Rational aspect ratio and suitable antibody coverage of gold nanorod for ultra-sensitive detection of a cancer biomarker

We report a simple, ultra-sensitive, and straightforward method for non-labeling detection of a cancer biomarker, using Rayleigh light scattering spectroscopy of the individual nanosensor based on antibody-antigen recognition and localized surface plasmon resonance (LSPR) λ(max) shifts. By experimentally measuring the refractive index sensitivity of Au nanorods, the Au nanorod with an aspect ratio of ~3.5 was proven optimal for the LSPR sensing. To reduce the steric hindrance effect as well as to immobilize a large amount of ligand on the nanoparticle surface, various mixtures containing different molar ratios of HS(CH(2))(11)(OCH(2)CH(2))(6)OCH(2)COOH and HS(CH(2))(11)(OCH(2)CH(2))(3)OH were applied to form different self-assembled monolayer surfaces. The results showed that the best molar ratio for antibody conjugation was 1 : 10. When using individual Au nanorod sensors for the detection of prostate specific antigen (PSA), the lowest concentration recorded was ~1 aM (~6 × 10(5) molecules), corresponding to LSPR λ(max) shifts of ~4.2 nm. These results indicate that sensor miniaturization down to the nanoscale level, the reduction of steric hindrance, and optimization of size, shape, and aspect ratio of nanorods have led to a significant improvement in the detection limit of sensors.     

Immunoassay of plasmonic gold‐nanoparticle clusters: Plasmon coupling effects for Parkinson biomarker detection

A simple signal‐on plasmonic optical assay for the detection of the Parkinson biomarker using gold‐nanoparticle clusters (AuNCs) for signal amplification is presented. This approach is based on the improvement of the optical density (OD) change of the plasmonic band of a localized surface plasmon resonance (LSPR) Au nanoparticle (AuNP) sensor interface using Au NCs conjugated antibodies. The amplification results in a 260‐fold improvement in concentration detection, from 1,000 ng/mL (unlabeled antibody) to 3.8 ng/mL (antibody‐conjugated AuNCs). The sensitivity enhancement can be ascribed to the further plasmonic coupling between the antibody‐conjugated AuNCs and the AuNPs on the LSPR interface and the enhanced amount of target molecule bound to the bioassay. This AuNCs‐assisted signal amplification strategy allows for improving the sensitivity of the plasmon‐based bioassays and can be extended to other optical‐based diagnostic technologies. Importantly, the simple detecting procedure and protocol assembly make it competitive with other existing sensing technologies such as ELISA, allowing for practical usage in clinical diagnostics.     

A new method for non-labeling attomolar detection of diseases based on an individual gold nanorod immunosensor

Herein, we present the use of a single gold nanorod sensor for detection of diseases on an antibody-functionalized surface, based on antibody-antigen interaction and the localized surface plasmon resonance (LSPR) λ(max) shifts of the resonant Rayleigh light scattering spectra. By replacing the cetyltrimethylammonium bromide (CTAB), a tightly packed self-assembled monolayer of HS(CH(2))(11)(OCH(2)CH(2))(6)OCH(2)COOH(OEG(6)) has been successfully formed on the gold nanorod surface prior to the LSPR sensing, leading to the successful fabrication of individual gold nanorod immunosensors. Using prostate specific antigen (PSA) as a protein biomarker, the lowest concentration experimentally detected was as low as 111 aM, corresponding to a 2.79 nm LSPR λ(max) shift. These results indicate that the detection platform is very sensitive and outperforms detection limits of commercial tests for PSA so far. Correlatively, its detection limit can be equally compared to the assays based on DNA biobarcodes. This study shows that a gold nanorod has been used as a single nanobiosensor to detect antigens for the first time; and the detection method based on the resonant Rayleigh scattering spectrum of individual gold nanorods enables a simple, label-free detection with ultrahigh sensitivity.     

Deposition of gold nanoparticles on β-FeOOH nanorods for detecting melamine in aqueous solution

This study demonstrates a facile but efficient approach to deposit metallic (gold) nanoparticles on β-FeOOH nanorods to obtain Au/β-FeOOH nanocomposites without the assistance of any polymers or surfactants at ambient conditions. In this method, a strong reducing agent (NaBH(4)) can be used to extensively produce Au nanoparticles, converting β-FeOOH into Fe(3)O(4) and depositing gold particles onto magnetic Fe(3)O(4) simultaneously. The microstructure, composition, and chemical properties of the obtained nanocomposites are characterized by various advanced techniques, including transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and UV-vis spectroscopy. Moreover, the Au/β-FeOOH nanocomposite can be used to detect trace melamine using UV spectrum in the ultraviolet wavelength range (190-260 nm), in which the nanocomposites show a higher sensitivity toward melamine due to the promotion of symmetry-forbidden bands (n→π(*)) of melamine molecules and also avoid the disturbance of commercial products containing solid colloids or food colorings that distort visual spectrum during the detection of chemical sensing. The deposition mechanisms and their sensing detection toward melamine are discussed.     

Amplification of localized surface plasmon resonance signals by a gold nanorod assembly and ultra-sensitive detection of mercury

Controlled assembly of gold nanorods induced by Na(3)PO(4) leads to a significant amplification of localized surface plasmon resonance (LSPR) signals. The strong affinity between Au and Hg alters the coupled LSPR signals due to the amalgamation of Hg and Au. This allows detection of Hg in aqueous solutions with ultra-high sensitivity and excellent selectivity, without sample pretreatment.     

银包金纳米棒的形成及维生素C的局域等离子体共振吸收位移测定法

本文以金纳米棒作为信号感应载体,在pH9.4弱碱性条件下通过维生素C还原AgNO3从而在金纳米棒表面形成包裹层,进而改变金纳米棒的等离子体共振吸收位移,据此建立了一种快速、简单、灵敏的维生素C的等离子体共振吸收位移测定法.方法的线性范围为0.25～10.0μmol/L,检出限(3σ)为0.12mol/L.该方法成功用于维生素C片剂分析,加标回收率95.4%～106.0%.与药典方法进行对比,有满意的精密度和准确度.     

A solution-based nano-plasmonic sensing technique by using gold nanorods

We have successfully demonstrated a novel sensing technique for monitoring the variation of solution concentrations and measuring the effective dielectric constant in a medium by means of an ultra-small and label-free nanosensor, the mechanism of which is based on the localized surface plasmon resonance (LSPR) of gold nanorods. The nanorods are fabricated in a narrow size distribution, which is characterized by transmission electron microscopy and optical absorption spectroscopy. In addition, we employ a simple analytical calculation to examine the LSPR band of the absorption spectrum, which provides excellent consistency with aspect ratio. The plasmonic sensing is performed by detecting the diffusion process and saturation concentration of hexadecyltrimethylammonium bromide in water, and tracing the effective dielectric constants of the medium simultaneously. This promising sensing and analytical technique can be easily used for investigating the nano-scale variations of mixing or reaction process in a micro/nanofluidic channel or the biological interaction in the cytoplasm of the cell.     

The use of gold-silver core-shell nanorods self-assembled on a glass substrate can substantially improve the performance of plasmonic affinity biosensors

We report on an effective strategy for the enhancement in the sensitivity of localized surface plasmon resonance (LSPR). It is based on the use of gold-silver core-shell nanorods (Au-Ag-cs-NRs) immobilized on a glass substrate. The nanorods arrange themselves by self-assembly, and the resulting LSPR band of the Au-Ag-cs-NRs becomes sharper and more intense. The sensitivity to refractive index (RI) of the Au-Ag-cs-NRs on the glass support is ~281 nm per RI unit, which is better by about 30 % compared to gold nanorods immobilized on glass substrate. The system was applied to study the streptavidin-biotin affinity system which is widely used in biosciences. It is found that the red-shift of the LSPR peak linearly increases with the concentration of streptavidin in the 95 pM to 1.7 μM concentration range. The detection limit (at an S/N ratio of 3) is at 35 pM. The results reveal the merits of this approach in terms of label-free optical affinity sensing. Figure

Au-Ag core-shell nanorods self-assembled on glass substrates. The refractive index sensitivity was enhanced obviously. A strategy to amplify the response and fabricate a label-free optical biosensor     

Light-induced selective deposition of metals on gold-tipped CdSe-seeded CdS nanorods

We introduce a facile approach for the selective deposition of metals on Au-tipped CdSe-seeded CdS nanorods that exploits the transfer of electrons from CdS to the Au tips upon UV excitation. This light-induced deposition method was used for the deposition of Pd under mild conditions, which produced a Pd/Au alloyed tip while preserving the rest of the semiconductor nanoarchitecture. The highly site-selective deposition method was extended to the deposition of Fe, yielding monodispersed, structurally complex Au core/Fe(x)O(y) hollow shell-tipped semiconductor nanorods. These structurally well-defined rods were found to exhibit magnetic functionality. The synthetic strategies described in this work expand on the range of metals that can be deposited on heterostructured semiconductor nanorods, opening up new avenues for the hierarchical buildup of structural complexity and therefore multifunctionality in nanoparticles.     

Aptamer‐Based SERS Assay of ATP and Lysozyme by Using Primer Self‐Generation

A simple bifunctional surface‐enhanced Raman scattering (SERS) assay based on primer self‐generation strand‐displacement polymerization (PS‐SDP) is developed to detect small molecules or proteins in parallel. Triphosphate (ATP) and lysozyme are used as the models of small molecules and proteins. Compared to traditional bifunctional methods, the method possesses some remarkable features as follows: 1) by virtue of the simple PS‐SDP reaction, a bifunctional aptamer assembly binding of trigger 1 and trigger 2 was used as a functional structure for the simultaneous sensing of ATP or lysozyme. 2) The concept of isothermal amplification bifunctional detection has been first introduced into SERS biosensing applications as a signal‐amplification tool. 3) The problem of high background induced by excess bio‐barcodes is circumvented by using magnetic beads (MBs) as the carrier of signal‐output products and massive of hairpin DNA binding with SERS active bio‐barcodes relied on Au nanoparticles (Au NPs), SERS signal is significantly enhanced. Overall, with multiple amplification steps and one magnetic‐separation procedure, this flexible biosensing system exhibited not only high sensitivity and specificity, with the detection limits of ATP and lysozyme of 0.05 nM and 10 fM , respectively.     

The use of gold-silver core-shell nanorods self-assembled on a glass substrate can substantially improve the performance of plasmonic affinity biosensors

We report on an effective strategy for the enhancement in the sensitivity of localized surface plasmon resonance (LSPR). It is based on the use of gold-silver core-shell nanorods (Au-Ag-cs-NRs) immobilized on a glass substrate. The nanorods arrange themselves by self-assembly, and the resulting LSPR band of the Au-Ag-cs-NRs becomes sharper and more intense. The sensitivity to refractive index (RI) of the Au-Ag-cs-NRs on the glass support is ~281 nm per RI unit, which is better by about 30 % compared to gold nanorods immobilized on glass substrate. The system was applied to study the streptavidin-biotin affinity system which is widely used in biosciences. It is found that the red-shift of the LSPR peak linearly increases with the concentration of streptavidin in the 95 pM to 1.7 μM concentration range. The detection limit (at an S/N ratio of 3) is at 35 pM. The results reveal the merits of this approach in terms of label-free optical affinity sensing.

Au-Ag core-shell nanorods self-assembled on glass substrates. The refractive index sensitivity was enhanced obviously. A strategy to amplify the response and fabricate a label-free optical biosensor

     

Development of silver/gold nanocages onto indium tin oxide glass as a reagentless plasmonic mercury sensor

We demonstrate the utilization of silver/gold nanocages (Ag/Au NCs) deposited onto transparent indium tin oxide (ITO) film glass as the basis of a reagentless, simple and inexpensive mercury probe. The localized surface plasmon resonance (LSPR) peak wavelength was located at ∼800 nm. By utilizing the redox reaction between Hg²⁺ ions and Ag atoms that existed in Ag/Au NCs, the LSPR peak of Ag/Au NCs was blue-shifted. Thus, we develop an optical sensing probe for the detection of Hg²⁺ ions. The LSPR peak changes were lineally proportional to the concentration of Hg²⁺ ions over the range from 10 ppb to 0.5 ppm. The detection limit was ∼5 ppb. This plasmonic probe shows good selectivity and high sensitivity. The proposed optical probe is successfully applied to the sensing of Hg²⁺ in real samples.     

Synthesis and electro‐optical characterization of new conducting PEDOT/Au‐nanorods nanocomposites

This paper describes a new strategy to obtain PEDOT/Au‐nanorods nanocomposites with different PEDOT: Au ratio. A polymeric ionic liquid (PIL) was used as stabilizer during the chemical synthesis of PEDOT dispersions. PEDOT/Au‐nanorods dispersions in organic media were obtained. Electrochemical characterization of PEDOT/Au‐nanorods nanocomposites revealed that the addition of Au nanorods modified the electroactivity of the conducting films by reducing the oxidation potential from +0.33 to +0.23 V (versus Ag/AgCl). Optical contrast (ΔT%) of the films decreased from 17% for neat PEDOT films to 8% for PEDOT/Au‐nanorods nanocomposites films (3:1 (v/v)) while switching times (from 1 to 4 sec) were similar to neat PEDOT. Conductivity of the films increased from 0.027 S/cm for neat PEDOT to 0.691 S/cm for PEDOT/Au‐nanorods nanocomposites. Nanoscale morphology and contact potential of PEDOT/Au‐nanorods nanocomposites were investigated in detail by Scanning Force Microscopy. Electrical measurements show a clear contact potential difference between the ITO substrate and the PEDOT/Au‐nanorods film. On the film, no contact potential inhomogeneity is observed indicating that the Au‐nanorods are uniformly dispersed in the film. Copyright © 2010 John Wiley & Sons, Ltd.     

Use of thermally annealed multilayer gold nanoparticle films in combination analysis of localized surface plasmon resonance sensing and MALDI mass spectrometry

A self-assembled film of gold nanoparticles (AuNPs) with a raspberry-like morphology was prepared on a glass plate by the layer-by-layer thermal annealing of multilayer films of AuNPs. It was possible to control the morphology of the obtained films of AuNPs by changing the annealing temperature, duration of annealing, and number of layers. On investigating the plasmonic properties of these films, we found that AuNP films with a raspberry-like morphology yielded the highest refractive index unit, which is a critical parameter in localized surface plasmon resonance (LSPR) sensing, as compared to other types of AuNP films. Self-assembled AuNP films with a raspberry-like morphology were subsequently functionalized with 11-mercaptoundecanoic acid (MUA) to enable the binding of lysozyme to the MUA-modified Au surface. The superior limit of detection for the LSPR sensing of lysozyme in a buffer solution was found to be in the picomolar range (～10(-12) M). The high sensitivity observed in the region was attributed to the raspberry-like morphology, where the AuNPs were packed closely together, and the electromagnetic field confinement was most intense (i.e., at hot spots). The MUA-modified, self-assembled AuNP films with a raspberry-like morphology were finally used in the combination analysis of LSPR sensing and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) for the selective detection and identification of lysozyme in human serum.     

A label-free sensing method for phosphopeptides using two-layer gold nanoparticle-based localized surface plasma resonance spectroscopy

In this study, a new type of localized surface plasmon resonance (LSPR) sensing substrate for phosphopeptides was explored. It has been known that LSPR response for target species is larger in the near-infrared region (NIR) than in the visible region of the electromagnetic spectrum. Several types of noble metal nanoparticles (NPs) with NIR absorption capacities have been previously demonstrated as effective LSPR-sensing nanoprobes. Herein, we demonstrate a straightforward approach with improved sensitivity by simply using layer-by-layer (LBL) spherical Au NPs self-assembled on glass slides as the LSPR-sensing substrates that are responsive in the NIR region of the electromagnetic spectrum. The modified glass slide acquired an LSPR absorption band in the NIR, which resulted from the dipole–dipole interactions between Au NPs. To enable the chip to sense phosphopeptides, the surface of the glass chip was spin-coated with thin titania film (TiO₂-Glass@Au NPs). Absorption spectrophotometry was employed as a detection tool. Tryptic digest of α-casein was used as a model sample. The feasibility of using the new LSPR approach for detecting a potential risk factor leading to cancers (i.e., phosphorylated fibrinopeptide A) directly from human serum samples was demonstrated. Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) was used to confirm the results.     

核壳型Fe_3O_4/Au粒子的制备及其在表面等离子体子共振传感器中的应用

合成了核壳型Fe3O4/Au复合粒子,并对其形貌、光学性质进行了表征.通过外加磁场将Fe3O4/Au复合粒子与兔抗人IgG的偶联体固定于表面等离子体子共振(SPR)传感器的金基底膜上,形成了Fe3O4/Au/抗IgG敏感膜.与传统的通过巯基丙酸连接蛋白的方式相比,磁场作用固定的Fe3O4/Au/抗IgG敏感膜制备简单,易洗脱,具有良好的再生性,且在一定程度上提高了传感器的灵敏度.并对人IgG进行了测定,结果表明,传感器对于浓度范围在1.25～20.00μg·mL-1的人IgG有良好的信号响应.     

CC Bonding of Graphene Oxide on 4‐Aminophenyl Modified Gold Electrodes towards Simultaneous Detection of Heavy Metal Ions

This paper studied the electrochemical sensors based on C? C bonding of graphene oxide (GO) on π‐conjugated aromatic group modified gold electrodes for simultaneous detection of heavy metal ions. For comparison, another sensing interface Au‐Ph‐NH‐CO‐GO, in which GO was modified to Au‐Ph‐NH₂ interfaces by amide bonding. On the basis of the principle of heavy metal ions complexation with oxygenated species on GO, the fabricated sensing interfaces were used for the simultaneous determination of Pb²⁺, Cu²⁺ and Hg²⁺. The performance of two sensing interfaces for simultaneous detection of three metal ions was compared. Au‐Ph‐GO sensing interface demonstrated higher sensitivity and better repeatability than Au‐Ph‐NH‐CO‐GO sensing interface.     

Bioelectronic modulation of single-wavelength localized surface plasmon resonance (LSPR) for the detection of electroactive biomolecules

The simplification of localized surface plasmon resonance (LSPR) detection can further promote the development of optical biosensing application in point-of-care testing. In this study, we proposed a simple light emitting diode (LED) based single-wavelength LSPR sensor modulated with bio-electron transfers for the detection of electroactive biomolecules. Indium tin oxide electrode loaded with nanocomposites of polyaniline coated gold nanorod was used as LSPR chip, and the applied electric potential was scanned at the LSPR chip for single-wavelength LSPR biosensing. Under the scanning of applied potentials, biological electron transfer of redox reaction was employed to demonstrate the bioelectronic modulation of single-wavelength LSPR for selective electroactive biomolecule detection. Without any additional recognition material, electroactive biomolecules uric acid and dopamine were detected directly with a sensitivity of 5.05 μmol/L and 7.11 μmol/L at their specific oxidation potentials, respectively. With the simplified optical configuration and selective bioelectronic modulation, the single-wavelength LSPR sensor is promising for the development of simple, low-cost, and high specificity optical biosensor for point-of-care testing of electroactive biomolecules.     

Label‐free Electrochemical Bisphenol A Aptasensor Based on Designing and Fabrication of a Magnetic Gold Nanocomposite

The present study focuses on designing and fabricating an electrochemical aptasensor for the label free detection of bisphenol A (BPA) using gold nanoparticles (Au NPs) immobilized on functional cupper magnetic nanoparticles (CuFe₂O₄‐SH) and multiwall carbon nanotubes (MWCNTs) modified with aptamer and 6‐mercapto‐1‐hexanol (MCH). A number of analysis techniques were used to characterize the nanocomposite, including Fourier transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, vibrating sample magnetometer, elemental mapping analysis and energy dispersive x‐ray diffraction. The results of the analyses revealed that the fabricated aptasensor had an acceptable linearity index (0.05‐9 nM) with an ultralow detection limit (25.2 pM) when used to determine BPA. Electrochemical experiments were conducted using a [Fe(CN)₆]³⁻/[Fe(CN)₆]⁴⁻ redox system. The results of the electrochemical tests indicated that the existence of Au NPs along with magnetic nanoparticles and MWCNTs in nanocomposite led to a synergistic augmentation on the surface of the modified electrode, thus facilitating the efficient sensing of BPA. This method is highly selective, sensitive and environmentally friendly. Moreover, proposed aptasensor has valuable potential applications in medical diagnostics and food industries where a fast and reliable detection of BPA is of paramount importance for the health of the public.     

铁氧化物/金磁性核壳纳米粒子的制备及其富集与SERS研究

本文用种子生长法制备铁氧化物/金磁性核壳纳米粒子, 并利用SERS对其磁场靶向性进行了检测.