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[Display omitted] • A molecularly imprinted surface plasmon resonance sensor was produced to detect selectively C-reactive protein. • Gold nanoparticles and graphene oxide were utilized to increase the SPR sensor's sensitivity. • Cysteine derived functional MAC monomer interacted with AuNPs eliminated the need for additional spacer arms or any complex processes. • Label free C-reactive protein detection was achieved by molecular imprinting method in one mode via amino acid based functional MAC monomer. C-reactive protein (CRP) level provides important information about the health status of the individual in predicting many diseases such as cardiovascular, chronic inflammatory, and neurodegenerative diseases. Therefore, determining CRP levels is important for correct health intervention and treatment follow-up. For the selective detection of CRP, we developed a (GO/Au-MIP) SPR sensor containing CRP-imprinted polymer modified with graphene oxide and gold nanoparticles. To prove the enhanced sensitivity of the sensor resulting from the presence of graphene oxide (GO) and gold nanoparticles (AuNPs), a CRP-imprinted (MIP) SPR sensor was prepared using the same method, excluding the incorporation of GO and AuNPs. In addition, a non-imprinted GO/Au-NIP SPR sensor was also prepared to evaluate the imprinting efficiency. In detecting CRP in PBS buffer, the GO/Au-MIP SPR sensor exhibited linearity in the concentration ranges of 0.1–2 ppm (R2 = 0.9721) and 5–100 ppm (R2 = 0.9740). The detection limit of the prepared sensor was calculated as 0.0082 ppm. In the study, the imprinting process efficiency was also evaluated by calculating the imprinting factor value (I.F=13.84). In the selectivity studies, the GO/Au-MIP SPR sensor was determined to be 9.23 times more selective against CRP protein than bovine serum albumin and 29.53 times more selective than hemoglobin. When the repeatability of the GO/Au-MIP SPR sensor was examined, it was determined that the GO/Au-MIP SPR sensor was able to detect CRP without any deterioration in performance in five consecutive reuses (RSD<1.5). Finally, CRP detection studies from the serum and urine solutions, which were selected as real samples, were carried out by the GO/Au-MIP SPR sensor to evaluate the matrix effect. CRP spiked serum sample was analyzed by the other standard method to validate the analytical results using CRP analyser. [ABSTRACT FROM AUTHOR]

The surface plasmon resonance (SPR) sensing in the ultraviolet (UV) region, achieved through the optimization of aluminum (Al) film conditions, has attracted attention due to its heightened energy levels and more plentiful molecular electronic transitions compared to the visible region. In this research, the stability of the UV-SPR sensor is improved by applying a protective thin layer of gold (Au) onto the Al film. This reduces spectral alterations observed when the Al film was uncoated in water pre and post flow system measurements. This exploration presents the initial experimental confirmation of the reliability of Al-Au bilayer coatings as SPR sensors in the UV region, highlighting advancements in UV-SPR sensor technology. [Display omitted] • Au-coated Al film successfully functions as UV-SPR sensor. • UV-SPR sensor could have high sensitivity due to molecular electronic resonances. • SPR property of Al film without Au layer changed during flow system measurements. • UV-SPR sensor stability enhanced with Au protective layer. • Flow system is introduced to UV-SPR sensor for real-time monitoring. [ABSTRACT FROM AUTHOR]

• A four layered sensor configuration (CaF 2 Prism-Ag-Ti 3 C 2 T x -Sensing medium) is studied at characteristic wavelengths ranging from visible to near infrared regime. • Maximum sensitivity achieved for the proposed sensor is 350.87°/RIU at 532 nm wavelength. • The proposed sensor outperforms over conventional SPR sensors. • Use of MXene (Ti 3 C 2 T x) enhances attachment of bio-analytes due to its unique sensing abilities. • The greater sensitivity is obtained at shorter wavelengths at the expense of detection accuracy. This paper evaluated the performance parameters of a CaF 2 -Ag-MXene-based surface plasmon resonance (SPR) sensor at different wavelengths. The MXene (Ti 3 C 2 Tx) layer is coated on top of the silver (Ag) layer to act as a protective layer against oxidation and to improve the sensitivity and figure of merit (FoM). The proposed sensor could provide novel opportunities for achieving high sensitivity at different wavelengths. At an excitation wavelength of 532 nm, the maximal sensitivity of 350.87°/RIU is achieved. At various wavelengths, a sensitivity of 245.45, 140, and 129.25°/RIU has been attained at 633, 1000, and 1300 nm, respectively. The study also reveals that greater sensitivity is obtained at shorter wavelengths at the expense of detection accuracy. In the study for implementing the proposed sensor, a fabrication perspective is also included. [ABSTRACT FROM AUTHOR]

Both increasing demand for ultrasensitive detection in the scientific community and significant new breakthroughs in materials science field have inspired and promoted the development of new-generation multifunctional plasmonic sensing platforms by adopting promising plasmonic nanomaterials. Recently, high-quality surface plasmon resonance (SPR) sensors, assisted by two dimensional (2D) nanomaterials including 2D van der Waals (vdWs) materials (such as graphene/graphene oxide, transition metal dichalcogenides (TMDs), phosphorene, antimonene, tellurene, MXenes, and metal oxides), 2D metal−organic frameworks (MOFs), 2D hyperbolic metamaterials (HMMs), and 2D optical metasurfaces, have emerged as a class of novel plasmonic sensing platforms that show unprecedented detection sensitivity and impressive performance. This review of recent progress in 2D nanomaterials-enhanced SPR platforms will highlight their compelling plasmonic enhancement features, working mechanisms, and design methodologies, as well as discuss illustrative practical applications. Hence, it is of great importance to describe the latest research progress in 2D nanomaterials-enhanced SPR sensing cases. In this review, we present some concepts of SPR enhanced by 2D nanomaterials, including the basic principles of SPR, signal modulation approaches, and working enhancement mechanisms for various 2D materials-enhanced SPR systems. In addition, we also demonstrate a detailed categorization of 2D nanomaterials-enhanced SPR sensing platforms and comment on their ability to realize ultrasensitive SPR detection. Finally, we conclude with future perspectives for exploring a new generation of 2D nanomaterials-based sensors. [ABSTRACT FROM AUTHOR]

Extensive efforts have been devoted to improving the resolution of surface plasmon resonance (SPR) sensors in the detection of trace levels of biomolecules considered essential for the early diagnosis of disease. As part of these efforts, we previously developed a bimetallic waveguide-coupled surface plasmon resonance (Bi-WCSPR) sensor configuration designed to dramatically reduce the linewidth of the SPR curve while preserving a moderate local field decay length, thereby addressing the resolution issue. In this study, we systematically quantified the enhanced resolution in Bi-WCSPR sensors used to detect C-reactive protein (CRP), a widely accepted biomarker of inflammation in cardiovascular disease. Individual SPR sensorgrams were measured at several CRP concentrations in both the intensity and angular interrogation modes, confirming that the Bi-WCSPR configuration with a high Ag-to-Au ratio provided a figure-of-merit (FOM) that was 2.53 times higher than that of conventional Au sensors and a limit-of-detection (LOD) that was an order of magnitude lower than the cut-off level for CRP. It was found that when using the Bi-WCSPR configurations, the resolution enhancement in the intensity interrogation mode becomes more evident as the CRP concentrations is lowered to the cut-off level. [ABSTRACT FROM AUTHOR]

In this study, 2,4,6-trinitrotoluene (TNT) binding peptide was synthesized and screened for TNT specific detection using surface plasmon resonance (SPR) sensor. The TNT binding peptide was rational design and synthesized through amino acid sequence from complementarity determining region (CDR) in the anti-TNT monoclonal antibody, which was produced from hybridoma cell using TNP-KLH conjugate as antigen. Three TNT binding peptide sequences were obtained from the heavy chain of CDR1 named TNTHCDR1, TNTHCDR2 from CDR2 and TNTHCDR3 from CDR3 of anti-TNT antibody. Screening process of three candidate peptides were carried out by using the SPR sensor with direct determination, which the peptide was directly immobilized on the sensor chip CM7 surface through amine coupling reaction. The results demonstrated that peptide TNTHCDR3 was determined as TNT binding peptide and no non-specific binding was observed. The selectivity of TNT binding peptide TNTHCDR3 was also testified by six kinds of TNT analogues. The results indicated the specific binding between TNT and peptide TNTHCDR3. [ABSTRACT FROM AUTHOR]

With the increasing popularity of nanotechnology, it is undoubtedly necessary to render the synthesis of nanomaterials more environmentally benign to allow for continued growth of the field. Natural extracts provide a green alternative to harsh chemical reducing and capping agents in noble metal nanoparticle synthesis. In this study, we not only report the first synthesis of silver nanoparticles (AgNPs) using avocado pit extract (APE), but also establish improved surface enhanced Raman spectroscopy (SERS) performance of these APE AgNPs over traditionally synthesized AgNPs. The exceptional size and shape monodispersity of these AgNPs is demonstrated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The excellent SERS performance of these particles is illustrated using both para -aminothiophenol ( p -ATP) and 4,4′-bipyridine (4,4′-Bipy) as Raman probe molecules. Finally, efficient and cost effective plasmon-enhanced screen printed electrodes fashioned using these APE AgNPs is demonstrated for electrochemical SERS (EC-SERS) studies of adenine. [ABSTRACT FROM AUTHOR]

We propose and demonstrate a cascaded distributed multichannel fiber surface plasmon resonance (SPR) refractive index (RI) sensor by using a gold film coating thickness adjustment approach. For a multimode fiber-based SPR sensor, different gold film thicknesses produce different resonance wavelengths, different dynamic ranges, and even different testing sensitivities. Therefore, we design and fabricate a cascaded distributed two–channel multimode fiber SPR sensor with the gold film thickness of 30 nm in #1 sub–channel and 60 nm in #2 sub–channel. The corresponding testing sensitivities are 1712 nm/RIU and 3038 nm/RIU with the RI range of 1.333–1.385. The experimental results indicate that, in the range of 20nm–60 nm, the smaller is the gold film thickness, the larger is the RI testing range, and the lower is the testing sensitivity, and the deeper is the resonance dip. In addition, it is worthy to say that, the testing sensitivity and the dynamic range of the cascaded distributed multichannel fiber SPR sensor keep unchanged after multiple sensing sub-channels being cascaded–connected. By using the gold film thickness adjustment approach, we overcome the limit of adjusting and separating the dynamic ranges of the multichannel fiber SPR sensors effectively. [ABSTRACT FROM AUTHOR]

A nanosensor, based on a metal-insulator-metal (MIM) plasmonic ring resonator, is proposed for potential on-chip temperature sensing and its performance is evaluated numerically. The sensor components can be fabricated by using planar processes on a silicon substrate, making its manufacturing compatible to planar electronic fabrication technology. The sensor, constructed using silver as the metal rings and a thermo-optic liquid ethanol film between the metal layers, is capable of sensing temperature with outstanding optical sensitivity, as high as −0.53 nm/°C. The resonance wavelength is found to be highly sensitive to the refractive index of the liquid dielectric film. The resonance peak can be tuned according to the requirement of intended application by changing the radii of the ring resonator geometries in the design phase. The compact size, planar and silicon-based design, and very high resolutions- these characteristics are expected to make this sensor technology a preferred choice for lab-on-a-chip applications, as compared to other contemporary sensors. [ABSTRACT FROM AUTHOR]

For the prism based SPR glucose sensors, glucose sensitive membrane (GSM) is a key factor that decides the performance of sensor. GSM consists of glucose oxidase (GOD) and matrix material (for example, polyacrylamide gel, PAM). As the prism based SPR glucose sensor coated with GSM is put in the glucose solution, some glucose and dissolved oxygen can diffuse into the GSM and produce by-products, then the by-products will change the refractive index (RI) of GSM and cause the spectrum shift of SPR sensor. In this paper, our proposes are to build the quantitative relationships among the resonance angle of SPR sensor, the RI of GSM, the concentration of glucose in GSM and the concentration of glucose in solution, and then to provide an efficient research method for the GSM of optical sensors. Firstly, we have reported the fabrication and characterization of GSM which is made of immobilized GOD on SiO 2 nanoparticles and polyacrylamide gel. Secondly, we have finished a serial of SPR sensing experiments and obtained the resonance spectra of SPR sensors coated with pure PAM gel film, with free GOD@PAMfilm, and with immobilized GOD@PAM film in PBS solution, respectively, also displayed their variation relationship of resonance angle with the concentration of glucose in PBS solution. Thirdly, we have investigated the effects of solution pH and the content of immobilized GOD on the performance of the sensor, and obtained the optimum solution pH and the optimum content of GOD. Finally, we have related the resonance angle of SPR sensor and the RI of GSM by the combination of SPR experiment data and theoretical simulation, related the RI of GSM and the concentration of glucose in GSM according to Gladstone-Dale mixing rule, related the concentration of glucose in GSM and the concentration of glucose in solution by using the adsorption isotherm model of GSM. [ABSTRACT FROM AUTHOR]

Antibiotic residues in foods, water and the environment reveal antibiotic-resistant bacterial strains, disrupting the ecological balance and causing serious health problems. For these reasons, the detection of antibiotic residues is crucial for the protection of human health. Herein, the detection of benzylpenicillin antibiotic from aqueous and milk sample solutions was carried out by surface plasmon resonance (SPR) sensor using synthetic receptor-molecularly imprinted polymer. The benzylpenicillin-imprinted poly(hydroxyethyl methacrylate-graphene oxide-N-methacryloyl- l -phenylalanine) (MIP-GO) SPR sensor was prepared. Benzylpenicillin detection was performed by MIP-GO SPR sensor in a 1–100 ppb concentration range of benzylpenicillin with 0.9665 linear correlation and 0.021 ppb detection limit. Selectivity analysis showed that the MIP-GO SPR sensor detected the benzylpenicillin molecule 8.16 times more selectively than amoxicillin and 14.04 times more selectively than ampicillin. To examine the imprinting efficiency, non-imprinted poly(hydroxyethyl methacrylate-graphene oxide-N-methacryloyl- l -phenylalanine) (NIP-GO) SPR sensor was also prepared using the same procedure without benzylpenicillin addition. Since graphene oxide (GO) was added to enhance the sensor signal response by increasing sensitivity, the control analyses were performed by a poly(hydroxyethyl methacrylate-N-methacryloyl- l -phenylalanine) (MIP) SPR sensor without adding GO. Moreover, repeatability studies of MIP-GO SPR sensor were statistically evaluated and the RSD of intra-day assays less than 1% specified that there was no loss of performance for the benzylpenicillin detection ability even after four cycles. As a real food sample analysis, the benzylpenicillin spiked and unspiked milk samples were evaluated and high-performance liquid chromatography experiments were carried out for validation. [Display omitted] • A surface plasmon resonance sensor decorated on graphene oxide was prepared for selective detection of benzylpenicillin. • A sensitivite, label free and real time detection of benzylpenicillin was enabled by SPR sensor system. • Benzylpenicillin can be detected with 0.021 ppb LOD in the 1-100 ppb concentration range. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Gn-AuNPs composite probes were prepared by the dip coating method. • Resonant wavelengths are red shifted with increasing irradiation time. • Laser sensitization has enhanced the sensor performance with sensitivity 0.725nm/ppm. • The laser sensitization is a promising method for enhancing probe performance. Surface plasmon resonance SPR fiber optic sensors are valuable optical tools in sensor technology in different disciplines. The sensor performance can be enhanced with tailoring the sensing probe especially using graphene. Here, sensing probes of graphene-gold nanoparticles composite were fabricated by dip coating method on the unclad fiber followed by laser irradiation at different times (0, 2, 5, 10 min). Optical characterization and SPR spectra were studied. Raman spectra confirm the deposition of graphene gold nanocomposite on the bare core, the resonant wavelengths are red-shifted 52, 55, 60 and 63 nm for 0, 2, 5, and 10 min of the irradiated Gn-AuNPs composite/core probe for the analyte range (0–200 ppm), respectively. Laser sensitization has enhanced the sensor performance with superior sensitivity 0.725 nm/ppm and lowest limit of detection for 10 min irradiation, the sensitivity was enhanced 129% with respect to that before laser treatment. The laser sensitization of dip-coated graphene gold nanocomposite is a promising method for enhancing performance parameters of optical fiber sensors. [ABSTRACT FROM AUTHOR]

The demand for advanced, sensitive, and low-cost sensor platforms is growing. However, sensors containing biological recognition elements sometimes present restrictions, which limit their use. This work focused on the development of surface plasmon resonance (SPR) based on a molecularly imprinted polymer (MIP) film, which builds a foundation for biomimetic sensors. The MIP films in the sensor chip were prepared by spin-coating method. The MIP film was found to be readily incorporated into the sensor for detection of histamine in aqueous media. The effect of pH conditions was also investigated. The sensing technique allows for the detection of histamine in a wide range of concentration from 25 μg L −1 to 1000 μg L −1 . By using structural analogs, the sensor platform was demonstrated to be specific for the detection of histamine. [ABSTRACT FROM AUTHOR]

In this article, theoretical estimation on sensitivity, detection accuracy and quality parameter have been done by introducing linear gradation in film layer of a surface plasmon resonance sensor. Using transfer-matrix-method the reflectivities of this sensor is calculated. It is observed that sensitivity, detection accuracy and quality parameter of this sensor are function of film thickness and become maximum only for small range of film thickness. Therefore for higher performance of this waveguide based surface plasmon resonance sensor only selective thickness of film region is recommended. [ABSTRACT FROM AUTHOR]

Sensitivity enhancement of an angular interrogation-based surface plasmon resonance sensor by using divergent beam illumination and digital interpolation is proposed. A small divergent beam of illumination generated inside a prism with a 4f optical setup provides a linear response of refractive index measurements, while a digital interpolation of surface plasmon resonance reflectance captured by using a moderate resolution image sensor enhances the angular resolution and the sensitivity without significantly increasing errors in the measurement. The proposed method is experimentally verified by varying glycerol concentrations from 0 % to 10 % w/w. The experimental results show that the sensitivity of about 10 − 7 RIU could be achieved without sophisticated interferometric instrumentation and computational complexity. [ABSTRACT FROM AUTHOR]

We use a glass slide covered with metal film as the sensing chip and the liquid over the glass slide as the prism (also called liquid prism) to excite the surface plasmon between the metal and the sample in a Kretschmann–Raether surface plasmon resonance (SPR) configuration. In this work, we demonstrate theoretically and experimentally that the lower refractive index of the liquid prism can enhance the angular sensitivity and the figure of merit (FOM) of SPR sensor. Meanwhile, the adjustment of the refractive index of the liquid prism is easier than the solid prism, and the more suitable refractive index of the liquid prism can be obtained for the specific sample to enhance the sensitivity and the FOM. The proposed liquid prism SPR configuration provided a new chemical and biological SPR sensing application with highly sensitive and high FOM. [ABSTRACT FROM AUTHOR]

Modelling of a surface plasmon resonance sensor for detection of ethanol or methanol content in water is presented. The reflectivities of these sensors are derived using transfer matrix method and hence the corresponding sensitivity and detection accuracy are obtained in the presence of high index overlayer, like silicon and chalcogenide. It is observed that the resonant wavelength of surface plasmon resonance sensor is shifted toward higher wavelength with increase of refractive index and thickness of overlayer. Hence, by adjusting their values, the desired spectral operation range of this sensor is obtained. The sensitivity of this sensor with silicon overlayer is larger than the chalcogenide overlayer but at the same time detection accuracy is smaller. This sensor can be used to detect the mass concentration of ethanol, methanol and other similar materials. A method to obtain the percentage mass concentration of ethanol is discussed. [ABSTRACT FROM AUTHOR]

Abstract: Small molecules or analytes present in trace level are difficult to be detected directly using conventional surface plasmon resonance (SPR) sensor, due to its small changes in the refractive index induced by the binding of these analytes on the sensor surface. In this paper, a new approach that combines SPR sensor technology with Fe3O4 magnetic nanoparticles (MNPs) assays is developed for directly detecting of deltamethrin in soybean. The Fe3O4 MNPs conjugated with antibodies specific to antigen serves as both labels for enhancing refractive index change due to the capture of target analyte, and “vehicles” for the rapid delivery of analyte from a sample solution to the sensor surface. Meanwhile, SPR direct detection format without Fe3O4 MNPs and gas chromatography (GC) analysis were conducted for detection of deltamethrin in soybean to demonstrate the amplification effect of Fe3O4 MNPs. A good linear relationship was obtained between SPR responses and deltamethrin concentrations over a range of 0.01–1ng/mL with the lowest measurable concentration of 0.01ng/mL. The results reveal that the detection sensitivity for deltamethrin was improved by 4 orders of magnitude compared with SPR direct detection format. The recovery of 95.5–119.8% was obtained in soybean. The excellent selectivity of the present biosensor is also confirmed by two kinds of pesticides (fenvalerate and atrazine) as controls. This magnetic separation and amplification strategy has great potential for detection of other small analytes in trace level concentration, with high selectivity and sensitivity by altering the target-analyte-capture agent labeled to the carboxyl-coated Fe3O4 MNPs. [Copyright &y& Elsevier]

Abstract: This paper presents a theoretical investigation on an analyte-filled core self-calibration microstructured optical fiber plasmonic refractive index sensor. The proposed microstructured optical fiber sensor introduces the concept of simultaneous detection in different ranges of wavelength because the sensing performance of the sensor in different wavelength ranges is relatively high, which will be useful for high accuracy measurement. The resonant peak 1 and peak 2 are stronger and more sensitive to the variation of analyte refractive index than any other peaks in this kind of microstructured optical fiber. An average refractive index sensitivity of −4354.3nm/RIU (refractive index unit) and 2280nm/RIU in the dynamic index range from 1.46 to 1.485 as well as −2660nm/RIU and −4240nm/RIU from 1.50 to 1.52 corresponding to the peak 1 and peak 2 can be obtained, respectively. The self-calibration sensor demonstrates high linearity and accuracy. The influence of the structural parameters on the plasmonic excitations is also studied, with a view of turning and optimizing the resonant spectrum. [Copyright &y& Elsevier]

Highlights: [•] Based on template-responsive shrinkage of imprinted gel film, a novel surface plasmon resonance (SPR) sensor is prepared. [•] The relevant electrochemical parameters are optimized. [•] The imprinted gel-SPR system has great capability for providing highly sensitive and selective analysis of 3,3′-dichlorobenzidine. [•] The present SPR sensor was successfully employed to detect 3,3′-dichlorobenzidine in tap water and soil samples. [ABSTRACT FROM AUTHOR]

Abstract: The sensitivity, detection accuracy and quality parameter of a surface plasmon resonance sensor containing a graded optical layer are studied. The reflectivity of exponential graded profile and Gaussian graded profile optical layers are derived using the transfer matrix method. The obtained results of the considered graded profiles are compared with each other and it is found that the exponential graded profile gives better results than the Gaussian graded profile. Also, by comparing these results with a uniform surface plasmon resonance sensor, it is observed that the overall performance of the sensor is improved by introducing graded optical layers. [Copyright &y& Elsevier]

The non-specific binding of non-target species to functionalized surfaces of biosensors continues to be challenge for biosensing in real-world media. Three different low-fouling and functionalizable surface platforms were employed to study the effect of functionalization on fouling resistance from several types of undiluted media including blood plasma and food media. The surface platforms investigated in this work included two polymer brushes: hydroxy-functional poly(2-hydroxyethyl methacrylate) (pHEMA) and carboxy-functional poly(carboxybetaine acrylamide) (pCBAA), and a standard OEG-based carboxy-functional alkanethiolate self-assembled monolayer (AT-SAM). The wet and dry polymer brushes were analyzed by AFM, ellipsometry, FT-IRRAS, and surface plasmon resonance (SPR). The surfaces were functionalized by the covalent attachment of antibodies, streptavidin, and oligonucleotides and the binding and biorecognition characteristics of the coatings were compared. We found that functionalization did not substantially affect the ultra-low fouling properties of pCBAA (plasma fouling of ∼20ng/cm2), a finding in contrast with pHEMA that completely lost its resistance to fouling after the activation of hydroxyl groups. Blocking a functionalized AT-SAM covalently with BSA decreased fouling down to the level comparable to unblocked pCBAA. However, the biorecognition capability of blocked functionalized AT-SAM was poor in comparison with functionalized pCBAA. Limits of detection of Escherichia coli O157:H7 in undiluted milk were determined to be 6×104, 8×105, and 6×105 cells/ml for pCBAA, pHEMA, and AT-SAM-blocked, respectively. Effect of analyte size on biorecognition activity of functionalized coatings was investigated and it was shown that the best performance in terms of overall fouling resistance and biorecognition capability is provided by pCBAA. [ABSTRACT FROM AUTHOR]

Grating coupled surface plasmon resonance (GC-SPR) sensors are widely used in analyzing gases, aqueous solutions, proteins and environmental pollutants. However, traditional GC-SPR sensors are difficult to detect absorptive fluids because the spectra of the light will be distorted after passing through the absorptive fluids. Here, we propose and experimentally demonstrate a backside illuminated GC-SPR (BIGC-SPR) sensor, where the light is incident from the transparent substrate side of the sensor chip. The grating chip is fabricated by a simple and cost-effective procedure. DVD-R disc is used as a template to imprint the grating structure onto a polydimethylsiloxane (PDMS) substrate, then a thin Au layer of 35 nm thickness is evaporated on it. By calibrating the sensor with glucose solutions, the sensitivity and refractive index resolution are measured to be 311.97 nm/RIU and 0.00043 RIU, respectively. Moreover, the BIGC-SPR sensor is demonstrated to monitor the concentration of blue engine coolant, green antirust cutting fluid and white antirust emulsified oil solutions. The designed sensor is able to detect colored or highly scattering solutions, and can be potentially used in the fields of medical diagnosis, environmental monitoring and biological protein detection. [Display omitted] • A backside illuminated grating coupled SPR sensor was introduced. • Nanoimprint was applied as a cost effective method to fabricate Au-PDMS gratings. • The designed SPR sensor was demonstrated to detect absorptive fluids. • The sensitivity and resolution of the sensor are 311.97 nm/RIU and 0.00043 RIU. [ABSTRACT FROM AUTHOR]

Abstract: A high performance sub-wavelength metallic grating coupled surface plasmon resonance (SWMGCSPR) sensor with metal and porous composite layer is proposed. Rigorous coupled-wave analysis (RCWA) is conducted to prove the design feasibility, characterize the sensor's performance and determine geometric parameters of the structure, which is also employed to compute the electromagnetic (EM) field distributions at the resonant wavelengths. Parameters of sensing platform are optimized to achieve the best performance of the SPR sensor. Obtained results reveal that the proposed structure can excite SPR with negative diffraction order of SWMG. Both wavelength and angular sensitivities are greatly enhanced because surface plasmon wave (SPW) exhibits a large penetration depth which will enlarge the distance of interactions between SP and analytes. The detection sensitivities and quality parameters are estimated to be 700nm/RIU and 509°/RIU with full width at half maximum (FWHM) less than 2.5nm using the same optimized structure. [Copyright &y& Elsevier]

Abstract: In this paper an optical surface plasmon resonance (SPR) sensor with metamaterial for four and five layered structure is studied. The numerical results presented in this paper leads to a significant properties of metamaterials in sensing field. Computed results of SPR sensors using metamaterial are compared with conventional optical SPR sensors for four and five layered structure. It is seen that wider dynamic range or effective range of measurable refractive index increases when metamaterial layer is used. It is also verified that SPR sensor with metamaterial layer can dramatically enhance the resolution and reduce the reflectivity compared with conventional SPR. Validity of the magnetic field results is proved on the basis of smooth match of the fields in the different layers of the proposed optical SPR sensor. [Copyright &y& Elsevier]

Abstract: Using the finite-difference time-domain (FDTD) method, optical properties are investigated for a sensor comprising a two-dimensional array of gold cubes placed on quartz pillars on a quartz substrate. Background condition is analyzed for an approximate ideal collective resonance. It is found that the resonance intensity is mainly determined by the quartz etch depth, and the spectra valley position depends mainly on the lattice period. Thickness of the gold film affects the wavelength of the transmission spectra slightly, which gives a low processing tolerance requirement for fabrication. Sensitivity of the biosensor is also discussed, spectral sensitivity as high as 596.7nm/refractive index unit (RIU) is obtained in the visible light region, making it an excellent candidate for liquid detection. [Copyright &y& Elsevier]

Abstract: A new type of differential surface plasmon (SPR) sensor integrated with a microfluidic system is presented. The working principle of the microfluidic device is based on hydrodynamic modulation of two laminar streams inside a microchannel to provide periodic changes of the environment on the SPR sensor. The modulated reflectance is then demodulated using a lock-in amplifier. The presented sensor provides sensitivities of index of refraction about 4×10−8 RIU together with a 4 orders of magnitude dynamic range. This method demonstrates a sensitive detection scheme which could be used for label-free detection. [Copyright &y& Elsevier]

Abstract: An ultrathin molecularly imprinted polymer film was anchored on an Au surface for fabricating a surface plasmon resonance sensor sensitive to acephate by a surface-bound photo-radical initiator. The polymerization in the presence of acephate resulted in a molecular-imprinted matrix for the enhanced binding of acephate. Analysis of the SPR wavenumber changes in the presence of different concentrations of acephate gave a calibration curve that included the ultrasensitive detection of acephate by the imprinted sites in the composite, K ass for the association of acephate to the imprinted sites, 7.7×1012 M−1. The imprinted ultrathin film revealed impressive selectivity. The selectivity efficiencies for acephate and other structurally related analogues were 1.0 and 0.11–0.37, respectively. Based on a signal to noise ratio of 3, the detection limits were 1.14×10−13 M for apple sample and 4.29×10−14 M for cole sample. The method showed good recoveries and precision for the apple and cole samples spiked with acephate solution. This suggests that a combination of SPR sensing with MIP film is a promising alternative method for the detection of organophosphate compounds. [ABSTRACT FROM AUTHOR]

Abstract: A surface plasmon resonance (SPR) immunosensor for detection of 2,4-dinitrotoluene (2,4-DNT), which is a signature compound of 2,4,6-trinitrotoluene-related explosives, was developed by using a novel oligo (ethylene glycol) (OEG)-based sensor surface. A rabbit polyclonal antibody against 2,4-DNT (anti-DNPh-KLH-400 antibody) was prepared, and the avidity for 2,4-DNT and recognition capability were investigated by indirect competitive ELISA. The sensor surface was fabricated by immobilizing a 2,4-DNT analog onto an OEG-based self-assembled monolayer formed on a gold surface via an OEG linker. The fabricated surface was characterized by Fourier-transform infrared-refractive absorption spectrometry (FTIR-RAS). The immunosensing of 2,4-DNT is based on the indirect competitive principle, in which the immunoreaction between the anti-DNPh-KLH-400 antibody and 2,4-DNT on the sensor surface was inhibited in the presence of free 2,4-DNT in solution. The limit of detection for the immunosensor, calculated as three times the standard deviation of a blank value, was 20pgmL−1, and the linear dynamic range was found to be between 1 and 100ngmL−1. Additionally, the fabricated OEG-based surface effectively prevented non-specific adsorption of proteins, and the specific response to anti-DNPh-KLH-400 antibody was maintained for more than 30 measurement cycles. [Copyright &y& Elsevier]

Abstract: A simple and sensitive method for the determination of a specific IgG antibody against ovalbumin (anti-OVA IgG antibody) for diagnosis of egg allergy by use of a surface plasmon resonance (SPR) immunosensor in a flow system is described. An OVA conjugate was immobilized on a sensor chip via a self-assembled monolayer of 11-mercaptoundecanoic acid through an amino coupling method. The determination of the anti-OVA IgG antibody was based on a kind of sandwich immunoassay using an anti-IgG secondary antibody in order to enhance the sensitivity of the SPR immunosensor. The sensitivity and detection limit of the present method for the anti-OVA IgG antibody were 7mdeg/ppm and 300ppb, respectively. The present method showed an enhanced sensitivity and detection limit for the determination of the anti-OVA antibody, compared with a direct immunoassay, by which the sensitivity and detection limit were 3mdeg/ppm and 1ppm, respectively. By assuming a Langmuir type of adsorption isotherm, the affinity constants of an anti-OVA IgG antibody immunocomplex with the anti-IgG secondary antibody and of the anti-OVA antibody to the OVA conjugate immobilized on the sensor chip were calculated to be 2.1×106 M−1 and 2.0×106 M−1, respectively. The present flow immunoassay for the anti-OVA IgG antibody by an SPR sensor has potential applications in both research and diagnosis of egg allergy. [Copyright &y& Elsevier]

Abstract: Molecularly imprinted polymers (MIPs) selective for lysozyme were prepared on SPR sensor chips by radical co-polymerization with acrylic acid and N,N′-methylenebisacrylamide. Gold-coated SPR sensor chips were modified with N,N′-bis(acryloyl)cystamine, on which MIP thin films were covalently conjugated. The presence of NaCl during the polymerization and the re-binding tests affected the selectivity and the optimization of NaCl concentration in the pre-polymerization mixture and the re-binding buffer could enhance the selectivity in the target protein sensing. When the lysozyme-imprinted polymer thin films were prepared in the presence of 40mM NaCl, the selectivity factor (target protein bound/reference protein bound) of MIP in the re-binding buffer containing 20mM NaCl was 9.8, meanwhile, that of MIP in the re-binding buffer without NaCl was 1.2. A combination of SPR sensing technology with protein-imprinted thin films is a promising tool for the construction of selective protein sensors. [Copyright &y& Elsevier]

Abstract: A rapid and simple optical immunosensor for detection of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) has been developed based on SPR technology. Functional sensing surface of the immunosensor is created by immobilizing an ovalbumin conjugate of 2,4-D (2,4-D-OVA) by simple physical adsorption on an SPR thin-film gold chip. It has been established that the Au surface of the sensor chip was completely covered by 2,4-D-OVA up to a monomolecular layer and that the 2,4-D-OVA immobilized sensor chip was highly resistive to non-specific binding of proteins. Selective binding of a monoclonal antibody against 2,4-D (2,4-D-Ab) is followed by an increase in SPR angle. The antibody complexed on the sensor surface could be removed simply by the flow of an acidic buffer (glycine.HCl; 0.2M, pH 2.0) for less than 1min, facilitating repeated use of a same sensor chip. A competitive immunosensing method has been applied for the detection of 2,4-D, in which binding of the antibody onto the sensor surface in the presence and absence of 2,4-D is investigated. When 2,4-D is present in sample solution, a competition is set off between 2,4-D in solution and 2,4-D-OVA conjugate on sensor chip for binding to 2,4-D-Ab. A lowest detection limit of 0.1ng/ml 2,4-D is established. Calibration curve of this analytical system covers a wide concentration range of 0.1–300ng/ml 2,4-D. One assay could be completed in 18min (binding, 15min; acidic eluent and followed carrier buffer, 3min). Enzyme-linked immunosorbent assay (ELISA) measurements for the detection of 2,4-D using analogous antigen-coat format showed a detection limit of 500ng/ml. The high sensitivity of the configured SPR immunosensor system and the differences between the performances of SPR and ELISA are discussed. Cross-reactivity of the SPR sensor against a few compounds structurally and environmentally relevant to 2,4-D is examined. The fabricated SPR sensor is found to be highly resistant to interference with a maximum cross-reactivity of only 4% for 2,4,5-trichlorophenoxyacetic acid (2,4,5-T). [Copyright &y& Elsevier]

Abstract: We describe here a novel method for generation of yeast-secreted, in vivo biotinylated recombinant antibodies, or biobodies. Biobodies are secreted by diploid yeast resulting from the fusion of two haploid yeast of opposite mating type. One yeast carries a cDNA encoding an antibody recognition sequence fused to an IgA1 hinge and a biotin acceptor site (BCCP) at the C-terminus; the other carries a cDNA encoding an E. coli biotin ligase (BirA) fused to KEX2 golgi-localization sequences, so that BirA can catalyze the biotin transfer to the recognition sequence-fused BCCP within the yeast secretory compartment. We illustrate this technology with biobodies against HE4, a biomarker for ovarian carcinoma. Anti-HE4 biobodies were derived from clones or pools of anti-HE4-specific yeast-display scFv, constituting respectively monoclonal (mBb) or polyclonal (pBb) biobodies. Anti-HE4 biobodies were secreted directly biotinylated thus bound to labeled-streptavidin and streptavidin-coated surfaces without Ni-purification. Anti-HE4 biobodies demonstrated specificity and sensitivity by ELISA assays, flow cytometry analysis and Western blots prior to any maturation; dissociation equilibrium constants as measured by surface plasmon resonance sensor were of K d =4.8×10−9 M and K d =5.1×10−9 M before and after Ni-purification respectively. Thus, yeast mating permits cost-effective generation of biotinylated recombinant antibodies of high affinity. [Copyright &y& Elsevier]

Abstract: The use of a surface plasmon resonance immunosensor for the analysis of histamine (β-imidazole ethylamine) is described. The method is based on an indirect competitive reaction of an anti-histamine antibody in a sample solution with histamine immobilized on a sensor chip and with histamine in the sample solution. A sensor chip immobilized with histamine was prepared using a self-assembly monolayer of 11-mercaptoundecanoic acid (11-MUA) as an anchor membrane, followed by an amino-coupling reaction with histamine after activation of the 11-MUA layer on the sensor chip by treatment with 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide and N-hydroxysuccinimide. The sensor chip can be reused, after regeneration with a 10mM HCl solution, which dissociates the anti-histamine antibody complex from histamine on the sensor chip. The affinity constants for the immunocomplex of the anti-histamine antibody with histamine in the solution and for that of the anti-histamine antibody with histamine immobilized on the sensor chip were calculated to be 1.5×107 and 7.2×105 M−1, respectively, by assuming a Langmuir-type adsorption of the anti-histamine antibody to histamine immobilized on the sensor chip. The detection limit of the method was determined to be 3ppb. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: This work reports the characteristics of a newly developed optical surface plasmon resonance (SPR) immunosensor for direct, label-free detection of 2,4-dichlorophenoxyacetic acid (2,4-D). The analyte 2,4-D is conjugated with bovine serum albumin (BSA) protein, and the analyte–BSA conjugate is immobilized on to the thin gold-film SPR sensor chip mounted in a continuous flow system by simple physical adsorption. The thin biofilm of 2,4-D-BSA formed on the sensor chip is characterized a monomolecular layer of 2,4-D-BSA conjugate. Functionalization of sensor surface by physical adsorption of 2,4-D-BSA conjugate and followed immunoreaction of surface-bound 2,4-D-BSA with a monoclonal anti-2,4-D-BSA antibody (2,4-D-Ab) are studied by SPR angle interrogation method. The antibody 2,4-D-Ab immobilizes firmly through selective immunoreaction over the 2,4-D-BSA physisorbed SPR sensor chip. Flow of a general protein such as BSA or a non-related antibody over the 2,4-D-BSA immobilized sensor chip showed negligible response indicating the resistivity of the sensor surface to non-selective adsorption of proteins. The quantification of free 2,4-D is based on competitive immunoassay format, which is performed by co-injecting the sample and the monoclonal antibody 2,4-D-Ab over the 2,4-D-BSA physisorbed thin gold-film SPR chip and measuring the amount of specifically bound monoclonal antibodies. When free 2,4-D molecules present in the analyte solution, competition between free 2,4-D and surface-bound 2,4-D-BSA conjugate for binding to 2,4-D-Ab decreases the affinity interaction of the antibody with the sensor surface. The change in the SPR angle in the presence of 2,4-D is inversely proportional to the concentration of 2,4-D coexisting. Such an analytical system has been shown to be capable of detecting concentrations of 2,4-D in buffer as low as 0.5ng/ml (ppb) with a response time of 20min, and the 2,4-D detection is possible in the concentration range from 0.5ng/ml to 1μg/ml (ppm). We used in this investigation a simple SPR instrument, which is not equipped with either regulated flow system or temperature-controller and is similar to a portable SPR analyzer. After an immunoaffinity binding test, the active sensor surface can be regenerated again by simply flowing a chaotropic solution of pepsin (10ppm in 0.2M glycine–HCl buffer (pH 2.0)) in the flow system for just 2min. This regeneration ability enables the achievement of as much as 20 measurement cycles of 2,4-D using a single 2,4-D-BSA conjugate immobilized SPR sensor chip with good reproducibility. [Copyright &y& Elsevier]

Abstract: The detection of butylamine as a malodorous substance was investigated by a surface plasmon resonance (SPR) sensor. When the A zeolite thin film on a gold surface via the thiol–alkoxysilane interfacial layers was formed, the resonance angle changed from 22.30° to 69.24°. Moreover, the anchored zeolite layers were exposed to butylamine, the shifts of the incident angle (Δθ) were observed. The Δθ increased linearly with the gas concentration region of 0% to about 1%. The sensitivity of butylamine was lowest among some amines. Also, the sensitivity depended on the kind of zeolite as follows; the sequence was 13X zeolite>5A zeolite≈mordenite>ZSM-5. [Copyright &y& Elsevier]

Abstract: This paper describes the formation and characterization of a regenerable surface plasmon resonance (SPR) immunosensor for the detection of benzo(a)pyrene (BaP) by employing a self-assembled mixed monolayer presenting BaP head groups as the sensor immunoprobe. The mixed monolayer was used as the base layer in the fabrication of immunoprobe to assure stability to the immunoprobe and inertness to non-selective haptens and proteins. Interfacial interaction of a monoclonal anti-BaP antibody (BaP-Ab) with the monolayer is studied by SPR angle interrogation method. With BaP head groups exposing out of the self-assembled monolayer, BaP-Ab undergoes selective immunoreaction with the immunoprobe and binds firmly. Flow of high concentrations of bovine serum albumin (BSA) showed negligible response indicating high resistivity of the sensor surface to non-selective adsorption of proteins. An indirect inhibition immunoassay method is employed for analyzing sensor responses to BaP. In this method, BaP-Ab is passed together with the free analyte over the sensor chip using a flow system. With the presence of BaP together in the analyte solution, competition for binding to BaP-Ab occurs between BaP molecules in solution and the BaP functional groups present on the sensor chip and thus the binding of BaP-Ab with the sensor surface is found inhibited. Extent of the inhibition of immunoreaction by the presence of BaP is followed in determining the concentration of BaP. Calibration curves corresponding to analyte concentrations ranging from 50ppt (pg/ml) to 100ppb (ng/ml) BaP are obtained. The lowest detection limit of the present SPR-based immunosensor is 50ppt (pg/ml) with a response time of ca. 20min. After the use in determination of BaP, active sensor surface is generated again for repeated use by dissociating the bound antibody from the sensor chip with the treatment of a pepsin solution. A same sensor chip is reusable in the determination of BaP concentration repeatedly for not less than 20 cycles without significant decrease in the sensor activity. [Copyright &y& Elsevier]

We studied the effect of UV irradiation on (non)specific bounding of bovine serum albumin (BSA) and mouse antiBSA immunoglobulin (IgG) using a surface plasmon resonance (SPR) apparatus Biosuplar-2 and special photodetectors. It was found that specific bounding of AG–AB complex is broken under UV irradiation. Contrary to this, UV irradiation of BSA layer before its contact with IgG did not demonstrate any peculiarities. On the basis of quantitative determination of kinetics of specific bounding and washing and precise measurement of photon flux, the product γσ of quantum yield γ and active centre cross-section σ was evaluated to be about 10-20 cm2. As the dimension of amino acid residues tryptophan and tyrosine is about 1 nm, we have concluded that the quantum yield of reaction is very small (about 0.001). This indicates at presence of a barrier for direct photochemical reaction between the interacting substances. [Copyright &y& Elsevier]

A biosensor based on surface plasmon resonance (SPR) is developed for the detection of 2-hydroxybiphenyl (HBP). A monoclonal antibody against HBP (abbreviated hereafter as HBP-mAb) is developed and used for the detection of HBP by competitive SPR-based immunoassay and enzyme linked immunosorbent assay (ELISA) methods. A novel HBP-hapten compound, HBP–bovine serum albumin conjugate (HBP–BSA), derived by binding several HBP units with BSA by an aliphatic chain spacer is used in the development of antibody and for the functionalization of immunoprobes. HBP–BSA linked to the Au surface of the SPR sensor chip undergoes inhibitive immunoreaction with HBP-mAb in the presence of free HBP. The SPR-based immunoassay provides a rapid determination (response time: ∼20 min) of the concentration of HBP in the range of 0.1–1000 ppb (ng/ml). Regeneration of the sensor chip is gained by treating the antibody-anchored SPR sensor chip with a pepsin solution (100 ppm (μg/ml); pH 2.0) for few minutes. The SPR sensor chip is reusable for the detection of HBP for more than 20 cycles with average loss of 0.35% reactivity per regeneration step. HBP concentration is determined as low as 0.1 and 3 ppb using the SPR sensor and ELISA measurements, respectively. The developed SPR sensor for HBP is free from interference by coexisting benzo[a]pyrene (BaP), 2,4-dichlorophenoxyacetic acid (2,4-D) and benz[a]anthracene; SPR angle shift obtained to the flow of HBP is almost same irrespective to the presence or absence of a same concentration of these carcinogenic polycyclic aromatic hydrocarbons together. The SPR sensor for HBP is proved to be applicable in simultaneous detection of HBP and BaP in parallel with another SPR sensor for BaP. [Copyright &y& Elsevier]

A surface plasmon resonance (SPR) sensor, which detects K+ ion using gold thin film, was constructed at different incident wavelengths, 670 and 830 nm. The properties of gold thin film and wavelength are very important factors in exciting surface plasmon resonance. We investigated the SPR phenomenon at different incident wavelengths when the surface plasmon resonated with evanescent waves. The resonance angle changed about 4.4° as the light source changed from 670 to 830 nm wavelengths in pure water. The sensor chip that is coated with a sensing membrane was tested at each wavelength. We found no resonance point at the 670 nm wavelength because the sensing film was too thick when the K+ ion concentration was varied from 10−8 to 1 M. As the light source was changed to the 830 nm wavelength, we could detect the resonance point even though the film was thick. Therefore, we could detect surface plasmon resonance phenomena at the longer incident wavelength and the smaller resonance angle. We could detect the K+ ion concentration from 10−8 to 1 M by using a 830 nm laser diode and sensing membrane. [Copyright &y& Elsevier]

• The dependence of side-polished D-shaped PCF SPR sensor on temperature. • Small lattice pitch or increased duty ratio enhance the temperature dependence. • D-shaped PCF SPR sensor fabricated by wheel polishing setup. A comprehensive temperature Drude theoretical mode has been established to study the temperature effects on the side-polished photonic crystal fiber (PCF) surface plasmon resonance (SPR) sensor. In the theoretical model, the temperature dependence coefficients of fiber material refractive index (RI), sensing film thickness and metal-dielectric function have been considered. The finite element method (FEM) is used to study the influence of side-polished depth, metal thickness, air hole size, and lattice constant on sensing performance with findings as following: (1) the dependence of the resonance wavelength on temperature is almost unaffected by duty ratio or lattice pitch of PCF; (2) the peak loss of the PCF SPR sensor with small lattice pitch (or increased duty ratio) is more sensitive to temperature variation; (3) for the sensor working in intensity interrogation mode, linear relationships can be found between the peak loss versus the RI and temperature. Moreover, we fabricate a side-polished D-shaped PCF SPR sensor by a wheel polishing setup, and the experimental results display a good agreement with the theoretical investigations. This study offers a detailed way to analyze the temperature effects on the sensor, and may lead to the better design and the data-progress improvement for D-shaped PCF SPR sensor. [ABSTRACT FROM AUTHOR]

• DNA nano-cage is synthesized for glycated hemoglobin detection. • Aptamer for glycated hemoglobin is embedded in DNA nano-cage. • Aptamer-embedded DNA nano-cages on SPR sensor chips bind with glycated hemoglobin. • Aptamer/DNA nanocage showed stable and selective binding with glycated hemoglobin. DNA origami-based cages functionalized with aptamer motifs were used to detect hemoglobin and glycated hemoglobin. The binding between the cages and hemoglobin was monitored using a surface plasmon resonance (SPR) sensor. One DNA strand in the nano-cage was replaced with an aptamer that demonstrated a high affinity to hemoglobin (Hb) or glycated hemoglobin (gHb). Three types of the DNA nano-cages designed to fit the size and shape of hemoglobin were evaluated: one without an aptamer, one with the Hb-affinity aptamer (HA) and one with the gHb-affinity aptamer (GHA). Both DNA nano-cages embedded with HA and GHA showed significantly more stable binding with Hb and gHb by 5 and 9 times, respectively, than the aptamers directly immobilized on the SPR surface. HA-embedded DNA and GHA-embedded DNA improved the sensor selectivities by 9 times and 37 times between Hb and gHb. [ABSTRACT FROM AUTHOR]

• Surface plasmonic resonance sensing of organic thin film overlayer was achieved. • SPR in the far- and deep-ultraviolet region of aluminum was utilized. • The minimum detection thickness of the organic overlayer reached 2 nm. • Al films under different conditions exhibited the same behaviors. • This is a practical advantage because accurate control of Al film is difficult. Recently, a focus has been placed on plasmonics utilizing ultraviolet light because of its higher energy and shorter wavelength, compared to visible light. Al is a suitable metal for plasmonics in the ultraviolet region. However, Al is easily oxidized, and accurate control for Al film deposition is difficult. In this study, organic thin films were formed on the Al films, and their surface plasmon resonance (SPR) wavelengths were measured by our original attenuated total reflectance spectroscopic system. With an increase in the organic film thickness, the SPR wavelength shifted to longer wavelengths. The minimum detection thickness of the organic overlayer reached 2 nm for three Al films under different conditions (i.e., different Al thickness and oxidation effects), and the spectra were reproduced by simulations based on the Fresnel equations. These results showed the practical advantage of the Al-based SPR sensor without accurate control of the chemical state of the Al film. [ABSTRACT FROM AUTHOR]