Highly sensitive gold nanoparticles biosensor chips modified with a self-assembled bilayer for detection of Con A

Preparation, Functionalization, Modification, and Applications of Nanostructured Gold: A Critical Review

Gold nanoparticles (Au NPs) play a significant role in science and technology because of their unique size, shape, properties and broad range of potential applications. This review focuses on the various approaches employed for the synthesis, modification and functionalization of nanostructured Au. The potential catalytic applications and their enhancement upon modification of Au nanostructures have also been discussed in detail. The present analysis also offers brief summaries of the major Au nanomaterials synthetic procedures, such as hydrothermal, solvothermal, sol-gel, direct oxidation, chemical vapor deposition, sonochemical deposition, electrochemical deposition, microwave and laser pyrolysis. Among the various strategies used for improving the catalytic performance of nanostructured Au, the modification and functionalization of nanostructured Au produced better results. Therefore, various synthesis, modification and functionalization methods employed for better catalytic outcomes of nanostructured Au have been summarized in this review.

Functionalization of Gold Nanoparticles by Inorganic Entities

The great affinity of gold surface for numerous electron-donating groups has largely contributed to the rapid development of functionalized gold nanoparticles (Au-NPs). In the last years, a new subclass of nanocomposite has emerged, based on the association of inorganic molecular entities (IME) with Au-NPs. This highly extended and diversified subclass was promoted by the synergy between the intrinsic properties of the shell and the gold core. This review-divided into four main parts-focuses on an introductory section of the basic notions related to the stabilization of gold nanoparticles and defines in a second part the key role played by the functionalizing agent. Then, we present a wide range of inorganic molecular entities used to prepare these nanocomposites (NCs). In particular, we focus on four different types of inorganic systems, their topologies, and their current applications. Finally, the most recent applications are described before an overview of this new emerging field of research.

Harvesting Low Molecular Weight Biomarkers Using Gold Nanoparticles

We developed and characterized a platform based on gold (Au) nanoparticles (NPs) coated with poly(acrylic acid) (PAA) for harvesting positively charged, low molecular weight (LMW) proteins. The particles are synthesized using a layer by layer (LbL) procedure: first the gold NPs are coated with positively charged polyethylenimine (PEI) and subsequently with PAA. This simple procedure produces stable PAA-PEI-Au (PPAu) NPs with high selectivity and specificity. PPAu NPs successfully harvested, separated, and detected various LMW proteins and peptides from serum containing a complex mixture of abundant high molecular weight (HMW) proteins, including bovine serum albumin (BSA) and Immunoglobulin G (IgG). In addition, PPAu NPs selectively harvested and separated LMW proteins from serum in the presence of another positively charged competing protein. Furthermore, PPAu NPs successfully harvested a LMW biomarker in a mock diseased state. This system can be applied in various biomedical applications where selective harvesting and identifying of LMW proteins is required. A particularly useful application for this system can be found in early cancer diagnosis as described hereinafter.

Electrochemical synthesis of nanostructured gold film for the study of carbohydrate-lectin interactions using localized surface plasmon resonance spectroscopy

Localized surface plasmon resonance (LSPR) spectroscopy is a label-free chemical and biological molecular sensing technique whose sensitivity depends upon development of nanostructured transducers. Herein, we report an electrodeposition method for fabricating nanostructured gold films (NGFs) that can be used as transducers in LSPR spectroscopy. The NGF was prepared by electrodepositing gold from potassium dicyanoaurate solution onto a flat gold surface using two sequential controlled potential steps. Imaging by scanning electron microscopy reveals a morphology consisting of randomly configured block-like nanostructures. The bulk refractive index sensitivity of the prepared NGF is 100±2 nmRIU(-1) and the initial peak in the reflectance spectrum is at 518±1 nm under N2(g). The figure of merit is 1.7. In addition, we have studied the interaction between carbohydrate (mannose) and lectin (Concanavalin A) on the NGF surface using LSPR spectroscopy by measuring the interaction of 8-mercaptooctyl-α-d-mannopyranoside (αMan-C8-SH) with Concanavalin A by first immobilizing αMan-C8-SH in mixed SAMs with 3,6-dioxa-8-mercaptooctanol (TEG-SH) on the NGF surface. The interaction of Con A with the mixed SAMs is confirmed using electrochemical impedance spectroscopy. Finally, the NGF surface was regenerated to its original sensitivity by removing the SAM and the bound biomolecules. The results from these experiments contribute toward the development of inexpensive LSPR based sensors that could be useful for studying glycan-protein interactions and other bioanalytical purposes.

A signal-on electrochemiluminescence biosensor for detecting Con A using phenoxy dextran-graphite-like carbon nitride as signal probe

A novel signal-on electrochemiluminescence (ECL) biosensor for detecting concanavalin A (Con A) was fabricated with phenoxy dextran-graphite-like carbon nitride (DexP-g-C3N4) as signal probe. In this construction strategy, the nanocomposites of three-dimensional graphene and gold nanoparticles (3D-GR-AuNPs) were used as matrix for high loading of glucose oxidase (GOx), which served as recognition element for bounding Con A. Con A further interacted with DexP-g-C3N4 through a specific carbohydrate-Con A interaction to achieve a sandwiched scheme. With the increase of Con A incubated onto the electrode, the ECL signal resulted from DexP-g-C3N4 would enhance, thus achieving a signal-on ECL biosensor for Con A detection. Due to the integration of the virtues of 3D-GR-AuNPs and the excellent ECL performance of DexP-g-C3N4, the prepared biosensor exhibits a wide linear response range from 0.05 ng/mL to 100 ng/mL and a low detection limit of 17 pg/mL (S/N=3).

Protein adsorption on a glycosylated polyacrylonitrile surface: monitoring with QCM and SPR

A simple and efficient method to fabricate a glycosylated surface on a polyacrylonitrile-based film is described. Construction and protein adsorption processes were monitored in situ using a QCM. A PANCHEMA film was deposited on the gold surface of the quartz crystal, and the glycosylated surface was then constructed through surface modification. Con A and BSA were used as probes to study the specificity of this surface to proteins. It can recognize Con A, while showing no specific interaction with BSA. The binding affinity indicates the presence of strong multivalent interactions between Con A and the glucose residues (cluster glycoside effect). Reproducibility and repeatability of the glycosylated polymer surface are sufficient to allow specific adsorption of Con A.

Emerging use of nanostructure films containing capped gold nanoparticles in biosensors

The localized surface plasmon resonance (LSPR) property of gold nanoparticles (GNP) has been exploited in a variety of optical sensor configurations including solution-based bioassays, paper-based colorimetric detection, surface-confined nanoparticle film/array-based sensing, etc. Amongst these, gold nanostructured films are of great interest because of their high stability, good reproducibility, robustness, and cost-effectiveness. The inherent optical characteristics of GNP, are attributed to parameters like size and shape (eg, nanospheres, nanorods, nanostars), eg, LSPR spectral location sensitivity to the local environment, composition (eg, gold-silver or silica-gold nanoshells), sensing volume, mesospacing, and multiplexing. These properties allow sensor tunability, enabling enhanced sensitivity and better performance of these biosensors. Ultrasensitive biosensor designs were realized using gold nanostructured films fabricated by bottom-up as well as top-down approaches. In this review, we describe the past, present, and future trends in the development of GNP-LSPR-based sensors, concentrating on both design (fabrication) and application. In the process, we have discussed various combinations of GNP size and shape, substrate, and application domains.

Electrochemical immunosensor for simultaneous detection of dual cardiac markers based on a poly(dimethylsiloxane)-gold nanoparticles composite microfluidic chip: a proof of principle

BACKGROUND

The emergence of microfluidic immunosensors has provided a promising tool for improving clinical diagnoses. We developed an electrochemical immunoassay for the simultaneous detection of cardiac troponin I (cTnI) and C-reactive protein (CRP), based on microfluidic chips.

METHODS

The quantitative methodology was based on ELISA in poly(dimethylsiloxane)-gold nanoparticle composite microreactors. CdTe and ZnSe quantum dots were bioconjugated with antibodies for sandwich immunoassay. After the CdTe and ZnSe quantum dots were dissolved, Cd(2+) and Zn(2+) were detected by square-wave anodic stripping voltammetry to enable the quantification of the 2 biomarkers. The 2 biomarkers were measured in 20 human serum samples by using the proposed method and commercially available methods.

RESULTS

This immunosensor allowed simultaneous detection of serum cTnI and CRP. The linear range of this assay was between 0.01 and 50 μg/L and 0.5 and 200 μg/L, with the detection limits of approximately 5 amol and approximately 307 amol in 30-μL samples corresponding to cTnI and CRP, respectively. Slopes close to 1 and the correlation coefficient over 0.99 were obtained for both analytes.

CONCLUSIONS

This strategy demonstrates a proof of principle for the successful integration of microfluidics with electrochemistry that can potentially provide an alternative to protein detection in the clinical laboratory.

Electrodeposition of thermally stable gold and silver nanoparticle ensembles through a thin alumina nanomask

Hemispheric gold or silver nanoparticle (Au and AgNP) ensembles were electrodeposited on a smooth ITO electrode through a thin Al(2)O(3) nanomask. The nanomask reduced the deviation in the particle size and interparticle distance. The absorption peak based on localized surface plasmon resonance (LSPR) of the AuNP ensemble redshifted with increasing environmental refractive index, suggesting that the ensemble would be used as a LSPR sensor for chemical analysis and bioanalysis. The Al(2)O(3) nanomask prevented the Au and AgNPs from thermal coalescence even at 500 degrees C, and consequently, it improved thermal stabilities of nanoparticle ensembles. The ensembles exhibit LSPR-based absorption peak in the visible region, even after annealing. The nanomask allowed AgNPs, which are thermally and chemically less stable than AuNPs, to be coated with sintered TiO(2). The ITO/AgNP/TiO(2) electrode thus obtained functions as a photocathode on the basis of photoinduced electron transfer from silver nanoparticles to TiO(2).

Electrochemical determination of carbohydrate-binding proteins using carbohydrate-stabilized gold nanoparticles and silver enhancement

A highly sensitive electrochemical lectin biosensor has been developed for the first time using carbohydrate-stabilized gold nanoparticles and silver-enhancement technique. A target lectin protein, Concanavalin A (Con A), was specifically bound to the self-assembled monolayer of thiolated mannose on a gold electrode. Mannose-stabilized gold nanoparticles were added to form a sandwich-type complex with the Con A and were followed by silver-enhancement process to coat the mannose-stabilized gold nanoparticles with silver metal. The coated metallic silver was dissolved in an acidic solution and the resulting silver ions were detected by anodic stripping voltammetry. The present lectin biosensor gave a linear response (R(2)=0.999) for Con A concentration from 0.084 μg/mL to 50.0 μg/mL with a remarkable detection limit (S/N=3) of 0.070 μg/mL, which is much lower compared to those obtained with the reported microgravimetric and colorimetric detection methods.

Fabrication of color changeable polystyrene spheres decorated by gold nanoparticles and their label-free biosensing

A novel and simple method for gold nanoshell synthesis with controllable core and shell sizes is reported here. A new 'tree-shape' surfactant bis(amidoethyl-carbamoylethyl) octadecylamine (C18N3) was synthesized and used as the glue for the fast combination of gold nanoparticles and the subsequent gold shell outside. The functionalized polystyrene (PS) cores were covered by a surfactant (PS@C18N3) bilayer. The presence of the surfactant double layer played the role of 'glue' in this method, so that upon controlling the amount of surfactant, it was possible to achieve: the manipulation of gold seed density on the PS@C18N3 spheres, the preparation of PS@Au hybrid structures, and a red-shift in the extinction absorption from 520 to 750 nm. Besides, the as-prepared PS@Au composites supported on a glass substrate exhibited excellent effectiveness in the molecular recognition of human-immunoglobulin G (h-IgG) and goat anti-human-immunoglobulin G (goat anti-h-IgG), showing a rapid response within 20 min with a low detection limit of 10 ng ml(-1). This demonstrates that PS@Au prepared and assembled using our method is potentially useful as a nanosensor platform for immunoassay.

Modulation of the surface charge on polymer-stabilized gold nanoparticles by the application of an external stimulus

A new approach to controlling the charge on gold nanoparticle surfaces is described. The method exploits the simultaneous coattachment of both charged and neutral polymers onto gold surfaces. The charged and neutral polymers were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization, and the RAFT end-group functionality was used as the anchor for attachment to gold. The approach described is general and can be applied to a wide range of monomers; those exemplified in the paper are poly(2-aminoethyl methacrylamide) (P(AEA)), poly(acrylic acid) (PAA), and poly(N,N-diemthylaminoethyl acrylate) (P(DMAEA)) together with neutral polymers based on poly(oligoethylene oxide) acrylate (P(OEG-A)). The hybrid polymer-stabilized GNPs thus formed were characterized in solution using dynamic light scattering and zeta potential measurements, transmission electron microscopy, UV-visible spectroscopy, X-ray photoelectron spectroscopy, and attenuated total reflection-Fourier-transform IR spectroscopy. The grafting densities of the polymers on GNPs were measured using thermal gravimetric analyses (TGA), as 0.4 chains/nm(2) (for PAA), 0.9 chains/nm(2) (for neutral polymers, such as P(NIPAAm), and 0.6 chain/nm(2) for the positive charged polymers P(AEA) and P(DMAEA). The directed coassembly of two different polymers (one charged and one noncharged) on the gold nanoparticle surfaces provided a mechanism (dependent on molecular weight) for shielding the surface charge imparted by the charged polymer component, allowing for a range of surface charges on the GNPs from -30 to +39 mV. In further work, the surface-charges were modulated by an external stimulus (temperature). The charge-modulation was controlled by the use of thermosensitive neutral polymers coassembled with charged polymers. The thermosensitive polymers exemplified in this paper are P(oligoethylene oxide acrylate-co-diethylene oxide acrylate) (P(OEG-A-co-DEG-A)) and P(N-isopropyl acrylamide) (P(NIPAAm). The temperature of the aqueous phase (from 15 to 70 degrees C) was then adjusted to tune the zeta potentials of the hybrid GNPs from +39 or -30 to approximately 0 mV. Finally, by manipulating the solution pH, reversible aggregation behavior of the hybrid GNPs could be induced.

Ru(II) glycodendrimers as probes to study lectin-carbohydrate interactions and electrochemically measure monosaccharide and oligosaccharide concentrations

We describe a novel platform on which to study carbohydrate-protein interactions based on ruthenium(II) glycodendrimers as optical and electrochemical probes. Using the prototypical concanavalin A (ConA)-mannose lectin-carbohydrate interaction as an example, oligosaccharide concentrations were electrochemically monitored. The displacement of the Ru(II) complex from lectin-functionalized gold surfaces was repeatedly regenerated. This new platform presents a method to monitor many different complex sugars in parallel.

Synthesis of fluorescent carbohydrate-protected Au nanodots for detection of Concanavalin A and Escherichia coli

This study describes a novel, simple, and convenient method for the preparation of water-soluble biofunctional Au nanodots (Au NDs) for the detection of Concanavalin A (Con A) and Escherichia coli (E. coli). First, 2.9 nm Au nanoparticles (Au NPs) were prepared through reduction of HAuCl(4).3H(2)O with tetrakis(hydroxymethyl)phosphonium chloride (THPC), which acts as both a reducing and capping agent. Addition of 11-mercapto-3,6,9-trioxaundecyl-alpha-D-mannopyranoside (Man-SH) onto the surfaces of the as-prepared Au NPs yielded the fluorescent mannose-protected Au nanodots (Man-Au NDs) with the size and quantum yield (QY) of 1.8 (+/-0.3) nm and 8.6%, respectively. This QY is higher than those of the best currently available water-soluble, alkanethiol-protected Au nanoclusters. Our fluorescent Man-Au NDs are easily purified and by multivalent interactions are capable of sensing, under optimal conditions, Con A with high sensitivity (LOD = 75 pM) and remarkable selectivity over other proteins and lectins. To the best of our knowledge, this approach provided the lowest LOD value for Con A when compared to the other nanomaterials-based detecting method. Furthermore, we have also developed a new method for fluorescence detection of E. coli using these water-soluble Man-Au NDs. Incubation with E. coli revealed that the Man-Au NDs bind to the bacteria, yielding brightly fluorescent cell clusters. The relationship between the fluorescence signal and the E. coli concentration was linear from 1.00 x 10(6) to 5.00 x 10(7) cells/mL (R(2) = 0.96), with the LOD of E. coli being 7.20 x 10(5) cells/mL.

In-situ synthesis of poly(dimethylsiloxane)-gold nanoparticles composite films and its application in microfluidic systems

We presented a simple approach for in-situ synthesis of poly(dimethylsiloxane) (PDMS)-gold nanoparticles composite film based on the special characteristics of PDMS itself. It is an environmentally safe synthesis method without the requirement of additional reducing/stabilizing agents. The region where the resulting gold nanoparticles distribute (in the matrix or on the surface of the polymer) and the size of the nanoparticles, as well as the colour of the free-standing films, can be simply controlled by adjusting the ratio of curing agent and the PDMS monomer. The chemical and optical properties of these composite films were studied. Using such a method, gold nanoparticle micropatterns on PDMS surfaces can be performed. And based on the gold nanoparticles micropattern, further modification with antibodies, antigens, enzymes and other biomolecules can be achieved. To verify this ability, an immobilized glucose oxidase (GOx) reactor in microchannels was built and its performance was studied. The experiments have shown that the resulting composite film may have a lot of potential merits in protein immobilization, immunoassays and other biochemical analysis on PDMS microchips.

Use of degradable and nondegradable nanomaterials for controlled release

Drug-delivery devices are fundamentally important in improving the pharmacological profiles of therapeutic molecules. Nanocontrolled-release systems are attracting a lot of attention currently owing to their large surface area and their ability to target delivery to specific sites in the human body. In addition, they can penetrate the cell membrane for gene, nucleic acid and bioactive peptide/protein delivery. Representative applications of nanodrug-delivery systems include controlled-release wound dressings, controlled-release scaffolds for tissue regeneration and implantable biodegradable nanomaterial-based medical devices integrated with drug-delivery functions. We review the present status and future perspectives of various types of nanocontrolled-release systems. Although many of the well-established degradable and nondegradable controlled-release vehicles are being investigated for their processing into nanocarriers, several new emerging nanomaterials are being studied for their controlled-release properties. The release of multiple bioactive agents, each with its own kinetic profile, is becoming possible. In addition, integration of the nanocontrolled-release systems with other desirable functions to create new, cross-discipline applications can also be realized.