Sensitive and real-time fiber-optic-based surface plasmon resonance sensors for myoglobin and cardiac troponin I

A sensor to detect markers of cardiac muscle cell death at less than 3 ng ml⁻¹ and in less than 10 min has been achieved. This fiber-optic-based surface plasmon resonance (SPR) sensor is being applied to detect myoglobin (MG) and cardiac troponin I (cTnI) in HEPES buffered saline solution. An in vivo sensor for the early detection of the onset of myocardial infarction (MI) will greatly enhance the patient care. MG and cTnI are two biological markers released from dying cardiac muscle cells during an MI, and their detection at biologically-relevant levels can be diagnostic of MI. Antibodies specific to an antigen of interest are attached to a carboxymethylated dextran layer on a gold SPR surface. With the method developed, the lower limit of detection (LOD) for MG is 2.9 ng ml⁻¹ at 25 °C. The biological level for MG reaches 15-30 ng ml⁻¹ in patient blood after myocardial damage. A Langmuir adsorption isotherm describes the binding well. For cTnI, a lower detection limit of 1.4 ng ml⁻¹ was achieved in preliminary tests. cTnI levels are in the range of 1-3 ng ml⁻¹ in patient blood after myocardial damage. The antibody reaction with the carboxymethylated dextran surface was optimized by modifying the reaction pH, the temperature, and the dextran chain length.     

Development of surface chemistry for surface plasmon resonance based sensors for the detection of proteins and DNA molecules

The immobilisation of biological recognition elements onto a sensor chip surface is a crucial step for the construction of biosensors. While some of the optical biosensors utilise silicon dioxide as the sensor surface, most of the biosensor surfaces are coated with metals for transduction of the signal. Biological recognition elements such as proteins can be adsorbed spontaneously on metal or silicon dioxide substrates but this may denature the molecule and can result in either activity reduction or loss. Self assembled monolayers (SAMs) provide an effective method to protect the biological recognition elements from the sensor surface, thereby providing ligand immobilisation that enables the repeated binding and regeneration cycles to be performed without losing the immobilised ligand, as well as additionally helping to minimise non-specific adsorption. Therefore, in this study different surface chemistries were constructed on SPR sensor chips to investigate protein and DNA immobilisation on Au surfaces. A cysteamine surface and 1%, 10% and 100% mercaptoundecanoic acid (MUDA) coatings with or without dendrimer modification were utilised to construct the various sensor surfaces used in this investigation. A higher response was obtained for NeutrAvidin immobilisation on dendrimer modified surfaces compared to MUDA and cysteamine layers, however, protein or DNA capture responses on the immobilised NeutrAvidin did not show a similar higher response when dendrimer modified surfaces were used.     

Performance improvement of plasmonic sensors using a combination of AC electrokinetic effects for (bio)target capture

Analytes concentration techniques are being developed with the appealing expectation to boost the performance of biosensors. One promising method lies in the use of electrokinetic forces. We present hereafter a new design for a microstructured plasmonic sensor which is obtained by conventional microfabrication techniques, and which can easily be adapted on a classical surface plasmon resonance imaging (SPRI) system without further significant modification. Dielectrophoretic trapping and electro‐osmotic displacement of the targets in the scanned fluid are performed through interdigitated 200 μm wide gold electrodes that also act as the SPR‐sensing substrate. We demonstrate the efficiency of our device's collection capabilities for objects of different sizes (200 nm and 1 μm PS beads, as well as 5–10 μm yeast cells). SPRI is relevant for the spatial analysis of the mass accumulation at the electrode surface. We demonstrate that our device overcomes the diffusion limit encountered in classical SPR sensors thanks to rapid collection capabilities (<1 min) and we show a consequent improvement of the detection limit, by a factor >300. This study of an original device combining SPRI and electrokinetic forces paves the way to the development of fully integrated active plasmonic sensors with direct applications in life sciences, electrochemistry, environmental monitoring and agri‐food industry.     

Thermoresponsive dendronized polymeric sensors

The first (G1) and second generation (G2) of dendronized copolymers carrying solvatochromic dyes were synthesized, and their thermoresponsive properties investigated. These copolymers were constituted with oligoethylene glycol (OEG)‐based dendrons to afford the thermoresponsiveness and disperse red 1 to act as the dye probe. The possible architecture and structure effects on sensoring were investigated by changing dendron generation from G1 to G2, and the interior structures of G2 polymers from hydrophilic OEG into hydrophobic alkyl chain. The sensoring ability of these copolymers to temperature and solution pH was examined with UV/Vis spectroscopy. Combined with the supports from fluorescence spectroscopy, remarkable thickness effects of dendronized polymers were discovered on the transitions of the dye moieties during the thermally‐induced aggregation process. This work enriches the field of thermoresponsive colorimetric polymeric sensors, and provides an in‐depth understanding of state changes of the dye probe during the thermally‐induced phase transitions within these bulky dendronized polymers. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1706–1713     

Recent advances in surface plasmon resonance based techniques for bioanalysis

Surface plasmon resonance (SPR) is a powerful and versatile spectroscopic method for biomolecular interaction analysis (BIA) and has been well reviewed in previous years. This updated 2006 review of SPR, SPR spectroscopy, and SPR imaging explores cutting-edge technology with a focus on material, method, and instrument development. A number of recent SPR developments and interesting applications for bioanalysis are provided. Three focus topics are discussed in more detail to exemplify recent progress. They include surface plasmon fluorescence spectroscopy, nanoscale glassification of SPR substrates, and enzymatic amplification in SPR imaging. Through these examples it is clear to us that the development of SPR-based methods continues to grow, while the applications continue to diversify. Major trends appear to be present in the development of combined techniques, use of new materials, and development of new methodologies. Together, these works constitute a major thrust that could eventually make SPR a common tool for surface interaction analysis and biosensing. The future outlook for SPR and SPR-associated BIA studies, in our opinion, is very bright. Surface plasmon resonance (SPR) is a powerful and versatile spectroscopic method for biomolecular interaction analysis (BIA) and has been well reviewed in previous years. This updated 2006 review of SPR, SPR spectroscopy, and SPR imaging explores cutting-edge technology with a focus on material, method, and instrument development. A number of recent SPR developments and interesting applications for bioanalysis are provided. Three focus topics are discussed in more detail to exemplify recent progress. They include surface plasmon fluorescence spectroscopy, nanoscale glassification of SPR substrates, and enzymatic amplification in SPR imaging. Through these examples it is clear to us that the development of SPR-based methods continues to grow, while the applications continue to diversify. Major trends appear to be present in the development of combined techniques, use of new materials, and development of new methodologies. Together, these works constitute a major thrust that could eventually make SPR a common tool for surface interaction analysis and biosensing. The future outlook for SPR and SPR-associated BIA studies, in our opinion, is very bright.      

Single-crystal sapphire-fiber optic sensors based on surface plasmon resonance spectroscopy for in situ monitoring

Single-crystal sapphire-fiber optic sensors based on surface plasmon resonance (SPR) for refractive index (RI) measurements of aqueous and hydrothermal water solutions are described. Accurate measurement of RIs is essential to efficient operation and control of broad range of engineering processes. Some of these processes are carried out with harsh environments, such as high-temperature, high pressure, and chemical corrosion. These extreme physical conditions are proving a limiting factor in application of the conventional silica-based optical sensors. Single-crystal sapphire is an ideal material for sensor applications, where reliable performance is required in the extreme environment conditions. With regard to the liquid species detection, most applications of SPR sensors are designed to function near the refractive index of water (1.3330 RI). The RI changes of aqueous solution can be easily monitored by silica-fiber (RI, 1.4601 at 550 nm) based SPR sensor. However, the sapphire waveguide has a prohibitively high RI (1.7708 at 546 nm) for unmodified monitoring of the RI changes of aqueous solutions. For that purpose, a practical SPR probe geometry has been applied to the ability to tune the SPR coupling wavelength/angle pair with sapphire-fiber based SPR probe.     

Optical detection of Cu ion using a SQ-dye containing polymeric thin-film on Au surface

In this study, we have fabricated Cu²⁺ ion sensor using a squarylium dye (SQ-dye) containing polymeric thin-film. Surface Plasmon Resonance (SPR) was used as a signal amplifier to achieve high sensitivity and large linear dynamic range for detection of Cu²⁺ ion. High selectivity to Cu²⁺ ion was obtained by the effective electro-static interaction between SQ-dye and Cu²⁺ ion in the polymeric film. The optimal analytical condition of high selectivity and sensitivity in the wider linear dynamic range obtained in this study may be a result of the cooperative ‘hard-soft’ metal ion-ligand interaction and effective detection of refractive index changes by the complexation of Cu²⁺ ion and SQ-dye in SPR measurement. Among 10 different alkali metal, alkaline earth metal, and transition metal ions, SQ-dye in poly(vinylchloride)–poly(vinyl acetate)–poly(vinyl alcohol) (PVC–PVAc–PVA) copolymer film showed the highest selectivity to Cu²⁺ ion. Although the interaction between SQ-dye and metal ions has not been well understood, both cooperative ‘hard-soft’ metal ion-ligand interaction and size-selective recognition of Cu²⁺ ion to SQ-dye may contribute to high selectivity. Furthermore, additional sensitivity in the detection of Cu²⁺ ion by SPR was obtained by matching the wavelength of probing radiation of SPR and absorption maximum of SQ-dye at 675 nm, which allow to detect small changes in the refractive index by complex formation on the sensing surface. This result may apply in development of the Cu²⁺ ion selective sensor for medical, biochemical, and environmental applications.     

Development of an optical RNA-based aptasensor for C-reactive protein

The development of a RNA-aptamer-based optical biosensor (aptasensor) for C-reactive protein (CRP) is reported. CRP is an important clinical biomarker; it was the first acute-phase protein to be discovered (1930) and is a sensitive systemic marker of inflammation and tissue damage. It has also a prognostic value for patients with acute coronary syndrome. The average concentration of CRP in serum is 0.8 ppm and it increases in response to a variety of inflammatory stimuli, such as trauma, tissue necrosis, infection and myocardial infarction. The interaction between the 44-base RNA aptamer and the target analyte CRP is studied. In particular, the influence of the aptamer immobilization procedure (chemistry, length, concentration), as well as the binding conditions, i.e., the influence on the binding of different buffers, the presence of Ca²⁺ ion and the specificity (against human serum albumin) have been evaluated. Using the best working conditions, we achieved a detection limit of 0.005 ppm, with good selectivity towards human serum albumin. Some preliminary experiments in serum are reported. Figure The assay on the CM5 chip     

Immunosensor Based on Surface Plasmon Resonance for Antigen Recognition

A novel immunosensor based on surface plasmon resonance（SPR） has been developed for the recognition of antigen. The sensor was designed on the basis of the fixed angle of incidence and measuring the reflected intensities in a wavelength range of 430--750 nm in real-time. An ultra-bright white light-emitting diode（LED） was used as the light source. Molecular self-assembling in solution was used to form the sensing membrane on gold substrate. It has been seen that the sensitivity of the SPR sensor with 3-mercaptopropionic acid（MPA）/protein A（SPA） sensing membrane is considerably higher than that with MPA or SPA modified sensing membrane. The kinetic processes on the sensing membrane were studied. The human B factor（Bf）, an activator of complement 3（C3）, was recognized among the other antigens. This sensor can also be used for other antigen/antibody or adaptor/receptor recognition. Under optimized experimental conditions, the sensor has good selectivity, repeatability, and reversibility.     

Au/Pt纳米柱阵列电极的制备及光电催化氧化甲醇性能

利用纳米压印、 电沉积和气相沉积方法构筑了有序均一的Au及Au/Pt纳米柱阵列电极. 通过反射光谱观测到580和660 nm附近的特征吸收谱峰, 并基于有限元电磁场(FEM)理论模拟, 确定其表面等离激元共振(SPR)性质分别对应于纳米柱柱顶的电偶极模式(584 nm)、 电四极模式(638 nm)以及表面等离激元极化子(666 nm). 制备的等离激元纳米柱电极用于甲醇光电催化氧化反应时, SPR效应能显著地增强甲醇的电催化氧化电流. 当表面负载2 nm的金属Pt时, 光电催化氧化甲醇活性最高, 光照使氧化电流增加, 同时甲醇的氧化峰电位随光强的增加逐渐负移, 证明SPR弛豫产生的热空穴参与到光电协同甲醇氧化中. 在恒电流甲醇氧化实验中, 光照使表面氧化反应时间延长6倍, 减小了CO的毒化, 证明SPR对于电极表面产生一定的清洁作用.     

Preparation and characterization of a polyclonal antibody from rabbit for detection of trinitrotoluene by a surface plasmon resonance biosensor

A polyclonal antibody against trinitrophenyl (TNP) derivatives was raised in rabbit, and the antibody was applied to detection of trinitrotoluene (TNT) using a surface plasmon resonance (SPR) biosensor. TNP-keyhole limpet hemocyanine (TNP-KLH) conjugate was injected into a rabbit, and a polyclonal anti-TNP antibody was realized after purification of the sera using protein G. Aspects of the anti-TNP antibody against various nitroaromatic compounds, such as cross-reactivities and affinities, were characterized. The temperature dependence of the affinity between the anti-TNP antibody and TNT was also evaluated. The quantification of TNT was based on the principle of indirect competitive immunoassay, in which the immunoreaction between the TNP-β-alanine-ovalbumin (TNP-β-ala-OVA) and anti-TNP antibody was inhibited in the presence of free TNT in solution. TNP-β-ala-OVA was immobilized to the dextran matrix on the Au surface by amine coupling. The addition of a mixture of free TNT to the anti-TNP antibody was found to decrease the incidence angle shift due to the inhibitory effect of TNT. The immunoassay exhibited excellent sensitivity for the detection of TNT in the concentration range of 3 × 10⁻¹¹ to 3 × 10⁻⁷ g/ml. To increase the sensitivity of the sensor, anti-rabbit IgG antibody was used. After flowing the mixture of free TNT and anti-TNP antibody, anti-rabbit IgG antibody was injected, and the incidence angle shift was measured. Amplification of the signal was observed and the detection limit was improved to 1 × 10⁻¹¹ g/ml.     

Preparation and application of triangular silver nanoplates/chitosan composite in surface plasmon resonance biosensing

This paper reports the utilization of triangular silver nanoplates (TSNPs) to enhance the sensitivity of surface plasmon resonance (SPR) biosensor. TSNPs modified with 3-mercaptopropinic acid (MPA) were simply mixed with chitosan and glutaraldehyde to form TSNPs/chitosan composite. The composite was deposited on Au film as immobilization substrate for SPR biosensor. The novel structures of TSNPs are preserved against etching by MPA and chitosan polymer. Moreover, chitosan cross-linked by glutaraldehyde enables antibody to be immobilized on fabricated substrate directly via Schiff alkali reaction. In the optimized conditions, the resulting biosensor based on TSNPs/chitosan composite shows a satisfactory response to bovine IgG in the concentration range of 0.075–40.00 μg mL⁻¹. While the biosensor based on chitosan without TSNPs shows a response in the concentration range of 0.6–40 μg mL⁻¹ and the biosensor based on Au film shows a response in the concentration range of 2.5–40 μg mL⁻¹. The experiment results show that the sensitivity of SPR biosensor based on TSNPs/chitosan composite was significantly enhanced and the immobilization procedure of antibody was simplified.     

Preparation and characterization of complexes of liposomes with gold nanoparticles

Gold nanoparticles (Au NPs), which are extremely useful materials for imaging and photothermal therapy, typically require a drug delivery system to transport them to the affected tissue and into the cells. Since liposomes are approved as drug carriers, complexes of liposomes with Au NPs were considered ideal solutions to deliver Au NPs to the target site in vivo. In this study, we prepared complexes of various liposomes with Au NPs via physical absorption and characterized them. The time dependency of the surface plasmon resonance of this complex, which is a unique property of Au NPs, shows that the liposomes promote the formation of stable dispersions of Au NPs under isotonic conditions, even though intact Au NPs aggregate immediately. From a release assay of calcein from liposomes and transmission electron microscopy analysis, the Au NPs were complexed with liposomes without membrane disruption. These complexes could be formed by using cationic liposomes and polyethylene glycol-modified liposomes, as well as by using phosphatidylcholine liposomes, which are useful for drug and gene delivery. We proposed this kind of complex as a nanomedicine with diagnostic and therapeutic ability.     

Optical interrogation of molecularly imprinted polymers and development of MIP sensors: a review

This article reviews the progress and developments achieved in the past five years (2000–2005) in the application of optical analytical techniques to the evaluation of molecularly imprinted polymer (MIP) characteristics. The MIP binding efficiency, recognition processes and selectivity have been intensively studied by optical means due to the general high sensitivity and simplicity of the utilisation of optical techniques. In addition, recent progress in the covalent linkage of MIPs to optical transducers has allowed for the realisation of highly efficient and robust optical MIP-based molecular recognition sensors. The review provides insight into the various approaches to the optical interrogation of MIPs, and is organised according to the type of optical technique employed (fluorescence, UV/Vis and infrared spectroscopy, surface plasmon resonance, chemiluminescence, refractive interference spectroscopy and Raman scattering) and the detailed strategies applied. The review also covers the recent progress achieved in the area of optical sensors based on MIPs.     

Surface plasmon resonance sensors for real-time detection of cyclic citrullinated peptide antibodies

Surface plasmon resonance (SPR) sensors have been used for detection of various biomolecules because of their simplicity, high specificity and sensitivity, real-time detection, low cost, and no requirement of labeling. Recently, molecularly imprinted polymers that are easy to prepare, less expensive, stable, have talent for molecular recognition and also are used for creation selective binding sites for target molecule on the SPR sensors. Here, we show that preparation of cyclic citrullinated peptide antibody (anti-CCP) imprinted SPR sensor to detect CCP antibodies. For this purpose, anti-CCP/AAm pre-complex was synthesized by interacting acrylamide (AAm) monomer with anti-CCP. Then, anti-CCP imprinted (anti-CCP/PAAm) SPR sensor was obtained by reacting with anti-CCP/AAm pre-complex in the presence of the crosslinker, and initiator/activator pair. Besides this, non-imprinted (PAAm) SPR sensor was also prepared without using anti-CCP template. The SPR sensors were characterized and then adsorption-desorption studies were performed with pH 7.0 phosphate buffer (10 mM) and acetic acid (10%) with Tween 20 (1%) in pH 7.0 phosphate buffer. Selectivitiy of sensors was investigated by using immunoglobulin M (IgM) and bovine serum albumin (BSA). To determine the adsorption model of interactions between anti-CCP solutions and anti-CCP/PAAm SPR sensor, different adsorption models were performed. The calculated maximum reflection, detection limit, association and dissociation constants were 1.079 RU/mL, 0.177 RU/mL, 0.589 RU/mL and 1.697 mL/RU, respectively. Repeatability experiments of anti-CCP/PAAm SPR sensor was performed four times with adsorption-desorption-regeneration cycles without any performance losing. Results showed that anti-CCP/PAAm SPR sensor had high selectivity and sensitivity for detection of CCP antibodies.     

表面接枝法制备睾酮素分子印迹表面等离子体共振传感器

构建了一种选择性检测睾酮素的分子印迹表面等离子体共振( Surface plasmon resonance, SPR)传感器。采用紫外光引发表面接枝技术,在固定引发转移终止剂的SPR芯片表面制备了以睾酮素为模板分子,甲基丙烯酸为功能单体,乙二醇二甲基丙烯酸酯为交联剂的分子印迹膜( Molecularly imprinted film, MIF)。利用SPR在目标共振角处现场监测使MIF聚合成膜过程更易控。偏振调制-红外反射吸收光谱表征证明MIF接枝成功。原子力显微镜结果显示,MIF 表面均匀散布着纳米尺寸的孔穴。利用 SPR 对2.5×10-16~2.5×10-6 mol/L睾酮素进行吸附检测,检出限低至2.5×10-16 mol/L,对低浓度和高浓度的睾酮素吸附分段进行线性拟合,得到拟合线性方程分别为y=19.69+1.21x(R2=0.9913)和y=11.5+0.45x(R2=0.9895);睾酮素类似物雌二醇、雌三醇和黄体酮的吸附实验结果显示,此印迹膜对模板分子有很好的选择性;5次重复洗脱吸附后,MIF仍保持较好的传感性能,说明此传感器具有较高的稳定性和重复利用性;在人工尿液样品中测得的睾酮素回收率为85.2%~92.8%,说明此传感器可以用于实际样品测定。     

基于自组装多层膜的葡萄糖表面等离子体共振传感器

利用伴刀豆球蛋白A和糖类的特异性相互作用, 研制了葡萄糖表面等离子体共振传感器. 传感器的敏感膜是构建于金膜表面的伴刀豆球蛋白A/葡聚糖自组装多层膜. 在葡萄糖的存在下, 该自组装多层膜被分解, 引起表面等离子体共振信号的显著变化, 信号变化的大小与葡萄糖的浓度相关. 结果表明, 利用该传感器可以选择性地检测0.1～50 mmol•L^－1浓度范围内的葡萄糖, 且敏感膜可以多次再生使用.     

Surface plasmon resonance biosensor for genetically modified organisms detection

The development of a surface plasmon resonance (SPR) affinity biosensor based on DNA hybridisation is described. This biosensor has been applied to genetically modified organisms (GMOs) detection. Single stranded DNA (ssDNA) probes were immobilised on the sensor chip of an SPR device and the hybridisation between the immobilised probe and the complementary sequence (target) was monitored. The probe sequences were internal to the sequence of 35S promoter and NOS terminator which are inserted sequences in the genome of GMO regulating the transgene expression. The system has been optimised using synthetic oligonucleotides, then applied to real samples analysis. Samples, containing the transgenic target sequences, were amplified by polymerase chain reaction (PCR) and then detected with the SPR biosensor.     

Interaction of ozone with gold nanoparticles

Gold nanoparticles interact with aqueous ozone to produce a surface plasmon resonance shift without aggregation of the nanoparticles. Given ozone's destructive nature, the surprising finding was that the gold nanoparticles returned to their original color and were able to cycle between the wavelengths as ozone was introduced and removed. Gold islands were made and tested for a gaseous ozone response. Similarly to the aqueous system, the gold islands show a cycling effect. Potentially, this system would be useful as a sensor that identifies the presence of ozone in gaseous media.     

Continuous Immunoassay for Sulfamethazine by Surface Plasmon Resonance-Based Biosensor

Regeneration of the sensor chip surface is difficult in many surface plasmon resonance (SPR) biosensor assays. Improper regeneration will reduce life span of the sensor chip and decrease the quality of the data. Considering the advantages of reducing the regeneration frequency, a theoretically feasible continuous SPR biosensor immunoassay for sulfamethazine (SMT) was developed. In the continuous inhibitive immunoassay, the sensor chip surface is regenerated only once after a definite number of tests instead of every test. The SMT-bovine serum albumin (BSA) conjugate was covalently immobilized to a carboxymethyldextran modified gold film. The immobilization conditions of the antigen were studied and the working dilution of the antibody was optimized. The antibody was mixed with SMT of different concentrations prepared with PBS buffer to construct the calibration curve. The limit of detection was 0.5 ng mL^?1. The continuous SPR biosensor assay was proved to be simpler and more practical than a normal one.