nanoparticles (AuNPs) provide excellent platforms for the development of colorimetric biosensors as they can be easily functionalised, displaying different colours depending on their size, shape and state of aggregation. In the last decade, a variety of biosensors have been developed to exploit the extent of colour changes as nano-particles (NPs) either aggregate or disperse, in the presence of analytes. Of critical importance to the design of these methods is that the behaviour of the systems has to be reproducible and predictable. Much has been accomplished in understanding the interactions between a variety of substrates and AuNPs, and how these interactions can be harnessed as colorimetric reporters in biosensors. However, despite these developments, only a few biosensors have been used in practice for the detection of analytes in biological samples. The transition from proof of concept to market biosensors requires extensive long-term reliability and shelf life testing, and modification of protocols and design features to make them safe and easy to use by the population at large. Developments in the next decade will see the adoption of user friendly biosensors for point-of-care and medical diagnosis as innovations are brought to improve the analytical performances and usability of the current designs. This review discusses the mechanisms, strategies, recent advances and perspectives for the use of AuNPs as colorimetric biosensors.

Biomedical Applications of Multifunctional Gold-Based Nanocomposites

Active application of gold nanoparticles for various diagnostic and therapeutic purposes started in recent decades due to the emergence of new data on their unique optical and physicochemical properties. In addition to colloidal gold conjugates, growth in the number of publications devoted to the synthesis and application of multifunctional nanocomposites has occurred in recent years. This review considers the application in biomedicine of multifunctional nanoparticles that can be produced in three different ways. The first method involves design of composite nanostructures with various components intended for either diagnostic or therapeutic functions. The second approach uses new bioconjugation techniques that allow functionalization of gold nanoparticles with various molecules, thus combining diagnostic and therapeutic functions in one medical procedure. Finally, the third method for production of multifunctional nanoparticles combines the first two approaches, in which a composite nanoparticle is additionally functionalized by molecules having different properties.

Integrating Deoxyribozymes into Colorimetric Sensing Platforms

Biosensors are analytical devices that have found a variety of applications in medical diagnostics, food quality control, environmental monitoring and biodefense. In recent years, functional nucleic acids, such as aptamers and nucleic acid enzymes, have shown great potential in biosensor development due to their excellent ability in target recognition and catalysis. Deoxyribozymes (or DNAzymes) are single-stranded DNA molecules with catalytic activity and can be isolated to recognize a wide range of analytes through the process of in vitro selection. By using various signal transduction mechanisms, DNAzymes can be engineered into fluorescent, colorimetric, electrochemical and chemiluminescent biosensors. Among them, colorimetric sensors represent an attractive option as the signal can be easily detected by the naked eye. This reduces reliance on complex and expensive equipment. In this review, we will discuss the recent progress in the development of colorimetric biosensors that make use of DNAzymes and the prospect of employing these sensors in a range of chemical and biological applications.

Gelatin-modified gold nanoparticles for direct detection of urinary total gelatinase activity: Diagnostic value in bladder cancer

Matrix metalloproteinases (MMPs), in particularly gelatinases (MMP-2 and MMP-9) were reported as urinary markers of bladder cancer. In this work, we developed a simple colorimetric gold nanoparticle (AuNP) assay for rapid and sensitive detection of urinary total gelatinase activity based on the surface plasmon resonance (SPR) property of AuNPs. Gelatin-modified AuNPs were stably suspended in solution even upon addition of an aggregation inducer as 6-mercaptohexan-1-ol (6-MCH). Gelatinases digest gelatin capping. Subsequently, addition of 6-MCH leads to AuNPs aggregation with red to blue color shift. In a pilot study, results of the developed AuNP assay were consistent with zymography for qualitative detection of urinary total gelatinase activity. The sensitivity and specificity of both assays were 80% and 90.9% respectively. The absorption ratios, A₆₂₅/A₅₃₀ of the reacted AuNP solutions were used to quantify the total gelatinase concentration. The best cut off value was 0.01895ng/μg protein, at which the sensitivity was 87.5% and the specificity was 86.4%. The developed AuNP assay is simple, low-cost and can aid non-invasive diagnosis of bladder cancer.

Different behavior of Staphylococcus epidermidis in intracellular biosynthesis of silver and cadmium sulfide nanoparticles: more stability and lower toxicity of extracted nanoparticles

Chemical reagents that are used for synthesis of nanoparticles are often toxic, while biological reagents are safer and cost-effective. Here, the behavior of Staphylococcus epidermidis (ATCC 12228) was evaluated for biosynthesis of silver nanoparticles (Ag-NPs) and cadmium sulfide nanoparticles (CdS-NPs) using TEM images intra- and extracellularly. The bacteria only biosynthesized the nanoparticles intracellularly and distributed Ag-NPs throughout the cytoplasm and on outside surface of cell walls, while CdS-NPs only formed in cytoplasm near the cell wall. A new method for purification of the nanoparticles was used. TEM images of pure CdS-NPs confirmed biosynthesis of agglomerated nanoparticles. Biosynthetic Ag-NPs were more stable against bright light and aggregation reaction than synthetic Ag-NPs (prepared chemically) also biosynthetic Ag-NPs displayed lower toxicity in in vitro assays. CdS-NPs indicated no toxicity in in vitro assays. Biosynthetic nanoparticles as product of the detoxification pathway may be safer and more stable for biosensors.

Green Synthesis of Gold Nanoparticles by a Metal Resistant Arthrobacter nitroguajacolicus Isolated From Gold Mine

Biosynthesis of gold nanoparticles would benefit from the development of clean, nontoxic and environmentally acceptable procedures concerning microorganisms from bacteria to fungi and even algae. Actinobacteria are soil bacteria which have the enormous ability as biotechnological tools. In this paper, we reported the biosynthesis of gold nanoparticles by a member of Arthrobacter genus isolated from Andaliyan gold mine in north-west of Iran. This metal resistance strain obtained from an acidophilic region ( ~ pH 5.6). The UV-vis and XRD spectra of the aqueous medium containing the strain and 1 mM HAuCl 4 for 24 h, demonstrated the formation of gold nanoparticles. TEM micrographs showed intra-extracellular production of gold nanoparticles with spherical shape and average size of 40 nm. The result of morphological and molecular tests revealed that the isolate was belonged to Atrhrobacter and has 100% similarity in 16SrRNA gene sequences to Arthrobacter nitroguajacolicus.

In vitro study of a pH-sensitive multifunctional doxorubicin–gold nanoparticle system: therapeutic effect and surface enhanced Raman scattering

A pH-sensitive multifunctional doxorubicin–gold nanoparticle drug delivery system, which has the potential to detect and treat tumors, was developed.

Large counterions boost the solubility and renormalized charge of suspended nanoparticles

Colloidal particles are ubiquitous in biology and in everyday products such as milk, cosmetics, lubricants, paints, or drugs. The stability and aggregation of colloidal suspensions are of paramount importance in nature and in diverse nanotechnological applications, including the fabrication of photonic materials and scaffolds for biological assemblies, gene therapy, diagnostics, targeted drug delivery, and molecular labeling. Electrolyte solutions have been extensively used to stabilize and direct the assembly of colloidal particles. In electrolytes, the effective electrostatic interactions among the suspended colloids can be changed over various length scales by tuning the ionic concentration. However, a major limitation is gelation or flocculation at high salt concentrations. This is explained by classical theories, which show that the electrostatic repulsion among charged colloids is significantly reduced at high electrolyte concentrations. As a result, these screened colloidal particles are expected to aggregate due to short-range attractive interactions or dispersion forces as the salt concentration increases. We discuss here a robust, tunable mechanism for colloidal stability by which large counterions prevent highly charged nanoparticles from aggregating in salt solutions with concentrations up to 1 M. Large counterions are shown to generate a thicker ionic cloud in the proximity of each charged colloid, which strengthens short-range repulsions among colloidal particles and also increases the corresponding renormalized colloidal charge perceived at larger separation distances. These effects thus provide a reliable stabilization mechanism in a broad range of biological and synthetic colloidal suspensions.

Tuning gold nanoparticles interfaces by specific peptide interaction for surface enhanced Raman spectroscopy (SERS) and separation applications

Surface functionalization and control over nanostructured interfaces represents a key aspect in nanoscience and nanobiotechnology. Nanoplasmonic structures for analyte detection typically require sophisticated nanofabrication techniques, as well as bioactivated nanostructures that need multistep conjugations for chemical ligation. An alternative to such complex processes is to rely on specific biomolecules adsorption for decoration or self-assembly of nanoparticles at solid/liquid interface. In principle, small biomolecules with specific binding properties to nanostructures could control the assembly without modifying the nanoparticle chemistry, pH of the solution or salt concentration. Importantly, such an approach could be direct, robust, and reversible. In this work, we report about the use of a specific peptide for direct and reversible adsorption on gold nanoparticles with tuned interfacial properties just by simply adjusting the ratio between the numbers of peptide molecules to the number of gold nanoparticles. This easy, direct and reversible assembly of gold nanoparticles mediated by the specific peptide makes this platform ideal for small-volume samples and low concentrations detection using surface enhanced Raman Spectroscopy, as well as for the capture or separation of biomolecules in complex mix.

Molecular fabrications of smart nanobiomaterials and applications in personalized medicine

Recent advances in nanotechnology adequately address many of the current challenges in biomedicine. However, to advance medicine we need personalized treatments which require the combination of nanotechnological progress with genetics, molecular biology, gene sequencing, and computational design. This paper reviews the literature of nanoscale biomaterials described to be totally biocompatible, non-toxic, non-immunogenic, and biodegradable and furthermore, have been used or have the potential to be used in personalized biomedical applications such as drug delivery, tissue regeneration, and diagnostics. The nanobiomaterial architecture is discussed as basis for fabrication of novel integrated systems involving cells, growth factors, proteins, cytokines, drug molecules, and other biomolecules with the purpose of creating a universal, all purpose nanobiomedical device for personalized therapies. Nanofabrication strategies toward the development of a platform for the implementation of nanotechnology in personalized medicine are also presented. In addition, there is a discussion on the challenges faced for designing versatile, smart nanobiomaterials and the requirements for choosing a material with tailor made specifications to address the needs of a specific patient.

Gold nanoparticles in biomedical applications: recent advances and perspectives

Gold nanoparticles (GNPs) with controlled geometrical, optical, and surface chemical properties are the subject of intensive studies and applications in biology and medicine. To date, the ever increasing diversity of published examples has included genomics and biosensorics, immunoassays and clinical chemistry, photothermolysis of cancer cells and tumors, targeted delivery of drugs and antigens, and optical bioimaging of cells and tissues with state-of-the-art nanophotonic detection systems. This critical review is focused on the application of GNP conjugates to biomedical diagnostics and analytics, photothermal and photodynamic therapies, and delivery of target molecules. Distinct from other published reviews, we present a summary of the immunological properties of GNPs. For each of the above topics, the basic principles, recent advances, and current challenges are discussed (508 references).

A gold nanoparticle platform for protein-protein interactions and drug discovery

Gold nanoparticles hold great promise for studying protein-protein interactions because of their intrinsic optical properties. Pink when in a homogeneous suspension, the solution turns blue-gray when particles are drawn close together, for example, when immobilized proteins specifically interact with each other. However, the nanoparticle stability, size, and method of protein attachment contribute to the unreliable outcome of current assays. To overcome these hurdles, we developed novel and reliable methods first to synthesize homogenous particles of optimal diameter and second to apply a heterologous NTA-Ni-SAM coating for controlled orientation and optimal presentation of histidine-tagged proteins. Both methods were proven to greatly enhance assay sensitivity and specificity by increasing the signal and minimizing the nonspecific binding. Our assay reproducibly detected known protein-protein interactions and unambiguously identified small molecules that inhibited them. We believe our gold nanoparticle bioassay is a versatile and trustworthy new platform for analyzing protein-protein interactions and high-throughput screening of small-molecule inhibitors.

Dispersions based on noble metal nanoparticles-DNA conjugates

Many biomolecules have specific binding properties in the nanostructure formation; they are attractive materials for nanotechnology. One such promising construction material for growing a well-defined nanostructure is deoxyribonucleic acid, due to its π-electron hydrophobic core and predictable recognition attributed to the specificity of Watson-Crick base-pairing. Hydrogen bonding provides the specificity behind the matching of complementary pairs of single-stranded (ss) DNA to hybridize into a double strand (ds) of helical DNA. The double-helical structure of DNA is determined by a subtle balance of noncovalent interactions among the DNA building blocks. The most prominent role is played by the interactions between the DNA bases, where two binding motifs can be recognized: planar hydrogen bonding and vertical stacking. DNA-based nanotechnology has generated interest in a number of applications due to the specificity, programmability, and reproducibility of DNA interaction with noble metal nanoparticles. 5' and 3' thiol moieties are used to prepare composite DNAs, DNA-gold nanoparticle conjugates and nanostructures with a variety of nanoparticle-based DNA assays. Particularly, color changes induced by the association of nanometer-sized gold particles provide a basis of a simple yet highly selective method for detecting specific biological reactions between anchored ligand molecules and receptor molecules in the milieu. Colloidal noble metal nanoparticles, in particular, have found application in a variety of assay formats in which analyte binding is coupled to particle adsorption. The extreme sensitivity of the bandwidth, the peak height, and the position of the absorption (or scattering) maximum of surface plasmon resonance spectra to environmental changes have prompted the development of approaches directly monitor the DNA hybridization. The same features that make DNA an effective molecule for the storage of genetic information also render it useful as an engineering material for the construction of smart objects at the nanometer scale because of its ability to self organize into desired structures via the specific hybridization of complementary sequences. Biocompatibility between gold nanomaterials and biological scaffolding is crucial to the development of smart biomaterials. These DNA/metal colloids are interesting for their fundamental properties as well as for applications in nanomaterials science and nanobiotechnology.

Emergent membrane-affecting properties of BSA-gold nanoparticle constructs

By adsorbing bovine serum albumin (BSA) on gold nanoparticles (Aunps) with diameters 30 nm and 80 nm, different degrees of protein unfolding were obtained. Adsorption and adlayer conformation were characterized by UV-vis spectroscopy, ζ-potential measurements, steady-state and time-resolved fluorescence. The unfolding was also studied using 1-anilino-8-naphthalene sulfonate (ANS) as an extrinsic probe, showing that BSA unfolds more on 80 nm Aunp than on 30 nm Aunp. Langmuir monolayer studies using two distinct methods of introducing the BSA and BSA-Aunp constructs accompanied with Brewster Angle Microscopy (BAM) and Digital Video Microscope (DVM) imaging demonstrated that BSA-Aunp constructs induce film miscibility with L-α-phosphatidylethanolamine not seen for BSA or Aunp alone. The changes induced by partial unfolding clearly give better film-penetration ability, as well as disruption of liquid crystalline domains in the film, thereby inducing film miscibility. Gold or protein only does not possess the nanoscale film-affecting properties of the protein-gold constructs, and as such the surface-active and miscibility-affecting characteristics of the BSA-Aunp represent emergent qualities.

Enzyme-nanoparticle conjugates for biomedical applications

Enzymes hold a great promise as therapeutic agents because of their unique specificity and high level of activity. Yet, clinically important enzyme drugs are for less common than conventional low molecular weight drugs due to a number of disadvantages. Most important among these are poor stability, potential immunogenicity, and potential systemic toxicity. Recent developments in synthesis and characterization of nanoparticles and exciting novel properties of some classes of nanomaterials have boosted interest in the potential use of nanoparticles as carriers of enzyme drugs. In certain cases, use of enzymes attached to nanoparticles can help to overcome some of the above problems and improve the prospects of clinical applications of enzyme drugs. Here, we review recent data on the use of nanoparticles as carriers for several clinically important enzyme drugs and discuss advantages and potential limitations of such constructs. While promising preliminary results were obtained with regard to their performance in vitro and in some animal models, further investigations and clinical trials, as well as addressing regulatory issues, are warranted to make these delivery systems suitable for clinical applications.

A multidentate peptide for stabilization and facile bioconjugation of gold nanoparticles

Gold nanoparticles of two different sizes stabilized by a 15-mer peptide ligand specifically designed for this purpose have been prepared in aqueous solution and characterized by UV-vis spectroscopy and TEM. The presence of the ligand and its binding mode to the particles via its four cystein thiols is evidenced by FTIR and NMR spectroscopy. Biotinylation of the particles via binding to a freely accessible lysine residue is demonstrated.

An optical biosensing platform for proteinase activity using gold nanoparticles

The surface plasmon resonance (SPR) wavelength of colloidal gold nanoparticles (AuNPs) can vary when the AuNPs aggregate, have different sizes or shapes, or are modified with chemical molecules. In this study, an optical biosensing platform for a proteinase activity assay was established based on the SPR property of AuNPs. The 13-nm AuNPs were modified with gelatin (AuNPs-gelatin) as a proteinase substrate and subsequently modified with 6-mercaptohexan-1-ol (MCH) (AuNPs/MCH-gelatin). After proteinase (trypsin or gelatinase) digestion, the AuNPs lose shelter, and MCH increases the attractive force between the modified AuNPs. Therefore, the AuNPs gradually move closer to each other, resulting in AuNPs aggregation. The AuNPs aggregation can be monitored by the red shift of surface plasmon absorption and a visible color change of the AuNPs is from red to blue. Such a color change can be observed with the naked eye. For detection, the absorption ratio, A(625)/A(525), of the reacted AuNPs solution can be used to estimate quantitatively the proteinase activity. A linear correlation has been established with trypsin activity at concentrations from 1.25 x 10(-1) to 1.25 x 10(2) U and matrix metalloproteinase-2 activity at concentrations from 50 ng/mL to 600 ng/mL.

Temperature-dependent optical properties of gold nanoparticles coated with a charged diblock copolymer and an uncharged triblock copolymer

We demonstrate that the optical properties of gold nanoparticles can be used to detect and follow stimuli-induced changes in adsorbed macromolecules. Specifically, we investigate thermal response of anionic diblock and uncharged triblock copolymers based on poly(N-isopropylacrylamide) (PNIPAAM) blocks adsorbed onto gold nanoparticles and planar gold surfaces in a temperature range between 25 and 60 degrees C. By employing a palette of analytical probes, including UV-visible spectroscopy, dynamic light scattering, fluorescence, and quartz crystal microbalance with dissipation monitoring, we establish that while the anionic copolymer forms monolayers at both low and high temperature, the neutral copolymer adsorbs as a monolayer at low temperatures and forms multilayers above the cloud point (T(C)). Raising the temperature above T(C) severely affects the optical properties of the gold particle/polymer composites, expelling associated water and altering the immediate surroundings of the gold nanoparticles. This effect, stronger for the uncharged polymer, is related to the amount of polymer adsorbed on the surface, where a denser shell influences the surface plasmon band to a greater degree. This is corroborated with light scattering experiments, which reveal that flocculation of the neutral polymer-coated particles occurs at high temperatures. The flocculation behavior of the neutral copolymer on planar gold surfaces results in multilayer formation. The observed effects are discussed within the framework of the Mie-Drude theory.

Lanthanide complexes on Ag nanoparticles: designing contrast agents for magnetic resonance imaging

This paper describes colloidal particles that are designed to induce hyper-intensity contrast (T(1) relaxation) in MRI. The contrast agents consist of discrete gadolinium complexes tethered to 10 nm diameter silver nanoparticles. The gadolinium complexes (1) [Gd(DTPA-bisamido cysteine)](2-) and (2) [Gd(cystine-NTA)(2)](3-), undergo chemisorption to particle surfaces through thiol or disulfide groups, respectively, to form two new contrast agents. The resulting nanoparticulate constructs are characterized on the basis of their syntheses, composition, spectra and contrast enhancing power. The average r(1) relaxivities of the of the surface bound complexes (obtained at 9.4 T and 25 degrees C) are 10.7 and 9.7 s(-1) mM(-1), respectively, as compared to 4.7 s(-1) mM(-1) for the clinical agent Magnevist. Correspondingly, the respective whole particle relaxivities are 27927 and 13153 s(-1) mM(-1).