Surface Of AuNRs Research Articles

Highly sensitive and selective visual detection of Cr(VI) ions based on etching of silver-coated gold nanorods

We report a visual detection of Cr(VI) ions using silver-coated gold nanorods (AuNR@Ag) as sensing probes. Au NRs were prepared by a seed-mediated growth process and AuNR@Ag nanostructures were synthesized by growing Ag nanoshells on Au NRs. Successful coating of Ag nanoshells on the surface of Au NRs was demonstrated with TEM, EDS, and UV–vis spectrometer. By increasing the overall amount of the deposited Ag on Au NRs, the localized surface plasmon resonance (LSPR) band was significantly blue-shifted, which allowed tuning across the visible spectrum. The sensing mechanism relies on the redox reaction between Cr(VI) ions and Ag nanoshells on Au NRs. As the concentration of Cr(VI) ions increased, more significant red-shift of the longitudinal peak and intensity decrease of the transverse peak could be observed using UV–vis spectrometer. Several parameters such as concentration of CTAB, thickness of the Ag nanoshells and pH of the sample were carefully optimized to determine Cr(VI) ions. Under optimized condition, this method showed a low detection limit of 0.4 μM and high selectivity towards Cr(VI) over other metal ions, and the detection range of Cr(VI) was tuned by controlling thickness of the Ag nanoshells. From multiple evaluations in real sample, it is clear that this method is a promising Cr(VI) ion colorimetric sensor with rapid, sensitive, and selective sensing ability.

Improving in vitro biocompatibility of gold nanorods with thiol-terminated triblock copolymer

Gold nanorods (AuNRs) are usually synthesized using cetyltrimethylammonium bromide (CTAB) surfactant as a structure-directing agent. CTAB is reported to form a tightly bound cationic bilayer on AuNR surface with the cationic trimethylammonium head group exposed to the aqueous media. However, CTAB is also known to be highly toxic in both in vitro and in vivo experiments. In this work, we investigated the cytotoxicity, colloidal stability and optical properties of AuNRs before and after substitution with thiol-terminated triblock copolymer of ethylene oxide-propylene oxide (PEO-PPO-PEO), or Pluronic F127® (PF127). For that, PF127 was first chemically functionalized with 3-mercaptopropionic acid (MPA) and further used as stabilizer for the AuNRs by replacing CTAB molecules. Unmodified PF127 was also tested and used as a control for biological experiments. Morphology of coated AuNRs was characterized by visible spectroscopy, transmission electron microscopy, zeta potential, and dynamic light scattering. We found that coating with PF127-SH guarantees both stability and biocompatibility of AuNRs for at least 45 days, besides improving cell viability when compared to the PF127-coated AuNRs, even after 72 h treatment. In addition, this new polymer coating can also provide hydrophobic domains assembled into the PPO blocks, which could be further loaded with organic active ingredients. The obtained results show the potential of this nanostructured system for future developments in multifunctional nanoplataforms for clinical applications such as drug delivery, hyperthermia, photodynamic therapy, and diagnostic imaging of cells and tissues.

Multicolor Aptasensor Based on DNA-Induced Au-Ag Nanorods for Simultaneous and Visual Detection of Inorganic and Organic Mercury.

Compared to inorganic mercury (Hg2+), methyl-mercury (CH3Hg+) and ethyl-mercury (C2H5Hg+) (organic mercury) not only have a much stronger toxicity but also are more easily accumulated by marine organisms to produce bioamplification. Therefore, the simultaneously onsite detection of Hg2+ and organic mercury is of great significance to ensure the safety of seafood, and it is also a hard challenge. We designed a T-rich aptamer, HT7, for specifically recognizing Hg2+ and organic mercury and developed a multicolor aptasensor for simultaneous discrimination and detection of Hg2+ and organic mercury with only bare-eye observation using HT7 as a recognition probe and gold nanorods (AuNRs) as a signal. In the presence of Hg2+ and Ag+, Hg2+ preferentially and specifically bind with HT7 immobilized on AuNRs surface and induce the formation of a monolayer Ag/Hg amalgam on the AuNRs surface after reduction, resulting in a change in color from orange to faint purple and a corresponding shift in the absorption peak from 820 to 730 nm in the solution. However, in the presence of CH3Hg+ or C2H5Hg+ and Ag+, CH3Hg+ or C2H5Hg+ preferentially bind with HT7 immobilized on the AuNRs surface and induce the formation of a monolayer Ag0 on the AuNRs surface after reduction, which results in the change in color from orange to atrovirens and the corresponding shift in the absorption peak shift from 820 to 670 nm in the solution. Thus, the inorganic and organic mercury (total of CH3Hg+ and C2H5Hg+) can be specifically discriminated and detected by only bare-eye observation. The method can be used to simultaneously detect inorganic and organic mercury in seawater by the bare-eye observation with a visual detection limit of 2.0 ppm for Hg2+ and 10.0 ppm for organic mercury. The success of this study is a useful enlightenment to develop an instrument-free method for an onsite detection of trace inorganic and organic mercury in environment by a bare-eye observation, although the sensitivity of the method is relatively low.

Plasmonic nanobiosensor based on Au nanorods with improved sensitivity: A comparative study for two different configurations

Biosensors presenting high sensitivity for the detection of biomolecules are very promising for diseases diagnosis. Nowadays, there is a need for the development of biosensors with fast, trustworthy diagnosis and mostly with low cost, mainly for applications in developing countries. Label-free plasmonic biosensors are good candidates to reach out all these characteristics due to the possibility of spectral tunability, fast sensor response, real-time detection, strong enhancement of the local electric field and excellent adaptability to assemble different nanobiotechnology architectures. In this paper, two different configurations for LSPR based biosensor were developed by using solution-phase gold nanorods (S–P-AuNRs) and AuNRs-chip. The LSPR sensitivities were evaluated by monitoring shifts in the longitudinal plasmon band with changes in the refractive index of the medium surrounding the nanoparticles. AuNRs-chip presented higher sensitivity of 297 nm RIU−1 (refractive index unit) against 196 nm RIU−1 for S–P-AuNRs. Figure of merit (FOM) for AuNRs-chip and S–P-AuNRs were 3.0 and 2.2 RIU−1, respectively. This result was assigned to the coupling of the lower energy longitudinal LSPR mode of propagation for AuNRs-chip among nearby nanoparticles in the film. In addition, an improvement of at least 18% in sensitivity was obtained comparing to others AuNRs based assay with similar aspect ratio. FOM is more appropriate to compare different approaches, in this case, the proposed biosensor reached improvements of at least 114%, presenting higher values even when compared to AuNRs of higher aspect ratio. As a proof of concept, AuNRs surface was chemically modified using mercaptoundecanoic acid followed activation with ethylcarbodiimide and N-hidroxysuccinimide to allow the interaction between Bovine Serum Albumin (BSA) antibody and correspondent antigen. Both configurations studied resulted in efficient plasmonic biosensors, presenting high sensitivity for changes in the refractive index and for surface binding with anti-BSA.

A “turn-off” SERS aptasensor based DNAzyme-gold nanorod for ultrasensitive lead ion detection

It is great significance to precisely monitor lead (II) ions (Pb2+) for environment protection and human health monitoring. We designed a sensitive detection strategy for sensitive and selective determination of Pb2+, based on a Pb2+-specific DNAzyme as the catalytic unit, Cy3-labeled DNA modified gold nanorods (AuNRs) as SERS reporter. Firstly, AuNRs surface were employed as a platform for the immobilization of thiolated probe DNA, and then hybridized with DNAzyme catalytic beacons. By taking advantage of DNAzyme digest, a molecular beacon, causes a “turn-off” SERS signal by disrupting the labeled probes. Under the optical conditions, the DNAzyme-AuNRs sensor system exhibited high sensitivity, acceptable stability and reproducibility with a wide linear range from 0.5 to 100 nM (R2 = 0.9973), and an ultra-low detection limit of 0.01 nM. The proposed strategy has additional advantages of being less time-consuming, low-cost and remote query, and avoids the interference of some metals such as Fe3+, Cd2+, Ba2+, Cu2+, Zn2+. The SERS biosensor system has been successfully applied for detecting Pb2+ in real samples with a satisfactory result. The result indicated that the proposed sensing strategy not only enriches SERS platform of monitoring Pb2+ but also exhibits potential for the point-of-care diagnostic application of the clinical screening in complicated biological samples.

Plasmonic Paper Microneedle Patch for On-Patch Detection of Molecules in Dermal Interstitial Fluid.

Minimally invasive devices to detect molecules in dermal interstitial fluid (ISF) are desirable for point-of-care diagnostic and monitoring applications. In this study, we developed a microneedle (MN) patch that collects ISF for on-patch biomarker analysis by surface-enhanced Raman scattering (SERS). The micrometer-scale MNs create micropores in the skin surface, through which microliter quantities of ISF are collected onto plasmonic paper on the patch backing. The plasmonic paper was prepared by immobilizing poly(styrenesulfonate) (PSS) coated gold nanorods (AuNRs) on a thin strip of filter paper using plasmonic calligraphy. Negatively charged PSS was used to bind positively charged rhodamine 6G (R6G), which served as a model compound, and thereby localize R6G on AuNR surface. R6G bound on the AuNR surface was detected and quantified by acquiring SERS spectra from the plasmonic paper MN patch. This approach was used to measure pharmacokinetic profiles of R6G in ISF and serum from rats in vivo. This proof-of-concept study indicates that a plasmonic paper MN patch has the potential to enable on-patch measurement of molecules in ISF for research and future medical applications.

Tracking Sub-Nanometer Shift in the Scattering Centroid of Single Gold Nanorods during Electrochemical Charging.

While conventional wisdom suggests the scattering centroid of a plasmonic nanoparticle reflects its geometric center, here we uncover the dependence of a scattering centroid of a single gold nanorod (AuNR) on its electron density when the geometric features (position and morphology) do not change at all. When periodically altering the electron density of a single AuNR during nonfaradaic charging and discharging processes, the optical centroid of the scattering dot in a series of dark-field images was found to reversibly shift back and forth by ∼0.4 nm, in pace with the sweeping potential. A Fourier-transform-based demodulation method was proposed to determine the centroid displacement as small as 0.1 nm, allowing for validating the generality of the observed phenomenon. The dependence of an optical centroid on the potential was attributed to the displacement of the electron density center as a result of inhomogeneous accumulation of injected electrons on the surface of a single AuNR. Not only does the present work shed light on studying the photon-electron interactions at sub-nanoparticle level, Fourier transform-based demodulation also provides a superior strategy for other fast and reversible processes such as electrochromic and photothermal conversions.

Urease-induced metallization of gold nanorods for the sensitive detection of Salmonella enterica Choleraesuis through colorimetric ELISA

We applied urease-induced silver metallization on the surface of gold nanorods (AuNR) to improve colorimetric ELISA for the rapid and sensitive detection of Salmonella enterica Choleraesuis. To this end, we introduced a biotin-streptavidin system as a bridge to determine the correlation between urease and S. enterica Choleraesuis concentrations. The captured urease can catalyze the hydrolysis of urea into carbon dioxide and ammonia, and the generated ammonia can then induce the deposition of silver shell on the surface of AuNR in the presence of silver nitrate and glucose. With the decreased aspect ratio (length divided by width) of AuNR, a multicolor change of AuNR solution and a significant blue shift in the longitudinal localized surface plasmon resonance absorption peak (Δλmax) of AuNR were obtained at the target concentrations of 1.21 × 101 to 1.21 × 108 cfu/mL. Consequently, the detection limits of our proposed colorimetric ELISA were as low as 1.21 × 102 cfu/mL for qualitative detection with naked eyes, and 1.21 × 101 cfu/mL for quantitative detection, in which changes in Δλmax of AuNR were recorded with a microplate reader. These values were at least 2 to 3 orders of magnitude lower than those obtained with conventional horseradish peroxidase-based ELISA. The analytical performance of our developed colorimetric ELISA in terms of selectivity, accuracy, reliability, and practicability were investigated by analyzing S. enterica Choleraesuis-spiked pasteurized whole milk samples.

Cytotoxicity and Cellular Responses of Gold Nanorods to Smooth Muscle Cells Dependent on Surface Chemistry Coupled Action.

Gold nanorods (AuNRs), with their unique physicochemical properties, are recognized as promising materials for biomedical applications. Chemical modification of their surfaces is attracting increasing attention with regard to cytotoxicity and cellular uptake. Herein, the toxicological effects of three types of polymer-coated AuNRs, which are cetyltrimethylammonium bromide-coated AuNRs, polystyrene sulphonate-coated AuNRs, and poly(diallyldimethyl ammonium chloride-coated AuNRs (PDDAC-AuNRs), on vascular smooth muscle cells (VSMCs) are investigated. The results show significantly different effects on VSMCs with different surface coatings. PDDAC-AuNRs, which were nontoxic in cancer cells in previous reports, display extreme toxicity to VSMCs. Initial contact between AuNRs and cell membranes is the important step in AuNRs cellular uptake. Force spectroscopy based on atomic force microscopy is exploited to study interactions between AuNRs and VSMCs membrane in the absence or presence of a corona on the AuNRs surface. The results show that the binding force and binding probability between AuNRs and membranes are closely related to cytotoxicity and cellular responses. These findings highlight the importance of assessing nanoparticle cytotoxicity in somatic cells for medical applications.

Rapid detection of heparin by gold nanorods and near-infrared fluorophore ensemble based platform via nanometal surface energy transfer

As a mucopolysaccharide sulfate anticoagulant drug, heparin plays important roles in clinic. In this work, heparin was analyzed based on the nanometal surface energy transfer (NSET) between gold nanorods (AuNRs) and tetrakis (4-sulfophenyl) porphyrin (TPPS4) fluorescent molecules. The results showed that AuNRs could bind TPPS4 by electrostatic interaction and coordination to quench its fluorescence. While heparin was able to bind AuNRs with a stronger electrostatic interaction to compel TPPS4 to leave AuNRs surface, leading to the fluorescence recovery of TPPS4, which was proportional to the concentration of heparin in a range of 0.05∼2 μg/mL with the detection limit as low as 6.7 ng/mL (3σ). Based on this, a NSET platform for the analysis of trace heparin sodium was proposed with fast response, high sensitivity and excellent specificity, which was successfully applied to the detection of heparin in injection with the satisfactory result. Importantly, the NSET mechanism was fully discussed.

Electrochemical study of UV erosion of Au nanorods by silver nanoclusters (NCs) allows the construction of a NC-sensitized photovoltaic cell

It was reported that gold nanorods (Au NRs), synthesized by the conventional seed-mediated method, show unusual photoresponse to UV illumination due to the presence of silver nanoclusters (Ag NCs) which etch away Au NRs to slowly shred them and make them shorter in length. Here we report the electrochemical experiments supporting this atypical behavior. These studies show that a redox reaction is taking place on the surface of Au NRs in the presence of excited Ag NCs. The excitation energy of Ag NCs can be released in the system as the flow of free charges and it can be utilized for a photosensitive electronic application. A NC-sensitized photovoltaic cell shows the possibility of conversion (with 0.17% efficiency) from UV radiation to electrical energy based on Ag NCs.

Dialysis assisted ligand exchange on gold nanorods: Amplification of the performance of a lateral flow immunoassay for E. coli O157:H7.

Ligand exchange on the surface of gold nanorods (AuNRs) is widely used, but conventional methods usually require multiple centrifugation cycles to completely remove cetyltrimethylammonium bromide (CTAB). This can lead to undesired aggregation of AuNRs. A dialysis-assisted protocol is described here for ligand exchange on AuNRs. Dialysis driven by a concentration gradient is shown to be a powerful tool to separate CTAB from aqueous solutions. The concentration gradient of CTAB in a dialysis bag can avoid the possible aggregation of AuNRs that can be caused by drastic environmental changes. It also supports the rate of ligand exchange on the surfaces of the AuNRs. The modified AuNRs were employed in a lateral-flow test strip immunoassay (LFTS-IAs) for the food pathogen E. coli O157:H7 in order to study of efficiency of ligand exchange. Compared to AuNRs where ligand exchange was performed via multiple centrifugation cycles, the AuNRs prepared by dialysis-assisted ligand exchange show improved conjugation to antibody and enhanced visual signals in the test line of the LFTS-IAs. A portable strip reader (absorption wavelength = 525nm) is used to records the testing results. The sensitivity of AuNRs modified by dialysis has been achieved even as low as 1 × 102cfu·mL-1 in a short time (within 15min), and the working range is 1 × 102 to 1 × 106cfu·mL-1, which is superior over the detection performance of conventional test strip using AuNRs modified by centrifugation. Graphical abstract Schematic presentation of the ligand exchange of AuNRs. TheAuNRs were dialysed in water to decrease the CTAB concentration. Then, 11-mercaptoundecanoic acid (MUA) replaces the CTAB capped on the surface of AuNRs. The modified AuNRs were employed in a lateral flow immunoassayfor E. coli O157:H7.

Preparation of phase diagram of gold nanorods in mixture solvent of DMSO and water and its application for efficient surface-modification

Gold nanorods (AuNRs) have been widely studied in various biological and biomedical fields. The complete removal of a cationic binary surfactant cetyltrimethyl ammonium bromide (CTAB), which is strongly bound to prepared AuNRs, is necessary due to their cytotoxicity as well as further functionalization of the surface. Here, we report an appropriate procedure which can remove CTAB and modify the surface by ω-mercaptocarboxylic acid efficiently. The detachment mechanism of CTAB from AuNR surface varying with the volume ratio of dimethylsulfoxide (DMSO)/water (VDMSO:VAuNRs) and the concentration of CTAB was also studied. For samples after twice-centrifugation (CCTAB = 15 μM), CTAB thoroughly detached from AuNRs under the condition of VDMSO:VAuNRs = 0.3–0.5, while AuNRs attained colloidal stability at either VDMSO:VAuNRs = 0–0.2 or 0.6–0.9. Especially, the complete removal of interdigitated CTAB bilayer was confirmed at VDMSO:VAuNRs = 0.5 by X-ray photoelectron spectroscopy surface composition analysis. Based on the colloidal stability of AuNRs related with the volume ratios of DMSO/water and CTAB concentration, the phase diagram of AuNRs was further drawn. Both the minimal and maximum DMSO-fraction thresholds for efficient removal of CTAB are generally increased with the increase of CTAB concentration. After the removal of CTAB, mercaptohexadecanoic acid (16-MHDA) was utilized for the further modification of AuNRs. In a wide range of CTAB concentration and with high DMSO fraction, there is no aggregation after the modification. This technique may be used to functionalize the surface of AuNRs for use in a diverse range of applications.

Inhibition of Lysozyme Fibrillation by Gold Nanorods and Nanoparticles.

Amyloid fibrillation has been implicated in many neurodegenerations, dialysis-related amyloidosis, type II diabetes and more than 30 other amyloid-related diseases. Nanomaterials as potential inhibitors of amyloid fibrillation have attracted increasing interests. In the present study, the effects of gold nanorods (AuNRs) and nanoparticles (AuNPs) on amyloid fibrillation were investigated using hen egg white lysozyme (HEWL) as a model system. Our results indicated that AuNRs and AuNPs, especially AuNRs, present significant inhibitory effects on HEWL amyloid fibril formation during all the kinetic processes, from nucleation to elongation and equilibration stages. The stronger adsorption capacity of HEWL on AuNRs surface is the key mechanism of inhibition of HEWL amyloid fibrillation. Furthermore, AuNRs lead to more stable α-helix conformation and hydrophobic microenvironment of aromatic side groups in HEWL molecules, which facilitate the system to form small amorphous aggregates rather than oligomer, profibril or mature fibril.

Molecular dynamics study of melting properties of gold nanorods

The melting properties of gold nanorods (AuNRs) are investigated by means of molecular dynamics simulations based on the Embedded-Atom-Method (EAM) potential. The diameters and lengths of the AuNRs are varied from 2.03nm to 9.44nm and from 19.43nm to 93.04nm, respectively. The premelting of AuNRs is characterized by studying the variation of the Lindemann index with temperature. The simulation results revealed that the melting of AuNR surface is an inhomogeneous, gradually occurring process. This behavior is discussed in the context of the surface atoms of AuNRs requiring different energy values to lose the solid ordering resulting from the fact that they are in contact with irregular number of nearest-neighbors. Furthermore, the ratio between the premelting temperature (Tsm) and melting temperature (Tpm) of the AuNR (also called premelting ratio (Tsm/Tpm)) is calculated for all sizes to provide a new insight into the size dependence of the premelting phenomenon. It is found that the AuNR premelting ratio increases as NP size decreases, thus suggesting that the premelting phenomenon is less pronounced in the smallest NPs.

Porphyrinic Metal–Organic Frameworks Coated Gold Nanorods as a Versatile Nanoplatform for Combined Photodynamic/Photothermal/Chemotherapy of Tumor

AbstractIn this paper, a simple, but effective method is reported to construct the core−shell gold nanorod@metal–organic frameworks (AuNR@MOFs) as a multifunctional theranostic platform by using functionalized AuNRs as seed crystal for the growth of porphyrinic MOFs on the surface of AuNR. Such a delicate tunable core−shell composite not only possesses the improved drug loading efficiency, near‐infrared light‐trigger drug release, and fluorescence imaging, but also can produce reactive oxygen species as well as photothermal activity to achieve combined cancer therapy. It is further demonstrated that the camptothecin loaded AuNR@MOFs show distinctively synergistic efficiency for damaging the cancer cell in vitro and inhibiting the tumor growth and metastasis in vivo. The development of this high‐performance incorporated nanostructure will provide more perspectives in the design of versatile nanomaterials for biomedical applications.

Accelerating Gold Nanorod Synthesis with Nanomolar Concentrations of Poly(vinylpyrrolidone).

A novel modification for the seedless synthesis of gold nanorods (AuNRs) has been developed. Nanomolar concentrations of 10 kDa poly(vinylpyrrolidone) (PVP) can be introduced to a growth solution containing 25, 50, or 100 mM cetyltrimethylammonium bromide (CTAB) to significantly reduce the dimensions of AuNRs. We found that PVP accelerates the growth rate of AuNRs by more than two times that of nanorods grown in 50 and 100 mM CTAB solutions. Additionally, there is a time-dependent effect of adding PVP to the nanorod growth solution that can be utilized to tune their aspect ratio. Because the concentration of PVP is far below the concentration of HAuCl4 in the reaction mixture, PVP primarily functions not as a reducing agent, but as a capping or templating ligand to stabilize the growing nanorods. Our reproducible protocol enables the synthesis of AuNRs in high yield with tunable sizes: 45 × 6.7, 28 × 5.5, and 12 × 4.5 nm for 100, 50, and 25 mM CTAB, respectively. We estimated the number of PVP chains per nanorod in growth solutions to be around 30, which suggests that the effect on the aspect ratio is caused by a direct interaction between the AuNR surface and the PVP.

Anisotropic Overgrowth of Palladium on Gold Nanorods in the Presence of Salicylic Acid Family Additives

We explored the use of salicylic acid (SA) and its derivatives 5-formylsalicylic acid (FSA) and 5-sulfosalicylic acid (SSA) as organic additives to cetyltrimethylammonium bromide (CTAB) in synthesizing gold nanorods (AuNRs) followed by palladium (Pd) capping at the ends of AuNRs. In the AuNR synthesis step, SA family additives in the presence of low concentration of CTAB (50 mM) serve as both the prereducing agent and the cofactor in nanorod growth. At an optimum additive/CTAB ratio (0.1–0.2), AuNRs grow to the longest length. At low additive concentrations, the gold seeds do not grow. At high concentrations, the longitudinal growth of AuNRs is disrupted because the excessive additive disturbs the ligand structure, leading to more isotropic growth. In the Pd overgrowth step, Pd starts to grow from both ends for AuNRs synthesized at optimum additive/CTAB ratios. Feeding more Pd grows the particles into a core–shell structure, possibly because there lacks a tight ligand layer on Pd that favors the longitudinal growth. For AuNRs synthesized at high additive/CTAB ratios, Pd growth loses preference, showing randomized Pd nucleation on AuNR surface. Finally, the palladium-end-capped–AuNRs’ catalytic activity was tested using the resazurin reduction reaction. This study shows a new way to produce controllable deposition of Pd on AuNRs.

Platinum-coated Core-Shell Gold Nanorods as Multifunctional Orientation Sensors in Differential Interference Contrast Microscopy.

We characterized the optical properties of single platinum-coated core-shell gold nanorods (Pt-AuNRs) under dark-field (DF) and differential interference contrast (DIC) microscopy. Furthermore, we examined their potential use as multifunctional orientation probes. Longitudinal surface plasmon resonance damping was observed for single Pt-AuNRs due to Pt metals coated on the AuNR surface under single-particle scattering spectroscopy. Despite the strong plasmon damping with a much-decreased scattering intensity, DIC microscopy allowed us to detect single Pt-AuNRs with much higher sensitivity. We found polarization-dependent DIC images and intensities of single Pt-AuNRs, which allowed us to determine their orientation angle under DIC microscopy. Therefore, we report that single Pt-AuNRs can be used to develop multifunctional orientation probes under DIC microscopy.

An easy and sensitive sandwich assay for detection of Mycobacterium tuberculosis Ag85B antigen using quantum dots and gold nanorods

Mycobacterium tuberculosis is a serious global infectious pathogen causing tuberculosis (TB). The development of an easy and sensitive method for the detection of M. tuberculosis is in urgent need due to complex and low specificity of the current assays. Herein, we present a novel method for M. tuberculosis detection based on a sandwich assay via antigen-antibody interaction using silica-coated quantum dots (SiQDs) and gold nanorods (AuNRs). A genetically engineered recombinant antibody (GBP-50B14 and SiBP-8B3) was bound to surfaces of AuNRs and SiQDs respectively, without any surface modification. The antigen-antibody interaction was revealed using M. tuberculosis-specific secretory antigen, Ag85B. Two biocomplexes showed a quenching effect in the presence of the target antigen through a sandwich assay. The assay response was in the range of 1×10−3–1×10−10μgmL−1 (R=0.969) and the limit of detection for Ag85B was 13.0pgmL−1. The Ag85B was selectively detected using three different proteins (CFP10, and BSA), and further specifically confirmed by the use of spiked samples. Compared with existing methods, a highly sensitive and selective method for Ag85B-expressing M. tuberculosis detection has been developed for better diagnosis of TB.